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View Full Version : OMC PROP with flo thru torque hub



gjohns6896
07-29-2002, 09:12 PM
I have a '92 18 footer, with the 350 SBC 5.7L with, I think, 1.43 gear ratio, and OMC King Cobra drive.

I am running the stock Viper 14.25 x 21" prop. I am only getting about 4000 RPM displayed on the tach and 56-58 MPH on speedo. Seems to me that the RPMS are low, and the speed is low as well. I KNOW the 350 has more of both in it, I just need to find it.

I want more speed, basically. It handles very well, and I am in smooth water...rarely ever get any chop at one foot or more. Only boat wake...and the biggest boat out here is a 28 foot Chris Craft.

Anyhow, I don't know which prop is best, and which will "fit" my application and desires.

I have heard of the 22/23 Mirage/Mirage Plus, but would need to acquire extra parts to fit it to my OMC.

Any suggestions?
George

MOP
07-29-2002, 10:48 PM
Not sure but I think the small blocks all had the Cobra not the king. The Kings do not have the shift interupter to studder the engine they shift with the cone shift setup like Volvo. If you have a pack bolted to the port elbow its a Cobra also no micro switch on the shift cable assy. Anyway beyond that there are alot of props available and Merc props can be re-hubbed to fit. try for suggestions as it can get expensive experimenting.

Eddie1823
07-30-2002, 06:27 PM
If you want to increase your rpm's you need to go down in pitch to a 19 from the 21. Check the tach first with an external meter to make sure it's correct. If you want to go with a Merc prop they all come thru only as a prop and you need to buy the hub adapter kit separatly. The adapter kits are available for most makes and models. If your only looking for top speed you might want to try a cleaver. That was the fastest prop on my 67 18 but the all around driveability wasn't as good as a round ear prop. If you do try a cleaver stick with the 21, the smaller blade surface will bring the rpm's up.

tailwind
07-30-2002, 11:46 PM
Hi George!

Noticed your post as I indeed have a very similar setup. Mine is a 1991 with the OMC 350 Spitfire, (Electronic ignition- no distributor). I have posted several times regarding speeds etc.

Now for the good news: youre OMC King Cobra is rated at 600 shaft horsepower, this is I believe listed in the operations and maintenance manual. From what you will see on this board, this will perhaps far exceed the limitations of the merc alpha drive! Newer Volvo Drives are based perhaps on this concept from what my local shop tells me. They buy all the used alpha drives, but no need to buy used King Cobra drives, for they would sit on the shelf.

Now off of my soapbox, Your VDO tach is a good one, but like mine periodically does need recalibration like all others. Second, check your drive ratio, mine is 1.5 to1. Third, the current "OMC Viper Prop" is 14.75 x 21, with alot more cup and savvy! Properly trimmed out with this prop, I realized an increase from 54 to 62.5 mph GPS. Your numbers should indeed be close to mine. I do have my old prop which I would be happy to let you try as a loaner, in which to verify our findings. Do you have trim tabs etc.?

Hope this helps and best regards,
Randy

gjohns6896
07-31-2002, 04:14 PM
No trim tabs, no exhaust. Just an engine and water all around.

What does the "cup" of the prop do? I have heard this mentioned before, but would like to know more.

Also, my Tach is NOT VDO it has DONZI stamped right on it. That tells me it is a Donzi gauge.

You might be right about the calibration thing...how do you do it though?

I am only using my ****ty speedo, too poor for a GPS. But my "pal" with the 31 foot C.C. walked right by me the other day, and he can ONLY do about 65 WOT. So, I must get more speed out of my 350!

HELP!

George