cobra gear ratio

[jchris1062]

I need to replace the drive on my 1989 21' four winns. The boat came with a 5.0 cobra. I replaced the motor with a 5.7. The drive is need of repair. I know that the ratio is different between the1989 5.0 (21/18) and the 5.7(21/17 before 1989 and 24/29 after) Should I look for a 5.7 cobra or repair the 5.0 I have? Would there be any real difference in performence? The est cost to repair my unit is around $1,000 without changing the gear set. Thanks for your help!!

 

[Darkhorse1201]

Re: cobra gear ratio

IMHO i would have the 5.0 repaired. A 5.7 drive might cost as much as the repairs and at least you know it works. If you bought a replacement drive for the 5.7 you might end up sinking more money into that after the fact. Have you seen what drives go for nowadays even on ebay? Any difference in the gear ratios could be ironed ouot with different pitch props. I runa 5.o drive on a 4.3 engine and just repropped it and it runs great! Once again - just my opinion.

 

[jchris1062]

Re: cobra gear ratio

Thanks. I can get a 5.7 from a friend for around the same cost as repairing the 5.0. I was just wondering about the gear difference and performence.

 

[lrlima]

Re: cobra gear ratio

what is the "rule" when re-propping due to different outdrive ratios? In swsidlo's case above, do you go to a smaller prop? Like a 17?

 

[lilmandavis]

Re: cobra gear ratio

5.o has 21/17 ratio
5.7 has 21/16 ratio...
not very much of a difference is that? but with the added hp, is the omc goin to be able to handle it?

 

[Don S]

Re: cobra gear ratio

As with any prop, too little pitch or too much pitch and you loose efficiency (speed, power, etc) when trying to compenstate for the wrong gear ratio. That is why the drive manufacturers have different gear ratio's, so they can stay within a certain range. Usually (but there are exceptions) in the 15 to 21 inch pitch range.

 

[DHPMARINE]

Re: cobra gear ratio

So many people figure this can be cured by a prop change.Were this true,ALL outdirves would have the same ratio on every engine.

DHP