How to tell OMC 5.0 from 5.7

TinPig · Dec 7, 2009

I bought a boat with an omc cobra set up. I was under the impression it was a 350 motor. However the tag on the outdrive listed the engine as 5.0 Does that outdrive work on either motor or is it in fact a 305 engine.

I'm new to the game, so please enjoy my ignorance...lol

I do however appreciate any and all comments. Thanks Guys!!

EDIT

The boat is a 1987 24 ft. Bayliner Trophy

JustJason · Dec 7, 2009

Re: How to tell OMC 5.0 from 5.7

Unless you've been the original owner for the last 22 years there's no way to tell other than pulling off the block someplace a model and serial number at best, engine casting numbers at worst.

Bt Doctur · Dec 7, 2009

Re: How to tell OMC 5.0 from 5.7

The GM family has the dist in the rear of the motor
The Ford family has it in the front of the motor (5.0)

Lou C · Dec 7, 2009

Re: How to tell OMC 5.0 from 5.7

Depending on the year....OMC used both the GM (Chevrolet) 5.0 and 5.7...in my '88 factory manuals it lists the 5.0 and 5.7 as both being available with the 4 bbl carb...and I believe the same was offered in '87
if you look over at
www.dougrussell.com
go in the parts section for your year OMC you might find more listings that can help you figure it out...the problem is that on the outside the engines themselves look pretty much the same....some OMCs when then still had the OE exhaust manifolds on em had a big sticker with the engine displacement on them...my 4.3 had a 4.3 4V sticker on each manifold...and I have seen 5.7s with a 5.7 sticker on the valve cover... I guess to make it clear that it's not just a 5.0...the only other difference that is notable is that the overall ratio in the drive is 1:50:1 for the 5.0 and 1.41:1 for the 5.7...the upper gear ratios are differnt but the lower gear ratios are the same...look at the tag on the drive to see if it gives ratio #s...

dan t. · Dec 8, 2009

Re: How to tell OMC 5.0 from 5.7

look at the back of the block behind the port side head for the casting number and go to www.mortec.com

TinPig · Dec 8, 2009

Re: How to tell OMC 5.0 from 5.7

thanks guys!!

I did notice that there is a tag on the outdrive, on the lower unit that states the enginge type as 5.0. could that outdrive still work with a 350?

I'm gonna look for the block castings next.

Alpheus · Dec 8, 2009

Re: How to tell OMC 5.0 from 5.7

Yest the outdrive will bolt up to a 5.0 (305ci) as well as a 5.7(350ci) the blocks are identical on the outside except for casting numbers. The 5.7 will have a 4" bore while the 5.0 will have a 3.736" bore.

Don S · Dec 8, 2009

Re: How to tell OMC 5.0 from 5.7

Have you determined if it's a Ford or Chevy engine? OMC used both.

Gary H NC · Dec 9, 2009