That's probably partly true, but our racing motors have plenty of overlap.
All of four stroke exhaust tuning theory has to do with extraction of the
burned gasses (and drawing in the fresh charge). With two strokes you add in
the complexity of packing the fresh charge back into the cylinder before it
escapes, which is why expansion chambers look so weird. A merge collector
will give you a powerful extraction pulse as the gasses expand past the
constriction, the trick is to have it arrive back at the exhaust valve at
the right time. With our relatively low revving engine, you probably need a
very long pipe before the collector.
Without a megaphone the extraction pulse will be relatively short lived, so
it won't help much when the RPMs are lower than the tuned peak. It helps
somewhat when RPMs are higher than the peak. Pipe length, cam timing,
atmospheric pressure, ambient and exhaust temperature, and which side of you
mouth you park your tongue in all effect the tuning.
> -----Original Message-----
> From: owner-fot@autox.team.net
> [mailto:owner-fot@autox.team.net] On Behalf Of joe dirt
> Sent: Friday, June 02, 2006 1:57 PM
> To: vinttr4@geneseo.net; fot@autox.team.net
> Subject: Re: [FOT] merge colectors
>
> Jack,
>
> From what I've read, a merge collector will really only
> show it's true worth when teamed up with a cam that is
> designed with it in mind. A bit more exhaust overlap I
> presume? I certaintly think it may be worthwhile to call
> your cam grinder.
>
> -Bob Adams
>
> "Jack W. Drews" <vinttr4@geneseo.net> wrote: The FOT list
> has been entirely too quiet lately. It gives me the
> heebiejeebies when I come in here and see this empty screen.
> Assuming that everybody is out playing with their cars but
> might look at their screens occasionally, my latest question is
>
> Does anybody know for sure if a merge collector is of any
> benefit on our four cylinder relatively low revving engines?
>
> I'd test mine with and without on the chassis dyno but that
> is a really difficult thing to change at the dyno shop.
>
> The reason I'm asking is that I put on a merge collector from
> Burns Stainless a couple of years ago and other guys still beat me.
>
> uncle jack
>
>
>
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