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do you have to run race fuel with a 13.5:1 piston

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is it really true you have to run race fuel with a 13.5:1 piston.i am thinking about gettting a higher comp piston for my 06 but dont want to run race fuel.and i dont want to have to worry about detonating the motor.as of now ui added a tage 2 hc and i really like the power but it seems like it lost a little low end.so i was thinking the higher comp might bring it back.

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very very low power gains in raising the comp to 13.5:1.I run 14.5 :1 in my trx450r race bike and regret it.The power to dollar ratio doesnt add up in my book.And definately not in my wallet.LOL.For the price send the head to a reputable porter.Also try messing with your gearing to get a little more low end power.

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You have just opened a can of worms. I asked the same thing on here and to other people before I put a 13.5:1 cp piston and stage 2 hot cam in my crf 250 with answers ranging from absolutely unnecessary, to absolutely needed. I even e-mailed motocross action magazine about it and they actually answered my question and put it on page 137 of the Sept. 09 issue. Their answer was

"Do not under any circumstances, run 110 octane (what the shop doing the work on my bike insisted it needed with these mods) in your crf 250. That octane rating is too cool and slow burning for a motocross bike. On the other hand, if you increase the compression and change the cam, you will be able to run gas with an octane as low as 91 octane (except in sand and high altitude)."

This was the most knowledgeable source to answer my question so I went bike to 93 octane pump gas and have had no problems what so ever. Though you bike is a 450, it is probably safe to bet you will be fine too with pump gas.

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very very low power gains in raising the comp to 13.5:1.I run 14.5 :1 in my trx450r race bike and regret it.The power to dollar ratio doesnt add up in my book.And definately not in my wallet.LOL.For the price send the head to a reputable porter.Also try messing with your gearing to get a little more low end power.

yeah if you are doing it just for the power I wouldn't bother, but if you are like me and needed a new top end anyway I'd say go ahead. Oh and just as a warning to you gixxer1kr you're probably going to get jumped on like crazy on here for calling a trx 450 quad a race bike.

  • Haha 1

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Not all pump gas is the same. and not all actually up to the min octane rating stated at the pump either.

So while some might be fine on their pump gas, others might not be so lucky. Also when it is colder like winter 30-40*, you are less likely to get detonation than say when it is 90* out with the same setup. Anything in the 13:1+ ratio I also add 1 gallon to 4 gallons to make 5 just to be safe.

110 is usually a leaded race gas. thus probably the reply from mxa. The 2 strokes love the lead, the 4 stroke like the oxygenated fuels for extra power.

$.02

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