I have been seeing a trend in the engine build off competitions in the mags lately. Guys are running stepped headers. For instance, the primary tubes may go from 1-5/8"-1-3/4"-1-7/8" then into the collector. Any science to this? I understand the velocity theory but, I am curious about the hp gains. Is it worth all the effort?
Hey Chris,I have a set of step S/C headers and plates that might come pretty close to fitting your ride.Or at least they might be able to be altered to fit and might save you and your dad a lot of work.Let me know if your interested and next time I come to the Big City I'll swing 'em by.Oh they also have anti reversion cones in 'em too.
I dont remember all of the details, but I remember the engine builder we were using in the Trans-Am series telling us that they had done alot of work on the flow bench and dyno in determining the size and placement of the "steps". Seems to me that they used 1 3/4 at the flange, stepped to 1 7/8 12" out, the stepped to 2", 18" from the first step. Keep in mind that these were 310 CID SBC road race engines that were not known for their high torque numbers and were shifted at 8500 rpm. I dont remember what the number gains were, but I do know that it was effective at making the powerband broader. It must have been worth something though since we were dealing with stainless headers that were a PITA to build and expensive to buy. By the end of the first season that these things showed up just about everyone was running them.
The step is typically tuned to the specific application. Smaller tube is used to keep velocity high in the primary to improve cylinder filling during overlap and the bigger tube aids in getting rid of the volume of exhaust. Also, you would be surpised to know that many use a step header to put really big tubes on a relatively small head. Think small block chevy, even with the stahl flange it is pretty difficult to bolt a 1 3/4 tube to the head. Hence the step is put in for those folks running 434 and up SB chevies with 23 degree heads. In a street rod application it would look "really racy" but probably would not add up much in the HP difference department.
Have you looked at this site? It's more about choosing the right length and diameter than looking at step headers and merge collectors. I plugged some numbers in and they came up with smaller headers than what I expected, just like the racingarticles site suggested. www.headerdesign.com
Very helpful article Mr. Root. Thanks. If a header pipe expanded as it moved toward the collector, wouldn't the scavenging effect of the pulse (entering the collector) become less, as the pressure is reduced in a larger dia pipe?
Do a search online for a program called "Pipemax",by Larry Meaux. I think it's around $40.Good investment. It will give you the necessary diameters and lengths,based on engine variables,and let you calculate any "improvement". Anything less is just guessing.
The Jalopy Journal
