[Alan Roehrich]

Billy, that's what I'm seeing as well. If your headers are too big, you can "crutch" them by using a merge collector with a small minor diameter, and even better, the longer of the two common correct tuned lengths. For example, if you had 2" primaries, and you should be running 1-7/8" or 1-3/4" primaries, you could use a merge collector that had a 1/4" smaller than normal minor diameter ( say 2-5/8" instead of 2-7/8"), and if the first tuned length was 7", you could go with 14".

Unless you buy your headers from someone who really knows what they're doing (there are not too many guys like Jere Stahl selling headers these days) or you have good header software (PipeMax is what I use) most people end up with 1/8" or more larger primaries than they need. In order to compensate for that, they need to add 3-4 degrees at 0.050" to the exhaust lobe. If you can't or don't spread the LSA out, that really limits you on the intake lobe and/or the ICL.

Here's a good example. On a Stock Eliminator engine, we did the preliminary dyno testing with a set of 2-1/4" dyno headers. Then we swapped to the 2" - 2-1/8" Stahl headers with Jere's semi merge collectors. We immediately gained well over 25 ft/lb of torque, but we also lost well over 10HP at the top over a 600 RPM spread. Then I looked at the dyno data closer, and realized that at the same place I lost over 10HP, the engine flowed almost 20 cfm more! Guess where the 10+HP went. Right out the exhaust as an "over scavenge" condition. The correct fix for that is around 4 degrees off the exhaust lobe, and 1-2 degrees more LSA. The reason for the whole thing was the engine previously had a set of Hooker headers that should have been on a Super Stock engine, the primaries were too big and too short. A set of Mark Lelchook's merge collectors were used to help "crutch" that. But even that was not enough. What we know about that, is that this particular car, with that cam and Stahl headers is a killer in the 1/8 mile, but a little off in ET in the 1/4, and down around 2MPH at the top. It's getting a different combination, but Jimmy Bridges and I had decided that, if we kept running that one, it would get 4 degrees less exhaust lobe, and 2 degrees more LSA. I'm pretty sure Jimmy is ten times smarter than I am.