the Official "NA Tuning" thread
Joined: May 2004
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From: DFW, TX
Originally Posted by HvRRZ,Mar 20 2006, 05:05 PM
There actually are companies that make 3inch systems for the S, but they all classify them as turbo systems. I believe amuse was the first to have a 70mm exhaust system for the S2K, and even that was they called the turbo version. although many used it on there NA S's.
I am not sure about your question regarding a 60mm with those specs. Although a resonaor does not cause a decrease from the gains received from an exhaust. It's merely used to quiet one. While your suggested 60mm would show good gains, the question is will it be best suited to have with your supporting mods. While the gains between the 60-70mm exhaust system may have minimul difference when having only the exhaust. The benefits of having the 70mm show once other modification are added(header, test pipe,etc.)
The J's racing is is one of the lightest s's out there, and I believe at the time when they only had the 60mm they got rid of the resonator to loose weight. In race cars like that they strive to loose as many lbs as possible.
Obviously the weight lost by doing that was regained by using the larger 70mm exhaust system, but the benefits/gains seen through the use of the 70mm mut have been to good to pass up.
It did take sometime though for companies to start coming out with 70mm exhaust systems for the S, but once the benfits were seen more companies have started to do so.
I think all it will take is for one company to release a 3inch system showing better results, and the res will follow.
I am not sure about your question regarding a 60mm with those specs. Although a resonaor does not cause a decrease from the gains received from an exhaust. It's merely used to quiet one. While your suggested 60mm would show good gains, the question is will it be best suited to have with your supporting mods. While the gains between the 60-70mm exhaust system may have minimul difference when having only the exhaust. The benefits of having the 70mm show once other modification are added(header, test pipe,etc.)
The J's racing is is one of the lightest s's out there, and I believe at the time when they only had the 60mm they got rid of the resonator to loose weight. In race cars like that they strive to loose as many lbs as possible.
Obviously the weight lost by doing that was regained by using the larger 70mm exhaust system, but the benefits/gains seen through the use of the 70mm mut have been to good to pass up.
It did take sometime though for companies to start coming out with 70mm exhaust systems for the S, but once the benfits were seen more companies have started to do so.
I think all it will take is for one company to release a 3inch system showing better results, and the res will follow.
Joined: May 2004
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From: DFW, TX
Oh...and the thing about back pressure...there is a balance. You can go too big on ANY engine...it doesn't matter what. But the bigger you go no matter what high rpm horsepower will always see gains. At high rpm's the primary goal is to get as much air in and out of the cylinder as fast as possible. At low rpm you still want to get as much fresh air in as possible but if the exhaust is too big the the "ambient" pressure on the outside of the exhaust valve is not much lower then the pressure on the intake valve and it doesn't suck out as much air as it can. The preferable effect is to have some vacuum on the exhaust side and as close to positive pressure as possible on the intake side. At low rpm the firings are so far apart that the exhaust isn't really filled with fast flowing air. Its kind of hard to explain but if you guys understand where I'm going so far, you can figure out the rest. Just think of the amount of air that flows and the speed that it flows at high RPM then think of that at low rpm...now see that each cylinder has its own tube "primaries" in the header...this tube only has gases in it from that respective cylinder...gases don't travel backwards...at the secondaries and the collector the scavanging effect helps to pull gasses out of the cylinders and create slight vacuum in the primaries. If you have too big of an exhaust the gases don't flow as fast as they would when you have a smaller exhaust. This is why smaller exhausts typically create more hp down low...it is because they optimize the scavanging effect at a much lower airflow (rpm)...
maybe it makes more sense now that I explained it twice two different ways?
maybe it makes more sense now that I explained it twice two different ways?
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From: Los Angeles, CA
Originally Posted by Silver9k,Mar 20 2006, 10:52 PM
Could you get some video clips of your exhaust...I'm going to consider going to a 3" like yours. Although, the main thing that makes me push towards J's 70 is that it is probably at least 15lbs lighter then yours if not 20lbs lighter...and the extra .25" is probably only good for a 1-2 hp. While it is cheaper...I don't think I've let out my full goal here. Yes 250whp N/A but while being at 2500lbs as well...25/25 It would be similar to a 300whp S/C S2k with some subs in the trunk since they'd be at about 3000lbs.
The canister on my system is the heavist part, and it's really light. The piping didn't add much(gatta love the fact that the S2K piping lenght is short).
I'm really big on saving weight, but I've always liked the carbon ti, and I couldn't resist getting it done.
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From: Northern Virginia
Guys,
The whole thing with backpressure creating power or torque is completely false. The reason why exhausts that are too big/open header LOSE torque is because the exhaust velocity is actually slowed, as it is inefficient. I would assume that anything larger than a 70mm exhaust would be too large unless forced induction was put in the picture. The whole reasoning behind "efficient exhausts" versus large exhausts can be proven by a turbo setup. All a turbo does in simple terms is speed along exhaust gases, and creating a vaccuum, IE forced induction. Having a 3 inch exhaust would probably actually lose exhaust gas velocity, and AT LEAST lose torque, if not also horsepower.
The whole thing with backpressure creating power or torque is completely false. The reason why exhausts that are too big/open header LOSE torque is because the exhaust velocity is actually slowed, as it is inefficient. I would assume that anything larger than a 70mm exhaust would be too large unless forced induction was put in the picture. The whole reasoning behind "efficient exhausts" versus large exhausts can be proven by a turbo setup. All a turbo does in simple terms is speed along exhaust gases, and creating a vaccuum, IE forced induction. Having a 3 inch exhaust would probably actually lose exhaust gas velocity, and AT LEAST lose torque, if not also horsepower.
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From: Los Angeles, CA
Silver I'm also going to put the stock CAT heat shield over the test pipe so I'll see if I can take the exhaust off to get a true weigh in for it.
It seems the J's 70mm is 10lbs so we'll say 10lbs lighter then my set-up which isn't bad. wish mine was full titanium.
It seems the J's 70mm is 10lbs so we'll say 10lbs lighter then my set-up which isn't bad. wish mine was full titanium.
Joined: May 2004
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From: DFW, TX
Originally Posted by Silver9k,Mar 20 2006, 10:06 PM
If you have too big of an exhaust the gases don't flow as fast as they would when you have a smaller exhaust. This is why smaller exhausts typically create more hp down low...it is because they optimize the scavanging effect at a much lower airflow (rpm)...
So far 70mm seems perfect for the S2k..but 3" might just be at the actual perfect limit. The perfect exhaust will increase top end hp to a max without sacraficing low end power..obviously if torque is hurt, hp is also hurt.
Right now 70mm has shown to not hurt low-end power...3" is only going up to 76mm. So again, it may just be the limit. Or, it may be such a small decrease in low end power that the extra hp gained up top is worth it.
And HvRRZ I think the J's 70rr weighs 11lbs as a header back. If at 18lbs that is not including the test pipe then your exhaust is actually only about 10lbs heavier which isn't bad. Lighter then I thought...did you use 505 Stainless? How many resonators? If it was only 10lbs but turns out you can make 3-5hp more then I'll look into that. But honestly, if a 70mm exhaust + 70mm testpipe already makes 15hp on an N/A car. Then my guess is that 76mm wont be more then 17hp. Definitly worth it in the hp/dollar catagory, but, thats where the weight will probably make a difference to me
Joined: May 2004
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From: DFW, TX
Originally Posted by HvRRZ,Mar 20 2006, 10:58 PM
Silver I'm also going to put the stock CAT heat shield over the test pipe so I'll see if I can take the exhaust off to get a true weigh in for it.
It seems the J's 70mm is 10lbs so we'll say 10lbs lighter then my set-up which isn't bad. wish mine was full titanium.
It seems the J's 70mm is 10lbs so we'll say 10lbs lighter then my set-up which isn't bad. wish mine was full titanium.
Also...I'm thinking about putting the cat heat shield over as well...except instead of simply just putting it on the exhaust I'm thinking about somehow welding the top part to the under body and just bolting it together...this way it should work with any exhaust and it would be easy to do. I don't really want to weld anything to a nice new J's exhaust, and I don't think there is anybody where I live who could anyway. So seems like a decent alternative
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From: Northern Virginia
Originally Posted by Silver9k,Mar 20 2006, 11:07 PM
Right now 70mm has shown to not hurt low-end power...3" is only going up to 76mm. So again, it may just be the limit. Or, it may be such a small decrease in low end power that the extra hp gained up top is worth it.
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well i have CAI ..no cat...apexi N1 single cat back and tunded with VAFC2 it came out 228.8 whp
and one of my friend he got ap2 knn air filter ,rick's header no cat..t1r catback tuned with vafc2 he got 239 whp..
we took it to sean church..in southern CA
and one of my friend he got ap2 knn air filter ,rick's header no cat..t1r catback tuned with vafc2 he got 239 whp..
we took it to sean church..in southern CA