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Mercruiser hp rating correction factors

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Old 08-16-2010, 11:31 PM
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Default Mercruiser hp rating correction factors

Just curious, does Merc use the STD/STP or the SAE correction factor when rating their engines?
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Old 08-17-2010, 12:02 PM
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ttt
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Old 08-17-2010, 03:01 PM
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That is a tough one...
They are all over the place in relation to stated horsepower.

A typical 525 makes north of 540 horsepower.
My 600sci made 587 horsepower stock
A couple of 700sci's made 679 horsepower on Dustin Whipples dyno
On the same dyno... a 1075 made 1103 horsepower stock

All of these were standard SAE correction

So... who knows???

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Old 08-17-2010, 03:53 PM
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What probably needs to be remembered is the stern drives will be rated at the prop shaft. The dyno pull with no drive attached is bound to show greater HP than advertised.
A 10% +/- of the advertised HP is normally acceptable.

Not sure whats going on though with those 600 and 700sci's?
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Old 08-17-2010, 03:55 PM
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If I recall the blue motors are rated crankshaft HP and the black motors propshaft HP.
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Old 08-17-2010, 04:22 PM
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Quote:
Originally Posted by Back4More View Post
If I recall the blue motors are rated crankshaft HP and the black motors propshaft HP.
Correct. The "racing" motors (500hp+) all get rated at the crank and the others get rated at the prop.

I know most performance companies use the STD/STP correction factor and I would assume it's because it shows more hp.

But I don't know if Merc uses SAE or STD/STP when they rate their motors.
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Old 08-19-2010, 09:07 AM
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Got that backwards! Merc Racing engines are rated at the prop and Mercruiser engines are rated at the crankshaft.
I believe Mercury Racing and Mercruiser both use SAE standards when measuring HP and torque on their dynos and this is pretty much the standard for the reliable marine engine manufacturers. We use SAE on our tests and we make sure the dyno has a recent recalibration, proper correction factors and is on the "stingy" side on outputs for specific engine packages.

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Old 08-19-2010, 12:01 PM
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Quote:
Originally Posted by Raylar View Post
Got that backwards! Merc Racing engines are rated at the prop and Mercruiser engines are rated at the crankshaft.

Regards,
Ray @ Raylar
I respectfully disagree as the 502 Mag was rated at 415hp at the prop and the HP500 were 500 at the crank(470 at the prop)

Mercruiser sterndrive examples:

502 Mag - 415hp at the prop
454 Mag - 385hp at the prop
350 Mag - 300hp at the prop

Merc Racing examples:

HP500 - 500 at the crank
HP575 - 575 at the crank
Scorpion 377 - 377 at the crank
HP525 - 525 at the crank

I think the confusion comes into play because the 525 is always WAY more than 525 hp.

Either way I was curious as to if Merc used SAE.

Thanks
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Old 08-19-2010, 01:27 PM
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I was always under the assumtion that the HP engines
were rated at the crank, due the the fact that they
could be had with different drive types ( bravo/ssm) which would net different p/s hp.
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Old 08-19-2010, 05:17 PM
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I agree with onesickpantera. I recall when the 525 first came out, it was rated at 500 hp on the prop, in the same way the HP500 was rated at 470 hp. Later on, Merc changed it to 525, and did not mention if it was on the crank. I think this change happened when they replaced the 575sci with the 600 sci. I even think I have an old brochure where the 600sc and 525sc are rated as 550 hp and 490 hp prop. I will see if I can make a good scan of it, if I can find it.
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