2.5 intercooler pipe
2.5 intercooler pipe I have an s10 with a mid mount 7875 and a 6.0L. I could only fit 2.5" intercooler piping and I am pushing it pretty hard at the track. Right now it is making somewhere in the neighborhood of 600+rwhp and I'm wondering how much further it can go. What is the most that can be made on 2.5 pipe? I know I have to be close to the max on cfm of this size but I can't fit any bigger without cutting up the truck.
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Joined: Jul 2011
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From: Seattle
I am curious about this myself. I was recently told by a builder I have the utmost respect for, that I should upgrade to the 3". I was under the impression that my 5.3 gt45 on 15 PSI was no where near an issue on 2.5"
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From: Ohio
I'm pretty sure I remember seeing a car make 1200 whp on 2" coldside piping. Technically, the coldside will move far less volume than the hotside. If you can make 900 to the wheels on a 3" exhaust, then you aren't anywhere close to maxing a 3" coldside.
Anybody have any real numbers that have been put down with 2.5" pipe? I guess I will keep turning up the boost until it stops picking up mph. That will be the real test.
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From: Ohio
There are guys here that have ran 8's on 2.5" piping. There was a thread on this a while ago, and someone posted a link to a setup that made 1800 HP on 2.5" (or smaller) IC piping.
Also, smaller engines will make the same amount of power with less CFM and more pressure, so a large engine will max IC piping at less power than a smaller one.
My assumption of maxing the piping out is coming from charts that people have posted for max cfm per pipe size. From what I have read the max cfm for 2.5" pipe is around 900cfm/ .40 mach. 900cfm is about 70lb/min which is where I'm at now. From what I read that is where the air will become turbulent and I don't know how much that affects hp.
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From: Ohio
Increasing pressure has no direct effect on CFM. You can max the CFM flow, but still gain power by increasing boost. You can still double power by running 1 bar of boost even though CFM is maxed.
LBS/min does not directly convert to CFM so there is your first mistake.
CFM x .069 = LBS/min. This is at standard temp and pressure. So 900 CFM = 62.1 lbs/min. However, the real calculation is LBS/min = CFM * density.
So 62.1 lbs/min while at 1 bar of boost is only roughly 450 CFM.
LBS/min does not directly convert to CFM so there is your first mistake.
CFM x .069 = LBS/min. This is at standard temp and pressure. So 900 CFM = 62.1 lbs/min. However, the real calculation is LBS/min = CFM * density.
So 62.1 lbs/min while at 1 bar of boost is only roughly 450 CFM.
Last edited by JoeNova; Oct 30, 2015 at 11:39 AM.
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Verdad Gallardo Increasing pressure has no direct effect on CFM. You can max the CFM flow, but still gain power by increasing boost. You can still double power by running 1 bar of boost even though CFM is maxed.
LBS/min does not directly convert to CFM so there is your first mistake.
CFM x .069 = LBS/min. This is at standard temp and pressure. So 900 CFM = 62.1 lbs/min. However, the real calculation is LBS/min = CFM * density.
So 62.1 lbs/min while at 1 bar of boost is only roughly 450 CFM.
LBS/min does not directly convert to CFM so there is your first mistake.
CFM x .069 = LBS/min. This is at standard temp and pressure. So 900 CFM = 62.1 lbs/min. However, the real calculation is LBS/min = CFM * density.
So 62.1 lbs/min while at 1 bar of boost is only roughly 450 CFM.
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Joined: Nov 2003
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From: Norn Iron
You aren't even remotely close to maxing out the flow of your 2.5" piping. I actually find it pretty absurd that you really think you are. If you stop picking up mph, it'll be from the 7875 you have, and not from the IC piping.
There are guys here that have ran 8's on 2.5" piping. There was a thread on this a while ago, and someone posted a link to a setup that made 1800 HP on 2.5" (or smaller) IC piping.
Also, smaller engines will make the same amount of power with less CFM and more pressure, so a large engine will max IC piping at less power than a smaller one.
There are guys here that have ran 8's on 2.5" piping. There was a thread on this a while ago, and someone posted a link to a setup that made 1800 HP on 2.5" (or smaller) IC piping.
Also, smaller engines will make the same amount of power with less CFM and more pressure, so a large engine will max IC piping at less power than a smaller one.
I'm going to doubt that, and if it has been done, there is little doubt a larger pipe would be more efficient.
If he's stuck with 2.5", then just run with it. If you really want to see if it's a problem, monitor pressure at the compressor discharge and the intake manifold, to see just how much pressure drop there is in the system.
I suppose I don't 100% understand the max potential on a 2.5" pipe once boost is added to the mix either.
Corky Bells book suggests multiplying the HP by 1.5 to get rough CFM rate. And also agrees the .4 mach is the max suggested velocity before air becomes turbulent.
So according to this site: http://www.1728.org/flowrate.htm
A 2.5" pipe flows 920 CFM (613 hp) at 450FPS (.4 Mach)
A 2" pipe flows 589 CFM (392 hp) at .4 Mach.
Assuming you were shooting for .4 mach on an NA setup, I think this is the correct way to size induction piping.
Once boost comes into play I'm not sure where to go....
I've been told you size the cold and hot side to the NA HP/CFM. With most LS setups being under 400 crank HP (600CFM) This means 2" piping would be fine for most since it flows 589 CFM (392 CHP).
It was explained to me that all engines are constant displacement pumps. The amount of boost run won't change the amount of air/volume displaced. It only adds density. So I was told to size the charge pipe to the engines NA needs regardless of how much boost is to be run.
That made some sense to me, but some how I don't think that's the whole truth. I know air temperature/density plays a big roll as well. Those things aside, I still feel somehow that the amount of boost run will play a roll in the best diameter pipe.
Corky Bells book suggests multiplying the HP by 1.5 to get rough CFM rate. And also agrees the .4 mach is the max suggested velocity before air becomes turbulent.
So according to this site: http://www.1728.org/flowrate.htm
A 2.5" pipe flows 920 CFM (613 hp) at 450FPS (.4 Mach)
A 2" pipe flows 589 CFM (392 hp) at .4 Mach.
Assuming you were shooting for .4 mach on an NA setup, I think this is the correct way to size induction piping.
Once boost comes into play I'm not sure where to go....
I've been told you size the cold and hot side to the NA HP/CFM. With most LS setups being under 400 crank HP (600CFM) This means 2" piping would be fine for most since it flows 589 CFM (392 CHP).
It was explained to me that all engines are constant displacement pumps. The amount of boost run won't change the amount of air/volume displaced. It only adds density. So I was told to size the charge pipe to the engines NA needs regardless of how much boost is to be run.
That made some sense to me, but some how I don't think that's the whole truth. I know air temperature/density plays a big roll as well. Those things aside, I still feel somehow that the amount of boost run will play a roll in the best diameter pipe.
I can't see making that much hp on 2.5" either. The air demand of a 6.0 is pretty high. At 15psi it should be around 72lbs/min at my shift point. The way I understood was you mulitpy that by 14.27 to get the cfm demand. I get that cfm changes with pressure but at some point the 2.5" pipe shouldn't be able to supply enough air to meet the demand. So at what point would it just not be effective? If this was a 2.0L I'm sure it would support over a 1000hp.
Airs sonic velocity changes with temperature at a given pressure.
At 10 psi 100 deg f, .4 mach would be .4x sonic velocity of 1159 fps. 463.6 fps
At 10 psi 150 deg f, .4 mach would be .4x sonic velocity of 1210 fps or 484 fps
Density changes with temp for a given pressure. At 10 psi, 100 deg f, 60 lbs a min of air flow would produce 503 cfm. At 150 deg f, 10 psi in the system would mean 60 lb min air flow is 548 cfm.
At 20 psi and 100 deg F sonic velocity doesnt change over the 10 psi 100 degf condition but now 60 lb min would be 358 cfm. At 150 deg f 20 psi, 60 lb min is 390 cfm.
Hard to say where the limit is as its depending on boost and resulting intercooled temperature. Add meth or water inj, the gas conditions change and sonic velocity changes at same pressure and temps.
I didnt gain anything over 2.5" dual inlets single 3" to stock ls1 tb at 24 psi 1000 whp mark, goin to 3" dual inlets to single 4" to stock ls1 tb at same boost. Maybe its the stock tb as a restrictor plate but its not stopping the car from making near if not over 1200 whp now
At 10 psi 100 deg f, .4 mach would be .4x sonic velocity of 1159 fps. 463.6 fps
At 10 psi 150 deg f, .4 mach would be .4x sonic velocity of 1210 fps or 484 fps
Density changes with temp for a given pressure. At 10 psi, 100 deg f, 60 lbs a min of air flow would produce 503 cfm. At 150 deg f, 10 psi in the system would mean 60 lb min air flow is 548 cfm.
At 20 psi and 100 deg F sonic velocity doesnt change over the 10 psi 100 degf condition but now 60 lb min would be 358 cfm. At 150 deg f 20 psi, 60 lb min is 390 cfm.
Hard to say where the limit is as its depending on boost and resulting intercooled temperature. Add meth or water inj, the gas conditions change and sonic velocity changes at same pressure and temps.
I didnt gain anything over 2.5" dual inlets single 3" to stock ls1 tb at 24 psi 1000 whp mark, goin to 3" dual inlets to single 4" to stock ls1 tb at same boost. Maybe its the stock tb as a restrictor plate but its not stopping the car from making near if not over 1200 whp now
Better way to look at it is back calculate pipe size for the hp you are planning to make.
Common equations state that it takes ~10 lb/min air flow to make each hp. Thats give or take some depending how effective motor is
100 lb min turbo is usually good to 1000 hp
Calc the pressure ratio required. This is the big number to look at. A 2.0 liter 4 cyl is gonna require alot more pressure ratio aka boost to make 100 lb min than a 5.3 v8.
If .4 mach is the flow limit in a pipe, then a larger motor using less boost to flow a given lb min weight flow is gonna need a larger cold side pipe than smaller motor because the density of the air stream is vastly different so the cfm is different.
Velocity is just flow over area of pipe. So a 100 lb min 2.0 liter 4cyl on 35 psi boost may calculate 416 cfm. Requires min pipe of 7/8" at 463 fps. Same 100 lb min at same temp on a 5.3 may calc 597 cfm since it only takes say 20 psi to flow 100 lb min. That means min pipe size required on the 5.3 is 1" pipe at 463 fps
Now thats assuming zero pressure drop in the system lol reality has a few psi. Point being things are dependent on pressure and temps of the air charge and motor size
Common equations state that it takes ~10 lb/min air flow to make each hp. Thats give or take some depending how effective motor is
100 lb min turbo is usually good to 1000 hp
Calc the pressure ratio required. This is the big number to look at. A 2.0 liter 4 cyl is gonna require alot more pressure ratio aka boost to make 100 lb min than a 5.3 v8.
If .4 mach is the flow limit in a pipe, then a larger motor using less boost to flow a given lb min weight flow is gonna need a larger cold side pipe than smaller motor because the density of the air stream is vastly different so the cfm is different.
Velocity is just flow over area of pipe. So a 100 lb min 2.0 liter 4cyl on 35 psi boost may calculate 416 cfm. Requires min pipe of 7/8" at 463 fps. Same 100 lb min at same temp on a 5.3 may calc 597 cfm since it only takes say 20 psi to flow 100 lb min. That means min pipe size required on the 5.3 is 1" pipe at 463 fps
Now thats assuming zero pressure drop in the system lol reality has a few psi. Point being things are dependent on pressure and temps of the air charge and motor size
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From: Norn Iron
I'm sure a lot will depend on the nature of the pipe too.
ie, a short straight pipe will flow more and easier than a pipe several feet long, with loads of joints, 90deg bends and couplers.
It'd be interesting to see a dyno test, where someone runs a nice efficient pipe setup, then just gets really stupid and starts adding loads of bends etc just to see how it impacts performance both on and off boost.
ie, a short straight pipe will flow more and easier than a pipe several feet long, with loads of joints, 90deg bends and couplers.
It'd be interesting to see a dyno test, where someone runs a nice efficient pipe setup, then just gets really stupid and starts adding loads of bends etc just to see how it impacts performance both on and off boost.
If you have ever done a rear mount on a s10 you would vomit. I think have somewhere around 19' of pipe and over 20 45*&90* elbows. It's hard to fit anything in the engine bay unless you cut it up. It's working really good so far though. Race weight is 3,800lbs and it has been 6.60@105 at 15psi. Stock 6.0 with ls6 cam.
To simplify things it would be easier to assume sea level with no temp/density changes/losses as boost rises.
Similar to how we get a good idea of "Turbo HP" by doubling the NA power per atmosphere of boost. We know that’s not quite possible it gives a pretty close estimate.
Most extreme example I always use is Quillens 482ci Pontiac. 8000+ RPM Made 2800 crank hp (Highest HP Pontiac ever made according to article) with 2.5” collectors and a single 90mm TB at over 40lbs of boost. I believe it also ran 3” charge piping. (might even be 2.75” by the look of it) Charge pipe size isn't not mentioned in the articles I've read.
Seems to me if the TB was a restriction, it would have been changed. Same goes for the charge piping, collector.
I realize there are 2 of everything but if you cut the motor in half…
It’s making 1400hp through one 2.5” collector and one 3” charge pipe… and one 1.75” throttle body?
According to the site mentioned above 3.5” (90mm) tubing is only good for 1800CFM/1200HP at .4 Mach. So how is he making 2800 on a single 90mm TB, through 2.5" collectors?
Similar to how we get a good idea of "Turbo HP" by doubling the NA power per atmosphere of boost. We know that’s not quite possible it gives a pretty close estimate.
Most extreme example I always use is Quillens 482ci Pontiac. 8000+ RPM Made 2800 crank hp (Highest HP Pontiac ever made according to article) with 2.5” collectors and a single 90mm TB at over 40lbs of boost. I believe it also ran 3” charge piping. (might even be 2.75” by the look of it) Charge pipe size isn't not mentioned in the articles I've read.
Seems to me if the TB was a restriction, it would have been changed. Same goes for the charge piping, collector.
I realize there are 2 of everything but if you cut the motor in half…
It’s making 1400hp through one 2.5” collector and one 3” charge pipe… and one 1.75” throttle body?
According to the site mentioned above 3.5” (90mm) tubing is only good for 1800CFM/1200HP at .4 Mach. So how is he making 2800 on a single 90mm TB, through 2.5" collectors?
Last edited by Forcefed86; Oct 31, 2015 at 10:10 AM.
9 Second Club
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From: Norn Iron
The guides say to use pipe sizes so that air velocities do not go supersonic....that isnt to say you cannot do this.
And doesnt look like that have a huge pile of room for larger pipes at least near the TB area...and there certainly isnt 20ft of pipe with 20 bends lol
And doesnt look like that have a huge pile of room for larger pipes at least near the TB area...and there certainly isnt 20ft of pipe with 20 bends lol
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Joined: Sep 2006
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If you really want to get into it, there is math involved. Here is a wiki:https://en.wikipedia.org/wiki/Choked_flow
Its been more than a couple years since I worked on this (fsae requires a restrictor), but IIRC flow will be able to increase until you go sonic, at the smallest point in the system.
This could be the tube, throttle body, or coupling.
Its been more than a couple years since I worked on this (fsae requires a restrictor), but IIRC flow will be able to increase until you go sonic, at the smallest point in the system.
This could be the tube, throttle body, or coupling.