GSR backpressure
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From: Salt Lake City, Chicago at heart, UT or IL, USA
Re: GSR backpressure (memicah)
I believe it's better to have a little backpressure if you're running NA. It should only give you 1-2 psi of backpressure. Plus, your car will be a tad quieter. Better put on that catback rather than running an open cat.
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From: norwalk, ca, u.s
Re: GSR backpressure (memicah)
2.25 woudlnt' lose much bp so dont worry...if you running NA and let say that you're running 2.5" with 200whp....you're good to go....
3" with 200whp you will expect to lose little more bp
as long as youre running stock path and not straight piping or open header...you're fine with 2.25, no problem at all
well here is a math...pipin with mandrel bending = 30% loss of bp + additional larger piping (5-10% loss of bp) and header setup (4-1=5% or 4-2-1=gain about 5% back)
so overall you're expecting to lose around 30%-40 of bp.....not a big problem
3" with 200whp you will expect to lose little more bp
as long as youre running stock path and not straight piping or open header...you're fine with 2.25, no problem at all
well here is a math...pipin with mandrel bending = 30% loss of bp + additional larger piping (5-10% loss of bp) and header setup (4-1=5% or 4-2-1=gain about 5% back)
so overall you're expecting to lose around 30%-40 of bp.....not a big problem
Darth ModerVader
Joined: Jan 2001
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From: Mustafar
Re: GSR backpressure (yeegsr)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by yeegsr »</TD></TR><TR><TD CLASS="quote">2.25 woudlnt' lose much bp so dont worry...if you running NA and let say that you're running 2.5" with 200whp....you're good to go....
3" with 200whp you will expect to lose little more bp
as long as youre running stock path and not straight piping or open header...you're fine with 2.25, no problem at all
well here is a math...pipin with mandrel bending = 30% loss of bp + additional larger piping (5-10% loss of bp) and header setup (4-1=5% or 4-2-1=gain about 5% back)
so overall you're expecting to lose around 30%-40 of bp.....not a big problem</TD></TR></TABLE>
I have almost no idea what you're saying or where any of these calculations or figures came from, but they're simply useless and incorrect.
To answer the question of the original poster, the consensus is that you don't want any back-pressure. What you want is a properly designed system that maintains exhaust gas velocity with minimal restriction. You mentioned the A'PEXi N1, which uses 60 mm piping (roughly 2.36"). If your setup is relatively mild, any quality system will yield similar results, assuming it utilizes a straight-through muffler and mandrel bends. If you will be running a "JDM-sized" header with a 2.5" collector, I'd suggest a 2.5" cat-back and 2.5" cat.
3" with 200whp you will expect to lose little more bp
as long as youre running stock path and not straight piping or open header...you're fine with 2.25, no problem at all
well here is a math...pipin with mandrel bending = 30% loss of bp + additional larger piping (5-10% loss of bp) and header setup (4-1=5% or 4-2-1=gain about 5% back)
so overall you're expecting to lose around 30%-40 of bp.....not a big problem</TD></TR></TABLE>
I have almost no idea what you're saying or where any of these calculations or figures came from, but they're simply useless and incorrect.
To answer the question of the original poster, the consensus is that you don't want any back-pressure. What you want is a properly designed system that maintains exhaust gas velocity with minimal restriction. You mentioned the A'PEXi N1, which uses 60 mm piping (roughly 2.36"). If your setup is relatively mild, any quality system will yield similar results, assuming it utilizes a straight-through muffler and mandrel bends. If you will be running a "JDM-sized" header with a 2.5" collector, I'd suggest a 2.5" cat-back and 2.5" cat.
Darth ModerVader
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From: Mustafar
Re: GSR backpressure (yeegsr)
I'm not curious, because the figures still have no real meaning or application. What does a "30%-40% loss of back pressure" indicate? Compared to what? What units are being used to measure this "loss". Who decided upon the "ideal" level of back pressure against which these percentages are judged? What 4-1 or 4-2-1 header was used to arrive at the +/- 5% figures, and why would the configuration of the tubing alone produce those variations? Where is the inclusion of the muffler in these "calculations"?
Again, in response to the original poster, a quality system with a high-flow cat would be the best choice. Most aftermarket systems are 60mm (2.36") with a few being larger and a few being smaller (systems manufactured in the US are often 2.25"). For a relatively mild GS-R, the gains of any well-made straight-through system will be very similar. Running "open cat" will yield slight gains over a good exhaust system, but won't be worth the noise penalty on a street car.
Again, in response to the original poster, a quality system with a high-flow cat would be the best choice. Most aftermarket systems are 60mm (2.36") with a few being larger and a few being smaller (systems manufactured in the US are often 2.25"). For a relatively mild GS-R, the gains of any well-made straight-through system will be very similar. Running "open cat" will yield slight gains over a good exhaust system, but won't be worth the noise penalty on a street car.
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From: norwalk, ca, u.s
Re: GSR backpressure (Padawan)
im trying to explain with my best so
1. main one is diameter's piping is larger, and most obvious is increase in FLOW CAPACITY cfm, DECREASED FLOW VELOCITY ft/sec basically the cross sectional area of exhaust is being larger
2. stock cat is small and restrictily for emission (give back pressure)
3. stock muffler big but also very restricty also for emission purposes (give back pressure due to restriction)
4. i call stock piping semicrush because it has crushes....at crush air particles bound off the wall making zig zag flow inside tubing this is where some pressure back also produced by stock pipe
5. this is minor but make sense, if you actually look at mandrel bending piping you will noticed that they dont make exact 90degree curve like some civic and integ does...mandrel can reduce the 90curve to 80-85 at every curve
6. if you do straight piping, and you know it you will lose massive pressure...
7. 4-1 header vs 4-2-1
a. 4-1 has long runners to collector where all 4 merging at once where 4-2-1, the header has 4 runners, and 2runners merge into 1 and the other 2 merge into another 1, before they merge exahust pulses are still at high velocity and so their temperature, when they are mergin those two runners have to squeeze exhaust pulese into a less flow capacity piping give backpressure...later those 1 and 1 merging into a final main collector 1 (4-2-[1] <---) agian at this point velocity still high because of the previous squeeze of e's pulses....merge 2-1 at collector also produce backpressure due to the squeeze of e's pulses
1. main one is diameter's piping is larger, and most obvious is increase in FLOW CAPACITY cfm, DECREASED FLOW VELOCITY ft/sec basically the cross sectional area of exhaust is being larger
2. stock cat is small and restrictily for emission (give back pressure)
3. stock muffler big but also very restricty also for emission purposes (give back pressure due to restriction)
4. i call stock piping semicrush because it has crushes....at crush air particles bound off the wall making zig zag flow inside tubing this is where some pressure back also produced by stock pipe
5. this is minor but make sense, if you actually look at mandrel bending piping you will noticed that they dont make exact 90degree curve like some civic and integ does...mandrel can reduce the 90curve to 80-85 at every curve
6. if you do straight piping, and you know it you will lose massive pressure...
7. 4-1 header vs 4-2-1
a. 4-1 has long runners to collector where all 4 merging at once where 4-2-1, the header has 4 runners, and 2runners merge into 1 and the other 2 merge into another 1, before they merge exahust pulses are still at high velocity and so their temperature, when they are mergin those two runners have to squeeze exhaust pulese into a less flow capacity piping give backpressure...later those 1 and 1 merging into a final main collector 1 (4-2-[1] <---) agian at this point velocity still high because of the previous squeeze of e's pulses....merge 2-1 at collector also produce backpressure due to the squeeze of e's pulses
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