[Discussion] 'Magic Formula' for 'fuel units' editing?

Hi all,
A bit of a two part question here:

1) Which values in a physics file affect the amount of (Magic Data) 'fuel units' needed per lap?
Obviously the rev limit does - higher = more fuel, lower = less fuel - and I'm assuming some of the drag values do as well, but are there any others, as far as people know?

2) Has anybody got a formula they use to adjust these 'fuel units' based on the changes to their physics file?
For example, if rev limit was the only thing to affect the amount of these 'fuel units' needed:

nFuel=vFuel*(nRPM/vRPM)
Where, 'nFuel' = New Value, 'vFuel' = Vanilla Value, 'nRPM' = New RPM & 'vRPM' = Vanilla RPM

For Melbourne 2001, for example, where the original value is 'Fuel=8260' and if my RPM limit was 15,000:

8260*(15000/16600)=7463

I used that formula for my previous mod and, though the results were close enough, it wasn't particularly perfect.
Is there a better method, or is 'getting close and then just tweaking it' the best way of going about it.

If a 'magic bullet' formula exists, I'd be able to build a tool that can calculate this, and could also do something so that people can update a list of fuel values online.

Cheers,
Doug.

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F1 Graphics Swapper --- Lensdump - Renders and Screenshots --- GP4 Performance Generator

not wanting to throw spanners in works but using the same magic data but changing the physics file used and with different rev limit changes it all as well.
good luck coming up with a formula as i have been tying without decent success for ages
regards to all