Muffler Condition on Engine Performance

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Muffler Condition on Engine Performance

Postby Schoobytwo (Bruce) » Sun May 30, 2010 9:55 pm

Hi all,

I been struggling with mufflers and the possibility of getting some reproduced. My concerns have been around the internal baffle designs and was always wondering in my mind why Bolens put a smaller muffler on the 502 with the 54R Hirth and a larger muffler on the 503 with the 190R Hirth.

If you follow the forum, you would have seen an earlier post about the port sizes in the cylinder heads and the recent discovery that the ports on the 190R motor are larger than those on the 54R motor. These larger ports would explain why the 503's have a little more get up and go than the 502's because with the larger ports, they can pull more fuel into the combustion chamber thus increase HP and RPM just a bit. Of course, these cylinder heads are interchangeable. Therefore, there is no telling which ones are on what motors.

So, back to the muffler thoughts. I talked with Greg Spaulding today. Many of you know of Greg. He makes reproduction parts for Ski Doos (http://www.spauldingvintagesnowmobile.com/) and we have been talking to him about making mufflers for the Diablos. Greg's two cents on muffler design are this:

- If mufflers are designed with too much restrictive flow, they can cause engines to run hot. Basically keeping the heat from exiting the combustion area of the engine and burning up pistons.

More interesting is this:

- If mufflers are designed with too little restrictive flow, they can cause engines to low on power because the heat leaves the engine too quickly. When the heat gets out of the engine too quickly, the combustion chamber never really gets as hot as it should and a properly heated chamber creates a better chamber for fuel mix to ignite.

The reason I'm curious about the above is many of us struggle to get our Diablos running at what we think is optimum performance. We have talked about ignition, timing, carbureation, engine seals and more, but another link to a great running engine may be having a good muffler. If we are running around with old mufflers that look ok on the outside but have the baffles rotted off on the inside, is the muffler (or lack of) hurting our performance.

I'd like to hear your thoughts. Thanks all for reading the forum and participating. You are a great bunch!

Bruce
Too many Diablos and parts to count.
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Re: Muffler Condition on Engine Performance

Postby pyzwhiz » Wed Jun 02, 2010 9:09 pm

Bruce,

If you come across a bad 502 muffler please let me know. I am still in discussion with the gent on a stainless steel muffler for my 502. Would need it for cutting apart to determine degree of and hole size of baffling. Would be interesting to compare baffling of 502 vs 503 muffler.

Two stroke mufflers are also prone to plugging up much like the old LawnBoy's lawn mowers therefore reducing engine performance and creating hard starting.

Mike
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Re: Muffler Condition on Engine Performance

Postby vmaxx4 » Fri Oct 22, 2010 9:56 pm

This topic reminds me about a story my dad told me about trying to repair some Boa-ski sleds in his shop. They were hirth 190 series powered sleds that had a real hard time starting and running correctly. He eventually found there was a baffle plate that had a tendency to break off internally and fall down, blocking off some of the outlet. Another thing to consider is the quality of oil and the mixtures run back in the day. A lot of sleds running around with a lot of carbon build-up restricting the exhaust flow.
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Re: Muffler Condition on Engine Performance

Postby Schoobytwo (Bruce) » Sun Oct 24, 2010 7:54 pm

Good Comments Guys. Thanks.

We are currently making new 503 mufflers (will fit all Diablos) and should have them available soon.

Bruce
Too many Diablos and parts to count.
Yamaha Apex (it outruns the Diablo for sure)
Yamaha 600 SX
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