Fabspeed has released their downpipes for the 135i and 335i N54 based vehicles. These downpipes eliminate the primary cats. The diameter of the pipes is 2.75 inches. Gains are about 25 whp with these pipes, 02 simulator included for no check engine lights.
Wonder why they chose 2.75" over the popular 3" idea. Maybe it causes less turbulence off the face of the turbine? What is the stock turbo exhaust outlet diameter?
It's easier to package 2 x 2.75" pipes than 2 x 3" pipes. I dont blame them either.
The power gains going from 2.75 to 3 are minimal on a street car anyway. They look pretty good.
Yeah they are both necking down to 2.5" anyway. I know that supposedly someone with 3" gained 7-15whp over 2.5" pipes with FBO at 15ish psi. I think they were vs Race Land's or one of the crappier ones though with bad cuts/welds thogh.
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