Race fuel

stangmx13

not Stan
I’m on my 3rd built engine.

The first I bought used from someone I trusted. I ran pump gas in it cuz it was “fine”. Turns out it had more time on it than I inferred and it blew. It melted holes in 2 pistons and was scrapped. A total loss.

I bought a used motor from a builder, which he built to MA regs, and it performed flawlessly on safe race gas. When he rebuilt it after a season, he felt bad refreshing it cuz it showed no wear. I’ll run it all this year.

Building engines is worse than suspension. Sometime you pay a lot for crap. Sometimes you get lucky with someone that knows their shit. Unfortunately, you often have to be the test dummy to learn this.
 

Holeshot

Super Moderator
Staff member
Berto, is your "refresh" seriously replacing all 16 valves and/or doing the seats every year or 2? Shims, rings, etc and that's a hell of a maintenance bill. Yikes!

Full rebuild is about $1K in parts, then labor. I can check and see...or just have Dorn or Will Reply here. IMO, a stock engine can get on the box on an AFM grid, well ridden at most of our tracks.

If your race budget is to include MR12 ($29+ per gallon), then hopefully your budget includes a SS motor build. Using MR12, or anything other than pump gas, you won’t get a benefit from it with a stock motor.

And if your budget includes MR12 and a SS build, you should also include a motor refresh every year. It’s a good rule of thumb.

You guys putting new fuel pumps in too?
 

rjbrittain11

923 Track Junkie
You guys putting new fuel pumps in too?

Get outta here with that nonsense! :x

In all seriousness, I know that Will has taken them apart at the end of each season and checked them over and cleaned them. I had to replace one a couple of years ago and I think the pump on my B-Bike is going bad...but haven't done much to diagnose it yet.
 

DonTom

Well-known member
My understanding is that octane raises the temperature of where the gasoline will explode. This is how it prevents pre-ignition or pinging.

Does this also mean if octane is way too high for your engine it will run very poorly because the gas may not explode as well?

-Don- Reno, NV
 

Holeshot

Super Moderator
Staff member
Easiest answer: yes. Theoretically, you want to run the lowest octane possible without detonation.
 

EastBayDave

- Kawasaki Fanatic -
That's the good stuff!
been running their stuff of various octane numbers & additives since 1978'. It's really good stuff! AND being in town here, it's convenient to fill my containers before leaving for the track. :teeth :thumbup
 

scratchpad

Well-known member
Cool, good info. Sounds like the takeaway is keep using pump gas until someone builds an engine for you and tells you what gas to use.


One thing that ive noticed with pump gas in the last 7+ years why i try NOT to put it in my race bike. It clogs up all my dirt bike carbs within a month or two of sitting and i have to pull the carbs and clean them. Imagine what happens to your injectors. Do you clean them, replace them or send them off to get cleaned and flow tested after every season?

My bike is mapped for MGP, mr12 and T4. I have maps for other fuels as well including pump but those are what i ran last year. The only time i run MR12 is for racing. Sometimes i dont run it, like at the hotter events i may not run it as its temperature sensitive just like alot of AFM'ers. :teeth Before i leave the track it is removed and a safe fuel (T4) is put in. Zoran at TWF opened up my motor this off season, after this one season on a mild build, and it was clean.

MGP and T4 on the dyno (for my bike) are very similar to pump gas but have a much higher price tag and different tune. I do not consider them "race" fuels but they are a safer alternative to pump.
 

puckles

Well-known member
The primary benefit of race gas is knock resistance. This in turn allows the engine to run a higher compression ratio which increases it's thermal efficiency. More advanced ignition timing is also possible. Additionally, race gas is a more consistent product as mentioned above and also includes other additives that help lubricate the fuel system etc.

Basically, race gas is a variable that can help a bleeding edge tune in the same way that stiffer valve springs or intake porting can help. In fact, higher octane race fuel actually has a lower energy density than pump gas. It is the increase in thermal efficiency of the otto cycle that allows the engine to make more power when tuned appropriately.
 

jtiisto

Well-known member
The primary benefit of race gas is knock resistance.... higher octane race fuel

There's high octane pump gas that provides all those benefits. Going to specialized race gas has additional benefits, mostly through oxygenation.

You are spot on for primary benefit of high octane gas. However, going from high octane pump gas to actual race gas as other benefits.
 
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