OMC King Cobra Outdrive gear ratios

[Striper Blues]

The manual on my 460 (7.5L) King Cobra i/o , 1989 vintage says the drive ratio is 21:17. I have a line on a spare and the fellow is telling me it will fit and has a ratio of 1 to 4.1? Must be the new math or something. How do I relate these two sets of numbers? Or what is the corresponding ratio to the 21:17?<br /><br />thanks,Pat

 

[HT32BSX115]

Re: OMC King Cobra Outdrive gear ratios

Pat, <br /><br />I looked in my OMC service manual, and found the following. (mine is a 1987 7.5L King)<br /><br />I have the 754BPFTC, upper gear ratio is 21:17, lower gear ratio, 17:30 <br /><br />you multiply the fractions 21/17 x 17/30 = 0.7 (similar to calculating the final ratio for a transmission/OD and rear end in a car or truck)<br /><br />0.7 means "1 rev of the U-joint shaft results in 0.7 revolutions of the propeller shaft" (taken directly from the OMC manual)<br /><br /><br />Overall ratios for <br /><br />2.3L ... 2.00:1<br />3.0L ... 1.71:1<br />5.0L ... 1.50:1<br />5.7L ... 1.41:1<br />7.5L ... 1.43:1<br /><br />According to the OMC manual, for the 7.5L drive, "1.43 revolutions of the U-joint shaft results in 1 revolution of the propeller shaft". <br /><br />So for the 7.5L, <br /><br />"Total Ratio" is 0.7 and similarly the "Overall ratio is 1.41"<br />(The 2 mean the same thing)<br /><br /><br />So this isn't "new" math.....evidently the person wrote it down or read it wrong. It's 1.41:1 ......This makes it a vertical drive from a 5.7L application. <br /><br /><br />Hope this helps!<br /><br /><br />Regards, <br /><br />Rick

 

[Striper Blues]

Re: OMC King Cobra Outdrive gear ratios

Rick,<br />thanks so much that is an excellent explaination. Much appreciated,<br />Pat

 

[Striper Blues]

Re: OMC King Cobra Outdrive gear ratios

Rick,<br />I should have also asked about the drive off the 454 chevy setup I think its a 7.4L. Is that the same at the 7.5 - 1.43?

 

[HT32BSX115]

Re: OMC King Cobra Outdrive gear ratios

Pat, <br /><br />I have the 1987 service manual. It only indicates the ratios available then. I believe the 7.4L (GM big block) might be a somewhat newer unit. Someone else here might be more familiar with the newer models.<br /><br />I don't know how long they offered the Ford (460) setup.<br /><br />Sorry about that!<br /><br /><br />In another post I asked about the similarities of the OMC's and new Volvo drives. Evidently the newer OMC Cobras are similar and in some cases identical to the Volvo SX type vertical drives. This doesn't help us though since our 1987/1989 drives (and up to about 1993 I think) were different enough such that the newer stuff will not interchange. I saw a practially new Volvo DPX-A 1.47:1 Duo-Prop vertical drive for sale on eEbay for a pretty reasonable price. To make it work one would have to replace just about everything from the flywheel---back! (and add a raw water pump) among the other stuff like steering, exhaust, trim pump etc. A pretty daunting job! <br /><br />We must remember that it's not always good to fall so completely in love with our boats that we spend more on them than is practical or keep them longer than we should!<br /><br />I for one tend to hang on to things way too long.....I have a 1966 Mark Twain 18' with a 150hp Mercruiser.(I was 13 when my dad bought it new....I remember that day well!!) I have decided it's time to sell it ....I have 1 too many boats now! I got the Four Winns from my brother who bought it new. It's about 19 years old now.....so I have to keep it at least 20 more years huh? (!!)<br /><br /><br />Cheers, <br /><br />Rick

 

[Striper Blues]

Re: OMC King Cobra Outdrive gear ratios

Thanks again Rick..<br /><br />Can anyone else tell me if a drive off the Chevy 7.4L (with the kone clutch) will fit my 7.5L ford set up? King cobras that is....

 

[Boatin Bob]

Re: OMC King Cobra Outdrive gear ratios

I'm pretty sure 1990 was the only year OMC offered both the 7.4 and 7.5 with clutch cone drive. I don't think you can mate a clutch cone drive (1990 and up) with a clutch dog assembly (1989 and lower), the transom mount and everything are completely different. Have a look on the Doug Russell site between a 1989 and 1990 7.5 Doug Russell

 

[Striper Blues]

Re: OMC King Cobra Outdrive gear ratios

Bob,<br />As far as I can tell from Doug Russell parts breakdowns the transom mounts and shafts are the same part numbers for a 1989 7.5 and subsequent 7.4L's. I've read before about the superior design of the Kone clutch and thought if I were going to pick up a spare drive, I should try to secure one. I guess I will look for a local shop to see if they have any experience with this issue.<br /><br />Thanks,<br />Pat

 

[Striper Blues]

Re: OMC King Cobra Outdrive gear ratios

I spoke too soon. The part numbers are the same on the 1990 7.5 and 7.4. It looks like the 1989 transom mount has a differnt pn......doh..

 

[rodbolt]

Re: OMC King Cobra Outdrive gear ratios

first its imperative to positivly ID your unit as a king cobra with a cone clutch, bayliner sold a bunch in the late 80's that had a king cobra decal but were clucth dog units,friend of mine owned one for years and when the 460 went we installed a 7.4 as the 460 was nla.<br /> best i remember the shift cables entered on opposite sides from the cone to the dog units and took a seperate shield and gimbal assy.<br /> there really is no interchange from any of the pre 94 jv units to 94jv units jv means Joint venture, its the time in the mid ninties OMC and VOLVO had a partnership. volvo bought out OMC and OMC stern drives dissapeared about 95.<br /> so be careful about labels it can bite you, my buddies 89 was a dog shift, I know cause I had to rebuild it once.<br /> but it had king decals.

 

[Striper Blues]

Re: OMC King Cobra Outdrive gear ratios

Thanks again guys. I'll pass on this unit and wait for an 89 to show up. Getting hard to find.<br /><br />Pat

 

[Boatin Bob]

Re: OMC King Cobra Outdrive gear ratios

Pat...they are out there, here is one for sale up here in Canada, bit pricey but I know this guy does good work KC Outdrive