Technical > Spud Miller's Cave

Engine won't run right with zoomie headers

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Roger:
Hey Digger

How much overlap does your cam have?

retroboy:
I've run them with out a second thought on Ford Windsor and Cleveland engines. Funny thing is I'm having some trouble sorting out my small block Chrysler and I never gave my Zoomies a seconds thought ?

DiggerDon:
Roger
The cam card is faded but it looks like 22 degrees

Roger:
Sounds low for an overlap figure, do you have the # of the cam? Reason I ask about overlap is the more overlap in the cam the rougher the engine with collector headers runs at idle. Put zoomies on it and it runs even worse. Zoomies don’t scavenge exhaust like a tuned length collector header. Then use some short pipe zoomies and it could be that exhaust reversion is taking place; exhaust moving into the intake port before the intake charge starts following towards the cylinder. It’s to do with exhaust pulses and all that stuff. Just like Crider said you add some length to the pipe and you start to reach the tuned length part of this deal and makes the exhaust pulses work in your favor so the engine idles better. I’m dealing with this same situation now as I start to assemble my new gas burning zoomie equipped engine: trying to figure out what camshaft to run knowing that all the advantages of tuned collector headers and their camshaft designs are tossed out the garage door. I’ll take a leap of faith here cause this a slow evening and suggest that a cam with a minimum amount of overlap is used to minimize exhaust reversion that might be affecting idle quality. Maybe try the zoomies again and loosen the lash on the intakes and exhaust which will take out some of the overlap, to see if it idles any better. Just my 2 cents worth.

Oldschool:
I run zoomies on my 434 SBC with a 1050 dominator and runs like a bat out of xxxx. The idle is great,but pipes not real short. Could not imagine not running them ,very cool ride.

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