4.3 to 5.7 swap gearing

[3car]

4.3 to 5.7 swap gearing

According to the Mercury prop selector site, 2000 model alpha one I/O's with small V8's had an outdrive ratio of 1.62, while V6's had a ratio of 1.81, which is about a 10.5% lower ratio.<br /><br />I have searched and read several threads pertaining to similar topics, but I am still unclear on a few things.<br /><br />The 4.3 and small block V8 engines have a similar powerband in stock form, so why are they geared differently to begin with? <br /><br />What would result from doing the swap, and upping the pitch of the prop? I have tried to find people with first hand knowledge on the subject, but all I have found is a wide range of opinions. <br /><br />I am fairly new at this, so take it easy on me. I know efficiency will suffer somewhat from this recipe, but what about acceleration and top speed performance?<br /><br />Anybody know of any calculators online that might help me figure this thing out?

 

[Don S]

Re: 4.3 to 5.7 swap gearing

Re: 4.3 to 5.7 swap gearing

Torque and horse power.<br />In general (boat size and weight also plays a part in the equasion)<br />The 4.3L carbed engines, 190 hp use 1.81<br />The 5.0L carbed engines, 220 hp use 1.62<br />The 5.7L carbed engines, 260 hp and up use 1.47

 

[3car]

Re: 4.3 to 5.7 swap gearing

Re: 4.3 to 5.7 swap gearing

I noticed on the mercruiser website that the 5.0L and 5.7L carbed motors have the 1.81 outdrive as an option for high altitude.

 

[Don S]

Re: 4.3 to 5.7 swap gearing

Re: 4.3 to 5.7 swap gearing

That's because they don't have the torque and horsepower at high altitude as they do at sea level.<br />Notice when the air and fuel and ignition is controlled by a computer on EFI engines that it's not necessary to change gear ratios.<br />Not sure how old you are, and you may not remember trying to drive a carburated, fully loaded station wagon from sealevel over the mountains. They wouldn't get out of their own way.