BucketMan

Off road downpipes with stock cat back sounds best IMO, I love mine. Was just curious to do the res delete to get a bit more whistle.

Moar whistle!!!!!!!!!!!!

phantomblackgto

I still disagree with the loss of low end torque theory with a 4" exhaust. I don't care how small the turbos are, you are making torque from the turbos operating efficiently, not from exhaust back pressure. Any turbo application needs to breath. Those dyno graphs from Full Race that everyone hangs their hat on actually show the open exhaust making way more torque down low than their 3". At 2250 rpm, the open exhaust is showing 325 lb-ft versus 225 lb-ft for the 3". It does show the 3" with slightly more at 2800 rpm, and that seems to be the only thing anyone is looking at. I pull an 8500 lb TT, and I haven't lost any low end torque with a 4" exhaust.

BucketMan

I think it was FR that said 3 or 3.5" is the optimal size for our exhaust.

vozaday

They did the test on a canned tune. Custom tunes will adjust for it. Turbos put backpressure on the engine, which like backpressure, but turbos themselves don't like back pressure. Now 3" very well could be the peak for gains as a 4" may not improve it (only a certain point before the size no longer makes a difference) but turbos should spool a touch quicker.

Schmidty_

Well said.. I do notice that the turbos spool quicker with the o/r dp.

sweetquarter farm

has anyone listened to the nasty sounding 3.5 ecoboost in the GT40?

http://www.roadandtrack.com/car-show...d-gt-start-up/

id kill to have my truck sound like that.

brucesears

I noticed a big difference when I put the catless downpipes on, I was already tuned and resonator deleted. The combo sounds pretty good without the ricer sound that comes out of most catback systems.

BucketMan

Any highway drone?
Do you have the Ford delete? I'd like to delete mine, but want to make it 3". Nobody sells one, so I hafta make one.
If I just got a 3" flange I suppose a muffler shop could mushroom out a piece of 3" pipe for it to work?

Gremlin85

After looking at the dyno sheet and comparing again, I am going to agree wth phantomblackgto.

Having that much more power early on is worth more than the 18 ft lbs at the peak.... with having nearly identical top end. I might go 3.5 or 4" exhaust when the time comes.

Just to get a better understanding, I am unlcear on if they used a stock down pipe setup through all this???

sweetquarter farm

Turbos recover energy from exhaust - no back pressure required on outlet. The quicker and easier they spool the sooner the boost and power is available.

The turbos themselves provide enough cylinder back pressure. Unlike NA applications where large diameter headers/exhaust can hurt low rpm performance.