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Exhaust pipe diameter question- OD or ID

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Old Jul 28, 2010 | 01:21 PM
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Default Exhaust pipe diameter question- OD or ID

Got a simple question about exhaust pipes and headers measurement.

When one speaks of 2 , 2.5 or 3 inch exhaust etc.., is this size the OD (outside diameter) or ID (inside diameter) measurement?

I am measuring headers and the header collector is 3 inch OD, not ID.
The headers were advertised as 3 inch collectors.
Thanks,
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Old Jul 28, 2010 | 01:42 PM
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The 2.5 inch exhaust pipe I pulled off my 71 was all OD.
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Old Jul 28, 2010 | 01:58 PM
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Originally Posted by Rebelrob
Got a simple question about exhaust pipes and headers measurement.

When one speaks of 2 , 2.5 or 3 inch exhaust etc.., is this size the OD (outside diameter) or ID (inside diameter) measurement?

I am measuring headers and the header collector is 3 inch OD, not ID.
The headers were advertised as 3 inch collectors.
Thanks,
Rule of thumb on header is bigger CI bigger headers. SB 2.5, BB 3". most give OD I believe. also unless your motor is super modified keep you exhaust pipes in the 2.25- 2.5 area or you will loose power with not enough back pressure.
Hope that helps
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Old Jul 28, 2010 | 02:40 PM
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Originally Posted by sniperdiver37
Rule of thumb on header is bigger CI bigger headers. SB 2.5, BB 3". most give OD I believe. also unless your motor is super modified keep you exhaust pipes in the 2.25- 2.5 area or you will loose power with not enough back pressure.
Hope that helps
Good grief. Will this old wive's tale never die?????
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Old Jul 28, 2010 | 03:13 PM
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All tubing (exhaust, brake, plastic etc) is measuered by od, all pipe (under 12") is measured by id.
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Old Jul 28, 2010 | 03:33 PM
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OK. That is what I was looking for.
Thank you for the all the replies........

Last edited by Rebelrob; Jul 28, 2010 at 03:49 PM.
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Old Jul 28, 2010 | 03:46 PM
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Tubing => specified nominal value refers to outside diameter (O.D.)
Pipe => specified nominal value refers to inside diameter (I.D.)

EDIT: Crap, Noonie beat me to it!
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