Octane for 525 sc's
 

can you run the older Merc 525 sc's on pump gas 89???? they do have coolers added.

how about if they don't have coolers?

ttt

I ran mine for years on 89...

I was told you could run 89 if you kept engines out of boost.

Kathy how do you get the boat on plane without boost? I pulled about 2lbs getting on plane!

Could only get on plane @ about 3000-3200 rpms, boost didn't kick in till about 3800. total boost was about 5-6lbs @ 5200.
Still only ran 93 oct. though.

Must be a heavy boat !!! And no I would not run 89 I had 525sc's and with 89 they knocked and burned a piston
To much static comp. I was told !! Don't do it !!!

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
Warranty: 1-year limited, 3-year limited corrosion

The 575SCI says 91 in the owners and service manual both so I run 93 :D

CESSNA, you had to have somthing come out of spec
What fuel psi did you see at WOT?
Did you Timing=35* at 4500?
I Ran them for miles on end at WOT on 89 for 4 seasons, and at rebuild was even able to use the pistons over with a slight hone to the cylinders...and again beat those for another season.
Sold them at the end of 01' and new owner ran them all last season.....
With the right plugs and tune up specs I had no issues.
Maybe I was lucky.