Rolling Road Shootouts

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here is some fascination with knowing what the power output of your car is, especially if you have made engine modifications. Check out magazines such as Fast Ford, Max Power, and similar, and you’ll often see “Rolling Road Shootout” articles, where a club of car enthusiasts take their pride and joy to a test centre (and often a test track) to establish the true output of the engine. On another note, the use of a rolling road is also essential to fine-tune some engine modifications, such as the Unichip.

A rolling road is a means of measuring the power output of the wheels through the entire engine speed range. Most tests are conducted by moving the engine up through the gears to fourth, then testing it in that gear. A rolling road printout can be used to conclude an argument where the owner claims that his car has a maximum power output far in excess of the standard engine.

I always take “Owner Estimates” with a huge pinch of salt, especially when it’s Kev’s Nova SR1300 with an induction kit and big bore exhaust. At the time of writing, Kermit has been chipped, has a PowerFlow exhaust and a high performance air filter, so I could conceivably estimate that the engine is pushing out 85 PS rather than the original 60 PS. That’s an owners’ estimate. I’ve read reports from Ka owners with an induction kit, a fancy exhaust, and a superchip, claiming that the donk produces almost 100 PS.

These Rolling Road Shootouts invariably show up the owners’ estimates as being lies, or at the least, overly optimistic estimates. I’ve lost count of the number of owners with claims of 200 PS from their Escort RS Turbo, only to discover that it is only pushing out 145 PS, with their claims that “it did it last time.” Sure!

Rolling road tests can be quite demanding on certain aspects of the car. The tester will nail it at low engine speeds and keep it nailed right the way through the rev range to the limiter. If your car has a nitrous system, it is important to give proper instruction to the tester: you don’t want to be using NOS at very low engine speeds, because if you do, internal engine components will be leaving the engine via unconventional exit routes.

Although rolling roads use large fans to direct a stream of air at the radiator, these are not as effective as driving the car through the air. It is important that the cooling system is working efficiently, otherwise you may encounter overheating difficulties. The other disadvantage of the using fans is that the airflow does not reach other parts of the car that, ordinarily, do not overheat. A favourite is the exhaust mountings at the back box, which can melt - thus rendering your car immobile until you fit new ones!