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2 strokes and race gas

23K views 25 replies 9 participants last post by  Toadmeister00 
#1 ·
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...

Did I get things right?
 
#2 ·
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.
 
#3 ·
Do you think it would be the same for a smaller engine (85cc)?
 
#5 ·
run the highest octane you can find in your two stroke. make sure the engine is jetted appropriately for race gas though. DO NOT run low octane
 
#6 ·
Well, I guess I will get 93 from now on. I can't fit a $10 gallon of gas in my budget... :anim_peep:
 
#9 · (Edited)
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.
 
#11 ·
i have 111 octane out of the pump avaliable here so im lucky but in all my bikes 2 or 4 stroke i run about a 50/50 mix of 111 and 93 octane...

if u do som elooking around you can fine around 110 octane from the pump way cheaper than VP... theres alot more around than you think...
 
#13 ·
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)
 
#15 ·
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 ;)
 
#14 ·
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 :-(
 
#17 ·
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.
 
#18 ·
I have no clue what you are talking about (squish and face, and all... :D) but I will sicky that thread for future use. :bannana:
 
#22 ·
Sort of...the smokers get you a little more at a time. Mine are THIRSTY! Fuel and oil costs add up when using race fuel and high dollar premix.

Hard parts (cylinder, head, piston, etc.) are still expensive if you have catastrophic failures.

That's why I run good gas, good premix and a lot of it, way rich on the jetting and hope for the best.
 
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