So you've seen them all - Schaffer, STP, STR, Motor Up, and everything else in between. They cost between $19 and $30 depending on how much "gains" these giants seem to flaunt.

Fuel additives come in all shapes and sizes, and work in many ways, such as increasing the octane rating of petrol, as corrosion inhibitors or as lubricators. On the most part, they generally allow you to increase the compression ratio of your engine's combustion cycle. Plainly put, one is able to mix a greater amount of air per 1 part of fuel, thus using less petrol for a specific amount of power.

It doesn't take an idiot to figure out, then, that this leads to "greater efficiency and power", as most of these companies would have you believe. I've never used fuel additives in my entire driving career, but here I am, four years later, and with two bottles of "FP Plus" (I'm going to refer to it as "FP" from now on) in my hands™

Claims, gains and blames

Our purchased bottles of FP claim to do exactly what most of the others out there replicate - increased horsepower, improved mileage and emissions, and believe it or not, reduced maintenance costs with consistent usage.

This particular brand with a 40-year old backing claims to "lubricant the fuel pump, fuels injectors and the upper cylinder area," or so it says on the bottle. Pardon the bad English, but since we're not here to spot grammatical errors, we then poured two fluid ounces of the stuff, as directed, into one full tank of petrol per car, or 45-litres, or 10-gallons™

Two cars were used for the trial - a high mileage, 2004 Hyundai Getz 1.3-litre automatic with a 40-litre fuel tank and 142,800km on the odometer, and a recently acquired, 2008 Chevrolet Optra 1.6-litre manual, equipped with a CNG tank that was barely pushing 4000km - a brand new set of wheels by all means.

These cars were driven along a fixed route of roads, both highway and city, at differing times. They were then spaced out in order to land them in a wide variety of traffic situations, and were sporadically refueled the minute their "low fuel" indicators were illuminated. We tested these cars on three tanks of un-drugged petrol, and a further three full tanks, all of which were mixed with FP.

Results

While no performance gains were felt by our relatively sensitive "butt dynos," the 2004 Hyundai appeared to be the one that benefited most from the fuel additive, clocking a record 507km on a single tank of petrol. Things with the Optra, sadly, didn't spell much of a difference though. We clocked a very close 529, and 530km on the trip meter for both non-FPed and FPed tanks of petrol.

We know what you're thinking - fuel additives tend to benefit cars with higher mileage, dirtier engines, a statement that seems to hold true with our single-product test this time around. Do keep yourselves posted as we'll be testing even more products to verify the consistency of our results in order to tell you if fuel additives really work. For now, the results are a close call, and seem to suggest mild improvements with cars that have been through the rough.