25 to 35hp johnson

[speedfreak]

14apache,
Not yet. Been busy with kids: LL football, gymnastics, etc. they are running me to death. Also, taking advantage of fixing a few little other things on the boat while we are at it. Been running through the break in process on 25:1. I'm being patient with it. Won't be long though, and I'll post some results.

[speedfreak]

Ok, first round of results from my little OMC 3 banger Mirage 25 to 35 conversion after a proper break in. Again this is mounted on a 1548 semi V aluminum duck boat. I'm turning 6500+ RPM's (hitting the rev. limiter), 38.5 MPH, with a 14P power tech SS prop. I think if I move up to a 15P SS, I'll bust the 40 MPH mark (that was my goal) and still have enough power to spare when the boat is loaded down. So what I have now is a 35hp power head bored .030" over with all the glue lines ground out and cleaned up, boyseen reeds, set of velocity stacks, rebuilt carbs with 35hp jets. Also running a CMC PT-35 trim and tilt. This is a 15" short shaft lower unit. Motor is pretty powerful on the bottom end for what it is. It just jets out of the hole.

[speedfreak]

Did a compression check, all 3 cylinders are right at 135psi. May have to shave a few thousandths off the head. Shoot for 145 - 150psi??????? Those little engines handle that? 15psi worth it?

[champ20B]

Did a compression check, all 3 cylinders are right at 135psi. May have to shave a few thousandths off the head. Shoot for 145 - 150psi??????? Those little engines handle that? 15psi worth it?

145-150psi are racing numbers for an engine of this size or less. My Yamato 80 has that much and my Champion HR has 160+. But I have to run non ethanol 97+ in them to be safe. Your motor is built tough and can handle a good load, but if you want those numbers in compression, I strongly recommend that you back the timing off a bit to start with until you see what it does after you mill the head down. You can reset timing from there and it will keep you from blowing out a piston or head gasket.

[speedfreak]

Thanks champ20B, Probably not going to mess with it until spring time. Time to use it right now. It's running strong.

[14apache]

How is it running

[speedfreak]

14apache,

Runs strong. 39-40 mph on the 1548 flat bottom. Happy with it. Gets there quick also. A lot of low end torque in that little thing, comes out of the hole hard.

[14apache]

14apache,

Runs strong. 39-40 mph on the 1548 flat bottom. Happy with it. Gets there quick also. A lot of low end torque in that little thing, comes out of the hole hard.

Did you stuff the crank case? Sounds like it runs good.

[speedfreak]

14apache,
No we didn't stuff the crankcase. Maybe later. Pretty happy with it.