Headers vs 340 manifolds

autopar3000 said

From me? Or from MopaR&D?

From my end I can tell you I noticed more difference in the sound than the power. I was running a worked over 318 at the time; small valve J heads, LD340. I don't remember the cam specs, but just to give you an idea it wouldn't support power brakes.

With the Doug's it seemed to feel like I was getting a bit more power throughout the range, but when you spend $850 on something you have to watch for psychology creeping in and making you see things that aren't there. The Doug's are coated so I'm sure temps are down under the hood, but I didn't actually notice that either.

Bottom line, those Headman shorties perform way better than conventional wisdom would suggest they should.

Click to expand...

I think he was referring to me since he quoted my post but still worthwhile to read your experience. I paid around $650 for my coated D453's including shipping as I used AutoZone's 15% off deal and ordered them last December before all the recent inflation.

I think for my case most of the gains will come not necessarily from the difference in the headers themselves but the fact that currently it has 2 1/4" downpipes coming off the shorty collectors with really tight (although smooth and mandrel-bent) curves going down then 180° up then 180° down again to clear the steering linkage. The secondary tuned length is very important on cross-plane V8s, moreso than the primary and having 3" pipes coming straight off the collectors on the Doug's going back a few feet is much more ideal. The Hedman shorties have 2 1/2" ID collectors so having the pipes neck down to 2 1/4" right there and at an angle kinda kills any exhaust gas velocity and pulse tuning that otherwise could be taken advantage of.