The problem with a road map, is you CANNOT do the job properly on some cars.

If you road map a car, all you can do is end up a safety margin away from detonation.

Now on a turbo car, typically that will be the optimum for power, but on many N/A cars you will see peak torque long before detonation occurs, and potentially it will then drop off as you further increase the ignition timing before det occurs too.

So consequently its impossible to map for peak torque/power without a mechanism for accurately measuring the power output through the rev range.

The same is true for mixture, there is not a magic value that works to give you the best power in all circumstances, sure there is a theoritical max, but in practice often slightly richer or slightly leaner than that can be the optimum for certain engines.
This also cannot be got through road mapping as you cant measure accurately enough what the power output is to know which is the optimum.

Again, on a turbo car, not really an issue as the final value after mapping tends to be dictated more by safety than by what would give every last BHP.


With all that said, I personally believe that you cannot achieve proper drivability on a set of rollers, the last thing I always do when road mapping a car is to ask the person in question to drive it how they normally drive it, to make absolutely sure that it is perfectly mannered for their use of the car, Im not convinced you can do that on the rollers.


So IMHO the only way to get the optimum results, especially if talking about a variety of cars, is a combination of the two.