Headers ,"I think I lost some boost?" p1sc
On The Tree
Joined: Jul 2005
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From: Pahrump, NV
All- I was really thinking about this one earlier today (probably a little too deep) and had some lingering questions. For example, he dropped from 6psi to 5 psi with nothing done other than headers. Ok the answer was given that the engine is able to breathe easier, lessening up on the restriction. I could understand a drop in psi on a turbo application if you changed the heads or intake, allowing the engine to breathe easier, but not after the fact on the exhaust. I remember Kane telling me when we put the headers on my car that he (before he went to an iron 6.0) was putting stock manifolds back on his car due to smaller tubes made the turbo spool faster. He explained it like this: Going to a larger tubing such as headers would have to fill the headers with MORE EXHAUST to spool the turbo, having more lag time than the stock manifold. Picture this- take a 3/4 inch hose compared to a 5/8 hose and blow through it while holding a paper at the end. Which one will blow the paper hardest? The 5/8s due to having enough pressure in the lines to effectively get the air to the PAPER where you want it to be. My question is: if you had a supercharger instead and did the same conversion to headers, would you lose psi?? My answer would be no, or at least non-legible. It is a constant source running off the motor, not the belt. I am in no means an expert on this, but the answers didnt sit right with me and wanted to throw this out there. I think the loss in psi is due to having a larger pipe, and taking up more exhaust to fill them. *EDIT* just realized this was a P1SC. Thought from yesterday it was a turbo. **** I am tired!!! Never mind.
no you wouldn't get the same loss with a turbo.... here is my reasoning
the turbo still restricts the air coming out of the exhaust manifolds, bigger manifolds does not change that, the turbo is still there and can only let so much air pass no matter how big the manifolds are....
a supercharger doesn't have such a complication on it:
supercharger>intercooler>motor>exhaust>done
turbo is:
turbo>intercooler>engine>exhaust manifolds/crossover>turbo again>downpipe>done
to expound on the difference the exhaust manifold on a supercharger does not have the backpressure like a turbo... a turbo usually has (and I could be very off on this) like 2.5 times the pressure in the exhaust manifold then it has in the intake manifold...
8psi intake
20'ish psi in the exhaust manifolds...
so even with bigger manifolds that still has to go through the turbo again before it can be free
***for some reason I feel my pressure ratio is off, someone please correct me***
the turbo still restricts the air coming out of the exhaust manifolds, bigger manifolds does not change that, the turbo is still there and can only let so much air pass no matter how big the manifolds are....
a supercharger doesn't have such a complication on it:
supercharger>intercooler>motor>exhaust>done
turbo is:
turbo>intercooler>engine>exhaust manifolds/crossover>turbo again>downpipe>done
to expound on the difference the exhaust manifold on a supercharger does not have the backpressure like a turbo... a turbo usually has (and I could be very off on this) like 2.5 times the pressure in the exhaust manifold then it has in the intake manifold...
8psi intake
20'ish psi in the exhaust manifolds...
so even with bigger manifolds that still has to go through the turbo again before it can be free
***for some reason I feel my pressure ratio is off, someone please correct me***
Last edited by Koncrete; May 2, 2006 at 07:51 PM.
TECH Senior Member
Joined: Nov 2001
Posts: 10,341
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Here it is in simple terms...
Boost value is a measure of restriction. Look instead at blower CFM rating, impeller speed and pulley size.
Headers reduce boost because they reduce restriction on the exhaust side of the engine.
At certain power levels if you free up restriction on the intake side of the blower you will see a boost increase. (ATI inlet hat and filter is a perfect example)
So to put it in simple terms you might have dropped 1# of boost but you are flowing the same cfm. changing the pulley and belt to bring up the boost will require a retune as you have changed the cfm of air going through that motor.
The Ls1 is just a big airpump.
Cheers,
Chris
Boost value is a measure of restriction. Look instead at blower CFM rating, impeller speed and pulley size.
Headers reduce boost because they reduce restriction on the exhaust side of the engine.
At certain power levels if you free up restriction on the intake side of the blower you will see a boost increase. (ATI inlet hat and filter is a perfect example)
So to put it in simple terms you might have dropped 1# of boost but you are flowing the same cfm. changing the pulley and belt to bring up the boost will require a retune as you have changed the cfm of air going through that motor.
The Ls1 is just a big airpump.
Cheers,
Chris
Originally Posted by Dave D
All- I was really thinking about this one earlier today (probably a little too deep) and had some lingering questions. For example, he dropped from 6psi to 5 psi with nothing done other than headers. Ok the answer was given that the engine is able to breathe easier, lessening up on the restriction. I could understand a drop in psi on a turbo application if you changed the heads or intake, allowing the engine to breathe easier, but not after the fact on the exhaust. I remember Kane telling me when we put the headers on my car that he (before he went to an iron 6.0) was putting stock manifolds back on his car due to smaller tubes made the turbo spool faster. He explained it like this: Going to a larger tubing such as headers would have to fill the headers with MORE EXHAUST to spool the turbo, having more lag time than the stock manifold. Picture this- take a 3/4 inch hose compared to a 5/8 hose and blow through it while holding a paper at the end. Which one will blow the paper hardest? The 5/8s due to having enough pressure in the lines to effectively get the air to the PAPER where you want it to be. My question is: if you had a supercharger instead and did the same conversion to headers, would you lose psi?? My answer would be no, or at least non-legible. It is a constant source running off the motor, not the belt. I am in no means an expert on this, but the answers didnt sit right with me and wanted to throw this out there. I think the loss in psi is due to having a larger pipe, and taking up more exhaust to fill them. *EDIT* just realized this was a P1SC. Thought from yesterday it was a turbo. **** I am tired!!! Never mind.
Thread Starter
9 Second Club
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Joined: Apr 2006
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From: Oxford, Chester County,Pa
That is the way ATI explained it to me. Quote, "I have 2 air pumps a little pump and a big pump the motor itself "end quote/ATI. That is how I started understanding this thing.
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TECH Resident
Joined: Oct 2005
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Originally Posted by mikep2002
That is the way ATI explained it to me. Quote, "I have 2 air pumps a little pump and a big pump the motor itself "end quote/ATI. That is how I started understanding this thing.
