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I have a OMC 920cc Stinger motor on a new race boat I have recently picked up. I know its a 920cc its a stinger and a OMC. And that's about it hoping that someone on the site can fill me in on the story behind these motors, what to look out for, rpm to aim for, fuel ration ect.
I cleaned out the carbs, found its got carbon reeds, 2 different brands though, bottom ones different to the top 2.
Looks like chokes been removed and a solenoid injection setup fitted instead, anyone know much about them?
I also don't have much of an idea what the 49 and 56 blocks are or what years different engines come form so please be as basic as possible.


http://postimg.org/image/ohjgx08mr/

http://postimg.org/image/w5svsoyzt/

http://postimg.org/image/olauw0efz/

920cc or 56ci, never came stock on a stinger. We just convert them. Because of the hood, it looks like you have an SST-60 with a Mod 50 front half. Those look like 2 barrel carbs on there. Very cool. It is the 56ci block. I'm guessing around 8000rpm (not really too sure with that setup). What kind of boat is it on?

Jesus..I don't like many 56'rs but that is a badass looking motor! I'm no expert but I think Kevi is right on saying it's a 56 with a mod50 style front (which would have to be homemade right?).

I'd love to see a pic of the carbs straight on..

I could be wrong but I'm pretty sure the Mod 50's came stock with the 2 barrel carbs.

Yes, mod50 came with the dual barrel carbs. Two different generations of front halves, the first gen had 8 petal reeds (same reeds as what is run in the two banger and v4's) and the reeds went in on an angle like the one in the pics. The next gen was 10 petal reeds but no angle straight in. From what I have read the engineers at omc worked with the mod50 front half on a 56er but could never get as much power out of it as the last generation of the actual mod50 motor even though the 56er had more cc's. The exhaust on the 56er is the limiting factor they say.

Ran the motor today, was slow, compression checked 120psi.
I would assume it should be closer to the 200psi mark?
I has a holly fuel pump and reg, would 5psi fuel pressure sound right?

How slow is slow? I guess it really depends on how it's ported as to how much compression it needs to make it all work 100% but I would figure it'll still run and work at 120....maybe it needs a leak down test to see if there are rings still in there. Pull the head an see what you've got. Maybe it needs freshened or maybe it's got a safe pump gas head on it...

120 psi is on the low side unless it's just a stock block and head. A sst60 setup is 170-180. Pull the head and measure the port heights and head depth.

5 psi for fuel is ok.

Did you pull your plugs and see what they look like? See what the piston burn looks like as well.

What pitch and diameter of prop are you running? Will need the rpm as well

It pulled 63kmph, should be double that were aiming for the 120kmph/85mph mark.
Is got a 23in prop on it, planed well sat ok just didn't go fast.
Plugs looked fine. Going by how slow its going I'm not even worried about porting or anything else at this point. I just want it going first then I will have a go at increasing performance.
To me slow as and 120psi is stuffed motor.

Even with 120 psi you should be able to run 60 mph plus no problem. Dok's yamaha 70 with 125lbs of compression runs 64 ish day in day out.

The reason Dok and I mention the port heights is because if your exhaust port is really high it could explain why you only have 120lbs of compression.

Best to get a tach in the boat, check to make sure the carb butterflies are opening up all the way