Now that we have testing equipment I like to test racers’ fuel’s RVP while we’re hooking up the sled/ engine to the dyno. I’ve caught several samples with no or low RVP, meaning we must have the engine very hot while tuning on the dyno to ensure adequate vaporization. No cool engine tuning can be done with stale fuel, even with excellent vaporizing carbs like properly sized Lectrons. Those “light” or “front” ends of the fuel are critical in ensuring good fuel volatitlity.
Heat and agitation cause the light ends to “boil off”, or escape and build pressure in a sealed vessel. During the heating only phase of the RVP test, fresh Sunoco Maximal will build about 3psi in the “bomb”. Then, the agitation phase of the RVP tests is removing the bomb from the water bath, inverting it which allows the heated gasoline to gurgle into the vapor chamber. Then, the bomb is inverted again so the fuel gurgles back into the small fuel sample container. This agitation causes more light ends to boil off, and raises the pressure by another 2psi (total 5 psi). If we unscrew the sample chamber from the bomb (it’s sealed with an Oring) we get a nice whoosh and about half of the light ends are lost to the atmosphere. Then if we take that same sample, reconnect it to the bomb and test it again the RVP will only register about half–2.5psi or therabouts! Let that 2.5psi escape and reheat and agitate the sample again, and now we’re down to 1 to 1.5 psi. I consider that dead, lawnmower gas (dead race gas becomes excellent octane booster for hot trail sleds when mixed with pump gas) It’s just like shaking up a part full bottle of Pepsi Cola and releasing the CO2 by cracking the bottle cap. You can only do that a few times before it’s flat and undrinkable.
A RVP test is very much like trailering a partially full sealed can of formerly fresh race gas to a grass race in August in a black trailer. You get to the track, open the can and kawoosh goes most of the good smelling light ends and your fuel is half dead. Because of the buildup of pressure some of the light ends remain dissolved in the fuel. But if you reseal the can and drive home again, if you open the cap you don’t get much of a woosh. But what about the fuel that’s in the sled’s fuel tank? There’s no pressure seal there, and I would submit that whatever fuel is in the tank is DOA (dead on arrival).
Typical testing results from sealed 5 gallon “pails” of race gas show RVP about 1psi lower than published by the refiner. I suspect that the lower pressure is the result of the severe agitation of the fuel when the pail is transfilled from a larger container by the dealer. Sunoco tells me that they only sell race fuel to distributors in bulk–railcars and trailers only. They fill no drums or small containers themselves!
What’s a racer to do to keep fuel fresh while transporting? First, have no fuel in the sled’s tank (or carbs for that matter). And only transport FULL cans or jugs of fuel to minimize headspace that allows the escaping of the light ends. Small drums of race fuel (ie: 30 gallon size) can be used for transportation even for small quantities of fuel as long as 6 psi of nitrogen head pressure (with one of Carl McQuillen’s N2 bung systems) is used to prevent loss of light ends and to prevent moisture contamination from humid air and to dispense the fuel while still under pressure. Also, military-style 5 gallon “jerry cans” appear to have the same bung threads as race fuel drums, and could be fitted with a nitrogen system for storage and transporting using a small 20 or 40 cu. ft. N2 cylinder.
When it comes to gassing up your high dollar race sled, those light ends are your friend. The refiners spend huge bucks putting those light ends in the fuel to make it volatile. Handling/ transporting/ storing the fuel in a cavalier manner can cost you horsepower and engines.