Before 1972 engines were rated at "Gross Horsepower" and after 1972 they were rated as "Net Horsepower"
Gross Horsepower means no accessories - no alternator, no air filter, no water pump, no fan, no exhaust system...bare engine, nothing that would draw any power.
Net Horsepower means "as it will run in the intended vehicle" - includes all accessories and a full exhaust system - Alternator, air filter, water pump, fan, power steering, air conditioning....whatever will be on that vehicle.
A bit of a search will bring up examples which show a drop from Gross to Net of anywhere from 8% to 24%.
Assumed the 8% drop would be for something like the roadster with just adding the alternator, waterpump, fan, air filter, and exhaust system.
Wheel dynos typically show 15 - 20% reduction from Net ratings....
Where does that leave us?
R16
Gross HP @ 96
Net HP (-8%) @ ~88
Wheel HP (-15% Net) @ ~75
SU U20
Gross HP @ 135
Net HP (-8%) @ 124
Wheel HP (-15% Net) @ ~105
Solex U20
Gross HP @150
Net HP (-8%) @ 138
Wheel HP (-15% Net) @ ~117
This is just an approximation, Net could be closer to 10% down, and wheel could be 18-20% down.
Someone on here once had 79 wheel HP on an R16...very healthy R16, or a happy dyno?
Before 311s.org on the mailing list I remember comments on even the solex U20s barely making 100 wheel HP. That was a long time ago, and I think most are doing better than that now.
So, keep in mind when you get your engine dynoed, is that Gross or Net HP?
