Turbo or Supercharger?

Why would anybody go with the single turbo hassle if a supercharger is as good?

What is the advantage of the turbo over the suepercharger?

I know the turbo doesn't run of the engine but the turbo HEATS up the air a lot more...

Why is this feever if it is easier to install a supercharger with less custom stuff and a lot cheaper to upgrade...

I mean you can use your headers and y-pipe and stuff...

It seems to me that a turbo is a tighter fit and more hassle for the performance...

What about changing your plugs with the turbo? and when you have a miss???

Just wanted to know what you guys think.

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94B4C M6
Finishing project
Borla Competition--
AFR Heads
383 + Paxton Supercharger :D

reasons im going to do turbo


1 - its different

2 - turbo spoool + blow off sounds way better than a blower

3 - less stress on motor.......a supercharger always runs........with a turbo, its very easy to drive around daily without hitting boost.....or if you have an electronic boost controller.....you can just turn your boost down very low for daily driving.

4 - pretty much EVERY story i read about a supercharger involves someone blowing/rebuilding their engine at some point. sure there arent many turbo lt1's around, but other turbo cars seem to handle daily driving alot more reliably than superchargers.

<font face="Verdana, Arial" size="2">Originally posted by got_hp?:
1 - its different</font>
Yes, at least for F-bodys

<font face="Verdana, Arial" size="2">2 - turbo spoool + blow off sounds way better than a blower</font>
Uhhhh....my roomate's has a BOV on his supercharged SS. And that supercharger whine (ATI D1) is pretty bad-ass.

<font face="Verdana, Arial" size="2">3 - less stress on motor.......a supercharger always runs........with a turbo, its very easy to drive around daily without hitting boost.....or if you have an electronic boost controller.....you can just turn your boost down very low for daily driving.</font>
Yes and no. I've never talked to any turbo LT1/LS1 owners in person (though I saw a sweet 800 RWHP TT LS1 at SLP day). But, I know a 5.0 owner who owns a portable dyno business, and his TT 5.0 makes boost really low. While crusing in a supercharged car, you are not making any boost either.

<font face="Verdana, Arial" size="2">4 - pretty much EVERY story i read about a supercharger involves someone blowing/rebuilding their engine at some point. sure there arent many turbo lt1's around, but other turbo cars seem to handle daily driving alot more reliably than superchargers.</font>
That straight up misinformation. First, you can never compare a car that comes with a turbo or S/C stock w/ a car that has a stock bottom end and you added a supercharger or turbo, simply because the originally N/A car wasn't designed for one. A turbo can be just as hard on a bottom end as a supercharger.

Personally, I like both. If somehow funds permit (which I highly doubt http://web.camaross.com/bb/frown.gif ), I'd like to go single turbo this winter w/ a 383. Instead, I'll probably just go built 396 and spray the piss out of it.


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94 Firebird Formula (http://www.nitrousbird.cz28.com) Ram-Air, M6, T-tops, N2O, 12-Bolt, Bolt-Ons; was running 11's internally stock.432.8 RWHP / 588.4 RWTQ (http://www.nitrousbird.cz28.com/id110.htm)
No new times or dyno numbers with new top end (CC306, 1.6RR's, ported heads, etc.)

I see that is different and that people tend to say WOW!!! but...

its the same thing... if you build an engine as I did for the use of a supercharger, everything will work out perfectly with no hassles...

I was just curious because people see turbo and the say WOW. but supercharger is expected.

I though it was a better idea to go with the supercharger since its already massed produced..

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94B4C M6
Finishing project
Borla Competition--
AFR Heads
383 + Paxton Supercharger :D

That's what I figure also, larger installed base = larger knowledge base.

LWM

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95 A4, SLP catback, KBDD sfc, airfoil, Vortech S-trim, 30# SVO injectors, Autometer electric FP guage, boost guage, Hotchkis STB, AS&M headers, AFPR, Vortech Aftercooler, 3.125" blower pulley, 7" crank pulley, Vigilante 2,800 stall, MSD 6 BTM, SLP 35mm front bar, SLP 21mm rear bar, LT-1 editor ... :), 437hp at the wheels. --- members.shaw.ca/mackenzl/LWMsZ-28/LWMsZ-28.html (http://members.shaw.ca/mackenzl/LWMsZ-28/LWMsZ-28.html) ... 01 vert in the making ...

Damn that Joe B. He said everything i was about to say.
I think the best thing about a SC is that they are easier to tune, and since more people have one, easier to trouble shoot.

<font face="Verdana, Arial" size="2">Originally posted by The Highlander:
Why would anybody go with the single turbo hassle if a supercharger is as good?

What is the advantage of the turbo over the suepercharger?

I know the turbo doesn't run of the engine but the turbo HEATS up the air a lot more...

Why is this feever if it is easier to install a supercharger with less custom stuff and a lot cheaper to upgrade...

I mean you can use your headers and y-pipe and stuff...

It seems to me that a turbo is a tighter fit and more hassle for the performance...

What about changing your plugs with the turbo? and when you have a miss???

Just wanted to know what you guys think.

</font>


SOME may do it for the WOW factor, but i feel that is stupid.

Anyways many of the serious guys who know the deal go for the turbo for the greater power potential. Full boost at lower Rpm also attracts people to.
(Not saying that serious guys don't choose blowers, because many do.)


Their both great power adders though. Buth the turbo has greater power potential.

<font face="Verdana, Arial" size="2">Originally posted by Joe Brodman:
[b] [QUOTE]Uhhhh....my roomate's has a BOV on his supercharged SS. And that supercharger whine (ATI D1) is pretty bad-ass.
</font>

true......i guess its just personal preference......
like i said ......those are the reasons "I" am going turbo.....not everyone feels the same

<font face="Verdana, Arial" size="2">Yes and no. I've never talked to any turbo LT1/LS1 owners in person (though I saw a sweet 800 RWHP TT LS1 at SLP day). But, I know a 5.0 owner who owns a portable dyno business, and his TT 5.0 makes boost really low. While crusing in a supercharged car, you are not making any boost either.
</font>

sorry about that.......i was under the impression that supercharger is always showing some level of boost at all rpms above idle.

<font face="Verdana, Arial" size="2">That straight up misinformation. First, you can never compare a car that comes with a turbo or S/C stock w/ a car that has a stock bottom end and you added a supercharger or turbo, simply because the originally N/A car wasn't designed for one. A turbo can be just as hard on a bottom end as a supercharger.
</font>

i know maaaaaaaaaaany NA-T cars (turbo onto original NA), that run as daily drivers, and have yet to hear any horror stories of blowing engines etc etc.
but everytime someone asks questions here about a supercharger, someone says "rebuild now, or you WILL rebuild later".

maybe i am misinformed, but it just seems that more people blow engines with superchargers than NA-Turbos.


<font face="Verdana, Arial" size="2">Personally, I like both. If somehow funds permit (which I highly doubt http://web.camaross.com/bb/frown.gif ), I'd like to go single turbo this winter w/ a 383. Instead, I'll probably just go built 396 and spray the piss out of it.</font>

hehe....yeah.....i want to go single 355........but im going to do it right and build up the engine first. until i can save up enough money for the turbo rebuild, im considering N20 as a temporary fix for my speed craving.

<font face="Verdana, Arial" size="2">Originally posted by got_hp?:
[B] i know maaaaaaaaaaany NA-T cars (turbo onto original NA), that run as daily drivers, and have yet to hear any horror stories of blowing engines etc etc.
but everytime someone asks questions here about a supercharger, someone says "rebuild now, or you WILL rebuild later".

B]</font>

you know many cars... or do you know many LT1 cars??? LT1's don't especially like boost. Cheap hypers won't hold up. Whether its from a turbo or blower, it shouldn't matter.

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94 Formula M6 w/ 98+ front clip, P&P heads, CC 306, RK Sport Headers, 1.6 RR's, CSI pump, LT4 starter, 1.5 drop springs, custom SFC's, Fittipaldi 18's

Pics of the Formula (http://www.hotrideornot.com/cgi-bin/showride.cgi?sid=792)

I agree, turbos are diferent and neat but they are harder to tune in and there is more info around on superchargered cars and its easier to get things done on them.

good luck..

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9 second street legal 1989 mustang lx, special effects purple, 306 Vortech t trim 20pds of boost, momo; seats-steering wheel and shifter knob, weld drag lites, stage 2 fuel system, cervini stormin normin hood and saleen wing, tfs ported heads and edelbrock rpm intake, 8pt cage.

new project, 1994 Z28, 383 stroker, 4 bolt block with bullet main caps, cola light weight crank, H beam eagle rods, je inverted pistons 9.2 compression with heads, comp cam custom grind cam and 1.6 non self-aligning rockers, afr stage 2 heads 58cc, fully ported LT1 intake powder coated LT4 red, 3 core race intercooler, polished procharger, 3:73 gears, custom torque arm, eibach springs, custom panhard bar and control arms, kyb agx adjustable shocks, ss hood, factory ss spoiler, 58mm bbk throttlebody, B&M ripper shifter, chrome zr1 rims, autometer phantom gauges, edelbrock headers,

There is two sides of this boat. I have run turbos for a while cause i personally like them. There is a few reasons for that but when it comes down to it I really like a turbo car. You gotta build what you like. I have thought of going to a blower a few times but they just dont pull my crank so to speak http://web.camaross.com/bb/smile.gif

There is alot of people running blowers on there cars and are very driveable. What it comes down to me really in the long run is you need to run a aftermarket computer with a turbo eventually if you are going to lean on the motor.

Just curious how does the turbo heat up the air more? the compressor side is seperate from the exhaust side. No matter what when you compress air it heats up. plain and simple. You might have a little heat there but the power you are going to lose from driving the belt on a blower is gonna out weigh the heat generated and if you have a good intercooler so that turns into a moot point.

Changing the plugs on my car with the single system i ran was not that hard to do. (ran the turbo tech system and a slp header) doing a plug swap on a set of bbk's was way harder on the drivers side WAY WAY harder
just my .02 http://web.camaross.com/bb/smile.gif

Steven

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383 Inches of stroked turbocharged fun.
If one is good shouldnt 2 be great????? :D:D:D
TURBO=TORQUE
TORQUE=FUN
Ask me about Burhead Headers If you are gonna use them
My Car (http://groups.msn.com/Zturbo)

Finally someone from first hand...

The thing is that if you put an intercooler to the supercharger we will end up in the same discussion of the egg and the chicken...

Anyways... I think it is as you say... A matter of taste... for what I have seen supercharger make more power per boost but turbo are like unlimited...

for instance... in my case its a PITA to change the opti since I have to drop the supercharger and the bracket for the waterpump to come off...

------------------
94B4C M6
Finishing project
Borla Competition--
AFR Heads
383 + Paxton Supercharger :D

How is it that a super charger will yeild more power per psi of boost? A SC eats up more power to make boost than a turbo. All a turbo does is a little extra back pressure in the exahust, but a SC is driven by a belt which means there is more restiction on the rotation of the engine. This is just what i have heard. If i am wrong somebody let me know so i will have my story straight from now on out.

<font face="Verdana, Arial" size="2">Originally posted by lt1camaroman93:
but a SC is driven by a belt which means there is more restiction on the rotation of the engine.</font>

too much backpressure can also slow down the motor.
the trick with turbos is finding the right amount of backpressure for your setup so that its not robbing performance, and it also spools efficiently.

i do believe you are right though, turbos sap less power from the engine.



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3000GT VR4 TT *sold*
new project, 95 t/a....will someone make a good turbo kit already?!?

I think the knowledge of turbos lacks on this board. First off tuning a turbo car is no different then a supercharged car. In a turbo, my car for example, boost comes on at 2K and holds it throughout the rpm band. Second on a supercharged car there is a lot of strees on the crank hub and the second main cap. And last, the best part about turbos is I have a 900hp daily driver http://web.camaross.com/bb/smile.gif

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1994 Turbocharged Camaro

How much for your setup?

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94B4C M6
Finishing project
Borla Competition--
AFR Heads
383 + Paxton Supercharger :D

<font face="Verdana, Arial" size="2">Originally posted by sleeperz28:
, the best part about turbos is I have a 900hp daily driver http://web.camaross.com/bb/smile.gif

</font>


excuse me?!?.......pics? webpage? timeslips?

Hey sleeperZ whats your set-up? Are you using an LT1? I am building a TT LT1 for my 69 Camaro and would be very interested in your set up. I'm only looking for about 600-700 HP though. Please don't keep us in the dark. Later.

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95 6 speed T/A
69 Camaro SS 396 with Twin Turbo 95 LT1 project
http://www.geocities.com/camaroracerlt1

As long as there is boost, there will be conflict among the OWNERS of the two types of set-ups. I personnaly have owned a supercharged mustang(10.70's @130) It was daily driven and had the AC and full stereo/interior, etc... I now want to TT my LT1. Why? I don't know. I have had a SC car now I want a Turbo one. I like how quit a turbo car idles and has a muffled sound(until swooooossshhhhhhhh!!!)

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Jamie Taylor
'94 Z28 M6
Mods: BBK 52mm TB, Granetelli MAF, MSD 8.5 wires, MSD coil, Bosch +4 plugs, gutted cat., In the final stages of HOT cam kit, ported heads, CSI H20 pump, Jet Hot Hooker LT's(thanks to the GP), custom 3" Y-pipe, and Custom CAI installations. It's nice being a welder, I can do all this custom tubing stuff easy!!!
1971 Datsun 240Z with V8 power. 500+rwhp

<font face="Verdana, Arial" size="2">Originally posted by The Highlander:
Why would anybody go with the single turbo hassle if a supercharger is as good?

I know the turbo doesn't run of the engine but the turbo HEATS up the air a lot more...


</font>

Heats up a lot more huh ?

Vortech V1 S Trim Adiabatic efficiency: 72% **

VORTECH V-1 T-TRIM Adiabatic efficiency: 73% **


Turbonetics :

T66 Max efficiency: 76%
T70 Max efficiency: 75%

No strain on crankshaft, easily adjusted boost, no belt to slip, like the sound better than a blower whine, silent at idle ( competition wont know whats about to hit them),

Now I just need to decide what I want to do, since the pcm wont see boost, JZ can you keep me updated as to your progress with the APEXI unit ?



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94 Teal 6 speed Z28
86 Z28, 93 LT1 swap in progress, TH350, intercooled turbo.

<font face="Verdana, Arial" size="2">Originally posted by The Highlander:
Finally someone from first hand...

The thing is that if you put an intercooler to the supercharger we will end up in the same discussion of the egg and the chicken...


How so?


</font>

<font face="Verdana, Arial" size="2">Originally posted by The Highlander:

for what I have seen supercharger make more power per boost but turbo are like unlimited...


[/B]</font>

What cars have you been looking at?

It's just the opposite.

Sorry guys no website or picts. My digital camera took a sht awhile back. As for money I try not to keep track http://web.camaross.com/bb/wink.gif On 12psi, I run a little faster then cars that run 10.40's@ 133-135mph. Im car is not approved to run 9's or 10's so I stay away from the track. However, I have one shot coming up here, I will post soon...

My comb is 383 with a T-76 turbo, and a 6 speed http://web.camaross.com/bb/eek.gif My exhaust is all custom except im using the turbo tech manifold.

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1994 Turbocharged Camaro

camaroz28racer2, I will start testing the APEX AFC controller as soon as I get the car back. Right now the motor is in its finishing stages. After that I just have to get the fuel system installed then install the new MAP and APEX AFC, and start tuning.

Jose


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97 SS #1500 T-76 383
88 Supra Turbo CT-26/T04
87 Buick Grand National T-70

Well...

As I have "seen", so not pinpointing any cars that was like the rule for me. I've been searching around the web and I've seen some turbo setups that pump a lot of CFM more than the supercharger, which was the main reason for the supercharger making more power per boost... Since all the turbo setups I had seen where very high on PSI but low on CFM...

<font face="Verdana, Arial" size="2">Originally posted by The Highlander:
Well...

As I have "seen", so not pinpointing any cars that was like the rule for me. I've been searching around the web and I've seen some turbo setups that pump a lot of CFM more than the supercharger, which was the main reason for the supercharger making more power per boost... Since all the turbo setups I had seen where very high on PSI but low on CFM...

</font>


??

Are you sure you were not comparing say a Vortech with an XX Trim on a built motor, vs something like a single T25 on a stock motor?

No... Not really... but it was regarding a paxton supercharger (novi 2000) which pumps 1700 cfms...

Anyways.. what you guys dont get is that There is nothing like a free lunch... Turbo's dont get boost free... They have 1.5x to 2x more backpressure for boost... That is backpressure that the pistons have to literally PUSH exhaust out.. Which means that the turbo does have pumping air issues that eat up HP and not to say that you can contaminate your intake charge if you do not eliminate overlap... So... The only advantage I see is lower rpm boost.. other than that... I dont know.. maybe its easier and has less back pressure HP loss, a TT than a singe supercharger...

If one were to use 2 smaller supercharger, things could be compared, but now, that would be a real PITA to install...

Another questions.. why arent NHRA Top fuelers using turbos???

I think that one common misconception is that boost kills engines.... No boost does not kill engines. Yes you have more crankcase pressure, yes you have more chance of blow-by due to the increased static compression but the actual defintion of boost is forcing so much air into the engine that it overcomes the natural vacumn and starts forcing more air in than the engine is asking for. With more air being compressed more heat is generated are there is more chance of detonation or preignition. That's the stuff that kills engines.

I myself had a Turbo Technologies 60-1 kit but I opted to trade it for my S-Trim and a couple other things... Linear power is way easier to tune. I mean if you really want to operate a turbo right you need an aftermarket engine computer and with that money I'd rather put a 355 in my car. I mean it all really depends on what you want but for me the supercharger was easier in many aspects... And I mean after working on my car I just tried to imagine how cramped the engine bay would be with a turbo and all its tubing and it would have been hell to work on and tune. Also superchargers (especially vortech) have been around for so long and have such a wide range of users that there is always somebody who has gone through what you are doing and can offer advice. That's just my opinion.

However, I can't deny that intercooled turbo's all-around are a better method of forced induction performance wise than a supercharger. If you are doing it for cool factor you are wack. If you are doing it because you have the need for speed, most excellent. But otherwise, there is no reason to go through the trouble of making a turbo work on a car that was in no way prepared to be turbocharged from the factory. I mean crazy boost levels with the turn of a dial is beautiful. And so much boost its sickening... But for me, the blower is doing the job nicely... and I'm just getting started =)

I know it is old tech, but I went the supercharger route on my 68, with a big block. The 671 added heat, weight, and power ;)
But it also had continous problems with bearings, which more than likely are not specifically related to the blower.

Now that is gone and I am trying the turbo route on a 96 LT1. Due to the fuel injection, there is a lot more to it, but I already had the DFI worked out pretty well in the N/A tune, with shot of spray.

I chose the twin turbo route to be different (like a FI LT1 in a back half 68 isn't different enough already! :D ), and because I like the idea of making horsepower, without taking horsepower back from the engine. I have seen more than one S/C car with broken snouts or spun balancers (I am a firm believer in dual keyways).
Now granted, those were in high boost situations, making around 500-600 RWHP. I plan on being a little higher than that once I get my 383 built, and don't foresee any crank problems!
I also found that going the turbo route I could do it quite a bit cheaper, as a do-it-yourselfer. That certainly isn't the case if you buy a turbo kit.. but that is me ;)

Hopefully I will get my wastegate problem solved, and actually see some boost on my setup.. and then have some solid numbers to brag on!

Here's what it looks like now.. just didn't have the oil lines on the twins in these pics..

http://images.cardomain.com/installs/190000-190999/190723_59_full.jpg

http://images.cardomain.com/installs/190000-190999/190723_60_full.jpg

For me, the primary advantage of a turbo is the superior "area under the curve" compared to a centrifugal supercharger. Supercharged (centrifugal) cars post lower track performance than their dyno numbers suggest.

For example, just take a look at the folks on this board. Some 600 RWHP blower motors can hardly trap 130 MPH in a 3600 - 3700 lbs. car. Hell, naturally aspirated motors can accomplish that with 100 RWHP less. Just check out LS1Tech some time:)

On the other hand, on our large displacement motors, spooling up a good size turbo (T76+) is not an issue. A properly set-up turbo will hit peak boost WAY down low in the rev band and hold it throughout in the power curve instead of peaking a few hundred RPM before redline as with a blower. "Right now" boost at 2K RPM - with a FAT torque curve to match - sounds good to me:)

And track numbers back this up. For example, Dale Basemann (http://www.databasemann.com/impalaindex.htm) traps at 134 MPH in a heavy ass Impala, with "just" 670ish RWHP.

In essence, dyno figures of blower motors are to some degree "misleading." The total average horsepower will be less than a turbo or n/a motor for any given peak figure. And average HP gets you down the track, not peak HP. Again, this all assumes a properly matched turbo configuration/motor combo.

Other benefits that have already been mentioned:

1) Less stress on the crank
2) Earlier peak boost
3) Superior area under the curve
4) TORQUE!
5) More 1/4 mile MPH per RWHP
6) No belts slippage issues
7) Adjustable boost
8) Quiet idle/sleeper effect if that's your gig
9) Allows for taller gearing = better to build boost = lower cruising RPM = eliminating premature hearing loss:D
10) Lower BSFC = less fuel system demands, which can become significant when making BIG power

I'm one of those rare weirdos that doesn't care much for blower whine:)

That about covers it for now:)

The area under the curve is a major advantage... I guess it depends on how much you want to delve into the project. If you want to do something to your car that has almost no aftermarket is a hefty task and I'm sure it can get very expensive with all the custom stuff involved. Blower is wham bam boost and you're done.

A single T76 moves around 1700 cfm... Hell.. you cant compare that flow with a Vortech S-trim that flows around 850cfm @ peak efficiency....

Put in a YS-Trim and you might get the same peak HP, but you will trap a lot more...

How much is yellow Z28 trapping??? He uses a YS-trim. You cant compare a t76 with an S-trim... just not fair...

The other thing...

Someone with an S-trim and 52x rwhp was traping 127 or so... I think...

The other thing... Backpressure... Backpressure does affect a turboed engine in a big way!!!! for each psi of boost you get 1.5 at least of backpressure.. that is pressure that the PISTON has to overcome to go up while in the exhaust stroke...

Lag....

I think that with comparable flow superchargers and turbos.. you should get more or less the same performance, maybe slightly better on the track for the turbo, but I think on the street the supercharger has an edge since there is no lag... and if it is not a skilled driver with turbos, he will loose the jump.

Originally posted by The Highlander

Lag....

I think that with comparable flow superchargers and turbos.. you should get more or less the same performance, maybe slightly better on the track for the turbo, but I think on the street the supercharger has an edge since there is no lag... and if it is not a skilled driver with turbos, he will loose the jump.

One must remember we're running relatively large V-8's - 6.0+ liters in stroker trim - not 1.6 liter Hondas:)

That said, lag really isn't an issue. In fact, you can run a pretty hefty turbo on our motors without much lag at all, hence the far broader area under the curve compared to a centrifugal supercharger.

And the track numbers back that up. If turbo V-8's were as peaky as you suggest, for any given HP, a turbo car would run slower times than an s/c car, which isn't the case. For the most part, the exact opposite is true. The disparity in boost response (compared to a turbo) is not nearly as significant in a roots or screw/Whipple blower, but centrifugals can only dream of hitting like either of those two.

how much is yellow Z28 trapping??? He uses a YS-trim. You cant compare a t76 with an S-trim... just not fair...

Agreed, which is why the comparison was never made in the first place:) The T-76 was merely used as an example of a decently-sized turbo that will hit boost very early in the powerband granted a properly matched set-up. But if you really want to compare it to an S-Trim, it will spin up its larger compressor wheel quicker, flow a hell of alot more air, and still hit boost earlier:)

IMHO, those virtues = better street and track performance.

Not to beat a dead horse, but "too much" boost down low with turbo set-ups can become an issue on the street. Just ask zturbo:)

yellow z28 traps at 139 with 700 RWHP. For the sake of benchracing, compare that to the aforementioned Impala. Although it weighs over 1000lbs. more with 30 HP less, it still traps within 5 MPH. Not too shabby at all.


The other thing...

Someone with an S-trim and 52x rwhp was traping 127 or so... I think...

My point exactly. Full weight n/a LT1's in the 470 RWHP range can hit the same trap speed. A turbo combo done right will fatten up the mid/low range hp/tq even more.

Another factor not mentioned is a turbo motor will be less sensitive to changes in DA than a blower, since impellar speed is independent of RPM. Wastegates vs. belts/pulleys. Granted, this works out better more in theory than in real life:)

Since I've never run either a centrifugal s/c or turbo, to some degree I'm talking out of my ass:) But I've witnessed enough examples of both turbo and centrifugal s/c combos, their dyno sheets, and time slips to formulate general observations of the pros and cons of each.

And no, I don't regret selling my T-Trim:)

like jim said, a turbo will make more power(given ~ cfm) and will make boost at a lower RPM. the only s-trim cars that will even come CLOSE to matching a T76 in low end boost is a wayyy overspun strim.. and the T76 wil make way more up top anyway.

highlander-
depending on A/Rs and other stuff, the backpressure can be = to the intake pressure. I have even heard that it can be less.

Originally posted by The Highlander


The other thing... Backpressure... Backpressure does affect a turboed engine in a big way!!!! for each psi of boost you get 1.5 at least of backpressure.. that is pressure that the PISTON has to overcome to go up while in the exhaust stroke...



Yep, turbos will increase backpressure. No getting around that. But the larger the turbo, the lower the backpressure.

At any rate, the power a turbo loses from backpressure is WAY WAY less than what a supercharged motor loses due from driving the blower via belt. If "backpressure does affect a turboed engine in a big way!," belt driving losses on a blower affects a blower motor in a bigger way.

On that note, as power demands increase with a blower - whether stepping up to a bigger head unit, a cogged belt, or spinning more RPM - loads on the crank and power lost driving the blower increase.

On the other hand, as power demands increase with a turbo, upgrading to a larger turbo decreases power lost due to backpressure and overall parasitic losses.

Chalk another one up for the turbo:)

Turbos are beautiful....

One thing that was neglected in this discussion is harmonics. This plays a major role in any machine. Everything in nature has a "natural vibration" or frequency to it. A book on a table, a slab of concrete, and a crankshaft in an engine all have this property. If you are familiar with Williams-Brice stadium in Columbia, SC, you'll hear that the song "Louie Louie" was never played there and never will be. Why? Because the frequency in that song corresponds to the natural frequency of the stadium's design and could cause a collapse if played. Structural Engineers and Mechanical Engineers are very familiar with this vibration/harmonics principle.

With that said, look at the turbo vs. SC thing. The SC adds more vibration to the rotating assy. Not only by the stress of the pully, but also with the compressor wheel's vibration transferring through the belt to the crank. Now not only is the crank being stressed by the resistive force of the drivetrain at the flywheel, but it is being stressed by the resistive force at the front of the crank due to the engine having to overcome the inertia of the compressor wheel/belt/pulley.

With a turbo, this is not the case.

With most SCs turning in the 50-60K rpm range vs a turbo's near 150K rpms, no wonder why someone can see that a turbo has more potential. The higher rpms that a turbo turns actually has a stabilizing effect on the harmonics of the engine.

As far as lag and overall boost: cam specs and header design are of most crucial importance. You will want your primaries to be the same size as your port opening so that you don't create a pressure differential as the exhaust pulses exit the head. The primaries should be designed in a way so that they point the pulses in the direction of the turbine housing. And as with an NA engine, you will want to try to have the primary lengths at certain lengths as to "line up" the exhaust pulses as they travel over the turbine wheel, which by the laws of fluid mechanics provides the greatest flow. Overlapping the pulses will produce turbulance. The turbo tech header is horrible for this, as you can see that it does not aim the pulses towards the turbine or even provide a smooth path for the gases to flow. The turbine wheel has significant effects on lag also. The GNX had a ceramic wheel rather than a steel wheel, because it was lighter and its inertia was much less than the steel wheel (which is very significant when you consider the turbos accelerating from a few thousand rpm to well over 100K in a matter of seconds).

Backpressure is not as great a factor as some people make it out to be in a turbo setup. You will notice that most turbo setups will produce more torque for any given amount of boost when compared to a SC(under equal circumstances). This is because of two things: that backpressure and the fact that torque is not having to be used to turn the compressor(SC). Torque is the true measure of how much force the engine can exert on something, it's power, it's "strength". When considering the cam, this is what makes or breaks a turbo setup. Yes, the piston has to work harder to push the gases out, but the turbo offsets this by aiding in the expulsion of gases during the overlap period (blowing the cylinder out).

You're probably sitting there thinking: well jeesh you can do the same thing with a SC! Consider this: with the turbo you have the flexibility to match your displacement: to your primary/collector size/length, to your turbo's compressor size, to the turbine housing size, and finally to wastegate size to get the results you're looking for (high-reving, mid-range, or low-reving torque monster). It is very complicated and is far beyond the scope of which I would want to type on here as to exactly how each of these things effect turbo performance. You'll learn it with time and patience.

It takes years to learn all of this and understand how to apply it. Get a few books and read and talk to people in the right places. Or even go back to school and study it if you're contemplating making a carrer out of the automobile industry. My Turbo Buick has certainly be a fun learning experience, especially when talking with the guys over on TB.com. I recommend going over there and browsing/searching/posting about the subject. Afterall, the turbocharger is what makes the Buick Turbo6 what it is. Kenny Dutt. and Mike Tom. posts over there every now and then; and a few other big names also. For the most part, it is a very proffesional atmosphere over there.

My nickel's worth

Well **** Caddie, you sure hit the nail on the head...

The thing that scares most people away from turbos, as it did me for a while is the "lag" everyone talks about.

I dont want to say turbo lag is a myth, becasue a 1.8 liter Honda with a 80mm turbine housing will definatley have some lag, but for our large V8 engines, turbo lag is almost non-exsistent. If you build the turbo system right, you wont even feel the little amount of lag that is there.

Since the turbine is driven from exhaust, a 1.8 liter engine will take a longer time to spool up the turbine vs a 6 liter engine, if the turbo is the same size. The smaller engines dont produce nearly as much exhaust gas volume as a large 6 liter engine will.

So if we are debating whether a turbo or a supercharger is better for a large v8, we must also know what the application is. Since only centrifugal sc's have been mentioned I guess we are comparing them to turbos.

For the street, if you want huge power throughtout the entire RPM range, a turbo system would be you best bet, IMO. Why? You can build a turbo system to attain full boost by 2500 rpm, and keep that till your redline. This may kill your rear tires everytime you leave the stoplight, but if this is what you crave, it will work well.

BUT if you are looking for a street system, that has large power gains at mid to high rpms, I think the centrifugal sc is what works best. Since they build boost exponetioally to rpm, you wont relaize full boost until 4500 rpms and up depeneding on the size of the sc.

I am no drag expert, so I will leave other to discuss that application.

If you are trying to choose between the two power adders, you must define what you want from your car, where you want the power, how you are going to drive it, and similar things.

I know I wanted huge power throught the rpm range after driving in a friends TT 3000 GT that would 4 wheel burnout in 4 of the 6 gears.....that got me hooked.

Ciao
Hunter

LAG?? Tell that to lingenfelter... they made a test of many cars and (he won of course) he was shy of a goal stated by a mag because he claimed that the lag held a bit the car when coming out of the corners...

Turbos are always sized bigger CFMs for a given boost pressure than SC.

I agree with all of you, specially in the harmonics... But I disagree in the overlap and turbos... You never want overlap, specially and even more in a turbo car than a SC car. Overlap will contaminate the intake charge with the backpressure, thus reverse split cams are common...

I have hit the books and read many things...

When you race on the street, if you do not know how to drive a turbo car, a SC car will ALWAYS have the jump, and the jump can mean the race.

Turbos are interesting, hence why lingenfelter chose them and not a simple SC as his wrench excess... but I do feel that there is a bit of a misconception with turbos and superchargers...

I honestly agree that a TT is better than a single... But for a single turbo.. I think I prefer a SC, im not saying its better, just a preference... but a TT is hands down a better system than a SC.

But one thing that I would like to see is a turbo car with more or less 400rwhp so I can compare it with mine and see the advantages and disadvantages of different setups...

THe other thing.. Why is it that with bigger turbos... backpressure is less???? and how can you have less backpressure than boost? That seems a bit difficult for me to grasp...

Originally posted by The Highlander
LAG?? Tell that to lingenfelter... they made a test of many cars and (he won of course) he was shy of a goal stated by a mag because he claimed that the lag held a bit the car when coming out of the corners...



Not to question the great Mr. Lingenfelter, but didn't he outsource development of his C5 TT kits to Incon? Just based on that alone, it's safe to say his areas of expertise are focused more in other areas of engine dynamics. And for the "competition he went up against? Hell, 90% of those magazine "tuner cars" are a joke. There are heads/cam LS1's that will easily destroy some of those C5 tuner machines with $40K in motor mods.

Just take a look all the successful turbocharged road cars sometime, from LeMans to Daytona to Sebring. Ever heard of Audi:)? Centrifugally supercharged cars are almost non-existant in such forms of racing. Need I mention 14 hp per cubic inch motors of the F1 Turbo Era?

Point is, if road racing is your cup of tea, turbos are very capable. Wouldn't exactly call LPE a world-renown road racing program:)

Now as for the potential for turbos and drag racing, just ask Bob Rieger, or his whiney b***h Tony Christian how well they perform:D

When you race on the street, if you do not know how to drive a turbo car, a SC car will ALWAYS have the jump, and the jump can mean the race.

:confused:Hopefully we're not reverting back to the turbo lag myth:confused:

THe other thing.. Why is it that with bigger turbos... backpressure is less???? and how can you have less backpressure than boost? That seems a bit difficult for me to grasp...

The same reason why a 4" Mufflex backpressure is less than with a 2.75" stock exhaust. That's the simple explanation:)

I'm switching to a single turbo because I wanted more power than what I could make with my S-trim, and because of adjustability and noise.

It will be nice to set the boost controller for 10psi on the street on pump gas, then double it at the track with race gas.

I am also looking forward to not having to hear a constant blower whine.

As far as lag, Innovative told me that my GT80BB (1.32 a/r) will be a bit lazy with my 357, and 'should' reach full boost by 4,500.

If that is true, then it should help tractability on the street (rather than having full boost at 2k).

The same reason why a 4" Mufflex backpressure is less than with a 2.75" stock exhaust. That's the simple explanation

The turbine on a t10000000 will weigh the same thing as t60 or so??? Not likely. Will there will be the same (non existant) turbo lag and NO backpressure, with lots of boost on the bigger turbine than on the smaller one? Then why not put the biggest turbine available?

The thing is that there should be a straight comparison with similar cars and similar turbos and superchargers to see where one gains and one lacks...

I dont think its fair the way people compare stuff.. I dont think something is that so much better. Turbos have been around for awhile and they have gotten better with time, specially with the hybrid ones.... And on the F1 turbo era? Honda was plain the best on it and they did what they had to do and they did it best with allan prost and ayrton sena...

I am not arguing the fact that turbos have their advantage... Im just saying that turbos are overrated on many aspects... Why is it that on the street turbos are very lazy.. maybe because of the smaller engines are the ones carrying them not like our engines...

Just look at the exhaust housings on a small turbo vs. a larger turbo. Smaller = more restrictive = more backpressure. However, just as with cylinder heads, the larger the cross sectional area, the slower the exhaust velocity = more lag.

This is exactly why Mitsubishi opted for "smaller" turbos in second generation DSM's. Although that move increased backpressure and ultimately peak compressor airflow, it also increased exhaust velocity and reduced lag.

And yeah, those "lazy street turbo" cars from the factory are smaller displacement motors, such as the 1.8T Beetles and Audi's; 2.0L DSM's, MR2's, and WRX's; 3.0L 300ZX's, 3000GT's, and Supras; 1.3L RX7's, etc.

Today I received the GMHTP mag and I saw an LT1 with a YS-trim doing 144mph traps... That is wicked...

I am not saying its better a supercharger, I just say I like it better than a turbo for the other reasons...

But it would be nice to see a comparison between 2 similar cars one with a similar Airflow supercharger to a turbo and see the differences...

For any given compressor wheel size a smaller turbine housing will spool faster than a larger, but a larger will give you more top end (at the expense of spool-up). This is, of course, if you have them properly matched. You have to match the compressor wheel size to your turbine size to get the results you're after. The compressor size and turbine size are independent of each other. Where you want your power range determines how your turbo is built.

The general consensus is to stay with with a single setup until one big single turbo will not supply the CFM needed. Will 8 cylinders spool two turbos faster than one? Not likely if the turbo is matched up properly. Many of the high-8 and 9sec buicks stay single until they hit the mid-low 8s for this reason. Then they go twins to get the CFM the engine needs for a given setup. IMO, twins are a waste on anything under 700rwhp b/c a single will do it and do it more effeciently. I plan on going with a single 90-series turbo on the Z rather than twins when I get around to it.

I won't argue with any of the big guys either, but I listen to Kenny Dutt with a particularly high sense of attention.

The SC vs Turbo this will go on forever, but only the owner can decide which is best for them. Just like anything, it is a compromise.

This is a very good thread, BTW.

Originally posted by The Highlander
But I disagree in the overlap and turbos... You never want overlap, specially and even more in a turbo car than a SC car. Overlap will contaminate the intake charge with the backpressure, thus reverse split cams are common...


That's not always true. If the exhaust ports, headers, turbine, and downpipe are efficient, overlap is desirable. I run a 254/254 cam custom mech roller on a 115LSA which has 24* of overlap at .050". By conventional turbo cam wisdom that's alot of overlap for a turbo cam, but for larger displacement engines with efficient heads (18*), headers, turbine, and downpipe/exhaust it works very well. My engine starts to produce boost by 2600rpm and pulls hard past it peak hp point at 6600 rpm. With almost 700 ft lbs by 3000 rpm, it gives a very wide usable rpm range.

Since I use a Hogan's sheetmetal manifold with a removable lid, it's very easy to determine if I have reversion, and with several dyno pulls and about 500 miles of street driving, there is no teel-tale evidence of it. Additionally, having discussed this with the guys at Fast Times, they have alot of experience with high-performance turbo applications. You'd be amazed at the amount of duration they run on their turbo engines (including Nick Scavo's and Chuck Samuels'). As with NA engines, larger displacement engines still need additional duration to aid in efficient cylinder filling, regardless of the fact that the manifold is under pressure the intake and exhaust flow still follow the rules of fluid dynamics.

Originally posted by Monty
That's not always true. If the exhaust ports, headers, turbine, and downpipe are efficient, overlap is desirable. I run a 254/254 cam custom mech roller on a 115LSA which has 24* of overlap at .050". By conventional turbo cam wisdom that's alot of overlap for a turbo cam, but for larger displacement engines with efficient heads (18*), headers, turbine, and downpipe/exhaust it works very well. My engine starts to produce boost by 2600rpm and pulls hard past it peak hp point at 6600 rpm. With almost 700 ft lbs by 3000 rpm, it gives a very wide usable rpm range.

Since I use a Hogan's sheetmetal manifold with a removable lid, it's very easy to determine if I have reversion, and with several dyno pulls and about 500 miles of street driving, there is no teel-tale evidence of it. Additionally, having discussed this with the guys at Fast Times, they have alot of experience with high-performance turbo applications. You'd be amazed at the amount of duration they run on their turbo engines (including Nick Scavo's and Chuck Samuels'). As with NA engines, larger displacement engines still need additional duration to aid in efficient cylinder filling, regardless of the fact that the manifold is under pressure the intake and exhaust flow still follow the rules of fluid dynamics.

ya true that......;)

There seems to be 2 schools of thinking with turbo cams. One is the popular theory that overlap is bad and because of that, more intake duration is usually the norm

The other is more of what monty is talking about and even Mr Duttwelier agrees with obviously because my cam for my TT motor has a small amount of overlap in it.

There are two very different schools of thought pertaining to turbo camshafts. Both sides are proven with great results.

Maybe.. just maybe.. the camshaft isn't that critical, as far as gross horsepower goes.

Hell, I'm running an old "blower" cam and my car hauls ass :D
I'm using the Comp Cams XE 224/236 on 114ls.

6.2X**( 1/8's first time out with a budget 355 and stock ported LT1 heads and intake with pump gas, ain't bad. ;)


**1/8 mile times are calc'd from a 600' foot track where I ran a 5.91.

Well, there aren't 2 schools of thought, the reason why some people recommend overlap is the combo. when you get up in the A/R ratio and turbo size, the boost to exhaust pressure ratio is at or near 1:1, you can get closer and closer to a NA style cam. When the pressure in the exhaust is high you have to run very little overalp. ie, small ARs and turbos.

I am running a reverse split due to i think that I am going to have a lot of exhaust pressure when running full boost. When I go to a GT80 Rtrim with a 1.32a/r, illl prolly change cams to a single pattern.

BTw, finished my turbos exhaust tonight, headers, cross over down pipe etc is all done.. weee!!

well if thats the case jordan, kenny's a moron cuz my gale bank turbo manifolds aren't the greatest things in the world and a header would be 300% better and i have single pattern but i gave him all my requirements and i think he gave me some overlap cuz i told him i wanted to run on pump gas most of the time and i wasn't willing to o-ring the motor. So sacrifice a little power for the ability to keep the heads on

not sure what kinda power you are aiming for, but there are head gasket technologies that can hold big power with out a traditional oring. anyway, more than likely he is guessin that you won't have a huge exhaust to intake pressure differential..

Turbo o Supercharger will be personal preference probably. Specially on the street.

Its like the battle with.. smaller engine and lighter car or bigger engine and torquier car... One can use the fact that top fuel only uses supercharger and some argue to why they only use them...

Its a PERSONAL PREFERENCE for me the SC, its not that is better, its that I like it more...

I am not really sure to which is better as I have yet to see a similar comparison between a single turbo of the same size as a supercharger...

I honestly think that the turbo doesn't get that power free as many people say.. There is Nothing like a FREE lunch... or so you guys say...

Originally posted by The Highlander


I honestly think that the turbo doesn't get that power free as many people say.. There is Nothing like a FREE lunch... or so you guys say...

Of course it's not free. But it is "more free" than with a supercharger:)

That is what I would love to find out for sure and by how much...

I do think its less power loss from a turbo, but, for how much and at the expense of what?

Bigger companies are leaning towards the superchargers...

GM was one that used turbo's in an era and now its using superchargers..

Mercedes is using SC
Jaguar is also using SC
Ford uses SC

Only the japs are the ones that use Turbos and nissan is moving towards SC...

Why? easier to troubleshoot? Easier on other aspects??? Why should it be easier a SC to them since they were the ones who perfected the art of using turbos...

Just a thought...

Again, it is a compromise with the big companies. The cost of tooling up to make the headers, crossovers, downpipes, boost control systems (wastegates, solenoids, PCM programming time, etc.) all outweighs the costs of their percieved performance vs. cost benefits. They can do it cheaper with the SC route. Especially since they're building cars for the masses. Think about it: if they can make a car pull (some) horsepower using a SC at about $1000 less per unit than with using a turbo set up, after making 50,000 cars they saved $50 million dollars. And thats not considering all the initial investments need to produce them.

The stage 2 buicks are prime testaments to turbos: 4.5L V6s making well in excess of 1600 hp and they're making more with every passing day. The most powerful SC'c V6 I've seen so far was a 1000hp 4.3 chevy.

Under equal circumstances a turbo will produce more power simply due to the fact that the crank's rotational force isn't being used up while turning a SC's compressor. Baxter was making about 1,100 hp with a SC, but I'll put money on it that the SC was consuming at or near 200hp. That's why I'm thinking that 1300 turbocharged horses are possible on a LT1 (especially considering the fact that turbos are much more forgiving on the rotating assy). It has been shown that for every 100hp you get out of a SC setup, anywhere from 20-30 is being used to turn the SC. The math is rough, but the concept has certainly been proven.

Talking potential, turbocharging is where it's at ---> relatively unlimited boost. Something was metioned earlier about the big guys using SCs in pro dragracing; that's because turbos were banned in the pros. They're making 5-6000hp with near 50#s of boost right now and with turbos how much boost do you think they'll be making? 70? 100? The traction technology simply can't contain that much power right now.

Like I said earlier, it's a compromise only the buyer can make. The depths of your pocket determines how fast you can go. If a SC will help you reach your goals, then go for it. But sooner or later you will end up going the turbo route b/c it will be much easier to attain higher hp numbers.

In addition to what Fast Caddie mentioned, one of the primary reasons why factory turbo cars are less common these days is emissions standards. Particularly at cold start-up.

Think about it. Throw in a massive hunk of metal, such as a turbo, between the exhaust ports and cat(s), and it will suck up precious heat that would otherwise bring the catalytic converter to operating temperature in a timely manner. Cold cat = non-functioning cat = lots hydrocarbons = failing emissions standards = pissed off Feds = not being able to market a car in the U.S.

Case in point: almost if not all European manufacturers, from Renault, to Peugeout, to BMW, to Mercedes, to Audi/VW, to Saab, to Volvo, to Porsche, to Fiat, to Alfa Romeo, to Skoda all offer turbo models. Most mentioned do not ship many of their turbocharged models to the States simply due to more stringent emissions standards.

Most stateside probably haven't a clue BMW and Mercedes even offer turbo models. This includes high-performance diesel models that really scoot, yet still yeild superb gas mileage. On this side of the Atlantic, "high-performance diesel" is an oxymoron:)

It's not that the Japanese are the only ones still producing turbo models, but rather they seem like the only ones still exporting them to our neck of the woods. There are actually more European turbo cars in production - we just don't see them here.

In essence, OEMs opt for SC's over turbos for the same reason as many 4th gen F-Body enthusiasts: far easier and cheaper to package, not necessarily for any performance advantages. In addition, for OEM's, SC's are simpler to mass produce.

However, of all the manufacturers you mentioned - Mercedes and Jaguar/Ford - each opts for roots-style blowers, not centrifugals. Hell, Shelby's the only "manufacturer" that straps on a centrifugal from the factory, if you can even call that operation a "manufacturer." No one else runs them:)

Again, the popularity of roots blowers from OEM's probably revolves around packaging and costs, but also "street performance (almost instant boost)" and longevity. Roots blowers have been proven to last over 100K miles. Not too shabby. Cheap, reliable, easy to R&D, and significantly improved power where it matters most for the general consumer - down low. For an OEM, what's not to love?

This debate would be much different if comparing turbos vs. roots or screw-type blowers rather than turbos vs. centrifugals. A roots significantly closes the "area under the curve" deficit a centrifugal sacrafices to a turbo.

The Lightning and Cobra come to mind as roots-blown cars with gobs of low end torque, especially compared to a centrifugal SC. Additionally, in smaller-displacement motors, the ol' roots flat out kicks a turbo's ass in street performance.

IMHO, unless shooting for really big power, the poorer adiabatic efficiency of a roots is insignificant for the majority of street motors. Up to about 500 - 600 RWHP, I'll take a roots over a centrifugal any day of the week. Lower ultimate power potential? Yes. More "total" HP/TQ for any given "peak" HP/TQ vs. a centrifugal? You bet:)

Yes, the die hard centrifugal blower fans could brag about their superior efficiency, but at the power level most are at, it wouldn't matter anyway. Plus, I'd have SO much more low/mid range torque to boot:)

Actually, I am not favoring per se the centrifugal type.. I was talking about the supercharger...

I do have a supercharger because it was easier on the $...

But one question is:

If I am getting my peak torque at 4200rpm why should I need more power lower if when racing I am never lower than that?

Anyways... the supercharger used in NHRA I think its a roots type..

The other thing I would like to say... In some points and rules (dont quite remember now) they banned the use of the paxton vr4 due to its superiority for short races...

You guys are right about the european cars and turbos and not comming here.. I knew about them, I just for got about them when writting the other post...

I still think that superchargers are underated... And also centrifugal type...

I wish I could mount a novi 2000 on a camaro and see where it goes, that I bet it will go as far and even better than a YS-trim for the street, which is comparable to a T76 turbo...

I think that turbos are unlimited due to the bigger cfm rating than your average supercharger.. (s-trim, t-trim)

Blower for off the line & turbo for the rest :)

dont confuse "roots" and "screw" type blowers.....they aren't the same

screw types are MUCH more efficient than roots and offer the low end punch of a roots. That is what is being used on applications like the GTP and Cobra

We can make points for each... it's all what your goals are for the car. For most, boost using a centrifugal blower is the easiest, cheapest, and least maintenance way to go fast. For others the intricacy involved in building a tuning a proper turbo system is a task they look forward too. I mean let's admit for power, especially torque, the turbo will kick a blower ass to hell. The main idea here is area under the curve... A blower's power is gradually increasing whereas a turbo's power kicks in at full force right when you punch the gas. I mean whats better than cranking the boost up from the driver's seat.

For turbo OEM cars... man, I don't even want to start... Audi and VW for example. With a simple chip to up the boost you already have a high 12 low 13 second car in an S4. Turbo technology is going to keep getting better and better as emissions standards get more and more strict... a turbocharged car will not waste all that gas unless your foot tells the car you need it.

I actually traded my turbo technologies kit for my vortech. And although I do sometimes regret it, I think of how much money I would have to have put into the car to make it run the way I want and then I am happy again =) I mean think... FAST, T-76 upgrade, wastegate, intercooler, blowoff valve, boost controller and many other upgrades... With my car there are so many people blown that its really easy to get help with the car. Well this is long enough I'm done =)

Originally posted by 89ProchargedROC
dont confuse "roots" and "screw" type blowers.....they aren't the same

screw types are MUCH more efficient than roots and offer the low end punch of a roots. That is what is being used on applications like the GTP and Cobra

Doesn't Whipple own the patent on all screw-type blowers? Consequently, if I'm not mistaken no current OEM runs screw-type blowers.

The Cobra (http://www.svt.ford.com/flash/svt_pdf/2003_SVT_Cobra.pdf) and GTP (http://www.automotive.eaton.com/product/engine_controls/displacement.html) do indeed use roots blowers.

if so, my mistake. I was told otherwise