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10-28-2017, 09:47 PM
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#1 |
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Registered User
Join Date: Jul 2011
Location: Calgary, Alberta
Posts: 153
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Exhaust diameter for a 71 stock GMC
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!!!!!! |
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10-28-2017, 11:51 PM
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#2 |
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Registered User
Join Date: Dec 1999
Location: Mid NE USA
Posts: 2,212
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Re: Exhaust diameter for a 71 stock GMC
2 inch
Ron
__________________
Member #111 68 C-10  Daily Driver70  4x4 Project76 Jeep CJ-5 Help Support the Board: http://67-72chevytrucks.com/vboard/payments.php He who knows nothing is closer to the truth than he whose mind is filled with falsehoods and errors. Thomas Jefferson |
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10-29-2017, 01:15 PM
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#3 |
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Registered User
Join Date: Jul 2011
Location: Calgary, Alberta
Posts: 153
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Re: Exhaust diameter for a 71 stock GMC
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???
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10-29-2017, 01:24 PM
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#4 |
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Registered User
Join Date: Jul 2015
Location: Lindenwold, NJ
Posts: 94
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Re: Exhaust diameter for a 71 stock GMC
C=πd
Pie=π C=circumference d=diameter |
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10-29-2017, 01:27 PM
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#5 |
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Registered User
Join Date: Jul 2011
Location: Calgary, Alberta
Posts: 153
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Re: Exhaust diameter for a 71 stock GMC
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".
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10-29-2017, 01:37 PM
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#6 | |
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Registered User
Join Date: Jun 2016
Location: Leslieville alberta
Posts: 374
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Re: Exhaust diameter for a 71 stock GMC
Quote:
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. |
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10-29-2017, 01:55 PM
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#7 |
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Registered User
Join Date: Jun 2016
Location: Leslieville alberta
Posts: 374
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Re: Exhaust diameter for a 71 stock GMC
I wrote down diameter not circumference my mistake. Diameter is Pi divided by circumference
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10-29-2017, 06:05 PM
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#8 |
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Registered User
Join Date: Aug 2015
Location: Alcoa;Tn
Posts: 208
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Re: Exhaust diameter for a 71 stock GMC
Pipe is measured I.D. Tubing such as exhaust ismeasured by theO.D. Retired pipefitter of 40 years.
__________________
'71 Cheyenne Super LWB - Second Owner in 39 Years! '70 CST/10 SWB - Soon to be Daughter's truck when finished |
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10-30-2017, 02:29 AM
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#9 | |
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Senior Member
 
Join Date: Feb 2010
Location: Falls City, Nebraska "100 Miles From Nowhere"
Posts: 2,219
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Re: Exhaust diameter for a 71 stock GMC
Quote:
 Short answer is; 2" You'd be surprised how many engineers don't know the difference between pipe and tubing...
__________________
Michael of the clan Hill, "Two Seventy Two's" 71 1-ton Dually 350 4-Speed 71 C/50 Grain Truck, 350 Split-Axle 4-Speed 02 3/4 ton Express 14 Indian Chief Vintage 1952 Ford 8N, "Only Ford Allowed On The Property" "Be American, Buy American" 
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10-29-2017, 06:21 PM
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#10 |
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Registered User
Join Date: Dec 1999
Location: Mid NE USA
Posts: 2,212
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Re: Exhaust diameter for a 71 stock GMC
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
__________________
Member #111 68 C-10 Daily Driver70 4x4 Project76 Jeep CJ-5 Help Support the Board: http://67-72chevytrucks.com/vboard/payments.php He who knows nothing is closer to the truth than he whose mind is filled with falsehoods and errors. Thomas Jefferson |
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10-29-2017, 07:13 PM
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#11 |
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Registered User
Join Date: Jan 2016
Location: Barber City, CA
Posts: 4,731
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Re: Exhaust diameter for a 71 stock GMC
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! 
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