Im going to get a local exhaust shop to make me a new y pipe because the hooker y I have now is sitting on top of my crossmember for my mwc tunnel mount tq arm. Thats only after I beat it with a hammer to get it to kinda fit. Now my exhaust is vibrating in the car. I know some of the noise is caused by the tunnel mount but having the y pipe sitting on the crossmember isn't helping. Im going to get a flowmaster merge but Im not sure if I should get the 3" to 4" or the 3" to 3.5"? Either way its running straight into a 3" cutout then to a 3" hooker catback. I read that the 4" helps with turbulence but if its going to a 3" cutout right after the y I dont see it helping that much. Any suggestions?

 

Anyone? I need to order one soon

 

The exhaust shop (Mufflex, Trenton NJ) that did my original custom setup of 3" Y-pipe branches into a 4" Mufflex catback used the Flowmaster 3" in/4" out merge. That was for an engine making 762HP at the flywheel at the time. Later, when we pulled the Y-pipe and 4" Mufflex off, to go to true 3" duals (engine by then at 800HP) there was no measurable difference in HP.

Unless you are making that kind of HP, I don't see any benefit in using a 4" out, then having to swage it down to a 3" IM pipe, cutout or whatever. Probably create as much pressure loss through the contraction as you'll lose through "turbulance".

What size are your collectors? I'd match the diameter on the inlet size, and opt for a 3" out if they are 2.5", or a 3.5" out if they are 3" collectors.

 

What I'd do is run it with the 3.5" Y-merger exit then into a 3.5" cut-out. After the cut-out use a 3.5-3 inch reducer to run it through you Hooker cat-back. This way you'll get Max exhaust flow, when you have the cut-out open.