1970 evinrude 25 hp question

I have a nice 25 hp rude and i,am considering cutting the cylinder head .010 to .030 to get compression up deliberatly. its not a have to just I want to. also while its off Imam going to mirror polish the combustion chambers. I dont mind running 100 oct. ave gas. anybody have knoledge or experience with this ?
thanks
bob in tn.

Having been a certified technician for 36 years. I would say you would be totally wasteing your time. Polishing the head would do nothing. These engines run using piston ports not valves. Actually high octane will not gain anything for you. These engined however can be modified to run on alcohol fuel. It would no longer be a fishing boat engine. Creating many problems.

Agree on polishing the chamber.....waste of time.
The engine will, however, respond to an increase in compression. With just .030 you should need nothing more than around 89 octane.
Start running more oil from this point on.

the reason behind polishing the comb chambers is to stop carbon buildup which easilt builds up tp sand cast finishes and to increase cylinder pressure has to build more power if you feed it with higher octane fuel. alky no way. 2-3 hp extra would be fine for me. I,ll post pictures of before and after the moddifications . guess I,am gonna just put a dab of clay on top of the hi portion of the piston to check piston to head clearence to be safe. Idealy as close to 10-1 compression is my goal.

lol you will have a long way to cut if you are trying for that ratio. And you would definitely need alcohol ! Some to drink and some to make it run
Most 2-stroke outboards are around the 7 range give or take. Trust me.....clay is not needed for a .030 cut.

boy i,d love to go .030 off the head and run stock thickness head gasket. theres too many problems with alky to run it IMO.

I think we have a disconnect here.
Going .030 is nothing...........run 89 octane, alcohol is not needed, not by a long shot.
There will be only one head gasket.......there is no thin and thick head gasket for that engine.

OK, GOT THE HEAD OFF gasket number 306163. head looks real nice but combustion chambers are normal sand cast rough and carbon has built up in spots. gonna glass bead blast it ( with spark plugs in to protech threads then have my machineist cut it .030 after combustion chamber polishing. the water jacket is painted brown oxide so i,ll recoat it with glyptol after all work is done. thanks pappy

Watch your plug color and heat range, run extra oil, and adjust mixture and timing as necessary. You should notice a difference.

LOOKS LIKE THE BLOCK COULD USE A CLEAN UP PASS, GONNA CONSULY MY MACHINEIST ABOUT IT ALSO. THANKS EVERYBODY

well got my machine work done. had to cut the top of block .015 to get it nice for head gasket seal then I cut the head .030 so a total of .045. this should make a compression difference for sure.