It's too bad you cannot use a simple 1.5 more air = 1.5 more hp, based on PSI. Because if that as so, then an engine with a more efficient top end that flows better, would make the same power at the same boost levels, which doesn't happen in "the real world".
Say you have 6 psi on your stock LT1, and it makes 400 RWHP.
Now, you swap out a ported LT4 intake, bigger TB, ported heads and a dedicated turbo camshaft. Now you still leave the wastegates set at 6 psi, but for some reason the darn car is now making over 500.. but at 6 psi. So how do we explain that? Simple. PSI does not tell you the amount of airflow moving thru the motor. Boost is not boost, as they say. 6 psi at 100 deg. IAT will most definately make more HP than 6 psi at 180 deg. IAT.

And to further this, I haven't actually measured the "psi" coming out of a nitrous system, but somehow it is able to add 150 hp, and I can pretty much guarantee that there is no where near the air coming out of that itty bitty nozzle as compared to a turbo.

 

I've done the calculations on this many times in the past to prove/disprove someone's claim to power gains. A while back, someone was on here claiming some outrageous turbo hp numbers. Coincidentally, I believe he was spraying Nitrous on the intercooler (air filter) also. I will respectfully add the following:

Stock LT1: 260 rwhp.

Use the following to calculate density of inlet air, keeping in mind that hotter air is less dense also:

density = P2a/P1a*T1a/T2a

So, 260 * (7+14.7)/14.7*(60+460)/(100+460) = 356 rwhp

Now, take into account that the actual compression ratio will be higher. I found the following formula somewhere on the net and it seems reasonable:

boostedCR = CR * (P2a/P1a)^.5 = 10.25 * (21.7/14.7)^.5
boostedCR = 12.5/1

So, for every full point in compression, you gain around 5% power.

Now, we have 356 rwhp + 28 rwhp (2.2*.05*260) = 384 rwhp.

Almost forgot pumping losses. I did some calc's a while back on this and determined that a supercharged motor in this range takes about 40 hp to drive. A turbo, by adding backpressure to the piston on the exhaust stroke, takes about 30 hp to drive. HOWEVER, most of this (maybe 70% of the 40 hp) is recovered during the intake stroke, since there is now positive pressure above the piston helping drive the crank. Let's call this a wash.

If anyone sees anything wrong with this methodology, please let me know so I can better understand these things.

I agree, as stated above.

The only reason this is true is if the T88 is running at a higher efficiency than a T70 at that pressure and flow. Then, the discharge temps will be lower, so the charge will be more dense. Otherwise, a large turbo and a small one will make the same power, unless, of course, the small turbo has reached choke flow.

I have to disagree here. I tested the pressure in my T-trim volute, then in the intake plenum. I got 14 psi at the blower and 13 psi in the intake. According to Corky Bell, this is exceptionally good. Also, most of the 1 psi drop is occurring in the 52 mm throttle body. Water/Air cores typically have much lower pressure drops than Air/air, since the boosted air is travelling over the tubes of water, while it has to go through the tubes in air/air.

True, usually about 30% more than a turbocharger. The turbo just takes it in a different way. Nothing is free.

I have to admit that his is true, though it is very annoying to me. Most guys who build that baddest stuff don't know much about how it REALLY works. They figured it out using trial and error, or just plain brute force.

Working on it. . .
I agree with this also. . .

Looking at the science behind it, there is very little difference between turbos and superchargers based on the drive methods. We're talking 10 to 15 hp difference at the same boost, which is probably a wash when you consider the more torturous exhaust path of the turbo. At low boost / high flow (if you have a 572 cid motor), a Vortech S or T will work better than any mid-frame (street) turbo since choke flow is much higher. However, at lower flow / high boost (350/383 at 20 psi), a mid-frame turbo will work better because you can't spin a S or T Vortech fast enough to build that much boost. A turbo will build more boost down low, but that can be remedied with a loose converter with the supercharger.

Hope I don't offend anyone here - I'm just trying to apply a little physics / thermodynamics to the issue.

Mike

 

all that theory is fine and dandy except Ive proven it to not work out in reality numerous times in multiple cars on various dynos aacross the nation.

 

The mistake a couple of you are making is assuming that the n/a motor is operating at 100% efficiency (which is the only way the motors could use all of the air available at 14.7). That's why your calculations are off. Most engines in street cars are not running even close to that especially with the cam timing, filters and smog equipment. FI brings the VE well above the 100%. That is why you can see such a large gain at lower boost levels.

You can also see an efficiency difference in types of FI, ie turbos, superchargers(a well set-up turbo system is far superior). You can then go a step further and see a difference in the efficiency of each kit ie intercooled, non-intercooled, Procharger v powerdyne.

So it not as easy as saying 7 psi equal approximately 50% more power. That can get you close sometimes, but what you should really be looking at is the amount of air that is being consumed. That is the best way to “guess” what kind of power an engine is putting down.

Later,
Dave

 

What??!! No hard fast formula? I can't believe that.. next you are going to try and tell me the world isn't flat... when will it end?!!

And not only the amount of air, but the "quality" of the air..

 

Are we now saying that calculations can't describe what goes on in a turbo/supercharged motor?

Must be magic, I guess.

 

I included temperature (if that's the "quality" you're referring to) in my calculations. I assumed 60 deg F NA and 100 deg F boosted.

 

That's actually exactly how the calculations work.

Let's say your VE is 80% NA. That means at BDC before the compression stroke, the pressure in the cylinder is 14.7 * .8 = 11.76 psia. Now, change the intake manifold pressure from 14.7 to 21.7 and you could expect cylinder pressure before compression to be 21.7/14.7 * 11.76 = 17.36 psia. This makes the boosted motor 118% VE. Now, use the cylinder pressure ratios (hence VE-based) to scale up hp and you get 17.36/11.76 * 260 rwhp = 383 rwhp. Hmmm. . . that sort of sounds familiar. Now scale it down based on higher temps, and up based on compression ratio, and I bet you get back to the same 384 rwhp I calculated earlier, just using VE as the method this time.

HOWEVER, if we assume 300 rwhp to start with and run through the same calculations, you get 442 rwhp. Maybe your LT1 is a hot one. . .

Mike

 

what kinde of turbo kits r these on the lt1 because ive been looking into some diff kits, ....if u could email me the info to bojbp@hotmail.com
that would be awsome

 

Well... i would love to chime in with all the math and stuff but engineermike has done the gross of the calculations...

What i would like to add is this:

I still prefer superchargers over turbos for lots of reasons... One thing i still can't figure is why turbos are not performing at par to its HP rating and superchargers are.

I did a topic about this once, long time ago... it could be brought up again and read.

ON small engines i see that the available superchargers are too big for the engine and turbos are better. Better "tuning" with the engine size maybe. The smallest anyone straps in a car is an s-trim and the s-trim is capable of 600rwhp... on a 2L engine 600rwhp is quite difficult although done many times...

I've never seen a supercharged Grand national and they are GMs turbo era and they were all fast... but on big engines, i tend to like the supercharger more. For whatever reason it is...

How do you explain that i beat a 590rwhp rx7 that did 10.5 @ 131mph in the quarter with only 607rwhp and more weight???????? TORQUE???? maybe, but that could be based on the engine type... still...

Superchargers do not mess with the exhaust system. The power difference is minimal at the same ammount of boost. A bad turbo header will hurt a lot more the engine than the belt that drives the supercharger... i dare any of the turbo guys to really remove the intake portion and run the car to see how much power it removes. Many of the log style turbo headers will create almost 4:1 back pressure and with ideal cam timing and such on a street engine with good turbo headers 2:1.

Again as said by engineermike.. There is nothing like a free lunch and turbos are pretty restrictive...

Mike said it correctly about the turbo size and psi which is something MOST people neglect. 7psi in an s-trim is not the same as a T-trim nor a YS-trim. The ys-trim will make more power at that boost level.

THe only REAL advantage of turbo vs centrifugal supercharger is area under the curve, but..... but.... I tend to see many turbo cars choke up on top end run vs supercharged car, and the centrifugal supercharger likes top end runs, or at least that is what i feel, seen, compared.

with the same HP PEAK i tend to prefer it this way:

N2O>N/A>S/C>Turbo

N2O is the only power adder with NO PUMPING LOSSES.
500N/A hp will tend to beat 500HP supercharged and/or turbo HP.

Anyways i don't know much so take this as a grain of mustard.

 

Thats way to many numbers for me to figure out. Id just put N2O on it and let her run. Not much to figure out there except this button makes the car go a lot faster!!!!!

 

Tell that to the top fuel guys

N2O>N/A>S/C>Turbo

 

turbochargers will always make more power than a comprable supercharger. period end of story. turbos make more hp and more torque. they are more efficient than superchargers. if properly sized they have very little lag, but the lag can be a good thing when you are running 500+rwhp. the only perverbial parasetic loss on a turbo set up is the flow capacity of your head and intake manifold. with the supercharger you have the parasetic loss of the belt. also find a supercharger that doesn't have lag. you can't they all have some lag thats why they still have to gain rpm to build boost.

 

Really? Then why did baxter's X-trimed LT1 top out at ~900rwhp and run 9.05 at 155.... and chris sikora's SC'd LT1 is running on edge at 8.90s... while bigrick's single turbo LT1 is making damn near 1200rwhp and running 8.30s at over 170? (he's the first person to build an actual max effort turbo LT1, we'll be seeing more of these i'm sure). That was on shakedown runs too, not even onthe 1200rwhp tune.. When he gets it back together and running full boost he'll be in the 7's... beating the current LT1 records set by superchargers by almost a full second. Turbos make more power. The mustangs boys will agree.... I think it's Millen or Murillo that went 6's at 206mph with a single turbo mustang.

Yes i remember the last 10 threads about turbos vs SCs you were involved in. And how MANY MANY times you were proven wrong WRT max power. You just won't listen.

Biggest reason buick went with turbos is because they have more potential and longevity.... they knew exactly what they were doing when they built a car that would crush chevy's flagship car, the vette. They'd rather use turbos for longevity... i know of many GNs with well over 150k miles still running the factory engine, turbocharger, injectors, etc. Never seen an automotive SC make it that far without a rebuild... or at least being in near brand new shape. As for the RX-7.... who knows. Why are many 600rwhp supras still in the 12s? Why does the universe go around? Hmmm.... too many things to consider.

So are SC's. Mike already stated, in his experience, that SCs exhibit more losses than turbos, go back and read it. And you're right about the turbo headers.... their design is crucial and can make or break a turbo setup. Just like some ****-poor SC setups, usually it's just one component that holds the car back and the owner/builder doesn't understand why

This we do agree on.... compressor size, blade design and pitch will all have about the same effects on the compressor's ability to move air. No matter whether or not that compressor is attached to a pulley or a turbine housing, it's still gonna be limited by these attributes. But where turbos do shine is in their ability to turn many more rpms. Most SC's top out at around 60k rpm.... Turbos will go well over 100k rpms. And kinda like in a engine, more rpms means more potential since you can move more air at a faster rate.

*cough* supra *cough* skyline *cough*
Since when do these "choke up"? Biggest problems with SCs in high reving engines is that the belts are a HUGE liability. Look around at the max-effort SC members on this board... their biggest pain is chucking belts all the time and can't get them to be very reliable. Yea, you can go with chain drives.... but you better hope to hell that it doesn't break or everything in the front of your car is in grave danger. The most wicked top end runners i've ever seen were turbocharged. LT1s, LS1, 4V modulars, the import guys with thier little 4 and 6 cylinders.

Well most of that is true. But pumping losses or not, it's the overall amount of power you make that shows where you're at. It'd be quite difficult to get 1000rwhp with a NA 350, no matter what heads you're using... or 1500rwhp with nitrous on the same engine since you can only inject so much without blowing the top end to pieces. But with FI you can go well beyond those limits. And it's kinda hard to put aside that the world's fastest cars are turbocharged... save for top fuel and the like since turbos are banned from those classes. Wanna know why? The same reason nitromethane was banned many years ago... too much power for the saftey of the drivers. Then technology caught up and nitro was allowed back in once people were running the previous best nitro times on gas. I'm sure that one day, when tire technology gets better, turbos may be allowed to run in TF. And then they'll probably be running a LOT more boost than the current average 50#s of boost they make with the roots blowers now.

I've always regarded you as one of the more knowlegable members on the net. I just don't agree with everything you say about SCs and turbos.

I think you guys are very knowlegable.... moreso than me.... but i just can't fall away from what people like kenny duttweiller, who is one of the world's best when it comes to FI, has stated and proven during his years. He's been in the FI game for decades and he can and will show you how he's crushed most supercharger setups with turbos. He almost uses them exclusively. The best one i've seen so far is the hot rot he built the engine for in SEMA the other year.... 502 BBC (Dart Big Cheif heads, IIRC) with twin turbos and intercoolers... makes almost 2500hp on pump gas. I'm telling you, turbos can and will make more power in the end...barring rules not restricting them from use. I've even talked to a few automotive engineers (one of which is from BMW in greenville) during my stint here at clemson who agree on most things about the 'ol SC vs turbo comparison. They see a much better view of it that we do. They each have their pros and cons, but if it's max power you're after, turbos are for the job no matter what engine you use.

And being a hyprocrit to my own words, i'll probably end up supercharging my Z28 just from the cost and packaging standpoints. It won't be a max-effort build, just a strong street runner.

Just my $.02

 

I always get the "what PSI are you running" PSI is not an exact measure of HP.

Turbochargers WILL PERIOD make more power than a supercharger if they are a campared size as someone stated here. Turbo makes power by wasted gas. Charge robs power to get power (belt driven). They ARE more efficient than superchargers as well. Most of the BIG hp guys out there are pulling BIG MPH with the turbo set-up's. A few guys here were running charge and now turbo and beating records. (not that anyone with charges are not) If you properly size the turbo, they have very little lag. (I know as I have a big turbo, but not like it will compare to the BIG name guys) The only loss on a turbo set up is the amount your head will flow, intake TB etc... Heck with the same boost on my set-up changing nothing BUT the head. I went from 608 RWHP & 561 RWTQ to a whopping! 620 RWHP 7 651 RWTQ JUST ON THE HEAD Exact same boost. Not to mention I didn't do the cams yet. The good thing about the charge is that it does not have lag. (IMO lag is overated anyway) Some set-up's will have lag as RPM build's boost.

No matter if the engine is stock or not, if tuned right it can take alot of power if tuned correctly.


My .02

Duane