Fuel Tips: Adding Additives

Why buy race gas when you can mix up your own high-octane fuel with an additive? These potions—auto parts store staples since the dawn of time—promise higher octane ratings, along with a thinner waist and whiter teeth. How can you lose? Well, not all additives are created equal–and the same can be said for street fuels mixed with said additives, explains Zachary Santner, technical specialist with Sunoco Race Fuels.

Octane Point: An octane point equals one-tenth of an octane number. When an additive promises to boost your fuel by “up to 10 octane points,” it means raising the octane from, say, 92 to 93–if you’re lucky.

Meet MMT: Many over-the-counter fuel additives contain MMT, short for methylcyclopentadienyl manganese tricarbonyl, which is very effective at raising octane. “We have done testing on fuel additives that contain MMT and they do raise the octane,” says Santner. But, he adds, there are a few caveats.

You Get What You Pay For: Octane additives without MMT aren’t nearly as effective as additives with MMT. The lower-cost additives contain much less of the ingredient–or maybe even none of it. There’s a big difference between an $8 “octane booster” and a $35 can of “race fuel concentrate.” The safety data sheets will reveal exactly what’s inside the bottle.

MMT Caveats: Sunlight is MMT’s enemy, Santner continues. Sunlight will oxidize MMT, turning it brown and destroying its octane-boosting effect. MMT, in larger doses, will also leave orange deposits in the combustion chamber. “Using high-MMT fuel in an everyday vehicle can cause less miles between spark plug fouling,” he adds.

Strong Foundation: When mixing up your own “race fuel,” you’re still limited by the base product–the pump gas that’s engineered to be used right away while meeting a price point. Unlike street gas, however, race fuels aren’t constantly reblended depending on the season. Plus, when properly stored, they can last at least a year or two.

Cleaner, Too: “Race fuels are also much cleaner than pump gas and even aviation gas,” Santner notes. “Race fuel will keep carburetors and injectors clean, unlike pump gas where varnish and gum will build up over time.”

Comments

Brett_Murphy GRM+ Memberand MegaDork
3/25/20 9:43 a.m.

What was that stuff you tested a while back that you were surprised worked as well as it did? It may not have been an octane booster, but it did produce results on the dyno if I recall. Maybe it was in a green bottle?

chaparral GRM+ Memberand Dork
3/25/20 9:54 a.m.

That was EFS Combust, but the last time GRM did a big fuels test methanol won resoundingly even without forced induction or high compression.

Paul_VR6 Dork
3/25/20 9:58 a.m.

I have always liked the Torco booster, its one of the few that has actually hit what 98 pump and 103 race gas can do. Gets spendy to use all the time though.

APEowner GRM+ Memberand Dork
3/25/20 10:23 a.m.

Paul_VR6 said:
I have always liked the Torco booster, its one of the few that has actually hit what 98 pump and 103 race gas can do. Gets spendy to use all the time though.

I dynoed my 640HP big block Camaro engine with both 103 race gas and pump gas with the Torco booster and I was able to run the same timing with both fuels. Interestingly it liked a little richer mixture with the pump gas Torco fuel.

Claude Taylor
3/25/20 1:00 p.m.

Has anyone heard of adding Mothballs to the fuel. sounds weird but i was told it was an old school trick.

ChrisLS8 Reader
3/25/20 1:10 p.m.

As far as fuel cleaners and whatnot, the testing on BITOG says that you want to find ones that contain PEA

Floating Doc GRM+ Memberand UltraDork
3/25/20 1:29 p.m.

I accidentally did a three year running experiment on fuel quality, when I bought a 2000 Tacoma with a TRD supercharger. The official line from Toyota was that the blower could be dropped on the stock engine, and run with zero modifications, and that's the way I bought it. It was a known problem, and there were people working on fixes, but I didn't have the money to modify the truck further.

Toyota subsequently admitted to the problem, and added a seventh injector to the intake with the new packages, but by then I had sold it.

The only time it would run without a high gear, low RPM ping was when it had Shell premium in the tank, and I tried them all.

I never tried any of the high value octane boosters or additives, but the stuff from the FLAPS all was pretty ineffective. I would still dump a bottle in the tank if I had to buy another brand of premium fuel, but honestly don't know if it had any effect.

I wish I would have known more about additives.

jerel77494 New Reader
11/23/21 1:23 p.m.

A friend of mine had a 1275 Midget set up for F Production with 13:1 compression ratio. The guy who built the motor did it right. Race gas worked fine, but he insisted octane booster was enough. We burned pistons every weekend and he ran it so rich trying to make it live, if he stalled it, it wouldn't restart.