Not exactly news that a 27 or 29 Fountain with a single 500 is as fast or faster than a 29 Outlaw with 454 mags or 496 mags.

Sorry dude, thats just not true. An HO will dyno 425ish at the crank and 385ish at the prop. Look up the recent thread called "496 dyno testing and mythbusting." bobl and raylar have been all over this on their dynos. Their test had a 496 making 431hp at the crank and 387 at the prop.

A 525 will make 550ish at the crank and about 500 at the prop. The 500efi was making 515ish at the crank and 470ish at the prop. It figures about a 10% loss through the driveline.

Cheers

Just spent 15 minutes reading that thread and browsing the mercruiser site. Can't find anything there about whether the ratings are crankshaft or propshaft. Will check my owners manual tonight. Wouldn't be the first time I've been wrong. But a dyno of one motor doesn't make it a lock in my book.

http://www.offshoreonly.com/forums/s...g+myth+busting


Second page.

431 crank and 387 prop. Its not the first 496 they've tested. All the ho's crank dyno between 420 and 430....figure a 10% loss to the prop.

From Ray:

"Just to clear the deck here and put in some facts. All Mercruiser engines are rated by SAE standards at the crankshaft. Most all dyno tests of the stock 496HO including ours show the engine produces approximatley 425HP at the crankshaft as advertised. Mercury Racing engines such as the HP525 are rated at the propshaft. The Merc HP525 when measured on a dyno is at about 540-550HP at the crankshaft.
Our 496 -525HP kit is rated 525HP at the crankshaft with stock exhaust. When equipped with a good set of headers, it also produces about 550HP minimum at the crankshaft at 5100 rpms. Just some facts to avoid mis-information here.

Ray @ Raylar"


"I've dyno'ed way to many 496HO's and I have the bills to prove it! I can tell you positively that 496HO's make right at 425HP at the crankshaft on calibrated dynos. Unless a Bravo uses 0 hp to get it to the prop, you are not going to see 425HP at the prop, more like 400HP at the prop. Mercury Racing HP525's make 525HP at the prop and about 540-550HP at the crankshaft. You can go the bank on these numbers!

Ray @ Raylar"

Jmeng, how are you doing ... haven't talked to you for a while

They are crank.....do you guys need to see the dynos yourself to give this a rest.....? Old news.

Wasn't doubting the dyno's just could have swore merc rated their black motors at the prop. They used to list crank and prop shaft horsepower. Looks like just crank now. According to the footnote in my owners manual: "Performance obtained and corrected in accordance with SAE J1228 Crankshaft Power". Just pisses me off cause Merc damn well knows that most people assume they're rated at the propshaft. Guess I'll have to boycott black motors on my next boat and go with those expensive blue ones. :D

Wow this really went off on a tangent. :D

You gentlemen need a little clarification here. First, all Mercury Racing Engines, 500EFI, HP525, HP500, etc. are hand built in Fondulac Wisconsin at the Mercury Racing Plant. They start with just parts and blocks and build the engines from the ground up. They dyno them and rate the horsepower at the PROP, not the crank! for example a Mercury Racing HP525 makes approximatly 540HP at the crankshaft and 525HP at the propshaft.

Mercruiser (black motors) Mercruiser, a different company division of Mercury receives standard GM Powertrain engines at their plant in Stillwater, Oklahoma, accessories them with Mercruiser external parts, sprays them BLACK and ships them to the builders and buyers. These GM Powertrain factory built engines are the same ones GM ships to Volvo, Crusader, etc and GM dyno's and measures the horsepower on these engines at the crankshaft! Hence, all black Mercruiser motors that come from Stillwater, Oklahoma are producing and are listed as horsepower at the crankshaft, period !!
I hope this puts this question and mis-statements to bed for the last time!

Regards,
Ray @ Raylar

http://sea-pro.com/mercurymarine/mer...496-MAG-HO.htm

Found the same thing at numerous sites by just googling 350 mag mpi or mercruiser 496 ho. Looks like a lot of people/businesses got misinformed (looks like "old" online Mercury brochure?), too .... peace.