AVGAS / Racing fuel

[orange dog]

Has anyone used AVGAS in a two stroke mx'r ?
does it increase power much and how does it affect plugs / mix etc ?

[scott411]

we run 50/50 avgas and 95 in some of our 2 strokes, they tend to like it and stops denotation,

don;t bother ruinning it straight, 50/50 is better

[Motu]

I haven't noticed any difference,but I like to use it,even a mix - because it doesn't go ''off'' like pump gas.Normally if leaving the bike for more than a couple of weeks I drain the carb,it won't start on old fuel (all bikes,not just one) But race fuel will start first kick 6 mths later.That's it's main advantage to me.If you run high compression it's a must though.

[Ivan]

the higher the octane the less chance of detonation the killer of the 2 stroke engine

[Jantar]

One point to remember with Avgas is that it is designed for slow reving engines. So if you are using it in a high reving 2 stroke engine then mix it with some other fuel (eg Benzine, methanol, ethanol, 95 octane) in order to improve the burn rate. Shell used to make a speciallist racing fuel which was based on 100/110 Avgas. I'm not sure if it is still available.

[Motu]

We don't call 2 strokes high revving these days,most 4 stroke bike engines rev higher than 2 strokes - but they sound like they are revving higher with more power strokes.

[Brian d marge]

Japanese 2 strokes are designed to run on 91 , if the thing is timed correctly and Jetted correctly then you will be fine in all my bikes I haven't seen any signs of detonation ,
Th e benefits are as motu says , but if you have jetted and timed the thing correctly it wont be needed
and octane doesn't increase power

Though ,,,,,,, IF you were mudplugging up a hill and the thing was cooking , then Avgas would help

Stephen

[Jantar]

We don't call 2 strokes high revving these days,most 4 stroke bike engines rev higher than 2 strokes - but they sound like they are revving higher with more power strokes.
Compared to a Lycoming or a Continental designed to run at 2500 rpm, 2 strokes are very high revving engines.

[scott411]

Japanese 2 strokes are designed to run on 91 , if the thing is timed correctly and Jetted correctly then you will be fine in all my bikes I haven't seen any signs of detonation ,


we run a lot of KX125's we have treid lots of jetting on 98, 95 and 91, howvever we go back to 50/50 avgas because under laod they will detonate with top riders on them, i know they are designed to run on unleaded but they seem to like the avgas,

however we can not tell a difference in four strokes, and we run 98 in them

[barty5]

however we can not tell a difference in four strokes, and we run 98 in them

yes but if you go out to ardmore avgas is cheap the station fuel and at the cost of petrol any savin is good these days

[Motu]

Compared to a Lycoming or a Continental designed to run at 2500 rpm, 2 strokes are very high revving engines.

Compared to 2 stroke diesel marine engines aircraft engines are screamers - your move....

[Jantar]

Compared to 2 stroke diesel marine engines aircraft engines are screamers - your move....
I somehow don't believe that 2 stroke diesel marine engines will run terribly well on Avgas. :shutup:

[terbang]

Compared to 2 stroke diesel marine engines aircraft engines are screamers - your move....

Ok then, put some 100/130 avgas into a diesel and the only screaming you will get is from the owner. However if you put jet fuel into a diesel it will run just fine.

Higher octane aviation fuel burns with a slower flame front than automotive fuel and with engines set up for lower octane fuels you can stop detonation but you can also start hammering (cooking) your exhaust valves/port.

[Motu]

We are talking about motorcycle engines with relatively small combustion chambers compared to aircraft engines,I think the speed of the flame front has no relevance in such engines....1000cc singles maybe,but not 250cc.

[Ivan]

Well us 125GP guys we run Avgas in our race bikes and they rev to 14000 RPM

Quite high revving engines

And run it straight well some guys run elf race fuel etc

[orange dog]

cheers for the info... and the entertainment !

[barty5]

f1 teams run on 95 octane and those engines scream 20,000 rpm plus now thats a screamer

[KLOWN]

f1 teams run on 95 octane and those engines scream 20,000 rpm plus now thats a screamer

zxr 250 will hit those revs, if you take it a little through the red line

[Brian d marge]

Its not about the speed of the engine , octane is there to stabilize the edges of combustion the part of the combustion chamber that hasn't seen the flame , but as the pressure rises the gasoline starts to fracture , and octane slows that process down , if the gas does fracture , separate off its prone to ignition and you get the 2 flame fronts colliding which is your detonation

Anyway , as both Scott and i pointed out you don't need avgas , but if the conditions cause heat , then a poor squish area , timing , carburation will promote detonation so a quick fix could be to add avgas, or re angle the squish , or what ever ...

Good point about the f1 cars , they run quite high compressions , scream to high rpm ,, but run pump gas ( ok tweaked pump gas as the rules allow ,) but pump gas all the same ,,reason is good combustion head shape , and lots of loverly cool gasoline ,,( wonder what ratios they run at ????

Stephen

BTW the above is from the top of me ( v tired ) head late at nite , ,,its as rough as guts but it will do ,,,

[scott411]

f1 teams run on 95 octane and those engines scream 20,000 rpm plus now thats a screamer


i ran ELf race fuel in my motard bike for hte street races ,i ran the blend called WRF, (World Rally Fuel) the stuff may be low in octane but its higher in oxegen and other agents, its expensive but you can feel the difference, I expect Formula one would run somthing similar, hardly tweaked pump gas,

But MR D'marge is right, Avgas is a quick solution to a bigger problem, (and a good one to)