Quote from: KRW on January 11, 2015, 12:15:01 AM
What little bit of research I've done seems to lean towards increased exhaust size (cat-back) and a cold air airfilter. Has anyone actually tried this? Neither of these should effect the warranty but i'm not sure if there would be any HP increase. I think the stock exhaust pipe is around 2.25 inches in diameter and it would seem to me that with twin turbos that the engine could breath better with a 3 or3.5 inch exhaust. And if so, then more air in would have to help also.
Any thoughts on this???
KRW: I'll try to be brief, but I suffer from logorrhea, LOL.
Using my '13 SHO dyno testing was done with stock tune during development/fitment of PPE downpipes...multiple back to back pulls at Black Market Racing. (BTW 4DR prototyped these DPs and Hotpipes). Results: Catted posted about 12 AWHP increase and non-catted posted about 17 AWHP increase as compare to OEM DPs. Both PPE sets resulted in much earlier spooling of turbos (about 2100-2200 rpm stock DPs --> 1500-1600rpm with PPE DPS. This earlier spooling moved the entire power band down about 500-600 rpm without affecting top end power. Result is a noticeably quicker early acceleration (which I still love!). This can be increased by having any tune modified for the downpipes (I did). Both LME and Unleashed can do this as well as other tune adjustments for modifications. The trick with the DPs is smoother design with elimination of the cat flange and less convoluted shape which gets more laminar flow. You can see these changes in the post about this and install. It's here:
http://www.ecoboostperformanceforum.com/index.php/topic,2054.msg28591.html#msg28591Call Ecopower Parts (in the vendor section) for pricing and options...
All currently produced downpipes are the same diameter as OEM exhaust. So not much can be gained mathematically by increasing diameters distal to this. There has even been some development of a single exhaust that is mathematically superior to OEM....
As far as larger diameter catback... rate of flow and laminar flow are also important to turbo function and exhaust temp dissipation. A bigger tube slows flow and may allow turbulence...effects? dunno. I am unaware of testing i
n our cars with Corsa Catback (or others) despite their flow claims. It is a beautiful exhaust. Stainless Works and LME are two other producers of cutbacks and DPs... Note that some degree of back pressure seems to be a good thing in the 3.5TT GDI engine as far as preventing turbo oil seal leaks.
As far as CAI, during the hotpipe dynos Mike, Jeremy, and I compared dynos of completely stock intake and filter with dynos of the entire filter removed and free intake of air into the 3.5" open end of the "saxophone" of the intake piping by completely removing all filter and intake piping in the comparison pulls. We found no dyno difference. This was with stock tune also. Again specific modification are readily available from LME or Unleashed and may affect this. I do not believe any CAI, certainly if it leaves the saxophone intact offers any HP increase. However, in real life drag racing several members have noted 0.1 sec increase in the 1/4 mile time of their cars with Airaid CAIs which they got back on the same day by reinstalling stock intake and filter. I am unaware of any other formal testing of CAI performance changes i
n our cars. Also, many folks have modified their Airaid to seal better on the hood ... not sure of tested changes if their are any. I am unaware of any testing using the K&N CAI.
I personally would avoid any CAI that could possibly draw any air from underhood.
All that said, there are other reasons people do the CAI and exhaust mods; eye candy and sound primarily. changing the exhaust note and hearing the turbos spool. I use an MDesign CAI, primarily for eye candy and because preliminary testing showed no power loss...and I didn't lose my 3.9-4.1 sec 0-60... Dyno testing should be accomplished in the next 2-3 weeks on the MDesign ...there are only 5 installed in the wild at the time of this writing with about 10-12 more shipping any day. Image below, CF, larger air intake,to start, turbo spooling heard, and it seems to stop the sooting of my tailpipes (no gas changes...all E10 winter gas pre and post). Finally, I can now check my transmission fluid without removing the CAI and have space for the future meth reservoir. Here's a pic...left click to enlarge:
Hopefully others will chime in also. Wishing you fun modding!
