I wouldn't. 1-5/8 primaries to 2 inch collector? On heads that flow enough to support 500 horse? I think between that and the manifold. It would be a wash.
So it's 2". Like I said.
As for Vizard, he's a genius and what not. Don't get me wrong. But I think you really need to study how the Otto cycle engine works. The right and left bank have nothing to do with each other if you don't have a cross over of some sort and have nothing to do with each other when headers are concerned. The idea behind headers is that exhaust gas is not "bumping" into each other as they run the exhaust. Causing back pressure. Hence the equal length. So that each exhaust "pulse" if you will travels directly behind one and in front of another. Like cars merging on the highway. That when the exhaust merge's it flows faster, allowing for scavenging. Something you really need to look into if you want to build high horse engines. Scavenging's affect on performance is huge. The cross over (whether H or X depending on style of engine) then comes into play past the headers and collectors. It also has an affect on scavenging. Allowing for one bank to help the other bank scavenge better. By allowing exhaust from the right bank to pull the left and vice versa.
But, it seems like once again you're just going to do what you want. So power to you.
Hahaha it is lousy performance! In all actuality guys have seen gains of 40+ WHP with headers and exhaust on them. Some serious gains for something so simple. Shows that the stock exhaust definitely left room for improvement.
