Exhaust diameter for a 71 stock GMC

[57rookie]

I am looking to see what the stock diameter ( the diameter that the muffler manufactures want, not sure if ID or OD) for a bone stock 1971 GMC with a 350 and a 4BBL carb. I dont have the measuring tool to clamp on and find the diameter.... My best guess is 2.5#. Looking to see what you experts know.
Thanks!!!!!!

[Husker]

2 inch
Ron

[57rookie]

the circumference is 7.5" around using a piece of tape. I am having a brain fart here - there was a formula posted using pie 3.14 to tell me the diameter - anyone have this formula???

[racerop]

C=πd

Pie=π
C=circumference
d=diameter

[57rookie]

So I figured it out. I re measured using piece of tape and it is actually 7.75" in circumference. Then you calculate and it came out to 2.468" diameter so my factory exhaust at the inlet of the single muffler is 2.5". I knew it looked larger than 2". The tail pipe is 2".

[Leonard60]

Originally Posted by 57rookie

So I figured it out. I re measured using piece of tape and it is actually 7.75" in circumference. Then you calculate and it came out to 2.468" diameter so my factory exhaust at the inlet of the single muffler is 2.5". I knew it looked larger than 2". The tail pipe is 2".

Pipe is measured by nominal inside dimension. So 2" pipe would be larger that 2" on the outside. The inside of your pipe is likely what you call 2".
If you don't have a vernier caliper you can use 2 squares to measure the out side of your pipe then use the formula Pi X d and that will give you the out side diameter. This measurement only gives yo outside diameter not the tru pipe size.

[Leonard60]

I wrote down diameter not circumference my mistake. Diameter is Pi divided by circumference

[71cheyennesuperlongb]

Pipe is measured I.D. Tubing such as exhaust ismeasured by theO.D. Retired pipefitter of 40 years.

[Husker]

2 inch inside. If your tailpipe is 2 then wouldn't that be the overall diameter.
It would restrict down to tailpipe. Just Askin.
Ron

[Killer Bee]

this should clear things up a bit without getting too far off into the weeds..

How to Measure Exhaust Pipe

simple tape measure is all you really need to measure common exhaust tubing unless you need to measure a section without access to an open end then a cheap dial caliper is sufficient as long as the jaws are deep enough..

here's a quick chart to get you in the ball park based on engine output..

good luck!

[Ironangel]

Originally Posted by 71cheyennesuperlongb

Pipe is measured I.D. Tubing such as exhaust ismeasured by theO.D. Retired pipefitter of 40 years.

Gospel truth. Short answer is; 2" You'd be surprised how many engineers don't know the difference between pipe and tubing...