Help Identifying my 307 Engine

mabacci

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Joined
Aug 7, 2012
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3
Hi,
It's my first post in this community.
I am from Argentina and i have a 23' DayCruiser with a Chevy or OMC 307 Engine.
I am trying to identify if my Engine is the Marine Version of the Chevy 307 build by OMC or it is a Vehicles Engine that was adapted to work on the boat.
I was looking in the OMC Model Number Guide that is in one of the sticky posts of this forum but can't find any of the numbers i have.

Where i have to look to find the Model Number?

This is my casting number 39700020 and this is my VIN number VIN 172499 V09111 with two additional letters that are not so clear may be it is one of this pairs OT/ST/GT.

Thank you very much in advance for any help you can give me.
Maximiliano
 

Boomyal

Supreme Mariner
Joined
Aug 16, 2003
Messages
12,072
Re: Help Identifying my 307 Engine

Your engine is most likely a 305 Chevy, not a 307. There are very few parts of it that are not the same as automotive. They do use brass instead of steel 'freeze' plugs. The cam is marine specific but they are very truck like. They are intended to develop maximum torque, low on the RPM scale AND with suitable overlap so as not to suck any water back into the engine (reversion). There is nothing marine specific about the cylinder heads or valves.

Of course most of the peripherals like the distributor, the carburetor, the starter and the alternator are marine grade.
 

mabacci

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Joined
Aug 7, 2012
Messages
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Re: Help Identifying my 307 Engine

Thank you Boomyal for your answer.
Regarding to the Specific Marine Parts, my engine has Marine Distributor for sure, it is a Mallory YL Series with points.
About the CID i'm sure is 307 ci, i found some time ago an Excel WorkSheet with all the Casting Numbers of Chevy Small Block engines and i found my Casting Number there as a 307 ci.
My real problem is that i have to be sure if it is OMC or Chevy Automotive engine because i need the RPM Range in Wide open throttle to check if i can put a larger pitch propeller than the one i have.
Thank you again for your answer.
Best Regards,

Maximiliano
 

Boomyal

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Aug 16, 2003
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12,072
Re: Help Identifying my 307 Engine

What year is your boat and which of the OMC outdrives does it have? Who knows what OMC may have used in your neck of the woods but the 307 was a fairly short lived variation of GM's small block V8. It was mostly used in Oldsmobiles and ended up being used in Chevrolets back when GM began to put any old engine in any car they sought fit. The 307 was also used in Australian cars and South African cars. If your boat is indigenous to Argentina, It would still be hard to believe that OMC would have made different packages for different areas. Perhaps someone swapped out the original motor for what was easily obtained.

As to propping your boat, I think you could safely say (assuming your motor was built for marine use, the cam being critical here) you could consider 4600 rpm a safe WOT number. Most all American V8's used in marine applications had WOT RPM's in the low to mid 4000's.
 

mabacci

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Joined
Aug 7, 2012
Messages
3
Re: Help Identifying my 307 Engine

Boomyal, my boat is a Paglietini 690, it is from the 60s, more exactly it was built in 1969.
Originally the shipyard used to put a Mercruiser Engine built from the Chevy 250 Engine.
My outdrive is a Volvo Aq280.
Here in Argentina old Cruisers usually have the engine and outdrive of different brands.
I found in this forum an Engine that is identical to mine, i copy you the Link to that post.

http://forums.iboats.com/mercruiser...ives/1972-slickcraft-omc-stringer-285397.html

I will take in count your advise about the WOT RPM's i read somewhere on the internet this afternoon that should be between 4000 and 4400 RPMs for the OMC Engine.

Thank you very much for your help!!!
Maximiliano
 

Boomyal

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Joined
Aug 16, 2003
Messages
12,072
Re: Help Identifying my 307 Engine

mabacci, as stated before, outdrive mfg branded engines, whether for Merc,Volvo or OMC, were usually always near production line automotive engines, be they Ford or Chevy. I think considering the age of your boat/engine/drive and the boat's size and weight, the 4400 rpm is a safe WOT rpm. That is what you should prop it to, even though you might not want to run it there for any length of time. Propping it to 4400 will keep the motor in it's torque curve even when running down in the mid to low 3k rpm range.
 

matt167

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Joined
Sep 27, 2012
Messages
3,630
Re: Help Identifying my 307 Engine

307 was a mutt engine but common in cars like Chevy Nova's. The Olds 307 is a different animal., Basically a large journal 283 block with a large journal 327 crankshaft. Never heard of them as marine engines but I guess they did exist. Not an ideal setup for sure. 307/327 stroke is 3.25" and a 305/350 is 3.48", so a 305 would actually be an upgrade in a boat because of the torque. 305 did not come out until '74-'75 or possibly even later than that ( in cars )
 
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