I'm in the process of building a 350 and was planning on using a 4'' mufflex exhaust but was told that it would hurt my performance because of my TPI and would be better off with a daul 2 1/2. Which one would work better?

 

4" is alot of exhaust but i wouldnt think it would be too much depending on your engine combo, single 3" all the way through will flow enough for roughly 400hp, if yours is a stock 350TPI or close(below 350hp) the 4" would hurt it. if its gona be around 400 or more i would use the 4". Dual 2.5" would be ok and prob still alil much for a mild 350. 4" single would be almost equal to dual 3"

 

Dual 2.5" is equal to single 3.5". Dual 3" is more than single 4". Dual 2.5" will support 450 HP if you go by the 2.2 CFM per HP garage formula.

Single 3" is fine for a 350 TPI. Stick with that if you dont plan on going bigger.

 

I'll be running a edelbrock TPI setup and have AFR heads, Comp hydraulic roller cam, and hooker super competion headers

 

A single 4 inch exhaust flows the same amount as dual 3 inch pipes. With your current combo I would say go with the 4 inch. Here is my reasoning, your building the motor right now and you may be close to that 400hp mark. Are you going to leave this motor alone when your done with it? Probably not. With that, go with the 4 inch and do the exhaust once and never worry about it again. Granted, you might have higher numbers with a smaller exhaust but as soon as you start doing more motor work, this "smaller" exhaust will become obsolete fast and be your bottle neck. So in the end, if your not going to touch the motor when its done, maybe go with the smaller exhaust, if your below the 400 hp mark. If you plan on this being just the starting point, go with the 4 inch.

Oh yeah, have fun!

 

what would be the point of a 4" catback if the front Ypipe and cat arent 4".... the shortie headers dont have collectors larger then 2.5" and the ypipe joins together at 3", even if u run a 3" to 4" reducer the smallest part will be the 3" yipe or the 2.5" collector on the shorties... the exhaust is only as good as its smallest part... so upgrading from a 3" catback to a 4" is futile unless u build the front equal to the rear.