What octane fuel for 420's?
 

I have stock 420hp 454's in my Formula. What octane fuel do they require? I have always been running super but I am wondering if I am tossing money out the back of the boat.

Jon

93 octane !

Yes you have!!! Pretty much all Mercury Marine including racing engines will run on 87 Octane. Now this doesn't include the SC motors.

Not true of the older HP series, which the 420 is.
My trusty 1990 Mercruiser HP sales brochure calls for 91+ octane in all the HP465, HP500, HP500 Bulldog and SC engines.
That being said, the 420 will probably run fine on 87, but I'd do a few runs & read the plugs before I would trust it.:drink::drink:

I have run it on 89 in the past as that can be all that is available on the lake and it seems to run fine on that. I guess if I was doing a poker run and running it hard then I woudl certainly go with super. What I am wondering is if the average day out with the family if I am ok with lower octane, or even if lower octane is prefered.

with the ethanol in todays fuel, the 420 needs 93 octane !
just like all other HP series engines ..! BUT SINCE U GUYS CAN'T READ MY POSTS..BLOW HER UP !!:lolhit:

The 420's are still 8.75 compression ratio engines, so they will be fine on 87 octane. Basically a 454ci version of the HP500 with a smaller cam.