Fast Fred's OMC Mod 50 secrets Thread #2

[Tim Kurcz]

Dixon and I ran boats yesterday in glorious weather, along with an overactive general public: 80F temps and opening day of duck season! We were unable to get side by side, but managed a little fun between (too much) boat traffic.

The turbo ran first and scalded the river in a shakedown (no GPS). Dixon drove next and was delighted by the quick throttle response and quiet brute power. It reminded him of the dramatic transition the turbo made on his 44 Merc in the early 90's.

Refueled and GPS on board, Virgo suffered a difficult restart and delivered a disappointing 91.0 MPH. No wonder as it returned to dock on two cylinders. It had blown the head gasket big time; #1 on the intake side. By the time it was replaced, the river was a madhouse. No further top end attempts were possible.

In a period of brief quiet, Dixon drove the drag boat with a 17P three blade which scorched the water. There's nothing like the 6-cylinder sound and fury.... My turn was brief: A Sheriff was spotted on my return run so it was back to the dock quickly. There was a drive by, but no stop - Whew! Dixon then tried a 15P four blade that proved too short. Tight going on, the 15P couldn't be removed so the day was done.

Though a 50/50 day, much video and images were shot including cockpit video from the turbo. Video and images to be posted soon after it's collected from the many sources.

Many thanks to our ever-patient pit crew: Roger, Jack, Jeff, and Pat. We all agreed next years outing will be mid-week where traffic will be non-existent.

See you at Suters!

[Tim Kurcz]

http://www.youtube.com/user/Unfairad.../0/TVKRSrHZYfc

Unfortunately, the sound was disrupted by the ignition system. This was the 91 MPH run on two cylinders. Still pretty - enjoy the ride!

[formeone]

not to take away from anything ,,this where this site directed me,,,,... frack the boost ports,,,now that i have bin working with them for 2 seasons,,,, went 106,5 with out them,,, tried them now2 seasons,,, had to make props smaller to spin,,, it all top end with boost ports,,, no torque,,,,,, wil NOT cut my record prop.... my 2 cents

[Tim Kurcz]

not to take away from anything ,,this where this site directed me,,,,... frack the boost ports,,,now that i have bin working with them for 2 seasons,,,, went 106,5 with out them,,, tried them now2 seasons,,, had to make props smaller to spin,,, it all top end with boost ports,,, no torque,,,,,, wil NOT cut my record prop.... my 2 cents

Hey Cheney,

Boost is the center (angled), then fingers (angled ala Mod-50), then transfers (90 degree entry). If you're talking about finger ports, they have to be cut at the correct angle to be effective. What ports exactly are you talking about?

BTW: One of my best engines was a short rod Wiseco with no finger ports. Ultimately, power is dependent on correct port geometry and a complimentary exhaust system.

Tim

[Tim Kurcz]

not to take away from anything ,,this where this site directed me,,,,... frack the boost ports,,,now that i have bin working with them for 2 seasons,,,, went 106,5 with out them,,, tried them now2 seasons,,, had to make props smaller to spin,,, it all top end with boost ports,,, no torque,,,,,, wil NOT cut my record prop.... my 2 cents

Hey Cheney,

What ports exactly are you talking about? Boost is the center (angled), then fingers (angled ala Mod-50), then transfers (90 degree entry). If you're talking about finger ports, they have to be cut at the correct angle and fairly deep to be effective. Ultimately, power is dependent on correct port geometry and a complimentary exhaust system.

BTW: One of my best engines was a short rod Wiseco with no finger ports.

Tim

[formeone]

haatim ,,longtime no chat,,,, i guess the finger ports ime talking about,,,, i have blocks with 2 fingers and 1 finger port and also with the middle port moved differnt heights,,,, learned alot... this season getting back to running fast and dependable,,i runwiseco"s,,,small rods,,,, when itake one aprt and will measue width/depth of fingers,,,my machinest just go"s in at about a 45degg angle to put fingers in guess on angle,,,,depth1/4- 3/8th inch.. guess just below liner into aluminum,,, when i filled them all in with right stuff/ie great silicon,, in piston sooo would NOT work way more bottom end...saw 95 mph on certifed speedo,,at lawerance lake/smallwheel/,,, just no water ,,, so shut it down re-adjusted... bin learning the new boat,,,, it 42" wide on bottom,,,14 feet long,,,biggest in feh deff,,,it karelson.. deff a gass driveing her...

[Billsboats]

I registered on this site just to compliment all the information that has been displayed.
I am building a motor just for pleasure and have learned a few things. Keep the info and pictures coming Thanks

[Tim Kurcz]

haatim ,,longtime no chat,,,, i guess the finger ports ime talking about,,,, i have blocks with 2 fingers and 1 finger port and also with the middle port moved differnt heights,,,, learned alot... this season getting back to running fast and dependable,,i runwiseco"s,,,small rods,,,, when itake one aprt and will measue width/depth of fingers,,,my machinest just go"s in at about a 45degg angle to put fingers in guess on angle,,,,depth1/4- 3/8th inch.. guess just below liner into aluminum,,, when i filled them all in with right stuff/ie great silicon,, in piston sooo would NOT work way more bottom end...saw 95 mph on certifed speedo,,at lawerance lake/smallwheel/,,, just no water ,,, so shut it down re-adjusted... bin learning the new boat,,,, it 42" wide on bottom,,,14 feet long,,,biggest in feh deff,,,it karelson.. deff a gass driveing her...

Good to hear from you too Cheney. Finger angle should match the boost, about 1/4" deep X 3/8" wide is about right. Tops must all match exactly to work well..... Good luck with the watering. It only takes 3-5 seconds at top to toast one. Voice of experience - ouch! Your new boat should get around a corner like on rails. Send pic.

Tim

[tumblweed9999]

I kept the flywheel and starter motor when I repowered my fishing boat after reading these forums. Changed out a 72 Triumph 65hp Electric shift up to a 1978 Johnson-70hp Mechanical shift. I see the teeth on the flywheels and starters dont interchange either.
I also kept the carbs because I believe they might be/maybe other than stock. Perhaps from an early 70-75 hp. They have an X stamped in upper left by front of carb bore above the choke plates. And a dab of Stinger Orange paint on the side of the body of each carb. There was something about this mentioned on Scream n Fly about the factory's instruction to mark carbs like this when the fix was performed. It was a service bulletin to fix the transition from low speed to hi speed circuit. Ream out idle holes and rejet the idle air jet to a 32 or something. Only thing I see that might be wrong with this picture is the bulletin is for fixed jet carb. these are Needle/mixture screw carbs. The bore of both sets of carbs are equal front and back but the unknown 72 carbs have a tighter venturi opening and the main jet ends at a 45 degree in the center of the bore. I guess what im after is the hole shot. The 72 had a manly hole shot. Real snort. the 78 has a girly man hole shot. the 72 never spit gas vapors when you quick revved/thumped it on the garden hose with the silencer off. The 1978 has a bit of spit back when you thump her. ( float level?) or is this a known difference between a 65hp and 70hp? The 70 is definitely more powerful 2/3 of the way up the power band. But the 65 spun up faster. if 49 cid is 49cid can i hurt anything running the other carbs? they have never damaged the 65hp. She was still kickin *** when i hit er in the head. I just wanted modern shifting and the parts availability that go with it. Thanks....old thread......might just be talkin to myself.....

[Tim Kurcz]

Hey Tumbleweed,

The OMC triple carbs come in three venturi sizes 1.125", 1.187", and 1.250". Smaller venturi's will get you stronger bottom end, larger venturi's get you better top end. These carbs all share a 2.375" bolt pattern and may be interchanged at will.

Whatever carb changes you make, you shouldn't EVER quick rev and engine! Spitback can be controlled with velocity my stacks ($175/set includes fasteners and shipping).

Best for you to do some lake testing. Just be sure to monitor plug reads frequently until you get it sorted out.

Tim