Unfortunately there doesn't appear to be any way to convert Wheel HP to Crank HP because of all the drivetrain variables. Front wheel drive cars have less, rear wheel drive next and the quattro probably the most loss. And of course, what condition is the drivetain in - new parts vs worn parts will have different loss values.
Figures I see are commonly 15% (average) with the range being 7% - 30%.
On an Audi quattro system I would probably use 20% as a minimum conversion number from wheel hp (on the dyno) to crank hp.
So if you have 150 wheel HP, that would be 180 crank HP, such as the stock V6 in A4's.
If you find a definitive source, please post it to the list - that would be a first for any bulletin board I have ever seen.
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