Is the 500HP (1998 carbed) engine rated at 500 horsepower? I've been told it's rated at 470? Please help me get this cleared up. I even called the dealers in town and they didn't seem to know.

500hp @ crank

What he said.

If it's completely original you can assume 25 HP less!

Thanks all, I've been misinformed all these years... I hate that.

how do you figure??????

Its a 500hp engine. The bravo drive eats about 30hp.

I always thought it was 500 at the prop. So just to confirm, HP500=470 at the prop. 500EFI=470 at the prop... true?

I guess it would depend on the drive..but one thing is certain..its 500hp at the crank.

The confusion isnīt helped by the fact that Marc racing rates 525 and everything thereafter with PROPSHAFT horsepower - but are very hesitent to quote a crankshaft figure. The 525 propshaft hp motor produces around 560 crankshaft hp (independantly tested).

The 496 motor, like the 500, is CRANKSHAFT rated - at 425 hp, as independant tests have shown.

Crankshaft hp
496HO - 425 hp
HP500 - 500 hp
525EFi - 560 hp

Another twist in the story is that in 2000, when Merc racing was offering both the HP500 (carb) and the 500EFi motors for the APBA Factory 1 race series, they loaded the EFi boats with a 250 pound weight penalty to keep things fair (Powerboat Magazine Sept 2000).