Fast Fred's Secrets of the OMC MOD50's Thread #1

[Detroit Whitey]

well lets see the internals i`ve been kicking this around for some time and even started to make one but lost the time to finish but i would like to see more

[850cc racer]

Hey there fred. its been aaaaages i have something trick to show you, gots me a 920 with ft front, and a trick head. ill take some photos in the next few days! no water goes back down through the midsection!

[Fast Fred]

cool, would like to see it.

[formeone]

haaa fred ...can you repost your port map seems a few of us cant down load/look at it ,,, still curious...

[Fastjeff57]

Disk valves really work efficiently only in a single cylinder motor--note the successful Kawasaki and Can Am dirt bikes of years ago. When cylinders are stacked one atop another, it requires an external barrel like the old racing Johnsons, and that kills the efficiency--long, dead air space in passages.

Jeff

[Mark75H]

Jeff, don't tell that to the thousands of racers who have driven disk valved 2, 3, 4, 6 and 8 cylinder König racing outboards.

The 4, 6 and 8 cylinders used an external disk, the stacked 2's & 3's used internal disks without the long dead air spaces. Konig also derived a 3 cylinder motor for Volvo with internal disks and no long dead air spaces.

The same designs were not used on motorcycles because it would have made the motors too wide with the power take off and clutch stacked on the side, not because it could not be done or didn't work good enough.

[Sam La Banco]

Great point SAM, the champ hot rod didn't do to bad of a job either.

By the way, in the mid 60ies there was a 2 cylinder bike with dual rotor valves
that was a rocket for their size. The BRIGSTONE 175 AND 350.

Both were killer fast.

[850cc racer]

okay so heres a 920cc head. me thinks someone has put some time into this one..


and some work to the block not gonna use this. it was meant to be "fully rebuilt" when i bought it, 2 pistons dont even have fingerports in them, and two have scores on them u cold grate cheese with!

[Bill Gohr]

While the Scott had what some people call "true" rotary valves, discs are too, any "valve" that rotates is one. While the Scott had the nice "add on" system it left alot of dead space behind it, if it was incorporated into the front half it would have been better.

And if you think that a disc is not as efficient, don't tell Rotax that they may disagree with you and their always successful bike and snowmobile engines, as, don't forget the Gamma, 500cc 4 cyl bike motor..................

[John (Taylor) Gabrowski]

Just looking at your Mod 50 as I have not done a thing to the new 49 incher 3 Holer SE motor that is stock yet, like your motor I am going to run into spots in the crankcase where there is a casting ridge, edge or something you would think would be smoothed out for better gas flow or is that not really nesessary? I got this thing a out any potential for a particle of aluminum to break free too. Its a kind of paranoia that worries that something small breaking loose can make a big mess.

A lot of 2 strokes for racing and pleasure have the bell shaped heads. Some use offset squish to one side into combustion chamber proper to make the charge very turbulent before ignition. How do the designers determine what makes the best combustion chamber for what kind of loop charged engine. Is there some kind of set of rules governing a given overall engine design or??