Ok, i got my new engine up and running but it just seems like there should be a little more. Im really thinking it is all and the exhaust and im wondering how much of a difference it will make. I have been told that you want 2 cfm for every hp and i belive i should have at least 350 whp, which means i need at least 700 cfm right or is it 2 cfm for every crank hp? My current setup is dual 2.5 piping with the factory cats (which im told they only flow about 200 each) and then a y pipe into a 3" flowmaster then exits dual 2.5. Now my question is how much should i expect to gain by just taking out the cats, and then how much more would i gain by a diffrent muffler? The engine is a 383 with slightly higher comp pistons, ported and d shaped heads, bigger valves, cam...etc etc

 

Doesn't sound like a very efficient exhaust setup.

 

ya...i know, It is not... I was asking how much power would i expect to gain from changing my exhaust setup to a better setup

 

rcfast, I dont see headers mentioned. If your truck does not have headers I think you are leaving a lot on the table. Personally you need 1 3/4" primary tube headers. Forget the shorty headers as they wont flow to the need of that engine. Since you claim to be making about 350 RWHP, it can be estimated you are making around 420 crank HP (350 x 1.2 for 20% drivetrain loss assuming automatic) This would necessitate around 840 cfm according to your 2 cfm per HP (yes I would use crank horsepower) On an engine making that much power I think you would benefit from a 2 1/2" true dual setup with high flow cats and some sort of balance tube (X or H) I would also ditch the flowmaster as they have been proven to not exactly "master exhaust flow". I would go with Dynomax Ultra Flows (if you still want that powerful sound) or with a Magnaflow muffler which flows extremely well and has a nice mild sound. I wouldnt worry about losing low end with this "bigger" exhaust due to the fact that the 383 on its own will make a boat load of torque. Hope this helps.

 

what's your a/f ratio?

 

so how much hrse power is he leaving on the table by not having headers?

 

I have thorley headers, forgot to mention that.. I am running dual 2.5 piping but only a single flow and as of today have the cats removed with a h-pipe... As far as a/f i haven't monitered it on atap as closely as i should, but i belive im getting around 12:8:1 or so, im going to double check that later tonight hopefully