525SC upgrades Marine Kinetics Cam
 

So I started with just some carb tune and head work and the list went on.....

Found worn out cams and decided to pull them. Went with new Cams MK Bob custom grind, hyd roller Morel lifters, Comp push rods, Comp springs and kept my gold crane rockers. Fresh valve jobs and bigger pulleys on my B&M 250's. Boat is a straight bottom 42 Fountain TRS drives.

Before I started I was spinning Bravo I 26P to 4800-4900 rpm and seeing 67-68MPH with 3.5-4lbs boost

Put motors back together last week and went out and worked them up to 5,500-5,600rpm trimmed @ WOT and got 70MPH with 5.5-6.0 lbs boost

Felt like she fell on her face around 4,800 rpm and did not accelerate from 4,800 to 5,600rpm

I think I need more prop wondering what I should try? Looking for nice cruise not concerned about WOT numbers but would like to be propped to 5,100-5,200rpm

Looking for some input.
Thanks BIll

I'm sure you'll get some good advice when MT or mike tkach sees this. Don't know how many other twin side by side straight bottoms are on here. He's 38 but close to the 42.

Something is wrong here Bill. If your RPM went from 4900 and 68 MPH pre and 5600 RPM and 70 MPH post the math says you had to pick up 10 MPH based on 15% slip so if you picked up 700 RPM top speed should actually be around 78 MPH, big difference.

Relative to falling on its face after 4800 there are a couple things to check;

1. Timing. Is the timing set correct?
2. Air fuel ratio. My senses are telling me that you are probably lean unless you fattened up the carb a ton when you made the mods. Pull the plugs and check them or better yet plug in an O2 sensor. Either way do not run that motor hard until you verify the air fuel or risk possibly melting some expensive parts
3. I don't know what the rev limiter is pre set on this motor but this could be playing a part

Hope this helps!

I hope ....
They came alive and sound totally different + at least sounding good around the docks LOL! got lots of compliments on Sunday. I know its going to be hard to reach top end speeds with the "Totally Run Slows" but I'm really concerned to increase my cruise speed.

Don,
I set Timing at 26
Demon carbs 825 with 80/90 on the jets
Plugs looked fine after running a few WOT runs.
To be honest I never really ran them hard before I did the upgrades the initial numbers could be off a bit but with my calculation after upgrades I'm coming up with 22%.. I guess I am really looking at my new numbers.

That means your slip went from 15% before to 22% after, puzzling. I would think the slip would be held constant but I don't know much about Fountains or TRS drives. Maybe the TRS lower blows out at a certain speed creating the huge slip number which would certainly explain the sluggish acceleration.

Are the motors crisp and zing right to 5600 RPM or are they also sluggish? If they pull hard and crisp to 5600 deffinately sounds like a prop slip issue.

Is this a stock 525sc you have and you also added the 250? Stock was a 177

454cid
7.5:1 compression
rectangle heads
Holley Dominator 1050 carb (jetted 98 square + 6.5 high flow power valves front and rear )
177 supercharger w/Dominator carb flange
AC Delco MR41T spark plugs - gap .035"
35° Total timing
Premium fuel required. Merc suggests min 92 octane

And following hyd flat tappet cam:
Merc 400 / 420 / 425 / 525SC

Crane Part#132561 Grind # H-228/312-2S-14 T1.2
Duration at .004” : 298°, 296°
Duration at .050”: 228°, 236°
Lift with 1.7 rocker: .530”, .551”
LSA 114°LSA
ICL 109° ATDC , ECL 119° BTDC

Seems to pull RPM without hesitation to WOT its the speed that seems to plateau after 4800

Rookie dont think they were factory 525sc. Similar build with 250 blowers. He just switched cam to HYd roller.

History shows Clone 454/425 with 250 B&M