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Ideal exhaust diameter?

D

darrencol

Messages
2
Hi all,

I've recently bought myself a cosmic grey EP3 premier edition. Loving it so far but it's completely standard atm and I've been looking at exhausts for them. I looked up a few videos and liked the way the the Scorpion system sounds, however I just found out that the outside pipe diameter is only 2 inch? Coming from a turbo'd car before having a 2.5 inch system, this seems very small to me. Is this a sufficient size for an N/A car or should I go custom and get larger? I plan to have the car mapped at the very least so would be seeing around 235-240hp, but if I can save enough money in the long run I may look at supercharging.


Thanks,

Darren
 
For utmost power, in most cases yes. But a good 2.5” system will have more torque and be easier on the ears. My 2.5” exhaust actually made more power than a full 3” system on the same dyno.
 
As Chris has said, 3" doesn't always necessarily equate to better performance. My understanding is that whilst 3" is unquestionably better for a car running forced induction, 2.5" is quite often better on an N/A K20 with the usual bolt-ons, providing it's well designed.

I guess the question is, what are your plans for the car long term?
 
jimbodeeni said:
The numbers they achieve may over read but I thought a comparison on the same rollers could be trusted?
Click to expand...

Rolling road number can be made to show whatever the operator wants. I'm not saying that the TDI North system is bad, just stating fact about rolling road numbers.
 
Chris. said:
Rolling road number can be made to show whatever the operator wants. I'm not saying that the TDI North system is bad, just stating fact about rolling road numbers.
Click to expand...

Fair enough, It would be nice to be able to trust what you read I guess
 
3 inch seems massive especially for N/A. Usually I wouldn't consider that size unless the car was over 300hp boosted. That dyno is interesting although it was going from 2.25 so could have possibly seen similar results with 2.5? Either way, the 2inch scorpion system is balls :lol:
 
http://www.exhaustvideos.com/faq/how-to-calculate-muffler-size-pipe-diameter/ suggests 2.5 is fine up to (and a bit beyond) 250hp. Remember that you'd also want to replace the manifold and cat once you get past that point anyway since both will be similarly restrictive.

Having too large a diameter pipe will result in loss of power too though, better to have slightly narrower exhaust diameter rather than too large.

When you start to worry about it to this kind of level though you've got a LOT of money to spend (k100/kPro, manifold, exhaust, intake - incl. manifold and throttle body). A decent system like the Fujitsubo RM01A or Legalis (or others) would probably be fine up to the power you're looking for in the mid term.

If it's just noise you're after though, sure, go for something big bore and chavvy ;)
 
There’s plenty of evidence to show that a 3inch system gives best power providing you’ve got the supporting mods and correctly tuned. TDI north have covered this topic many times and other tuners will echo the same.
On the other hand, 2.5inch will provide similar power (around 5-10bhp less peak) and be more subtle on the ears. So it depends if you’re after max power or slightly lower figures and a more friendly system on noise and ground clearance.


Sent from my iPhone using Tapatalk
 
There’s plenty of evidence to show that a 3inch system gives best power providing you’ve got the supporting mods and correctly tuned. TDI north have covered this topic many times and other tuners will echo the same.
On the other hand, 2.5inch will provide similar power (around 5-10bhp less peak) and be more subtle on the ears. So it depends if you’re after max power or slightly lower figures and a more friendly system on noise and ground clearance.
 
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