mercruiser gearing

[ianmac09]

Hi,
I just killed my outdrive, upper gears destroyed . I have a replacement gear and bearing set available cheap but it is the 1.5 to 1 ratio. The engine is a 1991 4.3litre V6 and it has a high 5 prop. I think the stock gearing was 1.68 to 1 but not certain about that. So I was wondering how much the change in gearing will affect the performance, anyone?
Thanks

[J3]

Since no one else has replied, I know replacement upper units come in 1.81 (for 1.84) 1.62 (for 1.65) and 1.47 (for 1.5). I think a lot of 4.3 v6s were mated with 1.84 gear ratio. I take it yours is a light boat?

For the 1.65 to 1.5 keeping the same prop, if it was perfect before the new would lug the engine a bit. Would this affect how easy/quick it is to get up on plane? Top speed? Hard to say without knowing the particular boat. If it was perfect before, I'd sell and buy a new one on ebay and get what you know works well.

[ianmac09]

Thanks for the reply, I discovered it is a 1.81/1 gear set (17-19) so changing to 1.5-1 is probably going to suck. For info it is a 1991 Campion Allante 175, so yes a fairly light boat. I bought the correct replacement parts online from Basic Power and so will get into fixing it next week, looks like a fun job.

[gonzo]

It will overload the engine. The piston will be really hot and may melt a hole. Also the valves may warp or burn.

[Jango]

With the 1.5 gear your prop will be turning about 500 RPM more, 3000 vrs 2486 @ 4500 motor speed. Assuming your present prop is correct, you will need to drop 3 to 4 in. of pitch with less Dia or the motor will be overloaded.
If you can work out the Prop the 1.5 ratio should be OK