Race or Pump Gas in your Thumpers???

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#1
Hey quick question... from an un-educated 2 stroker... what do you guys prefer to run in the tank? C12 or similar race gas or Pump Gas???

Anyone tried both? Any noticable differences?

RayoVac
 
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#2
I have only one completely unscientific result from using 100 octane...my klx300 didn't seem to care for it. I had more starting troubles than with 91, and it didn't seem to run any better.At 4.5/gallon, that won't happen again. Motor is stock internally, using big gun exhaust and 35mm fcr carb that were jetted using the 91.

Mark
 
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#3
Rayovac - What type of bike are we talking about and what type of riding are you doing?
 
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#4
Rich,

I currently ride a 98 CR250.... but am considering the CRF450. At Dirtweek a buddy and me where just sitting around discussing fuel... especially after the comments Eric made on Ethanol.

Some of the guys I ride with run C12 and I asked the question... "What would ya run in a 4 Stroker i.e. the CRF450 for MX use?" Did not know whether the 4 stroke guys found any reason or gain in running a race gas vs. a good pump gas.

RayoVac
 
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#5
many people are under the impression that higher octane gas will give you more power since it has a bigger number and because its "race" gas...THIS IS WRONG!!! lower octane pump gas actually burns faster and more powerful than race gas, but this is not necessarily a good thing. A gasses octane is its ability to resist detonation. detonation is the premature ignition of gas due to high compression or excessive heat. with high compression, the gas is compressed so much that it ignites before the spark goes off because it is so hot, this is bad because it explodes instead of burns. this is where the term "ping" or "knock" comes from...you can hear the gas exploding. although pump gas gives more power, you dont want to use it with a high compression engine. my friend bought a vertex race piston for his bike and ran it on pump gas...it lasted 2 rides. the idea is to run the lowest octane possible without having your bike ping. even though the race gas is less powerful, the higher compression will still end up giving you more power. one thing i dont understand is how the YZ250F has 12.5:1 compression, yet it still runs on pump gas...how is that possible?
 
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#6
Originally posted by YoTRacer158
! lower octane pump gas actually burns faster and more powerful than race gas
YoTRacer158 - I tried to save you from yourself by deleting your first post before too many people saw it, but if you are going to persist and re-post incorrect info out here you deserve to get your head handed to you. My advice is to DUCK becuase I doubt I'll be the only one lobbing bombs in your direction.

The octane rating of a fuel (low or high) has no direct bearing on how fast the fuel burns or it's energy content which ultimately determines a fuel's power potential. Flame speed and energy content are functions of the fuel's chemistry NOT the octane rating. The flame speed and energy content of conventional hydrocarbon based race and pump fuels doesn't vary enough to matter.

The rest of your post is so flawed it would take too much time to correct it all. Suffice it to say you should READ MORE AND POST LESS

Rayovac - C12 is an excellent all around fuel for the CR250 and has proven to be a good choice for the big bore YZFs as well. Along with improved throttle response C12 will allow you to safely jet leaner than you could otherwise and improve high rpm power and response as well. There are better choices than C12, but in terms of cost, performance, availability and ease of tuning it is very tough to beat. I can only speculate on the CRF450 at this point but given the claimed power peak and overall engine spec it's probably safe to assume that many of the lessons learned on the YZFs will transfer over to the CRF.
 

MWEISSEN

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#7
Octane is a part of the gas chemistry, and its rating is a general indication of the octane concentration of the total chemistry. Octane is a comparatively long-carbon-chain molecule compared to others in gasoline (7 carbons or fewer I think, and I think each type of molecule is pulled off of three condensing points on a fractionating column). It does indeed affect the burn rate of gasoline.

It's been a LONG time since I studied the organic chemistry of gasoline, so I won't go much further than that for fear I'll step too far into a pile of other organic chemistry (that originating from a cow).:)
 
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#8
all of the information i said was givin to me by the auto teacher at my school, several guys at the mx shop and many riders at the track...if the information was false you should have told me instead of just deleting my post and not saying anything. i thought that i just forgot to submit it so i put it up again. next time try and be a little more considerate, thanks
 
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#9
Originally posted by YoTRacer158
next time try and be a little more considerate
Tried that once and all we got was guys repeating useless junk they heard from some dink working at a motorcycle shop. GO FIGURE :) BTW, I sent you a PM and explained why your post was deleted.

Next time check your sources before you chime in. Chances are good your teachers have told you the same thing. :confused:
 
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#10
I believe in rich... he's got my bike running better now than when I got it.
by following his read more post less 12 step policy you can to

JB
 
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#11
being considerate is not deleting someones post and not explaining why...if you would have sent me a pm explaining why you took it off i would have understood...and i dont have any pm's like you said i do so try sending it again. i dont want to argue bc obviously this isnt gonna get us anywhere...theres a lot of stuff i'd like to say but i dont wanna be like that kx100 guy who thought it was cool to cuss out moderators because you guys do a lot of work keeping this place running
 
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#13
geez, for a moderator, rich doesn't seem very moderate. YoTRacer158's post made as much sense to me as rich's explanation. my brother is an internationally known expert on automotive combustion and emissions, and he says similar things: i.e, run the lowest octane that prevents knocks, otherwise you are wasting your money.

he claims that there may be a theoretical difference in btu's/gallon between octanes, but it's tiny, and probably not as meaningful as the differences between different brands/mixes of the same octane due to slightly different additive packages.

anyway, it's probably important to consider the individual machine, and its timing and compression. my klx300 runs fine on 87 pump gas. my wife's xt225 will ping on 87, so i use 91. my klr650 is fine on 87 in the winter, but in the summer sometimes pings a bit, so i go up to 91. this is probably as much lean jetting as anything else tho. i'd start with what the manufacturer recommends, then go up if you get any detonation.

so what's up with the deleting of posts anyway? doesn't really jive with the red, white and blue theme this week. in the america i live in, censorship is considered a bad thing.

-mark weaver
 
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#14
one thing i dont understand is how the YZ250F has 12.5:1 compression, yet it still runs on pump gas...how is that possible?
I don't know, but they do. Mine runs fine on pump gas.

Should I run VP? Is it worth the money?
 

biglou

#15
Originally posted by Sparkymarky:
YoTRacer158's post made as much sense to me as rich's explanation.
There was misinformation posted as to the flame speed/potency.
for a moderator, rich doesn't seem very moderate.
That is correct. The tolerance level for incorrect information is very low, if not non-existant.:)
 
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