I’m down to the line on getting a 331 kit for my ’10 KLX250 and noticed they offer either the 11.5 or 12:1 piston. The 11.5 is close to stock, just wondering about what the 12:1. What advantages or disadvantages come with it?

 

Hey Dave, how's it been going down there in humid CC? I kind of doubt you'll even notice a difference that small. The one thing I've liked about my 11:1 OEM 300 cylinder is that this bike seems clueless about the octane level I run in it. That said, I still usually fill up with premium because I can't help myself. Many times on my trips out west, I'll only be able to get low octane fuel for a couple of fillups, and I never notice any performance difference. I get no detonation whatever I run in this thing.

That said, I talked to Bill Blue, and he said he ran 87 octane regular in his 351 bike back at his home area and never has an issue with detonation. The KLX isn't very sensitive either way from everything I've done and everything you hear on this forum.

 

Humid is right! I just got back from a 10 day “ride-about” on my KLR 650 in the Leakey, Junction and yes, around Robert Lee. The first 5 or so days were comfortable but then it turned “Africa Hot” while I was in and around Robert Lee. Riding was like turning on a hair dryer and pointing it on your face. One afternoon it got up to 112 only to be followed by hail, high winds and much needed rain. One of the advantages of the lower lake level on Lake Spence is that it opened up a lot of areas to ride. ATV’s and dirt bikes were banned, but dual purpose (street legal) bikes had carte blanche in exploring the dried up areas. That along with the other back roads made for some great riding.

Back to my question… fuel is one of the things I’m pondering in my decision. I’m wondering about fuel consumption. My understanding is that the 12:1 is a higher compression which gives low end torque, but requires higher octane and more fuel consumption. Knowing that how we twist our wrist is the biggest influence in fuel consumption, I still want or need longevity and peace of mind when I’m out in those desolate areas.

On another note, I’ll be heading back out to Big Bend in early or mid December.

 

Yep, BBNP is always my birthday destination, so the last few days of Nov and the first week or ten days of Dec are marked off for sure. I've become very taken with BB Ranch State Park too. It has some decently rough and remote off road trails there, and the scenery is great.

 

i have 12:1 with my 331 cycle pro kit and have no issues with 87 FWIW.

 

you really don't have to move up to 89 untill 12.5-13.0:1 and 93+ untill 14.0:1 and race gas 100+ at 16.0:1 unless you have bad hotspots in the head and i believe the klx has a great head as far as cooling efficancy goes and castinf seems really clean so i'd say 12.0:1 will be great with anything you get from the pump

 

I have been wondering this for a while. It seems like bikes run higher compression than cars. Old muscle cars would run 11.5:1 and that was pretty high. 12:1 was getting into race gas territory. Why are bikes less likely to get pre-ignition with higher octane.

 

head design, material and casting defects and the 11.5:1 wasnt until the 70's mid 60's was closer to 14:1+ in the middle of the hp wars

 

+1...cylinder head design, spark plug placement, ignition performance, metallurgy, multiple intake/exhaust valves, etc.

 

Plus think of the power to weight ratio of a motorcycle vs car, alot less load on the engine.