Re: 1 3/4" vs. 2" Header Size
 

Paul,

I think Marc may have documented no significant difference between 1 7/8 v the 2” primaries. If there was a difference it could be easily lost somewhere else.

Re: 1 3/4" vs. 2" Header Size
 

Smaller primaries would likely be the better choice for road course racing where more time is spent in lower and mid-range rpm's and larger would be the better choice for drag racing.

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Re: 1 3/4" vs. 2" Header Size
 

I have a book by David Vizard, I think the SBC on a budget. It links exhaust flow to the size of the primaries. Also there are "stepped headers" that have a bigger initial size then going down to a smaller, i.e., regular size tube that sounds like it's the cats meow. I bet you could find the article on line.

Re: 1 3/4" vs. 2" Header Size
 

Don’t “stepped headers” have the opposite, smaller initial tubes, then get bigger down line to the collector?
I have had Watsons with 2” downtubes since 1995, and they’re pretty good, (117mph trap speed on an otherwise stock engine.)


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Re: 1 3/4" vs. 2" Header Size
 

Uff-da! (as they say here in da Viking country).

Gotta love that sea level DA! ;)

Re: 1 3/4" vs. 2" Header Size
 

Yes, you are correct. Smaller to bigger.