Exhaust connection fitting

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Marrcel
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Exhaust connection fitting

#1 Post by Marrcel » Mon Oct 23, 2017 10:37 am

Hello 2strokers i am new on this forum. I like to introduce myself.
In the early 90ties i ve ridden rd500 and 350. Recently I bought my old 350 back. It slept for 20 years. So lots of work. Image
I am working at fitting the new exhausts. The flanches are bigger than the exhaust port. My question: is it ok to dremel the port to the flanche. Here is a picturrImage
I marked the area to dremel. Please advise


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evan_calgary
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Re: Exhaust connection fitting

#2 Post by evan_calgary » Mon Oct 23, 2017 12:20 pm

Yes. I do this as well. You may trade some mid-range for top end. As they sit this will greatly inhibit the returning pressure wave. Don't mess with the actual port.

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T.RexRacing
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Re: Exhaust connection fitting

#3 Post by T.RexRacing » Mon Oct 23, 2017 1:51 pm

My opinion an nothing else.

By enlarging the exit you slow velocity of exhaust gases thus cooling (making them denser thus slowing movement through them) them faster than perhaps the pipe was designed for. This will change the timing of the return wave. If the pipes were designed for a stock cylinder this can be detrimental. How much? I cannot predict only that it will affect it. Don't see the worthiness of the effort.
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JackB
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Re: Exhaust connection fitting

#4 Post by JackB » Tue Oct 24, 2017 8:00 am

Also, do your pipes fit inside or outside those flanges? If the pipes slip inside the flanges then they will probably match the port on the cylinder.
1984 Rz350, Wicked Toomey rep pipes, Dynojet kit,Zeel unit,Toomey Y boot filter.

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T.RexRacing
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Re: Exhaust connection fitting

#5 Post by T.RexRacing » Tue Oct 24, 2017 8:22 am

Velocity is an often missed component of charge management. A garbage can will move a lot of charge. However it will not do it well.
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Questo vecchio rz
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Re: Exhaust connection fitting

#6 Post by Questo vecchio rz » Tue Oct 24, 2017 11:37 am

I'm in the same school of thought as T Rex & Jack B. The photo initially exaggerates the idea,as the pipe is not installed.

I'd be (very hesitant to do anything beyond a clean up or even very minimal material removal). As we all know this engines are sensitive to intake and exhaust changes, as all 2 strokes are.
Toomey has alot of experience with the RZ series as well and the velocity and tract length was a important feature if their final designs, which have proven to be a good performing setup.
Depending upon your flange & actual pipe diameter, if after the insertion of the expansion Chambers into the flange, if it reduces the step to (minimal area), I'd initially consider perhaps a single plane knife edge to ease flow on the return., Or even possibly a taper bore, which would clean up the lip, but NOT enlarge the tunnel).
Not sure what you guys would think about that ? But I think I'd be game for that, as long as it was (NOT) enlarging the port drastically.
If the tolerances were "fairly close after pipe install into the flange", just a method to maintain current dia & but clean up so it's a unobstructed tunnel and keep or possibly (in theory) increase velocity.
Last edited by Questo vecchio rz on Wed Oct 25, 2017 11:28 am, edited 1 time in total.
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Re: Exhaust connection fitting

#7 Post by (F5) » Wed Oct 25, 2017 4:22 am

I've spent a bit of time opening up port flanges, sadly erroneously. Turns out port velocity is important, more so on triple or bridged ports where modern designs actually reduce, but don't just open the port up.
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T.RexRacing
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Re: Exhaust connection fitting

#8 Post by T.RexRacing » Wed Oct 25, 2017 8:29 am

Velocity is important because you have limited time to move charge. In a port where the charge is moving at 200CFM for 185* of crank angle it will move less charge than a port moving at 300CFM for 185*.
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Marrcel
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Re: Exhaust connection fitting

#9 Post by Marrcel » Mon Nov 06, 2017 4:23 pm

OK the exhausts go over this connector. I do not touch the smallest diameter of the exhaust outlet. I made the diameter the same as the connector. As smooth as possible.
The gas flow is plug flow. Any ridge of, in my case, 4 mm wil disrupt i think.
Maybe a power measure will be done in 2018.
The exhaust will be from GR.
Image


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Re: Exhaust connection fitting

#10 Post by tacky1 » Tue Nov 07, 2017 11:33 pm

Marrcel wrote:OK the exhausts go over this connector. I do not touch the smallest diameter of the exhaust outlet. I made the diameter the same as the connector. As smooth as possible.
The gas flow is plug flow. Any ridge of, in my case, 4 mm wil disrupt i think.
Maybe a power measure will be done in 2018.
The exhaust will be from GR.
Image


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These are really nice pipes, Love the nice, tight to frame fit and silencer setup.
Who makes them
1985 RZv500
1984 RZ500 Hybrid
1986 RG500 Walter Wolf
1986 RG500 Skoal Bandit
1984 RZ350
1984 RZ350 Hybrid
1981 RD350LC
1981 RD350LC Hybrid
2009 CR500AF Supermoto 250X
2007 CR500AF 250X
1988 YSR50 (2)
1984 GPZ750 Turbo
1989 VFR750R RC30

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kenny
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Re: Exhaust connection fitting

#11 Post by kenny » Wed Nov 08, 2017 7:00 am

You should never match the port tunnel exit to the exhaust flange nor the gasket. This will loose you pick up and due to loss of gas velocity being much lower. Power may go up at top end but coming off low throttle will be worse. A small exhaust exit is the more modern way of porting and will pick up midrange and top end. In fact the 33mm exit on a YPVS is already to big. The step will cause an eddy going back for the plugging pulse but thats better than having a port exit to large.

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Re: Exhaust connection fitting

#12 Post by JackB » Wed Nov 08, 2017 8:55 am

It looks like a bad designed exhaust.The pipes look like they fit up to the bike real nice but the design should have started right at the exhaust port with it matching up. I dont know why they would design something like that with such a mismatch. Maybe for looks of bigger diameter header pipes.
1984 Rz350, Wicked Toomey rep pipes, Dynojet kit,Zeel unit,Toomey Y boot filter.

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Marrcel
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Re: Exhaust connection fitting

#13 Post by Marrcel » Wed Nov 08, 2017 1:05 pm

https://www.youtube.com/user/GRexhaustsystems" onclick="window.open(this.href);return false;



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Off Road
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Re: Exhaust connection fitting

#14 Post by Off Road » Wed Nov 08, 2017 4:44 pm

Gordon Jennings wrote a book called the Two Stroke Tuner’s Handbook.
In it, there is a chapter on Cylinder Scavenging, with sub-chapters on the Exhaust Port and Port-Edge Chamfers
On page 112 and 113, he writes the following:

“In the vast majority of engines there will be a fairly large increase in cross-sectional area between the stock exhaust window and the actual exhaust outlet.
Indeed, this increase often is too large to give best results with expansion chamber exhaust-systems:
What may seem to be no more than a flow-improving enlargement in area leading into the exhaust pipe during the outflow phase of scavenging becomes a sudden constriction for waves returning to the cylinder from the expansion chamber.
In fact, if the difference in the areas at the port window and the outer end of the port becomes as great as 1:3, virtually all of the expansion chamber's resonant effects will be lost.
What happens, in such cases, is that the waves returning to the cylinder are reflected back into the chamber by the abrupt constriction of the port.
Maximum transmission of these waves into the cylinder will, of course, be obtained with a 1:l port-window/port-outlet ratio, but that kind of straight-through passage represents something less than the optimum in minimized flow resistance during the blow-down phase of scavenging (the period beginning when the exhaust port cracks open and ending with the opening of the transfer ports).
Thus, the walls of the exhaust port should diverge somewhat, giving a progressively-increasing cross-sectional area out to the exhaust flange.
The most important thing to remember, here, is that sudden changes in section should definitely be avoided.
Neither gas-flow nor the effects of sonic waves in the exhaust tract are served by a bunch of lumps and jogs - this being far more important than a mirror finish on the port walls.
Given an absolutely free hand with an exhaust port (which seldom is possible, when you're modifying an existing engine) I would be inclined to make the exhaust passage's areas equal to those in an 8-degree cone.
However, unless you have a dynamometer available for the verification of exhaust passage experiments, the best approach to this whole matter is to leave unaltered the exhaust-flange end of the port, and carefully blend the enlarged exhaust window into the rest of the port.”

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T.RexRacing
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Re: Exhaust connection fitting

#15 Post by T.RexRacing » Wed Nov 08, 2017 11:40 pm

You guys do realize who Kenny is right?
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