rear mount tube size question
08-30-2010, 01:41 PM
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rear mount tube size question With a rear mount turbo how much horsepower will 2.25" dia intake tubing support? Reason I ask is my car has a ST80 rear mount turbo, I've seen 17lbs boost measured at the intake and it's thru 2.25" tubing. I'm surprised it supports that much boost on a 383 (ls based) W/heads and cam.
Is it hurting the performance? It's 2.25 until the intercooler where it's stepped up to 3" Just for reference the STS kit uses 2.25"
Is it hurting the performance? It's 2.25 until the intercooler where it's stepped up to 3" Just for reference the STS kit uses 2.25"
08-30-2010, 02:13 PM
#2
Wow. That just seems to small. I've been researching that topic myself. I found some calculations on theturboforums that take your piping diameter and the length of pipe to figure it out. I would guess at least 3" though.
Food for thought:
Two 2.25" pipes are about the same area as one 3.25" pipe. So if your car is low just run another 2.25". I may do that using a twin turbo style intercooler.
Food for thought:
Two 2.25" pipes are about the same area as one 3.25" pipe. So if your car is low just run another 2.25". I may do that using a twin turbo style intercooler.
08-30-2010, 02:53 PM
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Not to hijack this thread, but I have considered a similar situation. I got a T70 with a 2.5inch compressor outlet that I am thinking about mounting on the rear. I was wondering if I should use 2.5 all the way to the intake through the intercooler or reduce it down to 2.25 then back up to 2.5 at the intercooler to the intake.
Thanks...
Thanks...
08-30-2010, 03:04 PM
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t70 will be fine, but id think about the future to be honest. besides, it wont take a noticeable amount of time to fill that difference in pipe.
wish i wouldve done 3" to begin with. we'll see how it does, i will surely max out the 2.5 next season. my exhaust is already 3" but my charge is 2.5" we shall see what happens next year.
wish i wouldve done 3" to begin with. we'll see how it does, i will surely max out the 2.5 next season. my exhaust is already 3" but my charge is 2.5" we shall see what happens next year.
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08-30-2010, 03:21 PM
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08-30-2010, 04:57 PM
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You guys hijacked my thread
But let's see if some knowlegable people can help both of us. How much horsepower can 2.25"dia tubing support? I understand why people go larger on their builds but does anyone have any knowledge they can add?
Did anyone reach a point where a certain tubing size was holding back the performance?
But let's see if some knowlegable people can help both of us. How much horsepower can 2.25"dia tubing support? I understand why people go larger on their builds but does anyone have any knowledge they can add? Did anyone reach a point where a certain tubing size was holding back the performance?
08-30-2010, 08:58 PM
#10
I had a mix of 2.25"/2.5" to the intercooler then 3" afterwards and 2.5" exhaust to the turbo. According to the calcs I was making around 775 rwhp peak (average of 750), I'm guessing that's around 875 to 900 at the crank. After having it changed to 3" all the way on cold and hot sides I didn't get any improvement in track times. The changes that were made did improve spool and reliability due to coating / wrapping the exhaust and removing several couplers and several feet of piping from the setup so it was worth it to me.
Not the results I expected, but these are the results that I got. Car ET's / MPH's identical after the change. I suspect that I'm out of compressor due to my altitude, I've yet to turn up the boost past 15psi though to see if there is a difference now. Need more fuel. Goal is to run 20psi if I can. On the old 2.5" setup turning the boost up past 16psi yielded the same or slower track times. It could make 20psi but would run slower.
Not the results I expected, but these are the results that I got. Car ET's / MPH's identical after the change. I suspect that I'm out of compressor due to my altitude, I've yet to turn up the boost past 15psi though to see if there is a difference now. Need more fuel. Goal is to run 20psi if I can. On the old 2.5" setup turning the boost up past 16psi yielded the same or slower track times. It could make 20psi but would run slower.
08-30-2010, 09:21 PM
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I had a mix of 2.25"/2.5" to the intercooler then 3" afterwards and 2.5" exhaust to the turbo. According to the calcs I was making around 775 rwhp peak (average of 750), I'm guessing that's around 875 to 900 at the crank. After having it changed to 3" all the way on cold and hot sides I didn't get any improvement in track times. The changes that were made did improve spool and reliability due to coating / wrapping the exhaust and removing several couplers and several feet of piping from the setup so it was worth it to me.
Not the results I expected, but these are the results that I got. Car ET's / MPH's identical after the change. I suspect that I'm out of compressor due to my altitude, I've yet to turn up the boost past 15psi though to see if there is a difference now. Need more fuel. Goal is to run 20psi if I can. On the old 2.5" setup turning the boost up past 16psi yielded the same or slower track times. It could make 20psi but would run slower.
Not the results I expected, but these are the results that I got. Car ET's / MPH's identical after the change. I suspect that I'm out of compressor due to my altitude, I've yet to turn up the boost past 15psi though to see if there is a difference now. Need more fuel. Goal is to run 20psi if I can. On the old 2.5" setup turning the boost up past 16psi yielded the same or slower track times. It could make 20psi but would run slower.
08-31-2010, 12:27 AM
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If I understand zombie's post it doesn't sound like going larger on the cold side yields any gains, it sounds like the gains are from upgrading the hotside tubing.
08-31-2010, 08:26 AM
#14
It also depends on how much CFM you are trying to flow. If your turbo is trying to push 1000cfm through a 2" line or a 3" line, it's going to work easier with a 3" line. But if you go to big for the cfm, that can add a delay/lag to when you stab the go pedal. There are calculations for figuring this stuff out. Do some research/trial and error.
08-31-2010, 11:29 AM
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It also depends on how much CFM you are trying to flow. If your turbo is trying to push 1000cfm through a 2" line or a 3" line, it's going to work easier with a 3" line. But if you go to big for the cfm, that can add a delay/lag to when you stab the go pedal. There are calculations for figuring this stuff out. Do some research/trial and error.
09-07-2010, 04:32 AM
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i didnt use any calculations on my home built rear mount, but i used 2.5" for the cold side because the compressor had a 2.5" outlet. common sense tells me that the outlet size would be the size pipe to use. if the turbo was designed with X" outlet, using the same size pipe couldnt be a restriction. then just before the throttle body it steps up to 3" to slow it down (and because i plan to add a FMIC this winter, 2.5" in with 3" out)
and to prevent back pressure from becoming a problem, when i made my Y pipe, i put the waste gate in the side of the Y, so exhaust dumps before the single 3", makes it spool quick, but still has the topend
and to prevent back pressure from becoming a problem, when i made my Y pipe, i put the waste gate in the side of the Y, so exhaust dumps before the single 3", makes it spool quick, but still has the topend
