Last boating season I had to repair damaged spark plug threads on my 98 Evinrude 25hp twin cyl., Since I had the head off, I decided to have the head machined .030". I noticed the extra power first time out afterwards, and I was told at the machine shop, that machining the head .030" should only increase my compression by 10 psi or so. Since spring time is coming around the corner (it got up to 30 deg. today) I thought I would check out the boat, first thing I did was to make sure the battery was fully charged, removed the kill switch tether, pulled both plugs and performed a compression check, with the throttle wide open. I found both cyls. are at 140 psi cold. (20 psi over stock) Should I be running high octane gas through my engine, I don't hear any knocking or pinging sounds from my engine, however I'm hard of hearing, and the engine is so damn loud at wide open throttle, I cant hear myself think, yet alone a knock or ping.
BTW I'm using 87 octane right now.
BTW I'm using 87 octane right now.
and that is exactly what I am trying to avoid, I like the one piece style of pistons personally. I know just because I can't hear the knock, doesn't mean it is not happening. Here in Minnesota, the only way you can get non-oxygenated fuel is in 92 or 93 octane grade, in the past when using this grade of fuel, I've found a noticeable decrease in performance, thus only reinforcing my belief of using the lowest octane necessary. I think I will try the non-oxygenated fuel this season, decabonize often and verify my ignition timing. I just regret waiting so long to actually check my compression.