I need a drawing of ET84, exhaust nut

mercurycrest

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VOC Member
Sounds good. Who makes and sells them?
John


Dunno, got mine here in 1977, but they don't do outside work anymore... 001.jpg
 

davidd

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Mr. Ulver made me re-read the thread. I now think that you were asking about something like this, which I made several years ago:

ExNut2.jpg


The 1-3/4" pipe slips inside and three springs hold it to the head. I made it out of steel hex stock and I was never happy with the steel. It did not like staying in the head. I could have done better with the threads, but I always suspected the material was expanding at a lesser rate as I could tighten it with certainty.

David
 

johnmead

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Non-VOC Member
David,
Yes, that is what I want. I am going to expand the end of the pipe to slip over the flange and machine the inside to include an anti-reversion trap.

John
 

Howard

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David,
Yes, that is what I want. I am going to expand the end of the pipe to slip over the flange and machine the inside to include an anti-reversion trap.

John

OK - I give up. That's a new one on me. What's an "anti-reversion trap" and what does it do in an exhaust? I seem to have heard the name, but refering to something in the intake, not the exhaust.

As David says, there is a problem with difference in expansion. My adapter was much thinner, so it probably heated up quicker, and it was only used for 6 lap races, so it wasn't a big problem, but I had to check it after VOC half hour trials (races). Springs were hooked into holes in the head cooling fins, not the adapter.

H
 

johnmead

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Non-VOC Member
Howard,
When the exhaust valve opens and the exhaust gases run down the pipe there is a reversion pulse that comes back up the pipe along the outside of the inside diameter. This is the pulse that you use to "tune" your exhaust so that when the pulse reaches back to the combustion chamber it blocks some of the mixture coming in through the now open intake valve (during cam overlap) from going out and down the exhaust. The problem is that this pulse timing changes as the rpms change so you can only tune it for a narrow rpm range.

Using an anti-reversion trap in the exhaust allows you to tune the exhaust system for a wider rpm range which gives you a wider power band. The "trap" is a pocket around the outside diameter inside the exhaust pipe that blocks the reversion pulse from getting to the combustion chamber. I am going to have this trap machined into the adapter.

There are several US patents on this system. The ones that I looked at were submitted by the late Jim Feuling and Rivera Engineering.

John
 

Howard

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VOC Member
Sounds very technical. What rev range are you tuning your exhaust for? I assume you're making a special exhaust system.

Even with my Comet exhaust tuned for 6000 rpm and fixed advance, there always seemed to be a good spread of power.

H
 
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