Omc 140hp cross flow

[Jimmybar]

Need feed back on some things , any comments welcome ,1.6 L cross flow block stock bores , 140 specs , targeting 6000 rpm Max. 5300 cruise ,pushing an impeller pitch 14/22 1:1ratio bolted to a turbojet drive ,first question , scallop piston skirts vs piston windows , pro and cons . Piston skirt scallop reduces induction compression timing is there a better way , piston porting opens transfer port area much before bottom skirt on rise to tdc , then the skirt being full length still gives Max induction pressure at bdc You rarely see this MOD , we have used piston ports on v6 cf with excellent results giving 7600rpm on a 30"chopper dancraft hull , allways accused of cheating , these were slots on the piston side ( nothing new ) but I'm thinking holes low on the piston skirt matching the ports , why is this MOD no popular , ???? After all it's the same motor as a " clip on , !! Regards Jimmy .

[71V153]

Makes perfect sense to me. Go for it!

[powerabout]

Need feed back on some things , any comments welcome ,1.6 L cross flow block stock bores , 140 specs , targeting 6000 rpm Max. 5300 cruise ,pushing an impeller pitch 14/22 1:1ratio bolted to a turbojet drive
,first question , scallop piston skirts vs piston windows , pro and cons .
Piston skirt scallop reduces induction compression timing is there a better way ,
piston porting opens transfer port area much before bottom skirt on rise to tdc ,
then the skirt being full length still gives Max induction pressure at bdc You rarely see this MOD , we have used piston ports on v6 cf with excellent results giving 7600rpm on a 30"chopper dancraft hull , allways accused of cheating , these were slots on the piston side ( nothing new ) but I'm thinking holes low on the piston skirt matching the ports , why is this MOD no popular , ???? After all it's the same motor as a " clip on , !! Regards Jimmy .

Yes I would like to know about scalloped pistons or ports in the piston and cylinder wall

[spybot]

I'm thinking holes low on the piston skirt matching the ports

Can you tell us more about this mod ?

[Jimmybar]

Well ,,,this is the story, as most old skool racers know , factory mods would be leak out and everybody gets enough HP gain to get excited , it's only my option , but scallop the piston skirt is one of them ,,mercury did the same , but let me take you back 105years ago yes in 1905 a fellow developed a cross flow engine that out performed any four stroke in the time in power that's is mid range power and economy , bit like a fairy tale , it was a Scott squirrel , latter to be a Scott silk renowned for smooth power band and lots of it ,..
Up to 6000 rpm , back to the thread , in my wrecking yard is a omc factory v6 race block complete with six pac carb configuration , produced 8000rpm awesome piece of carburetor brilliance , short story , we had to carry twice as much fuel to run it weight penalty cost us in speed , ,,, Back to the drawing board , in our case the shed and beer fridge , so we .in our drunken wisdom came up with the theory that if you increase air velocity to a point were it has to go somewhere why not shoot in straight to the crown of the piston in two directions then give it Max induction pressure , that's a rough explanation, hence send the gas up the transfer port , at the same speed , keeps the piston and rings happy to. Never had engine fail , would go day racing on Sat the social ski on sun. Good thing , the same MOD produced nearly the same rpm and horse power as the factory MOD , the only reason I'll bring this to you is that someone one your forum produced a pic of the same MOD , great minds think alike , has anybody tried this on a v4 ???

[powerabout]

These photos belong to other members posts, hopefully they will jump in

[racer]

Powerabouts photo on the right is the best combination for power. Finger ported with scallop and post hole.

[Jimmybar]

Would like to post a pic , need help , thanks

[Jimmybar]

What's your assessment for the piston on the left ??

[powerabout]

Powerabouts photo on the right is the best combination for power. Finger ported with scallop and post hole.

Hi Racer
What should the port in the cylinder wall look like, just a round hole or a slot?

[FMP]

Something like this?

[powerabout]

interesting, finger ports to meet up with the original ports?

[racer]

Round hole

[Jimmybar]

Great mods , what do you suggest for my v4 5300rpm cruise 6000rpm squirt , ??

[powerabout]

All depends on boat weight, the fuel you can get and what you do with the boat.
Setup and prop is your best return re simple and reversable.
How fast and what prop do you have now