Fuel for Test Days on a Budget?

For people who are on a budget, what fuels are being used for 100cc air cooled engines? I’m currently running a rental kart series at my local track and I plan on running my own kart in 2020. Just trying to budget recurring costs and I can’t find any info about what fuel people use for non race days. At $15/gallon for c12, honing my driving skills can get pretty expensive

Get avgas at the airport. We use it in our TAGS here for the local stuff. Maybe $5 or $6 gallon. 100 Octane.

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What kind of 100cc engine are you talking about? I’ll chime in with some general info for now…

Most people use left over but not entirely spent race fuel, you’ll usually have some left over after a weekend. You could maybe even buy leftover fuel from racers that don’t want to have to bring it home.

Less expensive options (feasibility varies):

A less expensive racing fuel from a pump that’s intended for recreational vehicles.
100LL piston aircraft fuel.
Blend of pump gas (Non oxy\non ethanol) with racing fuel.
Pump gas (Again non-oxy, ethanol free).

As you go down this list, more caution should be exercised in terms of monitoring how your engine responds to tuning.

The octane needs of these engines tends to be low, so that makes the octane of pump gas suitable. Indeed there are low octane race fuels. However, other key differences between pump gas and “race fuel” that you should keep in mind.

Consistency between batches: Naturally quality is more tightly controlled in race fuel.
Storage: Again consistency and freshness is key for racing fuels. Not so much needed for road vehicles.
Lead content: Most racing fuels used in karting (for better or worse) are leaded. The lead leaves a nice coating on the internals of a two stroke engine adding some lubricity. This is where a blend of race and pump gas can be a good option.

Have you found any specific tuning differences or behaviors between 100LL and something like MS98, C12, VP111 etc?

I’m about 10 min away from Buttonwillow Race track and they have 110 at the pump. I’ll run it with Burris hirev castor sometimes. It’s not a huge savings at 9$ a gallon and oil is just a bit cheaper. I’ve heard the c12 is a bit faster.

Thank you for all the input guys. Any savings, especially in consumables adds up. To answer your question @KartingIsLife I plan on running the kpv or one of the tag 100cc depending on budget and popularity

I have not noticed. Don’t really mess with carb or jetting when running locally though. Just banging out laps to keep my driver in shape.

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You’ll be okay with premium pump gas. Badger Kart Club has a pretty decent 2-cycle crowd, and we’ve used 93-octane pump gas sourced from a local gas station as the spec fuel for everything from Kid Karts to TaGs since forever.

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2 friends of mine, an engine builder and the driver, entered the stock appearing class at the Atwater Nationals in 1977. The engine builder had a plan, 100 octane avgas. In testing, before the race, they wanted to see how much faster the avgas was than premium pump gas. It was actually slower, a fact that I had known for years. Avgas is formulated to operate from sea level to 10,000 feet, they have to put a lot of junk in it for it to perform at that kind of altitude change. Not sure really, but I think it has something to do with the specific gravity of avgas. It’s much lower than pump gas.
Octane, does not mean more power, it’s a measure of a fuel’s ability to resist detonation. You have higher compression, you need higher octane. Match your fuel to your engines compression. For example; a KT will pump about 160 psi, while a TT 75 will pump 225 psi. That’s the deciding factor on what fuel you want to run.

Ordinary 93 octane pump gas is an excellent 2-stroke fuel.

Lots of butane up front to get a quick light-off. Lots of ethanol to carry oxygen into the combustion chamber and resist detonation. Lots of heavy ends to need evaporating on the piston and protect it from overheating.

I have run TM K9s on it and haven’t had to back off the timing relative to a 98/100LL/110 setting. It does have a lower equivalence ratio than most racing gasolines and you will need to jet up to get to the same level of richness.

it has more to do with tuning for your fuel - different energy per unit mass, different ignition (start the flame) requirements, and different flame-front velocities.

To optimize race fuel in an engine relative to pump gas - you need to change ignition timing, compression, and even porting if you really get deep in it.