Can Adding Octane Boost Raise 91 Octane Gas To 94?

A reader asks: My car is now tuned for 94 octane gas. My local stations only provide a premium gas at 91 octane. Can I use AMSOIL Octane Boost to bring the 91 octane gas up to 94?

Our answer: We would not recommend attempting to use an octane boost to bring 91-octane gasoline up to 94-octane. With your engine tuned for 94-octane, damage from engine knock is a real concern if the fuel is not up to the task.

Therefore, the smartest option would be to re-tune your car for the locally-available 91-octane fuel.

Aren’t Octane Boosts Designed To Raise Gasoline Octane Levels?

Yes, but there is more to the story. For example, AMSOIL suggests that their Dominator Octane Boost product raises octane by “up to 4-points”.

But there are two reasons as to why using an octane boost additive may not bring the octane from 91 to 94.

First, gasoline quality can be very inconsistent. There’s no way of knowing that one is really starting with 91-octane. The actual octane at the pump may not be as advertised.

The second important factor is that there is a law of diminishing returns with octane boost products. The higher the octane starting point, the fewer octane numbers gained. Therefore, an octane boost will deliver a greater octane-number increase when 87 is the starting octane. Adding a boost additive to 91-octane gasoline may only yield a one or two octane-number gain.

It’s simply not possible to project whether an octane boost product is actually taking this fuel up to the desired 94-octane goal.

In our opinion, this particular strategy of trying to drag a 91-octane fuel up to 94 with an additive is based on hope and assumptions. The risk of pre-ignition issues far outweighs the benefit of tuning the car for an octane level that isn’t reliably attainable.

More About The Uses Of Octane Boost

We asked AMSOIL Technical Services about the correct applications for their Octane Boost product. They don’t recommend this product for modern, stock automotive applications. In fact, AMSOIL Octane Boost is not compatible with catalytic converters. However, it is compatible with oxygen sensors. This octane additive was created for street-rods, classic cars, off-road and race track use.

AMSOIL tells us that there are three suitable approaches for using this product.

Boosting regular or mid-grade gasoline delivers the largest octane number increase. Again, when starting from higher octane levels, octane boost will offer less actual octane-number gains.

Another main use is starting with fuel which has the correct octane number for the application. Using this octane boost can provide extra insurance against engine knock and optimize performance.

Thirdly, AMSOIL Octane Boost can also be used as a lead supplement for classic cars.

Related: Octane Boost Myths And Facts