Straight Pipes on, cars slower?
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Straight Pipes on, cars slower?
So had a friend of mine fab up a set of pipes for my stock K16's this weekend. The sound is AWESOME!! My question is my car seems to be slower?? I read through previous posts with guys noticing the same thing but I am curious why this happens? I thought that the less back pressue for a turbo the better? Can anyone explain this?
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I went from europipe to straight pipes and noticed car was slower, felt like a lot more turbo lag. I think there needs to be a certain amount of back pressure for turbos to run optimally. The sounds is crazy loud.
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I had the same problem (on my Z). What I found out after I had my test-pipes installed I basically loost some low end torqe. Although in my car I noticed a big difference in the mid-range rev’s. Low end torque is gone, but you make some mid-high end HP gains. Do you notice your car revving faster? Or do you just feel slower all around?
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Originally Posted by iLLM3
Had the same issue with my K16 car, went back to the FVD exhaust with cat bypass and it felt/sounded 100x better!
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I'm guessing that if you are loosing your low-end, pre-boost torque due to the ellimination of backpressure, your ability to create boost will be pushed to higher RPMs.
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Originally Posted by 996TTDave
please excuse my ignorance - how did you do a cat bypass?
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Originally Posted by Zippy
I'm guessing that if you are loosing your low-end, pre-boost torque due to the ellimination of backpressure, your ability to create boost will be pushed to higher RPMs.
I run my car 95% track and love the straight pipes. Also have K-24's which may be a difference.
Also between heel toe shifting and WOT at the track I really see no lag.
If I was just goofing around town I guess it may be a different story.
If you dont like the straight pipes have one of you race car driving buddies drive the car and see what they think.
I think most on this forum will not like the straight pipes and I would go with 100 cell cats and straight pipes and you will have a better overall feel.
I have had all, tooling around town the 100 cell cats seem to make the car better, at the track its better with the straight pipes.
Of course my opinion only, your results may varying.
Last edited by tom kerr; Apr 10, 2007 at 06:36 PM.
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Turbos don't need backpressure at all... much like normally aspirated engines.
Normally aspirated engines need flow velocity at low RPM's for power more than they need volume (which is still needed). That's why smaller pipes, which keep velocities up, tend to give you more low end power. Velocities help with scavenging:
http://www.magnaflow.com/05news/magazine/05sportc.asp
If backpressure was what was needed, simply crushing the pipes down would give you power.
For turbos, the less backpressure the more power they'll generate.
While straight pipes will help the turbos spool faster, below the spooling point, turbos act like normally aspirated engines. So, the power lost by the loss of flow velocity with a straight pipe will at some point be overtaken by the power gained by the spooling of the turbo. Where that point is depends on the turbo size, configuration, exhaust, etc.
Normally aspirated engines need flow velocity at low RPM's for power more than they need volume (which is still needed). That's why smaller pipes, which keep velocities up, tend to give you more low end power. Velocities help with scavenging:
http://www.magnaflow.com/05news/magazine/05sportc.asp
BACKPRESSURE = TORQUE?
An old hot-rodder's tall tale: Engines need some backpressure to work properly and make torque. That is not true. What engines need is low backpressure, but high exhaust stream velocity. A fast-moving but free-flowing gas column in the exhaust helps create a rarefaction or a negative pressure wave behind the exhaust valve as it opens. This vacuum helps scavenge the cylinder of exhaust gas faster and more thoroughly with less pumping losses. An exhaust pipe that is too big in diameter has low backpressure but lower velocity. The low velocity reduces the effectiveness of this scavenging effect, which has the greatest impact on low-end torque.
An old hot-rodder's tall tale: Engines need some backpressure to work properly and make torque. That is not true. What engines need is low backpressure, but high exhaust stream velocity. A fast-moving but free-flowing gas column in the exhaust helps create a rarefaction or a negative pressure wave behind the exhaust valve as it opens. This vacuum helps scavenge the cylinder of exhaust gas faster and more thoroughly with less pumping losses. An exhaust pipe that is too big in diameter has low backpressure but lower velocity. The low velocity reduces the effectiveness of this scavenging effect, which has the greatest impact on low-end torque.
For turbos, the less backpressure the more power they'll generate.
While straight pipes will help the turbos spool faster, below the spooling point, turbos act like normally aspirated engines. So, the power lost by the loss of flow velocity with a straight pipe will at some point be overtaken by the power gained by the spooling of the turbo. Where that point is depends on the turbo size, configuration, exhaust, etc.
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Originally Posted by cpu77
I have a fabspeed. Who makes cat bypass pipes?
http://www.fabspeed.com/996TT_X50_GT2.html
Last edited by Divexxtreme; Apr 10, 2007 at 07:09 PM.
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right, the flow velocity is the key here. turbos work off pressure differentials - the hotter the gases coming out, the faster the gases, the better. dumping those gases immediately out via a straight pipe might actually slow them down.
more velocity = faster spool. straight piples straight out the back, potentially less flow velocity. figure out an optimal length to maintain velocity, you could have your cake & eat it too.
- chuck
more velocity = faster spool. straight piples straight out the back, potentially less flow velocity. figure out an optimal length to maintain velocity, you could have your cake & eat it too.
- chuck
