Datsun Roadster Forum-311s.org

Did a bit of a dive into horsepower ratings for our cars vs more modern ratings...
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?

The reason why they changed from SAE gross horsepower to SAE net horsepower was because of the evolution of front wheel drive cars with transverse mounted engines. A measured loss in drag due to the differential of a rear wheel drive is on average double that of a front wheel drive car with a transverse mounted engine. So at the time people, magazines and the automotive industry realized that they needed to show horsepower in an SAE net formula to make comparisons between the types of drivetrain that were being produced.
Dave

So the downward progression of ‘real’ performance is:
Gross HP —> Net HP —> Wheel HP —> HP loss since new … —> Wagon Train & Harness?

Guess my poor little R16 didn’t have a chance …

Daryl Smith wrote: Fri Oct 18, 2024 1:15 am
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

The whp figures we see are not far off from your estimations.
A stock R16 dyno'd at 67hp/81tq at the wheels
A hot-rodded R16 made 79hp/95tq at the wheels

Several U20/Solex both freshly rebuilt and with many miles make from 108hp to 115hp at the wheels:
viewtopic.php?f=2&t=29922&hilit=kurt+dyno

Modified U20/Solex combos have made ~140hp at the wheels:
viewtopic.php?t=29300&hilit=brian+dyno+srl

Mine made a 141 hp, 132 # feet of torque at the wheels in 2006. Stock rods, stock pistons. Light crank, and flywheel. Rebello built head, (that has since been reworked for better valve geometry, same cam, different valves that are all the same length, unlike the ones originally in the head.) The bottom end had 60K miles or so on it, back in 2006, the head was fresh. Had small diameter primaries on the headers, 2.25" stepping to 2.5 inch exhaust. I think I had 39mm venturis in the carbs at the time.

Will