Safe to advance timing with this setup?

[fischer550]

Want to get some input on if it would be OK to advance the timing (about 3 degrees) with the following setup:

Yamaha 62t engine w/blowsion big bore sleeves, (at 846cc)

Stock Stroke

190-195 Compression (Freestyle ONLY, never ride WOT)

91 pump gas

MSD Enhancer

#Zero lightened stock flywheel

 

[bach6177]

I go 3 mm which is about 3 degrees. It's safe. Tho with that compression your boarder Line needing 50/50 race gas in my opinion.


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[fischer550]

Even with 195 compression on 91 octane pump gas?

 

[bach6177]

Even with 195 compression on 91 octane pump gas?

Yeah 195-200 is where I would rather be on the safe side and run 50/50 race.


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[Roseand]

Gotta know your squish, can't tell you that much without it. With 3 deg advance on top of 200 psi you're playing it close depending on squish and how accurate your tuning is.
If you already have your ski put together, it's not worth the hassle. It's not an extreme power gain. Plus, you already have a quite nice power increase going to the pipe you just bought.

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[fischer550]

Gotta know your squish, can't tell you that much without it. With 3 deg advance on top of 200 psi you're playing it close depending on squish and how accurate your tuning is.
If you already have your ski put together, it's not worth the hassle. It's not an extreme power gain. Plus, you already have a quite nice power increase going to the pipe you just bought.

I don't know my squish, will do a test tomorrow.

My engine is out of my ski, flywheel off and being lightened I think I am going to be running domes which will get me closer to 180-185

 

[MTRHEAD]

Never mentioned what pipe you using?

 

[fischer550]

B pipe limited chamber

 

[MTRHEAD]

,Next would be altitude, dome design(squish), prop size, and weight. Assuming all of those are on small to very conservative size I would agree with above - 50/50 high octane. If you push it in any of those other areas your asking for deto issues eventually

 

[RMBC Freeride]

As several people have said here; there is no way of knowing for sure if you can advance or not. Too many variables.

But in my opinion, (assuming you are riding this at altitude in CO?) you MUST advance your timing if you want it to perform at it's best. However, if you drop the compression back to the 180 range, you are probably negating any advantage of bumping the timing. I would say you can run pump gas here in CO with the advance and high compression, if you are tuned properly and your prop is pitched low enough. But if you go down to Havasu, you better run 50/50 race/pump and/or switch to the lower compression domes.