Hi, I have a 72 F250 4X4 with the 390 bored .060. I am having new exhaust put on as I write. I was going to get duals (out of the manifolds) as opposed to the single that is on it now. The shop called and said he could use the existing crossover and run a 3" aluminized exhaust from there and would be good to go. I am curious to hear what some of you think. I know that some of you will say I should have put headers on, but I have heard conflicting info and decided to wait. There is enough power to spin the 33's on it. Thanks.

 

Here is my take on the situtation. One three inch pipe is better than 2 two inch pipes. The three inch will have more cross sectional area than both the two inch pipes combined. It will also have less drag area. However the important thing is that it has more cross sectional area.

Area of a cirle is a constant (some number) times diameter squared. (Yes this is correct.)

#of.pipes diameter squared=constant times area (total area)
..2..times........2^2............................. =8..........
..1..times........3^2............................. =9..........
..2..times........2.5^2........................... =12.5.......
..1..times........4^2............................. =16.........
..2..times........3^2............................. =18.........


However, two 2.5 inch pipes would be better than one 3 incher.

So if you have the exhaust coming out of the manifold and goes directly into the 3inch pipe, go for it. But if the exhaust comes out of the manifolds and hits a 2inch single pipe before it goes to three, this is not good.

Best option would be true duals with 2.5 or larger inch pipes. Or a 4 inch single. (very rarely seen)

Did I confuse you enough?

Daywalker
92' F-250HD 351 4x4 xlt 4.10 ZF 5speed supercab longbed

 

Best thing I ever did was add headers and dual exhaust to my 360 powered 73 F250.

 

Some don't like headers because of the noise and some trouble with leaks, but I'm running headers on both a 360 and a 428 and the trouble to install them and stop leaks isn't that bad. Headers on an FE engine are one of the best upgrades you can do, the stock setup sucks. I've heard of 50HP gains from headers alone.

The other downside is heat to the starter, but a good starter wrap will help a great deal.