For a 600-620ish HP (Flywheel) combo with just under a 600 lift cam and only being spun to 6300, how much if any ET lost would there be with using a 1 3/4" header vs 2"? Car is 3150lbs. TTI headers in a A-Body. TTI recommends their 1 3/4 for 300-475HP, and their 2" for 500-750HP, not sure if that's flywheel or rear wheel.
Could be zero difference. If it was me I'd go with the 1 3/4 headers just so you can work on the car easier. I've tested different headers on the dyno and a really good dyno header will lose some power if it is too small. But chassis headers are not dyno headers. Look at the TTi headers and you'll see that they have sharp bends right off the ports. So you are already losing power with that first bend. Since even the big headers are going to be hurting the power over a set of dyno headers I'd just go ahead and use the smaller ones that fit better.
If you don't like that argument then think about the FAST guys who are running in the 10's with cast iron manifolds. Surely the 1 3/4 header is better than a cast iron manifold and
those guys are making more power and going faster than you are. In fact, I bet you could use a Tri Y header in a BB A body car and still run 10's without any trouble at all.
