Drag Racing Discussions > Front Engine Dragsters

Zoomie size?

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cad500justin:
I need to build new zoomies for the new motor. Because the new heads have a different bolt pattern.
529” injected alky/nitro 7000rpm limit
1.88 exhaust valve

Anyone ever try step tube zoomies? My current ones are 1-7/8-2” and work fine, but no dyno numbers to compare to.

I’m leaning toward 2” step to 2-1/8”, roughly 18” oal? (Old ones are 25”oal) But could go bigger? Could just do one size tubing without a step?

Anyone ever play with stainless for zoomies? 

JrFuel Hayden:
I have there is no advange of step headers on alky/nitro, but on gas it helps

THE FRENCHTOWN FLYER:
I never did buy in to the advantages of stepped headers. From a thermodynamic standpoint as the gas flows down the pipe it would get cooler, if anything, necessitating a transition to a smaller pipe size, not a larger one, to maintain gas velocity in the pipe. I get that you might suggest a megaphone effect by going larger but I don't think it would be measurable. From a fabrication standpoint I see where it would make building headers much easier because now you don't have to make perfect butt joints - just slip the next section into the previous one. I SUSPECT THIS IS THE REAL REASON WHY THEY ARE TOUTED BY HEADER FABRICATORS.

In automotive engineering circles we used to have a tongue-in-cheek saying," If you can't fix it, feature it."

As far as zoomies, a singular tube size just looks best to me, with the possible addition of a reinforcement sleeve near the flange, like T/F designs.

Roger:
I agree, a stepped header just slows down the exhaust flow as it moves past the step into a larger area and that slows flow a little bit. With as short in length as most zoomies are, there probably isn’t much if any, difference in performance between straight and stepped. Now if you move in the other direction and make a set of “zoomies” that have a pipe length of about 32” in your case, then you could get back the inertial scavenging effect of equal length headers, less the collectors. Could be a little known speed secret from the past:)

rooman:
 I can't see any advantage to stepped diameter zoomies but I don't think that the teams that do extensive dyno testing (pro stock) etc would be running them unless some advantage (power/torque etc) showed up on the dyno. I do know that my friend Mike from the Fab Shop here in Indy is in favor of them (along with big radius bends) and that his step headers have seen lots of dyno time.

Roo

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