[1ownerT]

Does anyone have the info or a link on how to figure exhaust pipe diameter? I have googled with no positive results.

[onovakind67]

The easiest way to determine the diameter is to measure it directly with a caliper or similar instrument.

[poncho62]

I think he is saying....How do you determine what size pipe you need to use............Am I right?

[Henry Highrise]

Originally Posted by poncho62

I think he is saying....How do you determine what size pipe you need to use............Am I right?

Thats the way that I took it also.

[1ownerT]

Originally Posted by poncho62

I think he is saying....How do you determine what size pipe you need to use............Am I right?

That is correct, I should have been a little more descriptive in my question.
I have searched this site, but found for the most part differing opinions on what would work. don't know if there is some magic formula used to determine size.
I am wondering about my Dodge Dakota, 5.2, performance cam, computer, TB, 1.7 rockers vs. OE 1.6, modified intake manifold, very minor bowl work to the heads. Current exhaust is 1 5/8" primary shorty headers, 2 1/8" collector, 2 1/4" Y pipe, 2 1/2" merge collector, approx 5' of 2 1/2" straight pipe to the muffler.
Thanks

[red_rider52]

Check this page out I think its what your looking for, should give you a general idea.

http://www.flowmastermufflers.com/faq.html

[jimfulco]

David Vizard's rules of thumb:

A straight pipe the length of a typical muffler will flow ~115cfm per square inch of inner cross-sectional area at 1.5inHg pressure differential.

Each hp produced needs at least 2.2cfm of flow capacity to avoid being restricted significantly.