How much better if any, do Headers flow better than 340 hi-po manifolds?

They flow way way better than manifolds.

The following is a chart that was in one of the magazines. It shows dyno results on different sb's with different exhaust bolted on.

Cool! Thanks! So it looks like you loose around 5 hp or so with the manifolds.

I think it's a good deal more than 5 hp. On my old Duster I went from early style 340 manifolds to a set of TTI's and cut the ET in the 1/4 by .5 sec and picked up 5 mph trap speed. In my mind that comes out to at least 30 hp., probably a bit more.

It would depend on the specs the motor is built to as to how much gain there would be with headers. With more compression and a larger cam the gain would be much greater with headers. If the motor is stock then the differences would be less.

I don't have a link, but look at what the F.A.S.T. guys are running through HP manifolds.

I remem that article claiming a 5 horse diff & I dont buy it unless the ex from the header pipe/or the collector was the same restricted size as I believe no matter what the backpressure you can only force so much total flow thru a particular dia orifice (in the rest of the ex sytem rearward) as power production, it's (mainly) about overall flow (in/out) but if an engineer (& there are several on here) enlightens me (that flow will always increase no matter what the dia in question if the psi is higher) then I stand corrected. Does a given dia reach a point where it will not flow any more (rate) no matter what??? & if so at what psi in oiling passages is enough & over that is wasted power & stress on the inter shaft/gear & pump as the bypass stabilizes it at that point.

FAST racing Lots of 340 cars in the 12's AND 11's using HP 340 manifolds and stock tire sizes.

Are headers an easier way to go fast? Yes, but they have drawbacks also. You can go fast without headers.

I sure do agree with that last post