Octane Boosters and the Truth Behind Them

By Drew Shielly

Octane numbers are something we see every day and probably take for granted. We all know this is a rating means to measure a fuels resistance to pre-ignition, but how does that apply in a practical sense. Let's first assume you have a car that runs well on 91 octane. What could you gain by altering the fuel you fill up with. By going down to 87 octane you will achieve better mileage, but could risk detonation depending on your cars engine. By going up to 93 octane you might allow your car to advance the timing gaining horsepower. Due to lower BTUs per gallon you will give up a few miles per gallon. So right off you can see that it is a balancing act.

Looking closer at this, you notice that the extra horsepower comes from the ability of the car to advance timing and not the fuel itself. Higher octane fuel has less BTUs, but still nets power due to the timing advance and higher boost it can achieve. In modern vehicles with knock sensors the timing is constantly varied to achieve the best balance between performance and economy. Because this adjustment takes time, simply switch to higher octane at the track is not good enough. The fuel needs to be run in advance to allow the car to compensate for it. So using 91 all he time and then going to the track and filling up with 95 is not going to help your track times. You will have a faster car on the ride home though.

The other end of the spectrum is less octane. The down side here is the risk or pre-ignition and high EGTS. Both of these can lead to melted or bend pistons. Valves and the head is also placed in risk. If you have a modern vehicle it will detect this and retard timing to prevent damage. This timing modification is easy to detect with an OBDII scanner and it an easy to diagnose too fuel with too little octane.

Because of the above reasons, a lot of people turn to the boosters as a way of having both good fuel commonly and good performance at the track. The problem with them is most do not work. If you do find one what works, adding it to your tank a day before you go to the track can be beneficial. Despite the benefit, use boosters sparingly as most rely on MMT as a means of boosting the octane. Excessive MMT can cause problems with sensors, injectors, or even the exhaust.

By now you are probably confused again by what all of this means. To sum it up, if your car has no changes to compression, raised RPM limiter, or lots of boost, you should probably use whatever fuel the dealer recommends. If you have a race built motor, stick to a race fuel that meets the need of your engine. If you have a lightly tuned engine and enjoy the occasional track day, throw in a bottle of octane booster the day before and call it a day. Do not rely on boosters all of the time.

Fuel Additives And Effects On Fuel

By Drew Shielly

We tested a common additive, Torco, to see if it could add performance to your vehicle or increase mileage. Before discussing this product, lets first address key differences between a racing fuel and pump fuel. The one everyone thinks of is octane. Under the US octane rating system AKI (Anti-Knock Index) pump fuel is graded as (RON+MON)/2. Meaning if a fuel had a RON (Research Octane Number) of 96, and a MON ( Motor Octane Number) of 90 its AKI would be 93. Race fuels can be graded on any of the standards AKI, MON, RON. So what is octane and why is it important for performance? Octane is what gives gasoline its ability to resist pre-ignition. As displacement, compression, boost, RPM, go up it becomes harder to keep the fuel mixture from igniting prematurely.

If under load or high heat, you experience knock with 87 octane, stepping up to 91 octane is logical step for both performance and longevity. If you experience no knock or timing pull at 91 there is no benefit to you stepping up to 93 or higher. Raising the octane further would only serve to decrease mileage. The additives that raise octane have less energy than the base fuel, effectively lowering the BTUs of the fuel. That is you will make the most power and have the best fuel economy with the lowest octane that is capable of preventing knock under your specific conditions.

Another major distinction between race and pump fuel is RVP (Reid Vapor Pressure). The easiest, overly simplified, way to think of RVP is as a system to rate the tendency for the fuel to want to evaporate. The lower the number the less tendency the fuel has to evaporate. In general racing fuels have a much lower RVP than would be found in pump fuel due to the poor starting characteristics that come along with low RVP fuels.

Burn -speed is another major difference. Race fuels are blended towards a specific application. The desired burn rate in a Kart at 16,000 RPM is very different than the target burn rate of something like a big-block V8 at 9,000 RPM. Too fast of a burn and you may experience less than optimum power. Too slow and your valves may be opening before maximum pressure is reached.

Without going into further detail such as specific gravity, dielectric constant, and numerous other variables, you should now have a basic understanding that there is a lot more to fuel than just octane. Altering these variables randomly can serve to be counter productive. For the purpose of objectivity lets look at one of the most common indicators. Octane.

Torco advertises that it can raise 93 pump to 107 when used in the highest concentrations. Tested in the highest recommended mixture we saw an AKI of ~99 though a secondary testing method. 8 full points from 107 if you assume Torco was implying 107 AKI and not 107 RON. This would mean it was raising 97RON to 107 RON. If you standardize the results on AKI you will see that 107RON is actually fairly close to 99AKI. This is much better than you could hope for with the more common additives such as with xylene or Tulene. If you assume $3.00 per gallon of 93AKI pump and $17.50 for a can of the Accelerator that works out to $6.50 a gallon. With race fuel such as VP and Sunoco in the $5.00 neighborhood this does not make since. On the other end if the spectrum, you could mix 1 can with 20 gallons. In areas where only 91AKI is available, this makes a little more sense at ~$3.80 per gallon to end up with 93AKI.

So an additives replace race fuel? No. Do they have limited applications? Absolutely. If you have a legitimate need for slightly more octane this is a great way to go. If you are tuning a highly modified engine for maximum power stick to race fuels.