By Rob Hosking – If you are a racer, you’ve probably had to make the decision of what fuel to run. Depending on your class you may have a few options, but what makes the most sense from a performance, and most importantly, a financial standpoint.
We’ll start from the top.
Pump gas. 87-94 Octane
For most classes, pump gas is adequate. Its cheap, convenient to buy, and you can only buy what you need.
It lacks a number of things from a performance standpoint. Its fairly volatile, because of its intended use in street cars with low compression there is little chance of preignition, but it has a hard time not preigniting when over timed or overheated. It is inconsistent because of (to name a few) Water content of the in ground tank, when the tank was refilled, when the tank was last flushed, and on what date is was made.
Even though there is some dispute over this, there is winter and summer mixes of pump gas. Winter gas is reformulated to ignite easier because of the lower temps. Depending on how busy your gas station is, you could have winter gas in the tanks come springtime and the first few races of the year.
Another real problem with pump gas, is the blending agents used in all pump gas, and the alcohol content used at some stations, namely Petro Canada and Esso.
In your street car you have a sealed evaporative emissions system, so no additives or alcohols can evaporate, in your race car that vents to open air, you are losing most of your octane throughout the week. The problem is with alcohol blended fuel, if they have used the alcohol to increase the octane 2 or 3 points, and most of it evaporates during the week, what octane is your fuel at come race day?
“AV” Gas. Generally 100 octane
Airplane fuel should be used in airplanes, and that’s about it. Almost everyone i know who uses av gas is constantly chasing jets and fuel related problems. This stems from the fact that the fuel and additives package is formulated for high altitude use. It is extremely humid above the ground, that’s why there are clouds up there, from Wikipedia: a cloud is a visible mass of liquid droplets or frozen crystals made of water or various chemicals suspended in the atmosphere above the surface of a planetary body.
So the packages are developed with very low burn rates because of the lack of oxygen (engine needs more time to burn the fuel), medium volatility because of the low effective compression up there, and very little top end lubricants because of the moistness of the air. Av gas is a reasonable alternative to some racers, but not if you run manifolds. AV gas tends to continue to burn as it exits the exhaust port, and does a awesome job of melting off plug boots and turning manifolds red.
Its difficult to explain fully in a reasonable sized paragraph, but av gas burns slow, and cool. It is not an effective “power adder” it will stave of SOME preigniton, but is not a fuel for serious competition. And because of little additives, and no top end lube, the only way to use is “properly” is to add 1/4 pint per 5 gallons of non synthetic 2 stroke oil, 1; to get some lube for your top rings 2; to add some color and get a read on your plugs.
On a side note it work really well in (racing) snowmobiles during the winter, as 2 stokes benefit from the slow burn rate, the air is cold and moist like high altitude, low heat created by the slow burn (keeps pistons cool), and already have the 2 stroke oil in the mix anyways.
Conventional race fuel. 95 to 114 leaded or unleaded.
“Real” race fuel is not made for driving to Zellers, or delivering supplies to the Arctic circle.
The “myth” is that race fuel doesn’t add any more power, so why run it? That myth is true, and false. If you run a 9 to 1 engine and don’t change anything, it will make very little difference. But if you jet, adjust the mixture on the carb, recurve the distributor and retime the engine, there will be a definite increase in power. With race fuel you have the CAPACITY to make more power. Race fuel is blended to prevent preignition, burn hotter, run the engine cooler, cool the pistons rings and exhaust valves, and it smells wicked cool.
Because of the high octane preignition is rare, and because of this you can add more total timing and be more aggressive with the timing curve. Most people add timing until the performance falls off, and back it off a bit. The problem is with any other fuel than race fuel, the performance is falling off because of preignition, and the piston being forced down before it gets to top dead center. Even if you back it off 3 degrees, there is a very good chance there is still detonation going on and you are damaging something. When you time an engine with race fuel, you generally reach the limitations of the combustion chamber design before you get into engine killing detonation. There is a large safety window with race fuel you don’t get with other fuels. You may be off a jet size or two, or the timing isn’t quite right, but the band aid of race fuel tends to leave some wiggle room.
That’s not saying its impossible to burn a piston down with race fuel, you just have to be really bad at tuning engines.
Nowadays leaded fuel really isn’t that important compared to what is used to be. The main function of the lead was to cool the exhaust valves when unleaded seats were common. Unless you are using old heads that have never had seats, or are using copious amounts of nitrous, the difference between leaded and unleaded boils down on what you can get locally.
Fuel additives and oxygenated fuel and special blends;
I firstly believe that ALL tracks should own a fuel sniffer. Go Kart tracks have them, why shouldn’t they? There are some nasty additives out there, and just breathing them or mixing them is dangerous, let alone in the event of a crash and the 30% easier to ignite science project gets on manifolds etc. I don’t use them, because i don’t like what they do inside an engine, and i generally try to follow rules and guidelines set out by racetracks.
Special blends are are 2 way street, they are incredibly expensive, but defiantly add more power than anything legal. VP and ELF make some awesome fuel, but bring the deed to your house. Applications included Late model sportsman blends, crate engine blends, 2 barrel blends etc.
Oxygenated fuel IE VP MS 109, is for the guy that wants that very cutting edge or that last 10th. Its a prick to tune and get setup, but when you hit it, its more power than anything available. It has extra oxygen carrying additives and has the potential to make 8 to 10% HP over regular race fuel. And on a 300 HP engine, that’s alot.
If you are racing circle track, there are very few situations where you would need more than 105 octane. 105 will Carry up to 13 to 1 compression, and with the rules packages these days, we wont see that ever again.
Questions? Comments? Hoskingengines@gmail.com Ontario Oval and I would like to answer questions from you in an upcoming column, drop me a line and get your engine question answered here.