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CrawlerD said:
Well something that has never been addressed. Race case is very hard on carb seals.


It's hard on anthing plastic or rubber. Like the tip of the float needle.



You also have to rejet to run race fuel. General rule of thumb is up two sizes on both pilot and main.



Most motorcycle engines and especially mini's, don't have high enough compression to run straight race fuel. You are just sending $ and HP out the tailpipe. Even though it runs better, you are wasting your $. 1/3 race gas to 87 pump gas is good. Or 50/50 as well. You will make more power and spend less money.
 

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kman153 said:
i believe that anything over 110 octane ruins the life of your valves




Just because this REALLY peaked my curiosity... How will anything above 110 ruin valves????



I run VP MS103 or C10 and love it... Great compared to pump gas. no carbon, The 103 offers a little better power but for practice and rec riding I run the C10... I refuse to run pump gas.
 

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Just stumbled across this and thought you guys may be interested in what I know about avgas.



I would not recommend using it other than in an airplane engine. I'm talking about 100ll (blue fuel)... I just had a friend stick a valve in a brand new yz450...he was using avgas.

Here a few things that i know about it:



The octane rating for avgas is derived from a different method/scale than auto gas. The antiknock index for auto gas is about 5 points higher than the octane rating for avgas...so 92 autogas would "equal" a 87 octane avgas



Avgas has a lower vapor pressure (6.5 psi) than auto gas (7 - 15psi). It's formulated this way to prevent vapor lock (boiling at high altitude)



Aircraft engines typically cruise around 2,200-2,300 rpm redlines are low because if prop tips go supersonic (700ish mph somewhere not too far beyond the 2700rpm range) they become very inefficient.....not 9 or 10,000 or 12,000+ rpm like some pitbike and mx bikes.



Avgas contains lead and bromine. The combustion process creates lead bromide.....this is highly corrosive. Aircraft oil is formulated differently than motorcycle and auto oil and is designed to help protect against lead bromide.



...also something to think about - auto gas frequently contains 10% or more or less alcohol (which can absorb 50 times as much water as gasoline). Always run with fresh gas and try to find a gas that does not contain alcohol.



It is possible to remove the alcohol from auto gas by adding water (yeah sounds crazy) and letting it separate and siphon off the gas.....but you will have a gasoline that now has a lower antiknock rating - alcohol has antiknock properties.



Fresh pump gas or a pump gas/race gas blend has always worked for me.
 

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xr1million said:
Most of ya'll who say your motor runs better with U4 or any of those other fuel is because of the oxygenation. Simply adding octane to a fuel with not help out a motor that will already run great on Jack Daniel's.



Also 4 strokes dont need octane the way two strokes do.



I ran my 124SE for 3 years on pump fuel with not a single problem, other than a shattered 2 year old piston that the skirt was much thinner than the new one they sent. Also all my 250f's and 525 SX have run on pump fuel with out EVER skipping a beat due to fuel. And my YZ 125 runs solely on pump fuel and Mercury outboard oil And has yet to skip a beat in over 2 years of WFO abuse!



I have tried higher octane fuels and oxygenated and could never feel a difference in power!




Ok, i didnt want to mention anyting about this topic but all the posts from poeple that have no idea what they are talking about made me respond. For one, running higher octane fule will NOT increase horsepower but it will help with throttle respone and your bike running cooler while building up less carbon. For two, i have a built 110 motor and i do know that running race gas does help with the life of the motor and the response the motor gives to the races gas. Anyone who is running race gas with a stock motor is wasting money. I have had many race motors in 125 two strokes and 250 four strokes and have tryed both, race gas compared to pump gas. The results i got were better throttle response and longer time on the motor. So all of you that think running race gas will increase your horsepower and turn you into james stewart should rethink yourselves...not only that, the fuel they are running we cant even get our hands on!!!
 

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MxNailor85 said:
Ok, i didnt want to mention anyting about this topic but all the posts from poeple that have no idea what they are talking about made me respond. For one, running higher octane fule will NOT increase horsepower but it will help with throttle respone and your bike running cooler while building up less carbon. For two, i have a built 110 motor and i do know that running race gas does help with the life of the motor and the response the motor gives to the races gas. Anyone who is running race gas with a stock motor is wasting money. I have had many race motors in 125 two strokes and 250 four strokes and have tryed both, race gas compared to pump gas. The results i got were better throttle response and longer time on the motor. So all of you that think running race gas will increase your horsepower and turn you into james stewart should rethink yourselves...not only that, the fuel they are running we cant even get our hands on!!!


Er, actually, running higher octane than needed leads to INCREASED carbon buildup. It doesn't do anything to alter throttle response.



As was noted, you may feel some effects from oxygenation, but piling on octane won't help in the least.
 

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Be very-very careful with jetting some of you guys are going forward, some backwards (the wrong way).



Someone stated race gas requires bigger jets - rarely. Most "race gas" requires one or two jets smaller or it'll blubber. Unless it's oxygenated.



OXYGENATED fuel like U2, U4, U4.1 requires larger jets - whomever said it didn't make more power - you prob didn't jet UP and get the extra fuel - the oxygen level is just about twice of regular pump gas. On big bikes you can see a several hp increase, 250F's maybe 1.5+ hp increase across the board etc... Even if you can't feel it - it's there. Oxygen helps to make HP.



The new pump gas with alky stinks -but- guess what. Most of the time, it makes more peak hp than regular pump gas. Alky has a way of doing that.



If you want to get into race fuel and find out the facts - google "RICH ROHRICH" he really has his act together -but- you'll also be confused after a few paragraphs - the guy can get pretty deep! haha. I was like whoa...



Race fuel - if you can advance your timing a degree or two, in most cases you pick up power.



2 Stroke -vs- 4 Stroke - someone nailed it. Thumpers don't needs a much octane as 2 strokes. Of course they're (2 strokes) doing double the work of a thumper and firing EVERY time, and making sick HP from low CC's. Face it, if a 125CC MX bike can make 40hp and a 125cc thumper is capable of ?



AV Gas - someone got it almost right - AV gas is made for steady speeds but not HIGH RPM but "low RPM". Plane engines are made to hum along slowly at lower RPM's. They also have de-icers in them. Sometimes with av gas you'll see bubblegum looking stuff in your carb if you let it sit for a while. In all fairness, I know guys that run AV gas and love it - just because it's designed for one thing doesn't mean it can't/won't work for something else. Guys that were very fast, very in-tune with their bikes. Personally I didn't like it...



Just get as much octane as needed for the situation you're in. If you're riding up hills, in deep sand washes - more octane might be needed to keep from detonating. If you're running a box stock bike and putting in super high octane fuel... chances are your bike is slower. If you're racing the "C" class chances are you aren't riding it hard enough to detonate the motor from hard riding unless you have a problem (no disrespect to the "C" riders). It's just that detonation usually comes from engines that are ridden hard, or in particular circumstances such as deep sand, uphill sections, heavier riders that ride hard, hot weather...



Peace and have fun. Oxygen doessss make power! : )



Mikeee P
 

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Yea my R1 (98 so it has carbs on it) had 9 more peak hp with MR-9.. It had 2hp more with U4.1.. And a slight decrease with anything on pump gas over 93 octane.. You only need HIGH octane if yo have over 250 to 255 psi per cylinder.. And most all stock bikes come with 190psi.. My mini after milling the head and all that has 205 to 210... So I run 93.. Or MR-9 and jet 2 sizes bigger.. 1 size on the pilot...
 

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Kurlon said:
I ran 87 octane with 300+ PSI per cylinder, more to it than just that. : )


Holy JEEZ bro' what were you running that kinda compression in? LOL



I think the highest I've seen is a works 125 SX bike with 225psi and the guage had the "short" insert so the true pressure would have been prob in the 240's low 250s... I can't imagine 300psi without it being an alky motor!



Was that on a full size bike? 250cc maybe?



Mikeee P
 

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MikeeeP said:
Holy JEEZ bro' what were you running that kinda compression in? LOL



I think the highest I've seen is a works 125 SX bike with 225psi and the guage had the "short" insert so the true pressure would have been prob in the 240's low 250s... I can't imagine 300psi without it being an alky motor!



Was that on a full size bike? 250cc maybe?



Mikeee P


300 psi is very common in engines with short cams or cam timing to give the engine "snap".

My road race engines depending on the track will have close to that compression but most of the time will be in the mid 250's.

SB16 is only 91 octane, but with right combustion chamber will tolerate that kind of pumping compression.

Also note that this fuel made 17 more hp at peak and 21 at peak torque compared to pump fuel in a 08 Supersport spec GSXR1000.

$48. a gallon too.



Most of my 250F's that I build will have that kind of cranking compression for SX but I will change things in the engine for MX use.

My 450's never have that kind of cranking compression because those engines don't need bottom end "snap".



I do occasionally toss in the random moth ball though...
 

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Oh what the... I HAD replied with a lil write up of that motor... and now the post is gone?! D-oh! In any case, Dood nailed it, 51 x 54 long stroke 110cc Honda build, high comp, with a short duration TB stock head cam, mill cylinder, copper head gasket, and .025" squish. Not very exciting, but absolutely rips for short track motard duty.
 

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so wait a minuite you can just put racing fule in a bike like that. You dont ave to do any thing special to the motor first. And if so whare can I get some race fule and what dose it cost compared to the normal gas (93 octane)
 

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klx110L said:
so wait a minuite you can just put racing fule in a bike like that. You dont ave to do any thing special to the motor first. And if so whare can I get some race fule and what dose it cost compared to the normal gas (93 octane)


The advantage of "race fuels" is consistancy. You know what specific gravity, oxygen content, octane, etc, etc.

You can run any race fuel in a stock engine as long as you jet for it.

Most high octane race fuels will not make more power, but hi Oxygen race fuels will.

VP, R-tech, ERC, F&L are some of a few companies that make power producing fuels.
 

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dood said:
The advantage of "race fuels" is consistancy. You know what specific gravity, oxygen content, octane, etc, etc.

You can run any race fuel in a stock engine as long as you jet for it.

Most high octane race fuels will not make more power, but hi Oxygen race fuels will.

VP, R-tech, ERC, F&L are some of a few companies that make power producing fuels.




consistancy in some race fules is a problem though i quit running U4.2 and went back to pump gas in my race bikes for that reason alone one can would make your bike run way diff than the can before it did
 

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Nonsense. The race fuel, unless subjected to excessive sunlight, high temps, or kept past it's reasonable use date, is INCREDIBLY consistent. Pump swill has such a wide variety of additives, regionally and seasonally varied, and when supplied by different vendors is a crap-shoot. Same octane, but can have widely different properties.
 

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firepower354 said:
Nonsense. The race fuel, unless subjected to excessive sunlight, high temps, or kept past it's reasonable use date, is INCREDIBLY consistent. Pump swill has such a wide variety of additives, regionally and seasonally varied, and when supplied by different vendors is a crap-shoot. Same octane, but can have widely different properties.




im just going off numbers MDK KTM gave me... they obviously know what they are talking about if they had a factory team i have had 2 pales of U4.2 run 2 jets apart from each other with the same reading on the RAD gage... yeah it makes more power than pump consistantly but still not worth the jetting hassle week in and week out for local races
 
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