air/fuel

**Fast Fred** · 09-26-2006

i 've been told that the air fuel mix of alkys is about 1/2 that of gas through the same carb.
so to say if i had a moda that ran good on gas, made the jets 1/2 the size in the same carb and ran on methonal i'd be close?

any body,
thanks
FF

John (Taylor) Gabrowski · 09-26-2006

You need in the area of twice as much methanol by volme as gasoline in the air fuel mix where it was just gasoline and air before, lube not factored in for 2 strokes. The octane on alcohols varies from just over 105 in ethanols to some 140 in methanol, I recall. Octane can vary by purity of the alcohol, very pure is one thing but add water and the anti-knock figure goes up being its actual octane. The higher the octane the slower the burn, the more BTUs built up on slowly the more power you get. All Alkys are oxygen bearing where gasolines are not until gasohols came along.

There are probably a host of guys hanging around here that can give you jetting references or ideas on rejetting gasoline carbs bigger but to say it is 2X bigger would be very global where an ajustable high speed needles are concerned but for a OMC, Tillotson or Minkuni or Kehien carbs there is a whole learning curve because of all their innards. I am used to what Carter Model Ns (and that is newer to me) than Vacturis in using Alky mixes and they have those twist them needles controlling the fuel to the air taken in. Tuning alky is not abrupt to changes in jetting as gasoline is by a long shot. That is why you used to see ALkys melt down pistons after the second lap or 3rd lap in 5 lap courses (used to be) in what some one thought was the best setup with Alky only to find out they were just a little lean and seized pistons or in cases melted a hole in the crown. It sneaks up on them. Anyone else???

**Mark75H** · 09-26-2006

Most of John's post is correct, with the exception of this

Originally Posted by John Taylor

The higher the octane the slower the burn, the more BTUs built up on slowly the more power you get.

Knock resistance and flame speed are not 100% correlated. Slow pressure rise does not create more power. Power is solely dependant on peak pressure and correct crank angle at peak pressure. Alcohols have lower BTU content than gasoline.

The fuel air ratio he describes is a good rough starting point

**Freddie Webb** · 11-03-2006

If your gasoline, high speed jet is correct you should be able to multiply times 1.6 and that will be really close. For example, .062 x 1.6= .0992 .062 would be your high speed gasoline jet and .093 would be your alcohol jet. I do not know what carbs your running but you need to make sure the needles are viton and all gaskets are alcohol resistant.

**Fast Fred** · 11-03-2006

dose Nitro % in to the mix change any thing?
thanks

**Skoontz** · 11-04-2006

When you boost nitro in blown a fuel motor, yoy change timing accordingly to best respond with the fuel. We used a wet/dry thermometer to determine the humidity in the air, which would in turn tell us how much pop the engine could drink. Changing very subtley by adding a hotter plug can cause superchagers to blow off the manifold. In the old days of front engines, that in itself caused alot of burn victims and deaths from the supercharger hitting the drivers.

Word of wise...Be careful with nitro, and you're best hooking up with a crew cheif who has experience with it to learn from. Last note here....Plan on ALOT more money spent per run.

**Roy Hodges** · 11-04-2006

Originally Posted by Fast Fred

dose Nitro % in to the mix change any thing?
thanks

Ask someone who has used blenzall. it comes in a pint can
has nitro,alcohol , racing castor oil , and whatever else it needs. ) i do not think with this mix , that you have to change anything . one can /gallon of gas. The can I still have is ALMOST a pint (15 3/4 oz.) But this tom cat piss is not cheap, if it's still available . It is supposed to be a 15% power gain, immediately .

**Fast Fred** · 11-15-2006

i looked for some, no dice, i need a case

**jphii1** · 11-15-2006

Hey Fred CLICK It's Blendzall, maybe that's why you had a hard time finding it. When we were racing F1 & F2 bikes either Blendzall or Castrol R were all we used. I never saw the octane booster before, but I think I'm gonna try it too.