So I have done some research and it seems to me that using race gas in a 2 stroke might be overkill (maybe even detrimental to performances).
Of what I understand, race gas is good for high compression engines, which 2 strokes do not have.
So maybe I should even run the lowest octane gas I can find...
IIRC my YZ250 manual calls for at least 95 octane. It runs alright on 93, but when I cut Sunoco super 112 octane 50/50 with 93 it runs ten times better. Not much more power, but the motor is definitely happier.
The benefits of race fuel are consistency and the lead content of leaded fuels is a excellent lubricant. The problem with a 2-stroke is it's sometimes hard to hear if it's pinging or detonating.
I run a 50/50 mix of C12 and pump 93.
A less expensive option would be to pick up some 100LL from a local airport. I think it's about $5-6 gallon right now.
To get the best out of race gas on your yz85 (assuming your talking about the bike in your sig) get the head re-profiled for higher compression, or buy a high compression head (vhm, bud etc..) and then it will only run well on race gas, but it will go faster, not sure how much extra power but the will be an improvemnt (wether noticeable or not I dont know)
Thanks for the tips. I won't touch the engine before a looooooong time. I have more to gain by changing my suspensions and riding for now. However, I will try to mix some higher octane gas, just to try...
I will keep that in mind though
4-stroke or 2, doesn't octane-suitability depend on compression-ratio? And in a 2-stroke is it not the port-heights, head volume (lower the volume = higher the CR), and squish that determine what the compression ratio is? And since using a chamber bumps up the dynamic compression ratio big-time, I don't think 95 octane will be overkill for most of the modern 2-strokes... no idea about race-gas though... we don't get that here very easily :-(
I would HIGHLY recommend getting the head machined. It will just make the bike more efficient.
Tell the tuner what you are doing with the bike. For these things we want tight squish but LOW compression. High compression on a 2-stroke helps bottom end torque but hurts the over-rev on top. The good tuners will machine the face and the squish band to get the squish right, then machine the bowl to change the shape and volume. You can get it done for about $75 or less.
Two strokes use a different formula to determine compression ratio, so the numbers are misleading when compared to four strokes. The compression is every bit what the four strokes run if not more.
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