Hey all, so I recently bought a 1990 Chaparral 2350 in need of an engine. It had a 350 OMC setup and I’m swapping in a 351w, also OMC. The chaparral and the donor boat both have 4.3 drives on them which work but I want the correct gear ratio. I found a deal on a big block king cobra drive and wanted to know if that unit will bolt up and work with the 351w or if I should keep hunting for another drive. Also don’t need opinions on the OMC, I’m not a huge fan but it’s what I have until I get my other boat restored. TIA

The 4.3 drive has a 1.68 ratio.

5.7L ratio 1.43
King Cobra ratio 1.41

Are you asking about mounting a King Cobra on a regualar Cobra transom assembly?

1.68 ratio isn't too bad for a small block. 1.43 is on the lower side.

Largely depends on what your max speed will be. Faster boats need smaller diameter props mltirning faster/more pitch to reduce drag.

Slower hulls you can get away with larger dia props turning slower to increase efficiency.

The 1st king cobra’s were a dog clutch style drive that was used with the
460 ford ( much like the 1st 454 magnum merc’s/ alpha 1) I as I recall,
it had a lower gear ratio ( in the 1.3 range)

As they (OMC ) did what Merc did when the Volvo cone clutch patent expired they came out with the King Cobra cone clutch drives,
around 89’. I’m thinking 1.4ish on the ratio on these, you would have to have a transom assy also and related components to make these work.

Is the drive any good on the 5.7 unit you already have?, if so,
I would use it.

Just be aware also that SEI makes a Conversion to adapt an Alpha to your Cobra transom assembly if you can't find what you need in the way of OMC stuff.