You wanna know something about Toluene
Mindful of the evil reputation of octane boosters in general, toluene is a very safe choice because it is one of the main octane boosters used by oil companies in producing ordinary gasoline of all grades. Thus if toluene is indeed harmful to your engine as feared, your engine would have disintegrated long, long ago since ordinary pump gasoline can contain as much as 50% aromatic hydrocarbons.
Toluene is a pure hydrocarbon (C7H
. i.e. it contains only hydrogen and carbon atoms. It belongs to a particular category of hydrocarbons called aromatic hydrocarbons. Complete combustion of toluene yields CO2 and H2O. This fact ensures that the entire emission control system such as the catalyst and oxygen sensor of your car is unaffected. There are no metallic compounds (lead, magnesium etc), no nitro compounds and no oxygen atoms in toluene. It is made up of exactly the same ingredients as ordinary gasoline. In fact it is one of the main ingredients of gasoline.
Toluene has a RON octane rating of 121 and a MON rating of 107, leading to a (R+M)/2 rating of 114. (R+M)/2 is how ordinary fuels are rated in the US. Note that toluene has a sensitivity rating of 121-107=14. This compares favorably with alcohols which have sensitivities in the 20-30 range. The more sensitive a fuel is the more its performance degrades under load. Toluene'* low sensitivity means that it is an excellent fuel for a heavily loaded engine.
Toluene is denser than ordinary gasoline (0.87 g/mL vs. 0.72-0.74) and contains more energy per unit volume. Thus combustion of toluene leads to more energy being liberated and thus more power generated. This is in contrast to oxygenated octane boosters like ethanol or MTBE which contain less energy per unit volume compared to gasoline. The higher heating value of toluene also means that the exhaust gases contain more kinetic energy, which in turn means that there is more energy to drive turbocharger vanes. In practical terms this is experienced as a faster onset of turbo boost.
Chevron'* published composition of 100 octane aviation fuel shows that toluene comprises up to 14% alone and is the predominant aromatic hydrocarbon. Unfortunately composition specifications for automotive gasoline is harder to pin down due to constantly changing requirements.
Chevron'* web site also describes the problems of ethanol being used in gasoline.
MTBE was heavily touted as a clean additive several years ago, and became a key ingredient in reformulated gasoline that is sold in California. But recently new studies arose that showed that MTBE was far more toxic than previously imagined. Organizations such as oxybusters have formed around the country to eliminate the use of MTBE in gasoline and several states, including California have passed new laws to eventually outlaw MTBE.
Q: How much toluene should I use per tank of gas?
A: Octane ratings can be very easily calculated by simple averaging. For example, the tank of an Audi A4 1.8TQ is 15.6 gallons. Filling it with 14.6 gallons of 92 octane and 1 gallon of toluene (114 octane) will yield a fuel mix of:
(14.6 * 92) + (1 * 114) / 15.6 = 93.4
The Audi A4 1.8T is a good example of a car that has very high octane needs if it has been modified to produce more turbo boost. The base compression ratio of this car is a very high 9.5:1 and when an additional 1 bar (14.7 psi) of turbo boost is applied on top of it, the resulting effective compression ratio is way beyond what 92 or 93 octane fuel can ever hope to cope with. Most modified 1.8Ts running without octane enhancement are running with severely retarded ignition timing and boost.
Q: Will toluene damage my engine or other parts of my car?
A: A 5 or 10% increase in the aromatic content of gas will most likely be well within the refining specifications of gasoline defined by ASTM D4814, which specify an aromatic content of between 20% and 45%. What this means is that if the 92 octane gas that you started off with had an aromatic content of say 30% and you increased it by 10% to 40% you would still be left with a mix that meets the industry definition of gasoline. So the above question would amount to: "Will gasoline damage my engine or other parts of my car?"
Even in the unlikely event that the 92 octane gas has a aromatic content of 45% the resulting mix would still be within the bounds of gasoline sold in other countries.
Q: Isn't toluene an extremely toxic substance?
A: The common perception of toluene'* toxicity far exceeds reality. Fortunately there is an ample body of information available that specifically addresses this question. Toluene is more toxic than gasoline but it is certainly not agent orange or cyanide.
US Environmental Protection Agency Chemical Summary
US Agency for Toxic Substances and Disease Registry (ATSDR)
National priority list of toxic substances
Note that the ATSDR also rates gasoline as a hazardous substance.
Mobil'* spec sheet for toluene even goes as far as saying that "Based on available toxicological information, it has been determined that this product poses no significant health risk when used and handled properly."
Q: Isn't toluene an active ingredient of TNT (trinitrotoluene) and is thus deadly?
A: In the same way that cotton wool is the base ingredient of nitrocellulose (guncotton) which in turn is the main ingredient in modern smokeless gunpowder. Using this reasoning one could conclude that cotton wool is a deadly substance. This question reflects a poor understanding of basic chemistry but unfortunately it has been asked often enough.
Q: How much does toluene cost, and where can I buy some?
A: $10/gallon in a one gallon can at a hardware store, about $6/gallon in a 5 gallon can from a chemical supply or paint store, or $3/gallon in a 55 gallon drum from a chemical supply warehouse.
Q: Can I just dump in 100% toluene into the tank like the F1 racers? vroom vroom vroom
A: First of all, the F1 racers did not use 100% toluene, but 84%. The other 16% in their brew is n-heptane, which has an octane rating of zero. The reason for this strange combination is because the F1 rocket fuel was limited to the rules to being of 102 RON octane. The n-heptane is "filler" to make the fuel comply with the rules.
Because toluene is such an effective anti knock fuel it also means that it is more difficult to ignite at low temperatures. The Formula 1 cars that ran on 84% toluene needed to have hot radiator air diverted to heat its fuel tank to 70C to assist its vaporization. Thus too strong a concentration of toluene will lead to poor cold start and running characteristics. I recommend that the concentration of toluene used to not exceed what the engine is capable of utilizing. i.e. Experiment with small increases in concentration until you can no longer detect an improvement.
Q: Why not simply use racing gasoline or aviation fuel?
A1: Most types of aviation fuel have very high lead content, which would rule out cars equipped with catalytic converters. Most piston engined aircraft burn leaded fuel. Also aviation fuel has a very different hydrocarbon mix to optimize volatility properties at high altitude.
A2: Racing gasoline could be a much more convenient way to run high octane fuel compared to having to constantly mix in toluene with each fill up. There are, however a few caveats:
You don't know for sure if you are really getting what is being advertised. You should find out if the fuel inspectors verify the actual octane of the racing gasoline in addition to ordinary gasoline. If you paid $3/gallon and only got 94 or 95 octane instead of 100 octane you may conclude erroneously that your car does not benefit from octane boosting.
You don't know what octane boosters are used in the racing gasoline. The worst case scenario is buying leaded racing gasoline without knowing it. Unleaded racing gasoline may still contain damaging octane boosters like MMT or methanol. A very high alcohol content will lead to fuel line erosion, accelerated fuel pump wear, very poor fuel economy and possibly lower performance, as alcohols have a less impressive MON rating than aromatics.
It takes smaller quantities of toluene to achieve the same octane boost compared to 100 octane racing gas. I have not seen unleaded racing gas for sale that exceeds the octane rating of toluene.
Since toluene is not officially sold as a fuel, gas taxes do not apply. Also racing gasoline tend to have higher markups being of interest to the performance minded enthusiast and thus is very likely to be more expensive to buy and use long term than toluene, which is typically used in more mundane applications like paint thinner.
Q: Ok, what is the catch?
A: It should be mentioned that in the US, efforts are underway to reduce the aromatic content of gasolines in general as a higher aromatic content leads to higher benzene emissions. Benzene is an extremely toxic substance. However it should also be noted that the proportions that is being discussed in this FAQ is relatively small and in the grand scheme of things is probably insignificant. Moreover, the industrial standard for defining gasoline composition allows plenty of leeway in aromatic content and the proportions present in US gas is already lower than most other countries. I therefore feel that the information provided here is useful to a performance minded car enthusiast while not being significantly detrimental to the environment.