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Jeremy2Wheel

XR600R + Race Fuel

10 posts in this topic

Just curious what fuel you guys are running in your xr600r's. I have an 87 that I recently rebuilt. Wiseco piston (10.5:1 I think), HOT RODS connecting rod, New Cam, Cam Chain.

Recently, I bought five gallons of 108 octane from a Shell station. I noticed my bike idles faster and may pull slightly harder (It was already a torque monster). I'm not sure if I need to be running race fuel, is it a waste of money, can it hurt the engine? I have read all of the articles about how octane is really gasoline's resistance to knocking and not necessarily about relative power. So, now I want advice from you guys. Thanks in advance.

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Just curious what fuel you guys are running in your xr600r's. I have an 87 that I recently rebuilt. Wiseco piston (10.5:1 I think), HOT RODS connecting rod, New Cam, Cam Chain.

Recently, I bought five gallons of 108 octane from a Shell station. I noticed my bike idles faster and may pull slightly harder (It was already a torque monster). I'm not sure if I need to be running race fuel, is it a waste of money, can it hurt the engine? I have read all of the articles about how octane is really gasoline's resistance to knocking and not necessarily about relative power. So, now I want advice from you guys. Thanks in advance.

i dont see how it could hurt, just expensive. using a high octane fuel like that may enable you to run more advance in your ignition. more power.

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At 10.5:1 you are not going to have a whole lot of margin before pinging sets in. However, what you are seeing is more likely due to the changes in jetting related to the race fuel. All fuels are different, but a lot of high octane race fuels are high in aromatics like toluene. The aromatics are denser and make the bike run a little richer.

I still have the 9:1 stock piston in my bike and it sometimes pings pretty badly. It is really easy to tell when it's happening. You should have no problem detecting it. If you have pinging isses the extra octane can help a lot. To save some $$$ you can mix it with premium pump gas. Even a low mix like 25% race might be enough.

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My XR628 had an 11:1 piston. During hot weather or when riding in sand I had to use a 50/50 mix of race gas and 93 octane to keep it from pinging.

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To save some $$$ you can mix it with premium pump gas. Even a low mix like 25% race might be enough.

great advice thats exactly what i would have said myself. Start at 25% race fuel / 75% pump and see how it reacts and if thats good then your set if not 50/50 should be the most you would need. AND when you find the right ratio that fits make sure to check that jetting still looks on.

What brand is this 108 fuel you got? leaded or unleaded?

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Thanks for the response guys.

The fuel I am running is Shell and it is leaded.

I should have been more clear. I am yet to run 100% race fuel. I started by refilling a half empty tank with race fuel for a 50/50 mix. I would guess that I am now at about 30/70 (race fuel being the 70). I have considered the jetting issues, but I hesitate to mess with my carbs (I have the two carb model) because it runs pretty good now.

Thanks again.

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I generally run a 50/50 mix of some sort of "racing" fuel. Right now it's Sunoco 100 octane unleaded.

Disregard all the rhetoric about whether you need it or not or whether it's pinging or not. It makes more power, pretty dramatically in my experience.

I rolled a 4th gear torque wheelie on my 600 the other day that would not have been possible on straight pump gas.

Good times!:banghead:

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From what I've most commonly heard is that high octane fuel won't make too much of an improvement in an stock engine until you get on hi-comp,cams,ignition advance and higher engine temps so I think you're covered up in that area.Good luck and happy roosting.

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From what I've most commonly heard is that high octane fuel won't make too much of an improvement in an stock engine until you get on hi-comp,cams,ignition advance and higher engine temps so I think you're covered up in that area.Good luck and happy roosting.

Compression and timing are the biggies. Higher compression and more advanced timing equate to a delayed desired ignition, therefore the necessity for a higher octane (resistance to ignition). You want the fuel/air mix to burn only, and I mean only, when your spark plug fires. If it pre-ignites, you'll get detonation and severe detonation leads to broken pistons. IF, however, you have too much resistance to ignition (i.e. overkill on the octane) then when your plug fires the mixture will burn and combust much more slowly, robbing your motor of power. You want the perfect octane, not too much, not too little. If you HAVE to error, it is better to error on the high side, however.

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:banghead: I'll start by saying this is my opinion, i am not saying the others are wrong. New motocross bikes are about 12.5 to 1 compression ratio and can run 91-93 octane without a problem. Like someone said to much octane will cost you power. So if you are running race gas I'd go 25% race and 75% 93 octain.

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