Exhaust Size Question

[cgilbert37]

Hey guys, just wanted to get your thoughts before I start welding...

I have a 351W stroked to 393ci, 13.5:1 c/r, Weber IDAs, swesome heads/cam and etc. I built it to provide useable power to about 6400rpm.

For exhaust I'm thinking 1 5/8" header tubes to a 2 1/2" dual exhaust.

Or should I really be thinking 1 3/4" with 3" pipes?

Thoughts?

[jhv48]

The last one.

If it's gonna rev, it's gotta be able to exhale!

[Maurice Butler]

Remember it sucks air in approx 700cfm, burns it so it hotter, therefore expands needs lots more space, back pressure stops the gas flowing out and leaves stale air for the next stroke, and stops the inlet charge coming in. Big is good to a point.

[RICK LAKE]

cgilbert37 THOUGHTS??? C, you are looking to run 13.5 on the street?? What size is the cam shaft?? You are looking for MAX HP at 6,400 rpms??
What are you looking to do with this car?
Dyno runs with an A/F meter, back pressure gauge, and EGT are the only way you are going to get a correct idea of what the motor is wanting to make either the most HP or Torque.
Bigger pipes are not always the better pipes. If this motor is going to live life at 6,000 rpms alot, go bigger. Bigger pipes also kill torque. This is what moves the car forward when driving until the torque band starts to drop and the HP band picks up to move the car. The closer the LSA the more peaky and narrow the power band is going to be. The more reversion you will get to. A little more info with specs on the motor would help, BUT this is all theory and not real world data.
I vote for smaller pipes without seeing the camshaft specs. Rick L. Ps What exhaust are you running and what are the inlet and outlet size?

[Dwight]

I think 1 3/4"


but 13.5 to 1?????????????????????????

listen to Rick Lake

more details please


Dwight