Let's try this one more time. The 93 carb 502 was rated 390hp AT THE PROP. 502 EFI was rated 415 hp AT THE PROP.

I'm not saying they should rate them at the prop. I'm not saying they actually made that hp at the prop. I am just saying that is how Merc rated them.

thats all I wanted!!!

Ratings are confusing. Definitely not apples to apples.

Blue motors have historically been rated at the crank. To help people understand that, the Merc Racing ad material also put asterisks on the number and NOTED that it was rated at the crank. Additionally, they ALSO gave a propshaft hp number for the drive it was likely to be paired with.

Thus the HP500 being rated 470 at the prop,
the 1075SCi being rated 1045 at the prop.

Early MkIV 502's were 410hp gross, 390hp net.

Not sure where the "black motors are rated at the crank and blue motors are rated at the prop" came from. That's not what I consistently see from Merc.

Of all the blue motors, though, the 525EFI seems to be universally claimed to be stronger than its rating would indicate.

The big Merc motors (850SCi and 1075Sci) also outperformed most other 850 and 1075 hp motors because of their boost control that kept torque and hp close to rated numbers regardless of temperature outside or altitude variation.

hmm

MC

Well, in an effort to find the answer to a simple question, everything leads back here to this 8 yr old thread. After reading through it 3 times, I still dont have a definitive answer.
Is the 415hp of the 502MPI rated at the prop shaft or at the crank(shaft) ? The boat in question is a '95 Baja 272 with a bravo 1 drive. I am attempting to get a close approximation of the "constant" for the speed calculator. Thanks for any help.

Merc’s “rating” doesn’t matter.

The truth is in dyno tests. A stock 502 MPI makes 410-430 HP at the crank.

I worked at a Harley dealer for a couple years bout the time FI was coming out. Same question was always asked " is that at the rear wheel?" well, we had a rear wheel dyno. Stock trans ratios, primary drive ratio and final drive were input. Someone brings in a bike with drive modifications and the numbers could really vary. Like holy crap, this 88" is making 140hp! No, your input numbers are wrong. Wonder if the prop shaft dynos have similar workings for the different drive ratios? I am new to boats, but it would seem like higher(numerically lower) drive ratios would have a little less mechanical leverage to move a heavy boat, and therefore require more torque ? Well then there is prop slip factor does this act like a torque converter/ slipping clutch? I have no ideas on any of this just guessing.

Black engine rating from Mercury at the propshaft, blue engine rating at the crank EXCEPT the 525EFI was rated at the propshaft from Mercury Racing. QC4V HP rating is at the transmission.

The key is the “rating from Mercury” being just that.... marketing.

If you look them up as bobtails... 430 HP for the new catalyst engines.

my 2 cents..
in 1998 i bought a pair of 502 crate motors , they were black.
i thought they were 450 hp motors.

Well this old thread certainly clears things up ...