25 OMC Mods

**JohnsonM50** · 08-06-2009

Originally Posted by DonChichoJr.

How Much Can Are Able To Mill The Head ??, Using 93 Octane Gas & 30 Degrees Timing ? On That 1990, 3.000 Bore Size Pistons .

.020" Or Maybe .030" ??

Regards,
Don

Theres is little clearance to begin with & I suspect that may vary a little so a fixed # I wouldnt venture. Best bet is to putty test the clearance you have & go from there. If it hits without the head gasket its too close. If you go oversized pistons watch for the aluminum at the bottom of the sleeve rubbing the piston skirt & the extra width of a 0.030" over piston can hit the edges of the squish band. may need some clearancing. If your compression is over 120 it wont make much difference.

**88workcar** · 08-10-2009

So these little engines don't like compression?

**JohnsonM50** · 08-10-2009

Originally Posted by 88workcar

So these little engines don't like compression?

Ive got 150psi out of 2 builds, havent tried to totally maximize that yet. Usually a used motor will have 120 to 135 with little difference

**88workcar** · 08-11-2009

So they will like compression

**JohnsonM50** · 08-11-2009

Originally Posted by 88workcar

So they will like compression

It will, like any engine to a point, All I meant was at TDC The outer edges of the pistons are flush or slightly above the block surface & the head is shaped to the deflector without much clearance. More compression will mostly gain more acceleration, not much top end.

**JohnsonM50** · 08-11-2009

Originally Posted by 88workcar

So they will like compression

I sent ya a couple pms.

**M2Guy** · 08-13-2009

I am also getting ready for a project on one of these motors and have been following this thread. Just as it was getting interesting a couple private messages killed it.

What is up with that? lol Can anyone else help with this? What kind of HP can I expect to see out of one of these motors?

Thanks

**JohnsonM50** · 08-13-2009

Originally Posted by M2Guy

I am also getting ready for a project on one of these motors and have been following this thread. Just as it was getting interesting a couple private messages killed it.

What is up with that? lol Can anyone else help with this? What kind of HP can I expect to see out of one of these motors?

Thanks

Hi M2Guy, Im not tryin to be secretive its just stuff thats repeated from old posts. I have no way of measuring hp only to assume it actually started out as whats rated then figure if its 10% faster then 10% more?? For running speedboats Im more concerned with the Rs itll increase a prop to. What do ya have?