Can I get away with 91 Octane with a 525SC
 

Hello All,
I have just Purchased 1995 27 Fountain Fever with a 525SC and I'm in love with it! The motor is Stock (or at least the way it came from Fountain) and I am wondering if I can get away with 91 Octane. The breather cover says 92 octane but I boat in a pretty rural area and all I can get on land is 91 octane. Thanks in advance for your help on this!

I would guess the 1 less octane point wont hurt anything.

:eek:mmmmmmmmmmmmmmmmmmmm

I wouldn't want to test the theory, blue engines cost too much. The best solution would be to add 5-7% race fuel 110 octane or better. I assume your tank is less than 100 gallons so 5 gallons of race fuel will do the trick and you’re safe.

If you must do it, then reduce boost to lower the effective compression ratio. I would not talk myself into 91 octane being ok. Fuel quality is hit and miss anymore and blower motors are more sensitive to detonation.

FWIW, I've been running 91 oct. in my blower motors (pretty much all you can find up here for premium fuel) for the past two seasons. My combo is 8:1 static 671's 8 lbs boost, Superchiller intercoolers, 28 deg total timing. No signs of detonation on the 91.

The 525SC is a 7.5:1 static comp motor, I believe it's less than 5 lbs boost. Merc timing spec is 35 deg total. I'd knock the timing back to 30-32 and you should be fine.

Chillers are the key. You can take timing out of that motor, but, you risk destroying the exhaust valves. My boat's previous owner felt he was more qualified than Merc Racing to determine the timing spec and with 144 hours on it, the engine had about 50% leakdown through the exhaust.

Just don't run the piss out of it and 91 will be fine.

I don't think 91 would hurt it at all. They are setup so rich out of the box anyway.
Run it hard for a few & then shut it down & pull some plugs to take a look if you feel like you need to.
I'd run 91 & not think twice about it if it were mine.

Ditto what biggus says. I would and do set my timing at 30* with 525sc blowers on my engines (454s). No valve probems after two yrs of hard running. I do run 93 oct but my static is 9.5:1 w/5psi. I run hyper pistons as well so you can be sure its not detonating.