Mike, you claim a bolt-on Lt1 would only have 250 rwhp? My car stock put down 260 rwhp BONE STOCK and while it may be a freak, its not special by any means. Another thing you must consider, A bolt-on Lt1 would have headers, which if designed correctly, his turbo manifold would reduce backpressure and increase flow. There are numberous LT header bolt-on cars with over 300 rwhp. So in effect, he's not really doubling the power output.

I also wanted to add, why is 15lbs of boost needed to get to 500 rwhp? What KIND of 15psi? 15 psi from a t3/4b, 15psi from a t88, 15psi from a t4-60-1? Boost is just a pressure, and can't you have more volume at the same pressure, with a bigger compressor?

 

exactly.

im no boost expert.......but PSI is not the only factor.......you also have to account for CFM at that particular PSI.

 

Power production is directly proportional to air density in the cylinder at BDC of the intake stroke. Air density is related to temperature and pressure ONLY. If motor A and motor B are identical and have the same intake air temperature and pressure, they will make the same power regardless of the method used to pressurize the air.

It's really just the basic laws of Thermodynamics.

However, if someone with a small turbocharger attempts to spin it fast to achieve a high amount of boost (or supply a high volume to too large of a motor), he will run the compressor out of it's efficiency range and heat the air significantly, cancelling out some of the power he hoped to gain. So, it would be beneficial in this case to switch to a larger compressor that will run efficiently at the higher boost (and flow) levels. Larger compressors will supply more air at the same boost because the temperature of the air is lower. You can, however, aftercool a small compressor's output and get the same results of a larger non-aftercooled compressor.

Flow ratings have largely to do with the ultimate capability of the compressor. For instance, if I install a 4000 cfm throttle body on my LT-1, will it make 4 times more power than my 1000 cfm unit. Don't think so. But, if I really needed that much flow, I'd gain from it.

Mike

 

A stock LT1 can only flow so much at any given boost level. It doesnt matter what you have feeding the boost in. At 15PSI, the LT1 will flow X amount of air. Given that the air is the same temperature of course. Just trying to simplify engineer's thermodynamics

Argh, now I forgot what else I was gonna say, but I agree 100% with Intmd8 and engineermike

 

at what CFM is the stock heads/intake/tb/maf combo maxed?

 

Actually, you are wrong...

I will offer some real world evidence... There are plenty of supercharged stock long blocks making that much horsepower despite the paracitic loss the supercharger draws off of it. And they are doing it at 10 lbs.

Second, simply doubling the pressure inside the intake manifold means little. Engines make horsepower by burning a certain amount of air with a certain amount of fuel. You are attemping to over simplify the process and your logic is flawed.

At 100% volumetic efficency a 349cid engine will flow 607.12 cubic feet of air per minute at 6000rpm. I don't know about your LT1 but getting 300rwhp out of full bolt on lt1 isn't uncommon. I'll meet you in the middle at 275rwhp which is roughly what they dyno stock. They generate peak power roughly around 5000 rpm which gives them a volumetric efficiency of about 78% at that RPM. That means that a stock LT1 is flowing about 450cfm at 75% VE and 6000rpm.

Because the engine is not 100% volumetrically efficient, the air pressure in the cylinders is less than ambient when the piston reaches the bottom of it's intake stroke. That means the air pressure in the cylinder is closer to 11.466psi @78%. If you were to ever install a boost/vaccum gauge on a naturally aspirated engine, you will notice that even at wide open throttle, there is vacuum in the manifold. Since the boost gauge references ambient pressure, in order to bring the boost it to 0, the turbocharger must push 3.234 lbs just to make the manifold pressure equal to ambient. Going beyond that to reach 10lbs, it is actually pushing 13.234 "lbs of boost" for a total air pressure of 10lbs over ambient. This more than doubles the air pressure inside the mainfold. Using your logic, that is a 115% increase in horsepower potential. If it were achived, that would be 591.25 horsepower to the rear wheels. See what happens when you try to over simplify things?

You didn't consider one thing in your equations... Density. By compressing air, you heat it. By heating the air you make it less dense. Ever notice your car runs better on cool dry days? A 75% efficient compressor will heat the air about 121 degrees over ambient. At 75 degrees that would bring the air at the compressor outlet to 196 degrees. Assuming a 90% efficient intercooler, that drops the air tempurature to 86.28 degrees. Now you have relatively dense air at high pressure flowing into the engine; something to the effect of 750 cfm

Another thing you forget is compression ratio. Last I heard, an increase in compression ratio results in an increase in horsepower. It seems to me that if an engine has, say, 10:1 compression N/A, if you introduce significantly more air into that cylinder, and compress it into the same volume, your compression ratio and horsepower will increase from that alone. (Remember I said these tests were made on race gas).

Now lets take it a step further. If the engine makes 275 horsepower to the rear wheels and there is 12% loss in the M6 drive train, that means the engine is making about 308 to the fly wheel. Not too many will argue with that. That means it takes 33 horsepower to drive the drivetrain. Sinse it doesn't take any more horsepower to drive an M6 drive train with a 550 horsepower engine than a 308 horsepower engine, we will leave it at 33 horsepower. Given the above we can estimate that the turbocharger is adding about 66 percent more air to the engine. Burned well, that means a horsepower output of 513.33. Take from that the 33 horsepower the drive train requires and walla.. 480.33 horsepower.

But it still not that simple. The day I dynoed 484/540, the air was cooler, and the car was very lean. We are also not considering the compression increase from boost which results in power. This also doesn't account for the better exhaust system, or the better ignition system. All added up, it probably should have dynoed more. But what can you expect from a stock engine?

Your lack of faith is amusing. I guess you assume I get my rocks off by making things up and posting them on this board. But the question still remains; how much are you willing to spend to prove I'm wrong? Enjoy!

PS - Happy New Years everyone and be safe tonight!

 

I will not bet money because you will not (and can not, practically) prove to me that what you are saying is true. Unless you're willing to come run it at State Capitol Dragway in Baton Rouge and completely disassemble the engine afterwards, don't offer up a bet.


Let's see here. . .

You would not need to make 3.234 lb of boost to reach ambient pressure in the manifold. You would need 3.234 lb of boost to reach ambient pressure in the cylinder. I'll bet that a stock LT-1 at full throttle develops less than -1 psi in the intake (not -3.234). So, your logic is flawed. The 3.234 psi positive pressure never actually makes it into the cylinder.

Next, a 75% efficient compressor (at 11 psi dp) heats the air 135 (of which 92 degrees was adiabatic, and 43 was due to inefficiencies in the compressor), for a discharge temp. of 210 (not 120 and 196, respectively as you said). Time to pull out your Thermo book. . . Or maybe you used the wrong units. . . You know you have to convert to Rankine degrees, then to Enthalpy before doing these calc's, huh?

I would check the rest of your math, but I really don't have time to play TA right now, and besides, I think you get my point. I have a party to go to.

During my next reply, I will be hung over.

Mike

 

Nice posts engineermike and turbospeed!

Some other guys post made me think about another common argument: Superchargers vs turbos. This first came up a few years ago and I am still sticking to my original response to that one. If turbos were so good, then why haven't NHRA funny cars and top fuel gone with them? They are running blowers, not turbos! And, they will never run turbos from what I hear.

And it doesn't matter which one you use to force air into your street motor, intercooling will help by decreasing the inlet air temperature and thus increasing the air density making more horsepower. This is what turbospeed was trying to say, on a cold night your car will make lots more power if it uses forced induction. With the increased power however, you need to compensate with more fuel. If you don't, you may be leaning out the motor and increasing combustion temperatures which causes detonation.

Another big factor in the power making capability is the camshaft and cylinder head design, this hasn't even been mentioned yet. These will basically regulate how much air is let into the cylinder, whether its NA or blown.

Anyway, Happy New Year. And engineermike, I hope my hangover isn't as bad as yours!

 

You say his times are BS and the dyno must have lied, even though other people wrote saying they saw it with their own eyes? Hell one guy even wrote about a ride in the damned thing, yet you still think it's all made up because your equations backed up by big words will never allow it to happen. Sounds a little like scientists with thick note pads trying to tell Chuck Yeager he was on a suicide mission because it was proven that sound barrier could not be broken. People on the ground thought the sonic boom was ol' Chucks demise, yet he was up there probably laughing in his helmet at those amazingly smart scientists. You don't have to believe... And no offense but if you think TurboSpeed is going to hop in the car, drive down to X dragway, tear down his set up all just to prove he's right, your not quite as smart as you like to think you are. Just an opinion and I don't mean to speak for TurboSpeed. I hope your not too hung over if you read this, but I do hope you had a great party and a nice New Year.

 

First of all they are not legal. And not needed. The cars are already making 6000- 7000+ hp. What would they need a turbo for? They have even done things to SLOW the cars down in the last few years. The NHRA officials and the DRIVERS THEMSELVES have even said the cars were getting to fast. Your response has no basis. Turbos are not needed , and I don't even think desired, nor are they being considered, in the TOP fuel (nitrometh) classes. Just because someone does not make something legal in a class or does not want to use it, does not mean the reason is because it's not as good.

But as far as classes where they are legal , look what the top runners are using. How many blown cars or nitrous cars do you see winning in PRO STREET, or PRO 5.0 now. The turbos, have taken over. Don't get me wrong ,supercharges and nitrous are awsome, but turbos are superior in terms of potential, and also engine reliablility to the others.

 

Ive read this forum for years,but never registered.But I did register just to reply to this one post.I was at the track,and was watching turbospeeds frustration after duct-taping the the plastic elbow to the point that it looked like a boa that just swallowed a large house cat.Then the clamps werent holding the intake tube to the elbow,then thats where the string came in.Ive been going to the Tulsa track for years,and when I had heard about his car,I was one of those non believers too.One thing is a fact.He did run the 128 mph.He made pass after pass,trying to get it to hook up with not too much luck,but was always running 122+ mph.Granted I havent seen the inside of his engine,I have seen the outside, and it is as he has says.Unless my eyes are bs,n me,guys,all this is stand up and straight.And my hats off to ts,cause he did all the construction,fitting and work himself.

 

I dont think alot of people are doubting that these are correct dyno's or that he is pullling 129 mph - 1/4....Those number can be easily obtained, just hard to beleive they can be with a stock car. My buddy's fully forged Blown 4v Cobra put out 540hp/440 tq to the wheels. He went 10.90's at 127mph. On the other hand my friends lt1 car blown with a cam, went 12.0's at 119 mph putting out 454rwhp. I am not calling bs yet, but if this is for real I will be one happy customer.
SCott

 

tubros were outlawed in top fuel years ago
why? because they were completely blowing away the competition.

by design, a turbo will create more power than a supercharger.

but years and years and years of them just using superchargers has led to much more advances in them.

if they had been spending all this time working on turbos in top fuel, the power levels would be insane.

 

I was at Route 66 that night when Kenny Bernstein went 330 mph. His car was probably making over 6500 hp - that is plenty enough insane. If turbos would push the cars much faster than that, the biggest problem, other than stopping, would be how to prevent the driver's retinas from being pulled off when the chute is popped.

As to the turbospeed car, I think most LT1 people around here are used to the fact that the power level needed to go 129 usually requires a better than stock fuel system and engine rebuilds are usually a spontaneous effect of going that fast on stock internals for any length of time. I also think it would take quite a bit of boost to overcome the limitations of the stock heads, cam, & valvetrain. Don't see how you could get away with stock springs, though, especially stockers with a few miles on them. Sems like the boost would play hell with the intakes.

Sounds like there are plenty of witnesses, though, so I guess we'll have to wait & see.

 

Who gives a **** if they are legal or not. Just like you said, the cars are making 6000-7000 hp, so a turbo is not needed. Well, a turbo would not be able to support this much horsepower my friend, otherwise they would have incorporated them a long time ago, don't you think. The supercharger remains the king, and will be king for a long, long, time. Just because turbos are supporting much lower horsepower in street cars doesn't mean it could feed a funny car or top fueler. Your comparing fish with sharks.