I was wondering when power wise to swap over from the 1 3/4 headers to the 1 7/8 headers?

 

http://www.wallaceracing.com/header_length.php
A pretty cool header calculator..I would say IMO only..not an expert
300-400 hp 1 5/8"
400-450 hp 1 3/4"
450-500 hp 1 7/8"
500-650 hp 2"
Of course what they merge into in equally important..as well as FI or NA..check out the calculator..seems to work pretty good..

 

That is pretty neat that is what I was looking for I knew someone would know.

Thanks

 

Is that referring to rwhp?

 

The better question might be what exhaust velocity would be best to get the most exhaust scavenging from my headers/collectors. That is one part of the equation to get over 100%VE. There are programs that can help determine that like Larry Mieux's PipeMax.