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Discussion Starter #1
Just found out one reason why the 99 & 2000 Machz's are faster than the non-dpm 01 & 02 mach's
99-00 timing is .102 B.T.D.C.
01-02 timing is .076 B.T.D.C. hehe
Why would they doo such a thing?
Carb's are identical except for 01-02 has 1 size smaller main jet.
Someone enlighten me here.
:(
 

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Well, here is a thought off the top of my head. With less timing, it would not be so dependant on 93 Octane gas. It would make it less prone to detonation. You can then lean it out a tad to keep the performance level up. So, you make timing less critical, and give it DPM to make jetting more precise! Now if you went back to the original timing with DPM, that sucker should really fly!
 

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Discussion Starter #3
Yes that does make sence with the timing but when you start leaning down the jets your right back in the same boat again.
Advanced timing has always been a performance trick in any combustion engine, the question is, how much is too much?
5 & 600' racers will always advance their timing big time, but take that same sled and run it across a lake and see how big a hole it can burn in a piston!
Maybe Skidoo had to many warrenty issues and decided to fatten things up a bit. I haven't heard of burndowns on the 99-2000 Z's.
 

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Newer engines may also have different timing curves in CDI which require less initial timing, and still have overall better performance ? I personnally don't know if the newer sleds are faster or slower bone stock, but the above changes could also make a sled faster or slower.
 

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They retarded the timing to get the pipes hotter. That was part of an update for the 98's. I've never tried it on the rear outlet pipes, but it sounds like they did. They also had issues with the pto piston scuffing because of poor cylinder cooling, that might help that also.
 

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Discussion Starter #7
Last I knew advancement was hotter. That's one reason for burn downs.
This started when I heard so many people wondering why the 99's and 2000 were a little faster than the new ones with non DPM. I got to looking around in the spec. books and the only difference i could find is lower timing, 290 jets and slightly different air box part#'s.
I dont know how much difference performance wise were talki'n here but these are the only changes I can find.
 

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Retarding the timing starts the burn later and more of that goes out of the exhaust port. Advancing the timing causes more heat in the motor as the piston is coming up. More heat in the pipes helped that motor with the side outlet pipes. It was part of Bulletin 98-10 for the Machz's. In 99 the mpem module was programmible for timing. The 2 wires in the right front were for a battery to power the mpem so it could be programmed.
 

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No the egt will be lower. What they did was let more gas burn later and go into the pipes burning. It's not a very good way to do it but it helped that motor. Some people wrap the pipes to get the temp up. You'll get way more egt temp compressing it and burning it in the cyclinder. The rear outlet pipes were way better.
It also helped the problem with the pto piston scuffing because of poor coolant flow to the cylinder on the pto side, less heat in the cylinder. That was a lot cheaper than actually fixing the problem. You could see the pipe temp go up with an infrared thermometer. This whole deal is why Machz's like a good set of pipes.
 

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The point at which sparkocours before tdc through the point where the exhaust port opens is the power stroke and also the time where through disipation (cooling effect)any heat not destined for the exhaust escapes.By retarding the timing there is less time for heat to escape through the aluminum and the cooling system(in crank shaft degrees)and therefore more of the combustion temperatures are available to heat the exhaust.Its the same way on 4 strokes more or less some engines(ie big inch small blocks say like a lot less timing that smaller bore engines)it just depends on the design of the engine,pipes,fuel quality etc,no hard and fast rule of thumb.
 

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Skidoo also increased the coolant flow by increasing the diameter of the crossover hose and a higher output water pump in the 01/02 mach.Now the fuel isn't used as a coolant as much,that's why the 290's are there.So now there is better cooling in the motor.I saw a 02 mach run 124mph with a 3/4 lug track and mild clutching(no motor work!)on hardpack so they are not slow by anymeans. :devil:
 

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The egt is showing the temp close to the port. The pipe temp I'm referring to is further out.
Thats the way it was explained to me and I didn't believe it till I checked the pipe with an infrared thermometer.

John Breedon's explanation is better than mine.
 
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