I'm curious to know if anyone has seen noticeable gains after only upgrading their dp and still using the stock cat and stock exhaust? A while back, in a past thread that I found by searching, TurboTrixRacing and Grod101 claimed to have seen a stock evo gain 20 whp from an RMR dp with stock cat and exhaust.

Has anyone seen similar gains to verify that this wasn't juss an anomaly??

If so, it'd be sweet to keep your car looking stock on the outside so as not to attract negative attention, but still be faster than stock. Not to mention saving $600 on a catback exhaust!

 

i highly doubt theres that much gain with or without an exhaust... i'm running a cat back on stock dp and cat and the car responds alot better then the stock catback did... faster spool, pulls throughout the whole powerband... etc

 

A DP will help out spool a bit, and yield a good amount of HP. Some as much as 15-20.

 

Considering that the stock catback is 2 3/8 with the stock DP coming in a 2" with a number of crush sections your best best is running a 2.5" DP at the most so as not to create even more backpressure. I had an HKS DP on my car which comes in at 2.6" inner diameter and untuned it picked up from a stop smoother, boost came on a little quicker although I was experiencing some timing pull accross the middle. Combined with some type of ECU tuning and a slip fit 2.5" High Flow Cat I think the stock catback piping is still useful, and best of all suppresses sound while still freeing things up enough to make smoother power, with noticeably quicker spool up.

 

i DID A FULL 3" TURBO BACK EXHAUST FROM ULITMATE RACING (sorry just realize the caps) and I felt the difference I would recommend the full 3" exhaust

w/ high flow cat
Adam

 

How my hp should I expect to gain when upgrading just the downpipe if I already have a cat-back? I have an hks hi-power cat-back and will be upgrading to an hks downpipe soon.

 

Prob 10-15hp at the wheels

 

Sweet! Damn, hearing that's gonna make me order my hks downpipe today. hehe..

 

i just have the rmr downpipe with stock exhaust and cat. Thanks turbotrix. it feels alot like there alot more torque. sounds deeper too (meaner) the whole engine.

exhausts just cost soo much.

 

i have the helix 3 inch and the d&d cat back on the stock cat... definately felt a difference when i put it on... the stock dp is a restrictor compared to the rest of the exhaust.

 

I have the MR downpipe with a B&B cat back, definitely gave the car a little power.

 

Got the HKS DP and Espiler CB and its a signifigant upgrade imo. (EvoG8r and Novtec1, you guys need to go to work or something LOL

 

So whats the best dp to get if i was to keep the stock cat and exhaust? (i would get the full turbo back but on a tight budget at the moment)

 

Geese, I'm going to sound like a Buschur spokesman today... for the most power per dollar, you'd probably best be served by a Buscher 2.5" DP. Then go to the local muffler shop with a rear section flange bought from RRE to have a muffler delete pipe fabbed up (if you are that short on cash). If you have a little more of the green stuff on hand, You can pick up a Megan Racing 3" DP and cat back for less than $500 off of Ebay.

 

I dont think that you will find any good side by side comparison of downpipes, you're stuck with different numbers thrown out by different vendors with testing on different dyno's. Not overly useful to compare. I doubt that there's any significant performance difference between the different downpipes commonly discussed on these message boards.

Works claims that their 70mm dp is the best size when using the stock turbo. (even better than a 76mm dp) They reccommend a 76mm (3 inch) DP for their upgraded turbo. I've heard that this is a common strategy for many tuner evo's in Japan. (70mm dp with stock turbo)

I doubt, however that any of us would be able to tell the difference between a 70mm and 76mm downpipe, in the real world.

I would add, however, despite a tight budget, it would be worth a little money to get an aftermarket AB exhaust in addition to your DP. I got my Works AB used for $125 and it added lots of power (on the butt dyno) over the restrictive stock muffler.

Good luck!