5.7 cobra with 5.0 cobra outdrive

[boatingfamily]

I own a 1989 Donzi Ragazza and had a engine coupler fail. After removing the outdrive I took notice of the serial # plate on the side of the outdrive. The plate reads model# 985271 serial#T0612251 5.0L. After a little research I found that this outdrive is a 1988 and the gear ratio is 1.5 to 1 instead of a 1.41 to 1 that was originally with the 5.7. Can anyone tell me how this will effect my RPM and can I compensate with a higher pitch on my prop. The prop that is on it is a 15x17. Any input will be greatly appreciated.

 

[bruceb58]

Re: 5.7 cobra with 5.0 outdrive

Re: 5.7 cobra with 5.0 outdrive

Shouldn't be a problem. Everything is identical. Same coupler is used on the 4.3 as well. The drive ratios between a 5.0 and 5.7 are not exactly the same.

Edit: The gear ratio may be the same as well.

 

[JustJason]

Re: 5.7 cobra with 5.0 outdrive

Re: 5.7 cobra with 5.0 outdrive

Welcome to Iboats.

Elaborating on what Bruce just mentioned, Merc 5.0's and 5.7's share alot of common gear ratio's. As long as when it's up and running, you have the correct WOT RPM's, your good to go.

 

[boatingfamily]

Re: 5.7 cobra with 5.0 outdrive

Re: 5.7 cobra with 5.0 outdrive

Thanks Bruce, I edited my original post after a little research and found the difference in gear ratios. Now I am just looking for info on a prop. Can I step the prop up in pitch to compemsate? Does anyone know what the WOT rpm should be on my 89 chevy 350 with a 4 barrel?

Thanks everyone,
Bruce Bennett

 

[Don S]

Re: 5.7 cobra with 5.0 outdrive

Re: 5.7 cobra with 5.0 outdrive

It would be best to post your prop question over in the prop forum. If your 5.0L is actually an 89, the WOT rpm is 4000 to 4400 rpm. If it's an 88, the spec is 4200 to 4600. Guess OMC didn't like those extra top end rpms they had on the older one.

 

[bruceb58]

Re: 5.7 cobra with 5.0 cobra outdrive

Can anyone tell me how this will effect my RPM and can I compensate with a higher pitch on my prop. The prop that is on it is a 15x17. Any input will be greatly appreciated.

Back when I had a Cobra with a 5.0 I was using a 15x17 prop for sea level so it sounds like you are fine.

The difference between a 1.50 and 1.41 is so small(less than 1 percent) that it is less than the increments of pitch you can buy for the props so no need to worry.

 

[boatingfamily]

Re: 5.7 cobra with 5.0 outdrive

Re: 5.7 cobra with 5.0 outdrive

It would be best to post your prop question over in the prop forum. If your 5.0L is actually an 89, the WOT rpm is 4000 to 4400 rpm. If it's an 88, the spec is 4200 to 4600. Guess OMC didn't like those extra top end rpms they had on the older one.

Thanks Don I will jump my prop question over there. I was asking about the WOT rpm on the 5.7 litre though, not the 5.0. Let me clarify to avoid any confusion. I have a 1989 5.7 litre chevy engine with a 1988 5.0 outdrive. As soon as I figure out what my WOT rpm needs to be I can start playing with props to get it there. Thanks for the all the help!!!!

 

[Don S]

Re: 5.7 cobra with 5.0 outdrive

Re: 5.7 cobra with 5.0 outdrive

Sorry, guess I got the numbers mixed up by the time I got to the book.
4200-4600 for the 89 5.7L.