Monday, October 08, 2007

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.

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