vfast

you most likely has gone to a shop who has trouble bending 2.5 inch pipes it would be better to order one that is mendral bent as I doubt that shop can do this..if it's not mendral bent your wasting your money as it will flow about as much as a stock mandrel pipe...remember it's your $$$$ ,your the cust..get what you want..good luck

roundman

if the collector is 3", go with 3" behind it all the way. the size question is more important when it comes to the headers themselves as you can go too big and lose low end torque, maybe that's what confusing the shop guys. you probably should have no bigger than 1-3/4 headers for that power level, any bigger and you kill your low end.

T5superduty

Well they are 1 5/8 with 3" collectors and there is still great low end torque even with the B cam. It pulls and pulls. The other thing I didnt tell you guys is the same muffler shop I am dealing with put either 1 5/8 or 2" exhaust on my first system. So once again do you guys think he is trying to screw me ? Why would someone put a smaller exhaust on. I just dont get it... I'm going somewhere else.

vfast

maybe the just don't know any better... unless you have 2" primary tube headers those 3" exhaust is just a waste of cash

T5superduty

This place can do the job. They did a custom 4" for my buddies 300zx TT So they shouldnt have any trouble bending 2.5

vfast

there is only a handful on people that can mandrel bend 4" pipe in the country. t5..do you know what I mean by mandrel?

T5superduty

lol... i'll send you a picture of the exhaust if you like... not sure about what mandrel is but they just use this machine thingy and push a button and it bends it. It looks a little like this but its not the same. Not even sure if its for the same thing but its similar http://www.ercolina-usa.com/mandrel-bender.htm

86lx

3" is too big,2.5 will be plenty for 400 hp. Put it this way, a friend of mine had a 85 gt with 2.5 dynomax super turbo cat back with a 3" dr gas pipe and went 9.6 1/4 mile and only gained 2 tenths with no cat back so 3" is overated.

T5superduty

I just really want to know why the muffler shop told me 2.25... I'm guessing everyone agrees at least on 2.5 right?

95mustang302

definately, i was at the muffler shop the other day and i asked if they could put a 3 inch system all the back but they told me that the 3 inch pipe wouldnt fit over the axel safely. i also have lowered my car 2" so i dont know if that has anything to do with it, but i would go with the 2.5 i f i were you