Quote:
Originally Posted by Alan Nyhus
Calvin, a couple of questions. I've got a set of your 4-2-1 headers on my 327/275 stocker motor and want to spend some time on the dyno this winter doing some camshaft work.
- Is backing up the exhaust duration by 4 degrees is a good place to start. Your thoughts?
- If an engine really is over scavenging due to the header design, what are some of the things to look for on the dyno or the track?
Thanks for joining in. -Al
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Alan, A 421 header is probably not going to overscavange anywhere as easily as a 4into1 might. The battle folks have with cams and 421's is the change in reversion at the bottom of your power curve. If the headers are helping protect torque, you can go places with cam timing that you could not before. This includes retarding the whole thing, widening the lob center and therefore having to shorten the exhaust duration, etc.
There are lots of times you can go much faster without changing anything because of the broader power curve. If you already have your cam timing advanced to the max with lobes as big as possible, then you will not see so much of a benefit bolting on a 421 header.
Making more power at the top of the curve is a matter of how well built the header is from a flow viewpoint. Too many tight bends and lousy port to flange transition is where most fall down. Most of that is right at the flange. It is very important and overlooked.