Technical > Matt Shaff's Engine Shop

Zoomies vs collector headers

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noslin:

--- Quote from: dreracecar on February 13, 2017, 04:20:29 PM ---Jim Fueling (rip) came up with those anti-reversion cones/headers back in the late70's, if they worked, they would still be used today you think?
 Again, long runs at a constant rpm could show some improvment (B'ville) but for the short duration of a drag race and that the classes that allow collectors are index/bracket---whats the point??

--- End quote ---

whats wrong with having a discussion about this (or anything else) even if your bracket/index racing?  The OP did not say anything about bracket/index racing.  its just a discussion between the two.

Roger:
That's OK noslin. Look at all the great discussion this generated. Everyone has different opinions and that's cool. I'm going to go back through all this and see if I can learn something from it.

Paul New:
When we ran our car injected alky with a mild SBC we switched from collector headers and lost a tenth and was never able to get it back with the zoomies..... we switched because zoomies look cool but HP was not the same. Later we ran at an event that required mufflers car went quicker again with the collector headers, even with this we went back to zoomies and sold the collector headers and put a blower on the car!!

Roger:
Here’s some of the little published info I could find on the subject:

ZOOMIES vs HEADERS
Stahl Headers Newsletter, Issue #4, March, 1988
“It appears that most current late model dirt engines are 406’s to 430’s. Zoomie pipes (8 individual exhaust stacks) will run quite well from 3500 to 4500 and from 7000 to 7500. But, they give up from 25 to 35 HP at 5500 to 6500 which ends up being on the chutes where you can use all the power you can make. However, compared to Zoomies the “Shorties”, as we have labeled that collection of pipes that vary in pipe length from 14” to 16”, are the real disaster. Reports from several prominent dirt late model engine builders indicate as much as 45 to 50 HP difference between 5500 and 6500.”

With this input in mind my little 325hp street engine that goes in the roadster first will never see the high side of 5700rpm and might see little if any loss of performance between headers and zoomies. Maybe run quicker with zoomies because the headers added weight! So, I’m going to run both on my car and see for myself. Then when the race engine is done I’ll do the same thing again with zoomies and a set of larger headers that I’ll beg, borrow, or temporarily appropriate. From all the actual experiences that’s been shared here I’ll have a good chance of being a tenth slower with the zoomies. I’ll find out.

The Denverflatheader posted what I thought was a really good article that starts to look at cam timing that could help get back some of the power that was lost without headers. After talking with 4 different cam companies (who all had a little different idea of what was needed) they all pointed to a cam that needed more exhaust duration, an increased lobe separation angle, and minimum overlap as compared to a similar cam used with headers. Jones Cam Designs told me they did some tests years ago using zoomies and were emphatic that the exhaust side of the cam needed 10 degrees more duration than the intake.

And I found this little piece of information:

“I have found a consistent 5-8% power increase if the primary pipes are kept separate (zoomies), with a megaphone fitted to each primary”. This was written by A. Graham Bell, a noted engine tuner and tester in England about the same time David Vizard was also running similar testing in England. Megaphones on the end of your zoomies? Not a chance with me:)

Thanks to everyone for all their input. After all, a little shared knowledge can go a long ways in helping everyone better understand the technical parts of our sport. And that’s the point.

denverflatheader:
Roger – am a strong advocate of empirical testing too, like your “plan to do” for your roadster.  Calculations and what-if scenarios are excellent today with computers, so easy, but the answers are hard to recall with passing of time.  First-hand testing, you remember forever.  Alan

dusterdave173 – good one on determining torque tube/collector length without a pyrometer.  Read that and saw immediately the benefit with your idea, and has a built-in correction factor (e.g. 4.00 versus 5.00 inch diameter).  You have to start somewhere… Alan

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