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.

 

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.

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.


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 *** 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.

 

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...

 

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

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

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 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.

 

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.