"Name That Outboard"

[Sam La Banco]

Good Answers Bob AND Tim. Here are a few more pictures of the block.

[Sam La Banco]

Tim the increase in volume was in the spacing of the manifold in front of the reed plate.

[Tim Kurcz]

Hey Sam,

Those images tell the "rest of the story" - thanks for sharing. This engine lends itself well to the side mount carb between the transfer passages. It's fun to see someone take full advantage of an engine's potential. Very clever making a radical pontoon boat motor!!!!

Also, thanks for the clarification about CC -vs- manifold volume. The out front spacing makes more sense! Here's to more wild engines on this thread!

Tim

[Sam La Banco]

One more block photo, Here is what the pistons looked like.

[Tim Kurcz]

Looky there....... Pressure fed piston rings to improve contact and the slick vertical passage feeding the cylinders. Not all engines have such features. Still, this is pretty complex machine work. Excellent tricks!

Tim

[Fastjeff57]

Early '70s motorcross engines were all piston ports (other than Yamaha). They made great power but loaded up like crazy if bogged at low rpm. A hydro might have trouble getting on plane with one, but it would go like stink afterward. The main advantage is a clean, open hole for air/ fuel to travel through without the restriction of a reed to open and stuff its way through.

Jeff

[Mark75H]

Early '70s motorcross engines were all piston ports (other than Yamaha). They made great power but loaded up like crazy if bogged at low rpm. A hydro might have trouble getting on plane with one, but it would go like stink afterward. The main advantage is a clean, open hole for air/ fuel to travel through without the restriction of a reed to open and stuff its way through.

Jeff

In the 50's and 60's Konig made successful piston port race motors. The "trouble getting on plane" problem is solved by the prop slipping like a clutch on take off.

[Sam La Banco]

Piston Ports are great, but they work best over a narrow RPM band.

In the case of this motor with the combination of both a piston port and large reed area, the intake timing is spread out over a lot of crank rotation time.

It's able to take quite a gulp with out to much spit back. With the folded meg closed exhaust system, I'm sure Dave has the volume figured out to get a good plugging pulse at the exhaust ports just at the right time to keep it in the cylinders too.

[Tomtall]

Well ------------ I just wanted to jump in here guys and post the answer from the engine builder of "Name That Outboard" engine#16. Some great stories and tech. topic created by this mod build. Keep it coming!

The builder has the following to say of what went into this build.


In summary, this is a uniquely modified 32ci OMC, from ~ 1980. The engine is a two cylinder cross-flow with;

*Dual path induction with progressive linkage
*Two barrel carb feeding reeds on the front
*Single barrel carb feeding piston ports on the side
*Low inertia flywheel powering a dual firing ignition system
*Dual spark plug fast burn combustion chamber
*Single ring pistons with pressure ported ring groove
*Each cylinder with paired transfer ports, paired exhaust ports, and single piston port
*Folded expansion chamber tuned exhaust, within the tower housing
*Mercury MK55H 1:1 gearcase

[Tomtall]

I believe this engine has caused more posts than any engine in the BRF "Name that outboard" thread and for good reason. Countless hours went into the R&D of this wicked mod engine and it was ahead of its time. I have one last bach of pictures that have been shared with by sources unknown that show some of the port work that went into this engine. Also a few pic's from Sams posting "Dave's motor made quite an impression at a race in Wis. when we just set it on my boat or Paul Pittmans to see what would happen, it was almost a riot."

Coming up next for engine #17 another Merc. mod engine in the works by noted engine builder Tim Kurcz.