down pipe size

[cseverens]

I am contemplating getting these. catted of course! it appears there are 3 major options. ppe 2.5" can be had for $760 (shipping cost unknown). stage 3 motorsports has some 2.5" for $766 shipped. and torrie at unleashed makes his own 3" for $799 plus $30 shipping. does the size really matter? mods now are k&n panel filter, 3 bar sensor, and a tune from torrie. in theory, my mechanic will be installing the ngk plugs and the 170* thermostat I bought from torrie weeks ago. he will issue new tune afterwards. I have no other mods planned after that.

 

[ZSHO]

I would personaly go with the PPE CATTED DP,from EPP,especially if your state is strict with emmissions testing,have mine for well over a year now and the best part is they never set any codes tuned or stock tune,and basically all have roughly the same power gains.  Z

 

[SHOdded]

With the 2.5s, you can support at least 600 awhp, so no worries.  With the 3.0s, you could probably get to more than 750 awhp (just a wild guess tho).  Stock is 2.25.

 

[cseverens]

I won't be anywhere near those power numbers!!

 

[SHOdded]

Then you have a huge margin of safety

 

[BiGMaC]

With the 2.5s, you can support at least 600 awhp, so no worries.  With the 3.0s, you could probably get to more than 750 awhp (just a wild guess tho).  Stock is 2.25.

I suspect that there are limitations on increased performance with increased DP size if the rest of the exhaust system behind it is still 2.25"...

 

[SHOdded]

True, but eliminating the OEM bends def helps.  With OEM catbacks, people are running 400+ awhp, not bad at all! 

 

[BiGMaC]

True, but eliminating the OEM bends def helps.  With OEM catbacks, people are running 400+ awhp, not bad at all! 

Definitely true Manu... And bpd's car is in excess of 600 AWHP without cutouts or DPs larger than 2.5"... Those stock DPS are definitely both unnecessarily crooked but are pinched without mandrel bends. Tuning helps too since the 3.5 GDI starts exhaust scavenging in the head when both exhaust and intake valves are open... Free flow makes it work. Size is a question because at some point increased size will negate the benefits of laminar flow.

 

[brewerp93]

So for the catbacks does anyone know if there are any that are actually 3"? I have looked around and most of what everybody is using is just the 2.5" so there should be no need to exceed that diameter with a 3" DP right?

 

[BiGMaC]

So for the catbacks does anyone know if there are any that are actually 3"? I have looked around and most of what everybody is using is just the 2.5" so there should be no need to exceed that diameter with a 3" DP right?

I have no evidence... But common understanding of physics would seem to dictate that putting a 3" pipe between a 2.25" connection to the exhaust manifold and a 2.25" catback woul create turbulence and only move a restriction a few feet down the exhaust system without alleviating it.

 

[SHOdded]

3 inch downpipes + 3 inch dual catback might be too little backpressure, more critical in a turbo engine to have enough backpressure.  So if you go with 3 inch single catback, that would be safer in the long run than duals.

You can check out the single pipe catback designed by MDesign some time ago.  There's a thread somewhere on this forum, with sound clips.

http://www.ecoboostperformanceforum.com/index.php/topic,3994.msg62625.html#msg62625

http://www.ecoboostperformanceforum.com/index.php/topic,3000.msg44515.html#msg44515