What diameter exhaust pipe should be used for a stock-ish '37 21-stud Flathead? I do have dual 94's and maybe a mild cam (engine built long ago, but minimal miles). Probably using the log-style manifolds that dump up front. Want to run duals, but not totally opposed to a single pipe. Any suggestions? Any examples? Videos?
You can use pretty much whatever will work and fit into your chassis. With a Ford flathead, the primary exhaust restriction is in the ports in the block. After the gases get through those tight passageways it is smooth sailing and there isn't much you can do to restrict it any further short of using 1/2" electrical conduit.
I have heard that 1 3/4" is enough for a flathead. (This was a couple of years after I spent a lot of time running 2" pipe all the way back on my old '36 3-window with a '50 Merc.)
My sedan has 1.75” all the way back from the headers. I’ve never found it seemed restricted. The Smitty’s mufflers are rusting out, and I think I’ll just replace them with straight tube.
I’m just learning about flatties with my new truck project (53 ford), so very curious about this. Being an old OHV guy, here are a couple of my cheat sheets. Full disclosure: the cheat sheets are post advent of the interweb
@NoSurf and @alchemy Either of you have a video with sound of your exhaust from the rear? And NO FART JOKES!!!
If you have room, use 2" pipe.........simply because it doesn't look anemic sticking out the rear of a car. You can get into all kinds of theory about what pipe will work best, whether you need some backpressure or are better off with free flowing. Then there is the muffler decision and will it restrict .....or not. Its not like you have a set up thats producing a lot of power and these decisions are gonna cost you 50 hp. I'd just use the 2" and a good sounding set of mufflers for effect.
I have a couple on my IG account. You'll have to request access, as my account is private. https://www.instagram.com/reel/CkEgz_yBs19O9xznk4MgNWvptcGnduObV1kqxg0/?igsh=MWx3emhsMzNmNjZ2Yw== It sounds a little deeper because I have the sidepipes capped.
The Jalopy Journal
