HP exhaust manifolds, how good are they?

[383Satellite]

I am building up a mild 383 and I am curious if it is worth it to upgrade to the HP manifolds as opposed to the non HP ones I have now. Are they really that much better? Should I just skip right to a set of headers? Thanks Steve

[dwc43]

Best to skip straight to the hooker or hedman headers. Dont go too big though. Keep your cam small too. The b is not too forgiving with big cams and headers like a 440 is. It will loose tq or bottom end quick if you over do a stock engine.

[ajmopar]

He's right. Unfortunately, 1 3/4" headers are the widely available size with 3" collectors. These are actually too big for most applications, and most are very very far from being equal length (I have a set here that measure 18" longer on one tube to another). To get the true benefit of headers, namely scavenging, you need to keep the velocity up in the useable RPM range. As well you need a tube long enough to allow the sonic wave reflection to take place in your usable rpm range. You also need a correctly sized and shaped collector to merge the flow from the tubes and create the scavenge on the end. I sized out a set for my 400 (approx 400 hp and 450 lb. ft. of torque) at 1 5/8", 36" primary tubes, 2 1/2 collector size. They probably seem too small to most people, but unless I use a 3800 stall converter and 4.56 gears, they will out ET the 1 3/4 tubes, be much more drivable (low and midrange torque) and get me better mileage. Unfortunately, this means I have to build them myself, but hey, they will fit better in my 48 pickup if I do it myself anyway.

Short answer, the headers will flow better than manifolds, but will not give you the performance of proplerly sized, equal length units.