I will be installing fenderwell exit headers on my 1978 F250, 400, soon. The headers have a 3" collector. I am wondering what size exhaust pipe everyone has run after the headers. I see no need for 3" all the way, so I was thinking of stepping it down to either 2.5" or 2".

What are yall's thoughts? What have you done that works well?

 

2.5 is what I'd run unless it's built up a bit. In that case I like 3" to let the beast out...

 

Based on the typical expected HP and RPM range, dual 2.25-inch, mandrel bent tubing as a minimum or dual 2.5-inch mandrel-bent maximum. If it not mandrel-bent, then 2.5-inch tubing.

Going to a 3-inch system is a waste of money unless your rig regularly sees more than 6500 RPM or making 500+ HP.

 

I have nothing past the fenderwell exit header mufflers on ol red as of now, but I plan on some turndowns.


2.5 should be ok.

 

Thanks!!

I will plan on reducing the 3" collectors to 2.5". Run it back to the bed, attach the mufflers, and then turn it out in front of the rear tires. Nice, cheap, and easy.