OK..my 1996 SL500 is listed as having 315 HP. I heard from a Mercedes "expert" that Mercedes actually measures HP AT THE WHEELS, whereas most manufacturers list HP at the flywheel.

Is the HP spec listed taken at the rear wheels or at the flywheel like everyone else?

 

Your talking net versus gross and the industry standards changed in 1973. Your car and every car since 73 has been listed as RWHP (rear wheel horse power).

 

Every other Mercedes, you mean? I know that this does not apply to domestics for sure. I have a Mustang GT with an advertised 260HP and I KNOW that it is about 12%-15% less than that at the rear wheels if I put it on a dyno.

 

Keep in mind although your GT may be rated at 260RWHP that is for the 'oneoff" car they tested which probably did have 260RWHP but not your mass produced version. Take the ZZ4 block, advertised 350HP at the crank. Well the one I had on the Vette put out 285HP @ 6200 RPM on dyno, however doing the math in reverse to get to the crank I came up with only 310 at the crank.
Never put much stock in Manufacturer's claims

 

No, but that's my point - the GT is rated at 260 at the flywheel. I had never heard of production cars specifications referencing RWHP - why is why this guys comments about the Mercedes being rated at the rear wheels seemed so unusual. Every manufacturer that I've ever heard of rates HP at the flywheel.

 

I'll try to get the exact refrence for you but in America, guessing about mid-1972 HP ratings went from Gross (flywheel) to net (rear end).

 

It's only horse-power at the rear wheels, such as you would obtain from a road dyno, which is of any interest from a performance point of view. The gross power of the engine is considerably more, since it has to drive a bunch of anciliaries like the alternator, power steering and air-conditioner pumps, oil and water pumps, all of which taken together extract their toll. The power consumption of a modern car is much greater than cars of 10 or 20 years ago.

If you add a supercharger, demands on the engine are still greater. In the SL55 AMG, the supercharger needs 91 bhp to run it at maximum power, so you're only ahead if the net contribution from the supercharger is more than this. No wonder the SL55 AMG has such an appetite for unleaded...