Fast Fred's OMC Mod 50 secrets Thread #2

[Jeff Akers]

Ah, good stuff. looking forward to that video!

[clough]

hey tim...just a question how is is that you have made it so that pressure can build up in the 2 stroke combustion chamber without valves? how does it not just blow through? or have you added valves?

[Mark75H]

It does not blow thru because the turbine holds it back.

That's the big advantage of turbos vs mechanical superchargers that have nothing to hold the charge pressure in.

With the turbo, it is as if the regular motor is in a giant pressure cooker

[clough]

it does not blow thru because the turbine holds it back.

That's the big advantage of turbos vs mechanical superchargers that have nothing to hold the charge pressure in.

With the turbo, it is as if the regular motor is in a giant pressure cooker

coolio! :d

[Tim Kurcz]

Regarding scavenging: Sam's answer is correct, the turbo restricts exhaust gas flow. I've given passing thought to installing a butterfly (and pressure guage) in the exhaust duct to test the effects of increased back pressure. More power, but more heat too. The power would reduce time to blowover, the heat would reduce time to piston meltdown.

Another often asked question is: Do the reeds close while under boost? I'd like to believe they do, but at high rpms and boost pressure it makes me wonder. Obviously they close for starting and lower power settings, but my guess is at some point they float. If I had access to an endoscope, the answer could be found within minutes in a test tank. Perhaps one of the factory engineers out there might answer the question?

The engine will be tested this weekend with all improvements previously listed, and possibly one more - a cockpit adjustable boost controller. It's an animal at 11-1/2 PSI. The controller will allow 15 PSI if desired......... Hmmmmm. Will report the weekend's outcome as time permits.

Tim

[clough]

Regarding scavenging: Sam's answer is correct, the turbo restricts exhaust gas flow. I've given passing thought to installing a butterfly (and pressure guage) in the exhaust duct to test the effects of increased back pressure. More power, but more heat too. The power would reduce time to blowover, the heat would reduce time to piston meltdown.

Another often asked question is: Do the reeds close while under boost? I'd like to believe they do, but at high rpms and boost pressure it makes me wonder. Obviously they close for starting and lower power settings, but my guess is at some point they float. If I had access to an endoscope, the answer could be found within minutes in a test tank. Perhaps one of the factory engineers out there might answer the question?

The engine will be tested this weekend with all improvements previously listed, and possibly one more - a cockpit adjustable boost controller. It's an animal at 11-1/2 PSI. The controller will allow 15 PSI if desired......... Hmmmmm. Will report the weekend's outcome as time permits.

Tim

i know the questions been asked but what kind of work would it be to setup some kind of exhaust valve? i know it wouldnt be operated by a cam so it is way above my knowledge but im sure theres someone out there that could do it! could be you tim!

[Tim Kurcz]

http://www.boatracingfacts.com/forum...t=7707&page=10

Here's an exercise on your exhaust valve concept.......... scroll way down the page.

Tim

[Mark75H]

The old Detroit Diesel that went into production as the Gray Marine motor sometime around 1930 and sold as Detroits starting in 1938. The design was a supercharged 2 stroke with intake ports and cam operated exhaust valves. GM engineered the motor and tooling but GM bean counters were afraid it would not sell so they leased it to Gray.

There were even versions without exhaust valves in the head, 2 rows of ports

Its an old time proven design

[Powerabout]

if you lose pressure out of the exhaust port, surely you just lower ther port.....
easier said than done

[Mark75H]

if you lose pressure out of the exhaust port, surely you just lower ther port.....
easier said than done

I don't understand