502 HP ratings
 

Just curious where I can find actual HP rating on the 502, Ive always thought my 93 502 carb was 415, after talking to some people I hear it was 390hp, anyone know for sure? also what are 94 502 fuel injected motors rated at??

thanks

Early 502's (Mark IV and Gen V's) were rated at 425 at the flywheel and 390 at the prop (carb). This number grew in the early 90's with the advent of EFI.

The EFI 502 went up to 415 at the prop and the 454 Mag went to 385 hp at the prop

thank you

Where was my horspower measured at??
 

My knowledge and information tells me that these engines are all Mercruiser (black) engines not Mercury Racing (blue) engines and most of the time during this period Mercruiser unlike Mercury Racing has most of the time rated their engines only at the crankshaft. So as measured by many in the industry those horsepower numbers were what appeared at the crankshaft, not the propshaft.
Just for example the Merc 496HO (Mercruiser engine) rated at 425HP measures about 395HP at the propshaft and the HP525efi (Mercury Racing) engine is rated at 525HP and measures that at the propshaft and actually makes about 550-560HP at the crankshaft.
Reason I feel this is more accurate is I have never seen a Mercruiser stock 502MPI rated 415HP outperform a stock Mercruiser 496HO-425HP.
I know it makes owners of Mercruiser (black engines) feel better about their powerplants when they believe their engine is making that HP number at the prop, but the truth most of the time is that is the horsepower they are making at the crankshaft.

Good formula to remember when identifying horspower numbers on Mercury marine inboard engines:

Motor in black horsepower at the crank,
Motor in blue horsepower at the prop.

Best Regards,
Ray @ Raylar

:evilb:that's it im painting all my stuff blue

Huh? Why would it? Its rated for less horsepower (at the crank or at the prop).

Great idea, that is the cheapest horsepower I have ever heard of. Mind if I do it too?

Powerquest is correct this is how they were rated.

From what I have seen all black engines are over-rated a touch and all blue engines under-rated a touch. Except the 525 which was under-rated by quite a bit. My guess is to keep the sales of the 600 up.

EFI Black engines are at the prop
Blue Engines are rated at the crank. However it seems the HP 525 is under rated.
http://brucebullockmarine.com/mercury/350-454-502.html
http://brucebullockmarine.com/mercury/500.html

I know that this horsepower rating information clarifications step on the capes of a lot of superman powerboaters but if you dyno a stock 502MPI at the prop you will see the real power at the prop. I believe Bob at full Throttle has done many such prop test power levels on his propshaft dyno and maybe he will be kind enough to reshare his findings.
Powerquest Baby, if it makes you fell better that a stock 502MPI makes 415 or 425hp at the prop have at it, I know what it really makes regardless of advertising or opinions here on OSO.

Best Regards,
Ray @ Raylar

Your not getting it. Your statement doesnt make any sense. Your saying you have never seen a 502 with 415 hp outperform a 496 mag ho with 425 hp. All Im saying is why would it? Im not debating hp ratings at the prop or crank--just the fact that the 496 is rated 10 hp more than the 502 therefore it should be able to outperform the 502.
Your logic isnt making sense.

Im still painting mine blue..just in case :evilb::evilb:
will keep u informed if i pick up mph:lolhit:

Sooooooooooooooooooooooo I always thought after 89 they were measured at the prop shaft, but what do I know,

Sooooooooooooooooooooooooo

my 93 502 carb was what at the propshaft?

potential new boat 94 502 EFI is what at the propshaft???


after we figure that all out when and if I get it I'll yank the motors go down to the hardware store and buy some blue paint:helmet:

While I agree that the propshaft hp number from Merc are optimistic, the original post asked what the RATINGS were. And they are 390 and 415.

What is odd about the black engines is that Merc rates the 502 mag at 425 at the prop yet OMC rated the 502 at 425 crank and 385 prop. The OMC engine is the exact same engine! Plus I really doubt that the 454 mag carb is going to go from 365 crank to 385 prop with the addition of fuel injection and a slightly different cam. I'm with Raylar that its marketing hype vs reality. Look at a Merc manual for example, the cam specs are all over the place.

When you get to the hardware store you might want to remember that Superman's cape was RED!

:lolhit:

Best Regards,
Ray @ Raylar

Ray, I remember seeing the Merc Racing specs on the HP500 carb motor and it stated: 470HP at the prop. So therefore, they were rating it 500HP at the crank.

Is this correct?

Yes the 500EFI and 500HP were rated at 500hp at the crank and 470hp at the prop.

Mercruiser(black engines) are rated at the prop.

Mercury Racing(blue engines) are rated at the crank.

Note I said RATED.

well... just a couple of observations...

first going from 365 to 385 with injection and cam work is a piece of cake...

second my factory workshop manual for my late 502 says
425 and they make no mention where but the presumption has to be at the flywheel...

why would it make any sense to measure it thru a drive ? losses thru various drives would differ and just add a variable that would make the number meaningless in general... the spec would have to read " 425 hp at the prop thru a bravo 1 at 365 deg temp using 65wt saemc gear oil "

huh ?

i know its just bench racing... but it has to make sense to some degree...

and a 496 vs a 502 w/ a 10 hp dif " outperform " one another ? what does "outperform" mean ? accelleration ? top speed ? on paper you might think the one with more hp would have to be better but the shape of the curve vs the shape of the hull and the drag profile might mean that the higher hp motor never makes the revs necessary to get to where the hp is made because it can't push thru the drag to get there... in one hull one motor might be MUCH better and in another hull the opposite would be true...

and do they actually say " at the prop after the drive" or do they say " shaft hp" because shaft hp could easily be crank hp. when you dyno a specific car on a chassis dyno you might say ' at the rear wheels" but you can't then say that as a standard that motor makes that power at the rear wheels of EVERY car you put it in... just that one type and spec


just to fan the flames of discontent...

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!!!:thankyouthankyou::thankyouthankyou:

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 ... :lolhit:

I just had 2 new 454 mags on dyno 419-425 HP pulls so at prop 365 HP is about right 385 Fuel Injected ?Oh yea black motors:duel:

What correction factor? Merc's with wet exhaust, etc?

How much torque and how early is a much more important value. Especially in a heavy boat. HP rating looks great on the sticker but a 390 horse small block ain’t the same apple as a 390 horse 502.

Does it matter, lots of other things will effect your boats performance long after the prop vs crank, dyno correction factor discussions.

My engine is on a stand, I am waiting for a few pieces for the boat, to drop it in. It is NOT stock. I was wanting to get a more accurate "constant" for the speed calculator, so I could get a ball park prop selected. I know what a stock 272w/ 502 runs, so plug in those numbers and calculate a constant. The hp rating makes a significant change to that constant, when measered at the prop v. the flywheel. Once a more accurate constant is obtained, I plug in my horsepower number and at what rpm, then select a pitch that approximates the speed that the calculator came up with. The engine rebuild went WAY over budget, so I would like to be close with the prop pitch, as I may be stuck with it for a while.

It is still going be a total guess and unfortunately real world testing is the only thing that will tell you. Contrary to what I have read here, dyno tests are the most inaccurate of all, they get adjusted until they are ridiculous.

Agreed. I just hope I have a fun and reliable Summer. I built the engine, and the dyno is owned by friends. The numbers were, of course, much less than I was hoping for. We joked about it, and how if they had built that engine for a picky client they would owe him some money back lol. Of course shops "adjust" the numbers, they are a business and in the business to make money.

Which one have more hp on prop shaft:
a.) https://www.mercurymarine.com/en-gb/...ercruiser/82l/ ?
b.) https://www.mercuryracing.com/outboa...s/verado-400r/ ?

J607 CF or SAE 1349? Mercruisers almost always test higher on smaller shop dynos because of the CF used. J607 yields 3.1% higher numbers automatically, I use it on my own dyno because the majority of other shops use it and its the only way to get comparative results. Hence a "385" hp motor automatically makes 11 more hp. If the air conditions in dyno room are not prefect, CF adds even more "theoretical" hp, did you get to see your "observed" numbers, they hurt peoples feelings sometimes!

Correct