qqwqeqwrqwqtq

LOL. Not sure what else to say if you want to argue with real world results and a logical explanation to support them. Why did you dismiss my examples? Those are real world results.

A single GT35R can probably make around 700rwhp on a 2 liter. Say it's 40psi boost and 40psi backpressure.

You think a single GT35R would make 700rwhp on a 454 LSX? It would probably make 10psi boost with 100psi backpressure. This you think makes no difference as long as you haven't exceeded the compressor wheel flow potential and I'm the one making no sense?

As has already been explained to you multiple times, for any given turbo when you increase displacement you will move further and further away from ideal (one to one) intake/exhaust pressure, shifting powerband to the left and decreasing max hp potential.

If the 2.0 liter maxes out the turbo at 7000rpm and the 7.4 liter maxes out the turbo at 4000rpm you think this will have no effect on the power curve and effective RPM range? HP=torquexrpm/5252. If the larger engine reaches the same mass flow at an earlier RPM how could it possibly equal the same horsepower as a smaller engine reaching that same mass flow at a higher rpm?

Not sure why you think that further reasoning can make your theory trump reality.

ddnspider

iTrader: (26)

thank you! This thread is full of fail. I've always leaned way more on real world examples as opposed to people's theory, although in this case it's very logical to prove via math already posted that rpm, indirectly or directly affects a given turbo

slow67

iTrader: (2)

HAHAHAAHAH....you have some learning to do. Most modern turbocharger turbines are a combination of implulse turbines and reaction turbines. BOTH of which get more efficient as heat increases, so YES they care what temp the fluid is.

IF its a constant regardless of temp and pressure, why do they have to put the atmospheric pressure and temperature on the maps? You have to use the ideal gas law to convert between either. They are both variable based on temp and pressure.

And you are moving the same amount of cfm.

Orr89rocz

iTrader: (13)

lbs per min is a mass flow. mass can not be created or destroyed, its constant no matter what. It doesnt care about temp or pressure. What maps are you seeing that have temp and pressure listed?

mass flow * specific volume (which is just inverse density) = CFM. Specific volume is directly related to pressure/temp of the gas mixture and why CFM changes with pressure and temp.

Now the mass flow required to hit a hp number may change depending on how efficient the motor is. Just because you have X lbs per min, not all motors will make Y hp corresponding to that X lbs per min. That does change with air fuel ratio/bsfc/ve of the motor.

stoverz28

iTrader: (8)

A turbo is limited by horse power. Horse power is rpm and torque dependent. Therefore, at a given torque output, the turbo will choke at x rpm or y horse power however the hell you want to look at it.

Don't really see whats so complicated here.

05HD

Despite you being the only person posting in this thread that knows what they are talking about, I am going to have to disagree with you here. A Precision 76/75 would be a perfect choice for my 454. WTF are you talking about you say? Well, my 454 is an L29 big block planted in a crew cab dually. Everything about it is completely optimized for making torque from idle to 4 grand. It is wheezing like a 2 pack a day smoker trying to run a marathon by 5 grand.

Will that 76/75 make 1,000 rwhp on my big block like it does on a 2JZ? Well, of course not. I'd be surprised if it made 700. Turbos make torque!!! Horsepower is just a measure of how fast you can make that torque but, the application dictates what the optimum RPM range to make that torque is. A 2JZ with a 76/75 wouldn't do a very good job in my dually pulling around an enclosed car hauler.

slow67

iTrader: (2)

Right, but turbos aren't mass flow devices. They are volume flow devices. Change the inlet conditions, but with the same shaft speed and P/R, the mass flow will be different, but the volume flow is the same.

Orr89rocz

iTrader: (13)

Change in mass flow will be change in hp/tq. Either way you look at it, mass flow or volume flow, you can calculate one or the other if you know the inlet conditions your dealing with. Most maps deal with lbs per min which already factored in a desired hp level, cubic inches/rpm, temperatures, etc based on your motor. You calculate the lbs/min required and go from there.

slow67

iTrader: (2)

agreed, I just think compressor maps should be in cfm, so people don't just say its worth "XXX HP". It would also be helpful for compound turbo calculations.

gregrob

iTrader: (8)

This thread makes we want to ******* eat light bulbs.

Fbodyjunkie06

iTrader: (10)

Go ahead I started throwing **** on page 1!

Mr. Sir

So... I have a new question, relating back to the 4.8/6.2 questions. If you were to introduce a flow restriction on the 6.2 and bring boost up to 40 psi, would you now be able to make the same hp as the 4.8 at 40 psi? It's pretty much unargued that for a given volume of air, a given volume of exhaust is produced, at a (generally) comparable heat value for all engines, meaning similar exhaust pressure, regardless of engine size. So given exhaust pressure is similar (turbine speed is similar), if the compressor was bumped from seeing 10 psi to 40, would power output between the engines be the same? And I know someone will come on here saying that intake restriction = less power. psi is nothing more than a restriction value. By that merit, 40 psi of restriction, regardless of how it is obtained, should get a similar volume of air into the engine. So by running some form of restrictor (preferably one that only activates at higher rpm), could you generate similar power?

98Z28CobraKiller

iTrader: (17)

You can can't do that but if you figured out a way to do it, then the turbo would perform the same.

Mr. Sir

...cool. And you could probably do it, just make a significantly stronger throttle, and there's your restriction. Or maybe a second throttle thing, but it moves up and down, and is controlled electronically.

qqwqeqwrqwqtq

Impossible.

Turbos operate in closed loop. If you restrict the inlet you restrict inlet flow and will not generate enough exhaust energy to drive the turbine.

Lets pretend for a moment it was possible and their was enough exhaust energy available to drive the turbine hard enough to create 40psi between the turbo and throttle plate.

Boost is not an arbitrary measure of restriction, it's a targeted value of atmosphere available for consumption. By having all of the pressure in front of the throttle body it is no longer available for the engine to consume so power would be absolutely dismal.

topend

Speaking general here (ignoring all efficiency)

7.4L x 1892 rpm = 2.0L x7000 rpm

using the same gt35r turbo for both engines

7.4L x 1892 rpm x 40 psi = 2.0L x 7000rpm x 40 psi

using the same gt35r with a Manually set wastegate for 40 psi both engines at 7000 rpm.

7.4L x 7000 rpm x 10.81 psi = 2.0L x 7000rpm x 40 psi

boost dropped in the bigger engine because the turbo could not keep up at 7000 rpm in the 7.4L.

7.4L x 7000 rpm x 10.81 - does NOT equal a - 2.0L x 7000 rpm x40 psi in power

because it takes more power to spin a 7.4L engine to 7000 rpm vs a 2.0L engine to 7000 rpm.

Mr. Sir

Restricting inlet flow is the point. The 6.2 won't need 40psi to generate 700 hp. You simply need the turbo to be operating in it's range of effeciency for the given exhaust pressure, and the easiest way I see to do that is to emulate a greater restriction (40 psi worth). Even if only 20 psi gets through, that's still enough (in this theoretical world we speak of) for 700 hp (the same as the 4.8 at 40 psi). Also, I take back my earlier post, since to much turbulence would be created adding a flat object into the intake piping. What I'd now suggest is having 2 pipes, and having a switch only allowing one to be open at a time. The free flowing pipe will help the turbo reach it's peak rpm quickly, and the second, restricting pipe, will keep the pressure ratio higher (as high as the 4.8). As I said before, it doesn't matter how the restriction is added. I also retract that statement. As long as the restriction doesn't result in a large difference in turbulence, the volume of air moved into the engine (of any size) will be the same. I doubt anyone's tried this, so you probably don't have anything (in the real world) to prove my theory wrong. If there's advanced math capable of proving it wrong, I want to know.

As for boost being a measure of restriction... there was a thread about this a few years ago. If you think about it, if the compressor is moving 150k rpm, but it's not hooked up to anything, it's acting as nothing more than a fan, and produces no psi. by putting it in a closed system, you're subjecting it to restriction. A profitable restriction, but a restriction nonetheless. So the way I see it, psi is both a restriction (in the eyes of the turbo), since it needs 40 psi of restriction to operate efficiently, and "a targeted value of atmosphere available for consumption", or simply put a volume of air (in relation to the engine), since a given volume of air produces a given amount of horsepower. Balancing these two definitions is what this entire argument is about.

Oh, and thought I'd add that not all the pressure is being stopped by the throttle plate, that'd be retarded. I thought you'd understand that there would be an ideal throttle position where air is still getting by, but the throttle would be a big enough restriction to generate 40 psi.

qqwqeqwrqwqtq

I understand what you're trying to think is possible, but try to look at the situation in it's simplest terms.

Say you are wide open throttle on any turbo car and you roll off the throttle, what happens? You reduce airflow/boost/hp/rpm.

Now, say in your example, you keep your foot planted to the floor but your device starts to introduce a restriction on the induction side, it is effectively(and actually) the exact same thing as lifting your foot off the accelerator and closing the throttle.

You reduce airflow/horsepower and you also reduce the exhaust energy available to drive the turbine.

The situation you describe is impossible to achieve.

However, assuming the impossible, that you can in fact do what you describe. Any inlet restriction, be it from losses from the intercooler plumbing, the intercooler, throttle body/etc, directly effects turbine drive pressure, overall efficiency, and engine output.

To expand on that, lets say you have 20psi at the intake manifold, and 30psi exhaust backpressure. Now introduce an intercooler or air inlet restriction of 5psi and you've also increased the turbine drive pressure by the same amount to achieve the same pressure at the intake manifold.

So now you're at 20psi intake boost pressure and 35psi exhaust backpressure.

Basically what I'm saying is even if your example was possible, any inlet restriction will reduce engine horsepower/output, even if the restriction is putting the compressor in a more favorable position on a compressor map, you are still restricting flow to the engine.

Logically, you cannot increase airflow/horsepower/efficiency by introducing a restriction.

Mr. Sir

So... what's wrong with these theories:
4.8 has W exhaust backpressure and X psi
6.2 has 1.5W exhaust backpressure and 0.5X psi
so in NA form, the 6.2 generates more exhaust. This is the only thing not covered yet, but it would be logical that more exhaust would spin the compressor faster (even if it worsens the pressure ratio). If it would somehow drain power because of the offset pressure ratio, then there's always a wastegate.
now for the intake. To increase psi from 0.5X to X, you need to double intake restriction, preferably by having 2 pipes, only allowing 1 to be open at a time, and having the second pipe being a major restriction (a 40 psi restriction). I know you say airflow will be reduced, but if a 4.8 has 40 psi, that means airflow is naturally reduced on it as well (by virtue of it being smaller, less room for the air to go, so greater psi). So, given similar restriction between the engines, it would be logical that the same volume of air is moved on both. By this reasoning, similar horsepower numbers are obtainable.

Turbo sees W exhaust backpressure and X psi, therefore it moves Y volume of air.
Engine gets Y volume of air, combustion occurs at T cylinder pressure, and it produces W exhaust backpressure.

Turbo sees (1.5W-.5W) exhaust backpressure and (0.5X)x2 psi, therefore it moves Y volume of air.
Engine gets Y volume of air, combustion occurs at T cylinder pressure, and it produces W exhaust backpressure.

If you can explain how having more exhaust NA will generate less boost, maybe it'll make sense how less hp is obtainable. Also if you can explain how similar restriction (psi) between the 2 engines will favor the 4.8 (or the base of this statement; how does the 4.8, with similar restriction as the 6.2, get a greater volume of air. Given tubulence is similar, the restriction is before the intake manifold on the 6.2, and the restriction is in the cylinders of the 4.8); I'd like to know.

qqwqeqwrqwqtq

To respond to your post in detail would be for the most part, quoting the post I made just before yours.

If you did read it and still believe what you describe to be physically possible, there is nothing more I can say to convince you otherwise.

Your example is completely ignoring the fundamental basics of how a turbo engine operates.

Gregrob, pass the lightbulbs