gas question

[boardadikt]

At my local texaco I can get 100 octane unleaded racing fuel for $4.15, 110 leaded racing fuel for $4.00, or 93 octane ethanol free unleaded for $1.89.

I have a 01yz250 2 stroke and use amsoil 2000 racing pre-mix and ride mostly supercross and motocross tracks.

Here are some question for you all. 1. What is the difference between leaded and unleaded...as far as how it makes your engine run (duh-there is lead in it). Is it bad for your engine? 2. I have heard 2 separate ideas about gas with or without ethanol. I heard that you don't want ethanol because it can cause detonation. Another said it is good to have ethanol because it "oxygenates" and makes your bike run better. At the pump they say that the non-oxygenated ethanol free is for motorcycles, boats and other high reving engines. What's the real story on ethanol free gas? Does racing gas have ethanol in it? 3. Of the gases I listed at the top, which would be better the 100 unleaded or 110 leaded?

Thanks for helping setting me straight on the right gas.

 

[jmics19067]

although I am at the tip of the tip of the iceberg on these things I will try and help out.

lead for lack of better words helps to soften things up. It helps prevent detonation,and valve face slamming into valve seat. I believe that it has no bearing on a two stroke except for effectively raising octane ratings. Some people say that they do get better service from the two strokes by using lead but I think if the type of oil and mix ratios is correct for the application it should be more than sufficient. Lead being "bad" for your engine is only an issue for catylitic converters and certain design valve train incertain applications. IE you want to idle your car with non rotating valves for 200,000 miles lead deposits can be an issue to the valves.

Ethanol is useless as a performance fuel if you want to run alcohol for power use methanol. Ethanol has less btus of energy produced per pound of air consumed than most common gasolines while methanol will produce approximately 9% more. Taking engine tune into consideration. Alchohol<either> will absorb water causing jetting problems on a day to day basis with the effectiveness of the alchohol getting worse each day if not stored properly.

I know extremely little of distillate rates which is what you want to look at when purchasing a performance fuel. I would not know which of those fuels is best for you situation. If you are extremely conscious of jetting and performance predictability and those fuels are out of a bulk container I would say look elsewhere for something sealed. If you are thrifty and only wanting to prevent detonation I would guess that you could mix the 110 fuel with the 93 in a ratio that would prevent detonation but will most likely be a splooge producer with predictable proper performance being second to cost.

Hope this helps

 

[boardadikt]

As far as the ethanol goes, I assume that all regular pump gas contains it and that's why they have one separate pump that says "non-oxygenated ethanol free premium for motorcycles, watercraft" etc... The ethanol (or methanol) is not something that I personally would add to the gas for performance.

So leaded gas is better for 4-stroke motors to prevent valve damage? My dad has a yz250F, and he was trying to find out the what kind of gas works best in them.

 

[Rich Rohrich]

Originally posted by boardadikt
So leaded gas is better for 4-stroke motors to prevent valve damage?

This is not relevant in late model motorcycle engines. Lead serves no useful purpose for 99% of today's four-stroke riders.

 

[jmics19067]

I could not tell you whether leaded fuel is ok or not for a yzf. My best uneducated guess is that the proper maintenance and inspection will outwiegh any pluses or minuses of the lead on the valves.

The only study I have ever seen concerning fuel was that unleaded fuel was not a major contributing factor to maintenace costs on New York City taxi cabs on the older leaded fuel designed engines.

Maintenance costs on someone abusing a fleet of car engines is worlds different than someone racing an engine designed for 13000 rpm.My best theory is that leaded fuel will not be a problem with deposits with proper and timely maintenance and may help with valve seat recesion beyond the intended service life of the engine. I don't believe you can lap titanium valves and if lead deposits where allowed to form, burning the valves would be the evil in the opposite direction.

I have no experience in 13000 rpm titanium valved engines so hopefully somebody else can share some education on this.

 

[Rich Rohrich]

Originally posted by jmics19067
My best theory is that leaded fuel will not be a problem with deposits with proper and timely maintenance

At 6 grams per gallon which is pretty common on some of the newer fuels deposits in the exhaust ports build up amazing fast if the jetting and cam timing are not dead on. On small port engines like the 250F and TTR 125, they can build up faster in fact then I would have believed possible.

The valve acceleration rates on current MX engines are harsh enough that lead won't combat recession issues. For better or worse, OEM valve train parts have pretty much become disposable commodities.

 

[jmics19067]

Awesome I was hopin you would step in Rich :worship:

so the only reason to use leaded fuel <in these applications> would be just availability of the octane and distillation rates you want? at the risk of deposits<sorry to sneak that in if you are replying>

 

[Rich Rohrich]

IMO, on most new design four-stroke singles lead is more a liability than an advantage. Most don't need very much octane (SFO's YZ444 can run pump gas at 13.8:1 compression). It's just a cheap effective way for fuel blenders to hit octane targets. Sometimes I think they just overdue it when catering to the more lead is better crowd.

Lead won't really hurt anything if it's in a fuel that has the OTHER specs you want, it's just kind of a PITA to deal with in a high revving four-stroke because of the additional clean up you have to do in some cases.

The good news is there are so many great unleaded race fuels these days you can easily find something without lead issues that will work.

Lead is still pretty usefull for a lot of race applications, it's just not the universal prescription it once was. ;)

 

[jmics19067]

Thank You,

as always your opinions and explanations are greatly appreciated over here

 

[boardadikt]

So Rich, in your opinion I should just go with the 100 octane unleaded racing fuel? Also, if I am to just get pump gas should I get the ethanol free premium? (if you read my first post-could you take a shot at my questions).

Is there a certain octane rating or other spec I should be looking for a 250 two stroke engine? Texaco is close and they have those racing fuels on pump (as stated in my first post), so its easy to get and fairly inexpensive.

Thanks for your help guys.

 

[Rich Rohrich]

Ethanol free fuel is always the best choice if you use pump fuel.

Without specs on the race fuel I have no idea if they are a good choice or not.

 

[Zerotact]

what about this ?
Fuel Property Typical Specifications
Specific Gravity .717
Antiknock Index (R+M)/2 112.0
RON, Research Octane
115.0+
MON, Motor Octane 109.0
Reid Vapor Pressure, psi 9.8
Distillation, 0 F
Initial Boiling Point
90
10% Evaporation
120
50% Evaporation
190
90% Evaporation
230
Final Boiling Point
255
Leaded
Yes
For Off-road Use Only
Color
Green
Oxygen, Wt.%
2.7%

 

[Rich Rohrich]

Originally posted by Zerotact
what about this ?

For use in what application.