Restricted exhaust

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BOOT
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Re: Restricted exhaust

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ptuomov wrote: Sun Dec 10, 2017 8:53 pmThen I’d run the muffler all the way at the rear bumper after exhaust gas has cooled and all the pulses have been combined. The key is to cool the exhaust with minimum restriction before the muffler, how about running aluminum exhaust pipes to maximize cooling?

I've always thought keeping the gas hot was the goal because it's less dense. I was also told wrapping a header primary makes it seem shorter.
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Re: Restricted exhaust

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BOOT wrote: Tue Dec 12, 2017 4:08 am
ptuomov wrote: Sun Dec 10, 2017 8:53 pmThen I’d run the muffler all the way at the rear bumper after exhaust gas has cooled and all the pulses have been combined. The key is to cool the exhaust with minimum restriction before the muffler, how about running aluminum exhaust pipes to maximize cooling?
I've always thought keeping the gas hot was the goal because it's less dense. I was also told wrapping a header primary makes it seem shorter.
My understanding: Given a pipe size, hot gas has to flow faster, generates stronger pulses, and has a greater pressure loss. I think that, in net, tuned header should benefit from keeping the gas hot?

I think the situation reverses in the tailpipe after the blowdown pulses have been combined, there's been one chamber muffler, etc. Now, one just has a tail pipe to a rear muffler. If the gas has cooled, one can force more air mass thru the same size hole.

So I'd say keep it hot early and then cool it after the cross-over between banks. Whether it's right or wrong, that's how we're doing it. Thermal barrier coating until the cross-over and then bare metal pipes after that.

In any case, I don't think this is terrible relevant to the original poster, who's got a single cylinder engine. The whole pipe probably needs to be pulse tuned, but it's also very restrictive size so whether hot or cold is better is a question above my pay grade.
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Re: Restricted exhaust

Post by Ron E »

You could add enough oil to the gas to make some good smoke. Then run it with the bare exhaust port. Take note where the port is most active and make sure you favor that area when you fit the pipe to it. Most O.E. heads have a dead floor. Yours may also.
Oh, and gut the muffler.
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Re: Restricted exhaust

Post by RCJ »

What I'm finding is the open (minimum rules) motor pipes are 19'' with .904,1.075, 1.185 steps.The restricted pipes are in the 8 or 9 inch range.I'm going to try a rough finish vs. smooth inside the pipe.
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Re: Restricted exhaust

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ptuomov wrote: Mon Dec 11, 2017 10:46 amWhat I'm thinking is gutting that silencer and making it effectively "a step" in the exhaust primary. Then extending at the appropriate size pipe from the silencer.
How 'bout clamping a "can" with a side hole(s) over the gutted muffler to provide a reflection surface like some older kart 2-stroke expansion chambers. Like this:

https://www.ebay.com/itm/VINTAGE-Kart-R ... og&vxp=mtr
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