Which Fuel ???

[2strok4fun]

I am new to this board so go easy.

I am sure the info is out there but I cant seem to find the specific info i am looking for.

I am in southern Cal and it seems most of the shops around carry 76 leaded race fuel at 110 octane. The specifics are listed on the can as far as the boiling temps and stuff. I have been reading all the info by Rich in recent posts with great interist, my feeble mind can comprehend what I read but cant retain any, having no chemical background. I have been mixing 91 pump with the 76 race and understand for performance this is not the thing to do. For performance I dont mind spending for 100% race fuel within reason. I am a play rider, am anal about jetting, and jettting with pump gas has gotten impossible (it seemed possible 10 years ago).

My question is this is using the 76 110 worth using for good throttle resopnse and less spooge (it runs about $6.50 per gallon around here in 5 gal steel cans) or should i look for phillups was it 35? or VP? or what?

Thank you for beig patient with a board rookie ;)

I should add:
98KTM exc 250
FMF fatty
TC II silencer
delta 2 reeds

 

[jmics19067]

I know exactly how you feel. I am learning this myself. it seems to me that the most preffered fuels are phillips b32 and b35 and vp c12 and mr2 depending on price and availability. I personally couldn't tell you anything about the 76 fuel. The best place to ask this question would be in the advanced technology forum since that is where most of the really techincal fuel questions are. Who is buying the bulk of the 76 ? drag racers that are are hard on the throttle for a few seconds and then shutoff? My guess is that it wouldn't be the best for you.

I have been fortunate enough to find a vp dealer near me who races oval dirt track cars. The tracks around here for them guys are pretty ridiculous with their rules . A lot of the different tracks specify different fuels so I am able to burn his ear off with questions about the benefits / differences he sees in the different blends he runs and he keeps in stock. It helps me too almost make a semi educated guess on the different ones I want to try.

 

[skhasky]

Funny thing about octane... it's the RESISTANCE to igniting that raises the number. Higher octane does not equal more power. It can actually reduce it. We use higher octane when the compression is so high, or the timing so advanced that premium will pre-ignite. Race fuel is commonly used in high compression motors and because it is very clean and consitent lot-to-lot. I would venture to guess that if you are running stock compression, you will do best with premium unleaded. Further, the high octane stuff usually degrades throttle response a bit. If you want or need to run a higher octane fuel, I recommend Phillips B-35. It is 99 octane unleaded. B-32 is common too, but it is 110 octane (much higher than needed for a standard dirt bike) and is lightly leaded. Now, lead is both poisonous and bad for the environment, and it's only value - besides raising octane - is that it lubricates valve guides in afour-stroke. You don't need 110 and you don't have valve guides, so stick with the B-35 if premium is pinging. An awesome mechanic once told me that the best fuel to use was the lowest octane that would not result in pre-ignition. Your engine will produce the best power and throttle response on that fuel.

 

[MX145]

You may want to check into using VP red instead of c12 or mr2. It will be a more consistent fuel than superunleaded yet won't completely empty your wallet. Go to the VP racing fuels site for more info.

 

[2strok4fun]

While i understand that the octane rating is the resistance to pre-ignition not energy level, what i am after is that after reading info on fuels on the advanced tech section that has piqued my interest, but i admit to being somewhat lost. So trying to match the fuel to the thermal demands of the engine is what i am after, i just dont know what is available near me that is suitable to work well. Besides the minimum recomended octane for the KTM is 95 in stock form, so i am going to use "race" fuel at some level, mixing it in or using something straight.

looking for somthing that will offer predictable jetting, clean throttle response and not blowing unburned all over the silencer.

 

[jmics19067]

I would venture to guess that if you are running stock compression, you will do best with premium unleaded.

I agree with most of your post except this statement . the problem with pump fuel anymore is that a lot of them is using alchohol too help oxygenate the fuel. Also overtime the gas starts becoming stale loosing its throttle response. So as the pump gas sets in the tank it is getting stale and also absorbing water from the alchohol that is mixed in it plus whatever junk that inadvertantly get kicked into the tank when the guy is filling them.

the main plus is consistency with buying a sealed 5 gallon jug of race fuel. The higher octane will also let you play around with the tuning of the engine. The difference between b 32 and b35 and or vp c12 and mr2 is more than just octane numbers and lead. one of the two brands choices is also oxygenated with something I think it was mtb. With extra oxygen in the fuel you have the potential of gainng more throttle response and power.

If you have a super busy gas station in the area that is getting fresh deliveries of high test every week . And the fuel isnt containing alchohol then yes I would say that you are doing great and you dont need to do anymore.
Another problem with areas like mine that have cold winters and hot summers. Can and will hit zero in winter and also hit 100 in summer is that the gas companies alter the blending of the fuel to try and compensate for the weather. I dont know how detrimental this would be since you will probably rejet for the weather conditions any how<still would have to do the with the race gas anyway> . But I have seen wierd problems with over the road trucks that head to Fla in january fill up their tanks in Georgia cause it is cheaper down there then come up here and freeze up. Also heard complaints of guys filling up here and saying that thier exhaust temp is high and the have no power when they get down there .

 

[enmerdeur]

Keep in mind that the KTM manual calls for 95 RON (Research Octane). The octane we see at the pump is usually the average of RON and MON (Motor Octane). Thus we see the octane method being displayed as (R + M) / 2. So 91 octane would have to have a MON of 87 in order to have a RON of 95. I suppose the only way to know these numbers is to call the refinery or customer service of the oil company that you are buying your fuel from. I have sent an email to my clients at the Flying J refinery here in Salt Lake City to see what the RON value of their 91 octane (which by the way is the highest octane rating of any pump gas here in Utah) fuel is. If it is below 95 then I will probably be switching to a 50/50 race gas to pump gas mix. I talked to Red-X racing fuel and that is what they suggest doing when you are running their fuel in a non-modified engine.

 

[2strok4fun]

enmerdeur-

yes, you are correct, KTM call for 95 RON, so octane wise 91 pump probably meets the octane requirement.

I have spent allot of effort on jetting and have come accross jetting that has been slightly leaner than I accounted for, I blame this on the fuel because it cant be my error :D JK

I keep good jetting records and compare seat of the pants, plug chops, to RAD #'s using a hand held GPS with a barrometer for current pressure and humidity from local weather stations.

With my riding time limited, and keeping this a hobby, I like to have my set-up as good as "I" can get it.