I plan on building a 525SC and would like to know what are the engine specs. Also, does anybody have a input shaft and both top pulleys for a 1988 merc 525SC blower?

Thanks in advance

For the parts you want PM jeff1000man, he probably has some takeoffs from my boat. As far as the specs, what do you want to know?

HP525SC Specifications

Propshaft Horsepower: 490 (365 kw)
Displacement (Liter/CID): 7.4/454
Cylinders: V-8
Bore (in/mm): 4.25/108
Stroke (in/mm): 4.00/102
Compression Ratio: 7.5:1
Fuel Requirements: 92 Posted Octane (R+M)/2
Full Throttle RPM Range: 4800-5200
Ignition Type: Thunderbolt V
Alternator (amps/watts): 55/776
Length (in/mm): 47.625/1210
Width (in/mm): 32.75/832
Height (in/mm): 28/711
Weight (lbs/kg): 1470/667

Holley 1050 carb #98 jets all around and 6.5 PV's front & back
5.5# of boost and 2:1 over driven on a Weiand 177
Cam is a Crane 132561
GM crank and rods
GM Rect port heads

The splined blower input shafts are were for merc only and are not available. You will have to switch to the key way shafts.

THe Merc HP 3 manual wil have all the clearance specs.

and they made 3 different blower lenths over the years, just had to have 2 custom made as they no longer make them..

is 2:1 100%?

The blowers are rated for for a max of about 13000rpms. I actually had mine overdriven at about 2.5:1 and it had 500hrs on it. I did change the lube about 25-30hrs.

I believe i may have all the info you are looking for from the merc service manual. It contains all specs from piston to bore clearace to bearing clearences . all the specs to build to. If you can find a service manual for that motor its in that book. I can make a copy of mine and mail or fax it to you or you can find your own book. send me an email at
[email protected]