Why do people think a turbo cares about engine RPM?
#61
FormerVendor
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.
Last edited by qqwqeqwrqwqtq; 02-03-2012 at 09:51 AM.
#62
10 Second Club
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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.
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.
#63
Gingervitis Addict
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I think you have moved away from turbines in general and on to gas turbine engines? gas turbine engines will get more efficient as temp increases because the heat is used to create Delta and thus an increase in temperature causes a larger delta and less flow is needed for the same work. In general a turbine could care less what the temp of the fluid is as long as delta is equal
And you are moving the same amount of cfm.
#64
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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.
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.
#65
TECH Resident
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Ok guys, I understand that more RPM's equals more air flow. But again, why would a turbo care about the RPM's of an engine? It DOESN'T. It only cares about a VOLUME of exhaust entering the turbine. The force that hits the turbine wheel is a volume of exhaust which has nothing to do with RPM.
90% of the people that told me I was wrong in this thread, spouted off a bunch about this that and the other thing, but failed to even mention RPM of an engine.
For example... The above is all very true information, but not once is RPM even mentioned.
This is why a 2JZ spins to 10,000rpm and can push a 90mm turbo but a say a 427 only spins to 6,000rpm can max out a 90mm turbo. Again, RPM has nothing to do with it. It is about exhaust volume, which can be translated (in a vague way) to horsepower.
When you go on Precision Turbo's website (or most turbo sites) to shop for a turbo, do they categorize their turbo's based on RPM or on a horsepower level?
So this is EXACTLY what I was stating... RPM has NOTHING do do with it. It is ALL about exhaust VOLUME.
90% of the people that told me I was wrong in this thread, spouted off a bunch about this that and the other thing, but failed to even mention RPM of an engine.
For example... The above is all very true information, but not once is RPM even mentioned.
This is why a 2JZ spins to 10,000rpm and can push a 90mm turbo but a say a 427 only spins to 6,000rpm can max out a 90mm turbo. Again, RPM has nothing to do with it. It is about exhaust volume, which can be translated (in a vague way) to horsepower.
When you go on Precision Turbo's website (or most turbo sites) to shop for a turbo, do they categorize their turbo's based on RPM or on a horsepower level?
So this is EXACTLY what I was stating... RPM has NOTHING do do with it. It is ALL about exhaust VOLUME.
Don't really see whats so complicated here.
#66
If someone said "I have a Precision 7675 and a built 408. Is this turbo too small for my engine?"
I would say- Yes, it is not ideal and will be restricted on the exhaust side at higher rpm regardless of the power/boost level. It will peak early at 500rwhp and it will peak early at 700rwhp because it is not a good match for that displacement. It will basically choke after 5000rpm no matter what boost level or power level you are at.
So yeah, you can safely say "X" turbo will not produce a favorable power curve on "X" displacement without even discussing the power level.
I would say- Yes, it is not ideal and will be restricted on the exhaust side at higher rpm regardless of the power/boost level. It will peak early at 500rwhp and it will peak early at 700rwhp because it is not a good match for that displacement. It will basically choke after 5000rpm no matter what boost level or power level you are at.
So yeah, you can safely say "X" turbo will not produce a favorable power curve on "X" displacement without even discussing the power level.
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.
#67
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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.
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.
#68
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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.
#69
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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.
#72
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?
#73
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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?
#74
...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.
#75
FormerVendor
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.
#76
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?
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?
.
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?
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?
.
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.
#77
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.
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.
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.
#78
FormerVendor
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.
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.
Last edited by qqwqeqwrqwqtq; 02-05-2012 at 02:36 AM.
#79
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.
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.
#80
FormerVendor
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
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