Any problem going from 21p to 17p prop?

[ritewing]

I took lower unit from 470 merc and put on 140 upper. And I left the 17p prop, cause it was in better shape. Will it do alright on the morphed drive? The boogered up lower from the 140 had a 21p prop. The diameter is the same. Thanks

 

[jestor68]

Re: Any problem going from 21p to 17p prop?

According to my chart, the 470 had a 1.84 gear ratio; while the 140 used a 1.98 gear ratio.

Since you put a 470 lower unit on there, you now have that gear ratio(1.84) and can use the prop better suited to that ratio(17).

You will need to run it and see if it performs within it's proper rpm range. The WOT rpm range you're looking for should be 4200-4600 rpm.

 

[thumpar]

Re: Any problem going from 21p to 17p prop?

According to my chart, the 470 had a 1.84 gear ratio; while the 140 used a 1.98 gear ratio.

Since you put a 470 lower unit on there, you now have that gear ratio(1.84) and can use the prop better suited to that ratio(17).

You will need to run it and see if it performs within it's proper rpm range. The WOT rpm range you're looking for should be 4200-4600 rpm.

The ratio is set in the upper unit. So no change in ratio when changing the lower.

 

[jestor68]

Re: Any problem going from 21p to 17p prop?

I think I got the rpm range right; or did I screw that up too? :faint2:

 

[Bondo]

Re: Any problem going from 21p to 17p prop?

I think I got the rpm range right; or did I screw that up too? :faint2:

I took lower unit from 470 merc and put on 140 upper.

Nope, yer right,.... It's a 1.98:1 Upper....