Technical What exhaust size diameter ?

Was going to put a set of headers I had on a 21 stud motor (1936) and run dual exhaust. What would be best size exhaust diameter for this application ? Not sure if I’m gonna run straight pipes to rear or maybe glass packs

 

No more than 2" diameter...

 

my original guess was 1.75” to -2” .

figured anything too big will just make it run worse

 

What size is the exit on the headers?

 

Flatheads are much less sensitive to down stream exhaust pipe size than other engines because the primary restriction is the exhaust ports as they take a very tight and convoluted route around the cylinder walls to exit the block. That restriction dictates your in-cylinder back pressure and there is very little effect from down stream exhaust componentry, no matter what it looks like.

 

Agree what FrozenMerc said so just run the size you want from 1-1/2 all the way to 2 -1/4 inch will work perfectly for what your doing.
Ronnieroadster

 

Just talked with a flathead engine builder last week and he said no reason to use tube bigger than the hole in the valve seat. So, 1-3/8”. Maybe 1-1/2” on the center port. Whatta you guys think about that?

 

I need to go by my storage unit and measure I don’t recall off top of my head, they were a custom set someone made . I will post that info once I can get over there and measure

 

My normal go to on a v8 flatty is 1.75"

 

Any size up to 2 inch is practical.
"W" style will give you exactly .9 more hp over swept style.

 

I had dual 2 1/4" with glass packs on mine...didn't care for the sound...the signature burble of the flathead got too washed out. If I did it again, I would use less that 2" (probably 1.5" or 1.75").

 

Running 1 3/4" through cherry bombs. Nice sound not too obnoxious.

 

https://youtube.com/shorts/SVGUYukbnbg?feature=share

Pardon my buddies bad video skills... But this is straight piped 8ba 1.75" And here is the same car at idle.

 

Go small, 1-1/2"-1 3/4' no mufflers, it will have a good rap to it. I just had a SBC with 1 3/4" and it sounded so good.

 

My headers were 1 1/2' so that's what I ran back to the mufflers and they were 2' so I ran 2" the rest of the way rather than adding adapters at the back of the muffler.

 

You want large sound...large tail pipes.

My neighbor had a 3" exhaust pipe installed on is little...Dodge Valiant, "stock" slant 6.
The thing ended up sounding like a "good" running V-8. He claimed, he felt no loss in power or mileage!

Mike