DRAG

I have been digging around for info on these newer Merc Racing engines mostly out of curiosity, but also to see a power curve to optimize the props on my boat and to feed the disease of making a plan for more power. I'm shocked after 8 years of use that there is really very limited info available. There must be dozens of threads on all the popular forums asking questions about these engines, but they end after a few comments with little info. I figure I would put this thread here to have a place to put some info as I find it, so that others looking around online can find answers. I'll update the post as I find info, and if I post something incorrect and someone can correct me...just let me know and I'll change it. I'll be comparing a lot to the 525 mostly because there are so many out there, everyone has rebuilt them, everyone has had them on the dyno, etc. Its the benchmark.

The 525 was considered an overachiever by many, with independent dyno operators showing 540-550hp fully dressed with wet exhaust. You dig deep enough into some of the racing threads and you'll see guys talking about late model engines being dyno'd at 580, 600, and some way over....some pretty outlandish claims that don't match up to on water speeds. Many of those are probably rebuilt with smaller chambers from head surfacing to bump compression, ported intake manifolds, and using dry dyno headers....but I will update if corrected. I spend a lot of my time running my Superflow dyno and they aren't engines anything like these. My experience level on these engines is zero...all I do is push the throttles at the lake and enjoy. But I know how much affect I can have on my dyno numbers with an improper calibration, being careless about my weather station, etc. As the operator I have a lot of control over those numbers, and must be honest in operating it. Fluffing numbers is the norm....not the exception trust me. It takes some effort to make sure you are setting up equal conditions for your dyno tests. If anyone has a bone stock fully dressed wet exhaust 525 dyno chart, I'd love to add it here for reference. The only one I found online showed 529hp and 572tq. I also found a Land and Sea prop shaft dyno test that showed around 525.

I took a few minutes to look over some hard parts to see if anything was shared between the engines. Obviously the bottom ends are different because they are different displacement. Here are some Notables....

• 520 and a 540 are the same engine, but the 540 has CMI exhaust. The same exhaust part #s are used on the 525, 540, and 565.
• If you got a 540, in addition to the CMI exhaust you got the same intake manifold with a little nicer looking machining on top and "Mercury Racing" machined into the valve covers
• 525 / 520 / 540 share the same 4.0" stroke although the crank part # is different on the 525. The 520 / 540 gets is extra displacement from a larger 4.56" bore.
• 565 shares the same bore size as the 525, but it uses a 4.25" stroke to get its extra displacement
• All 4 engines share the same valve spring and retainer
• All 4 engines share the same camshaft
• 520 / 540 / 565 share the same rocker assembly
• 520 / 540 / 565 share the same valves, which are larger than the 525s valves. Cylinder head part numbers do not match.
• All 4 engines share the same oil pump
• The 520/540 has a forged I-beam connecting rod, the 525 and 565 have an H-beam.

DYNO SUMMARY
MR 525 - 560hp @5300 / 592tq @ 3700 (updated)
MR 520 - 526hp @ 5200 / 592tq @ 4400
MR 540 - 574hp @ 5200 / 606tq @ 4700
MR 565 - unknown

Mercury Racing 520 dyno and 520 with CMI (540 numbers assumed from 520 with CMI data)
Source: CMI Headers
Dyno: Innovative Marine
Download the detailed 520 upgrade Dyno data




I did call Mercury to see if I could buy a new 540 to dyno and build a setup around the Drive by Wire, but they have discontinued the engine (even though they still sell the same 520). I don't intend to have my boat down while I tinker. It is a 520, so I may just get that longblock and go from there but I only want to dyno with the actual exhaust. I had to sleep on it and consider how much of a massive waste it would be on my part to do this...so I ordered some of the hard parts that would be a HP limiting factor such as the rods...which I'm skeptical about based on the price. I'll have them in my hands soon.

hogie roll

Mercs ratings are with a more conservative SAE standard correction. I believe the difference is something like 4% different from the typical aftermarket Dyno procedure.

The 565 will likely make 600 on a typical Dyno setup. The 39 velocity did 99 with them. I think the 36 OL ran upper 90s too. Just not nearly as many boats built with them to get many comparisons to the 525.

But you can be sure the difference in rated power from 525 to 565 is real, as it’s an SAE requirement.

DRAG

The SAE numbers for that test are in the link. There is a lot more info there than I posted.

Would be nice to see all the engines on the same dyno. The 565 is definitely strong.

IGetWet

Interesting thread. Thanks for sharing. If the 520 and 540 are the same except headers, can’t you get another 520 and buy headers separately and essentially have a 540?

The I/O sport boat market sure isn’t the same that it was in the early-mid 2000s. 525s were like the 400r or 450r’s nowadays

Has anyone been able to crack the computers on the newer motors? Mother mercury may of hurt itself by limiting upgrade-ability

DRAG

I definitely can. I was a little skeptical of the intake having differences but as I learn more…it’s the same engine. I really wanted to hear Merc say that to confirm but no dice. I’ll make a decision once the rods show up.

No idea on the computers. I have a pair of Motec m150s i planned to make a jumper for the stock harness. Integration with the DTS may or may not be a hurdle. Keeping that is a must…it’s awesome

sutphen 30

do you know the specs of the 565's cam

good info,thanks

DRAG

same cam as the 525.

Unlimited jd

iTrader: (5)

Interesting how similar the 525 and 520 are. I’d give up a few hp to be able to run those inexpensive manifolds vs the overpriced cmi’s

IGetWet

I bet retaining DTS and smartcraft would not be possible with the Motecs...

sutphen 30

his motec's can do drive by wire,,not sure what else dts gives you.

https://www.motec.com.au/gpa-m150/gpa-m150-ft/