Identification help

Is this the motor in your '75 Skier?



Do you have a reason to believe that its not a 307, as you have listed in your diary? Im not sure which year OMC went from offering the 307 to the 305... but Im guessing it was '75 or '76.

Either way, unless youre talking about a much larger engine in a different boat, the 12x15 and 12x16 Federal props are both way too big for a 305/307. A 12x14 Federal would have been the more commonly equipped prop, and even a 12x13 Federal would probably perform pretty well on it.

If youre considering upgrading props, either the 12x13 OJ or Acme 1210 (12.5x12) would be the 2 choices I would consider.

You can call the factory and see if they can look up the build sheet for your boat. Not sure if it would have any more specific information than "OMC 225" though. If your original owner's manual says its a 307, then I would believe it. OMC also called the 305 a 225 if Im not mistaken, just a year or 2 later. I would expect the 2 motors to perform pretty similarly either way. Its just a bore/stroke difference between the 2, if Im not mistaken.

No idea why some boats came with the "wrong" prop installed. My Skier supposedly came with a 12x15 Federal from the factory as well. The holeshot was not very good, and the 12x14 would have been better. Heck, Im currently running a 12x13 Federal and its probably better on my particular boat than either of the others.

I really liked the 12x13 OJ that I tried- easily my 2nd favorite prop on this boat. The Acme 1210 that I normally run is the best all around performer. You'd be amazed at what a prop change can do to the way the boat runs.

[QUOTE=TRBenj].

No idea why some boats came with the "wrong" prop installed. My Skier supposedly came with a 12x15 Federal from the factory as well. QUOTE]

Tim,I'm curious as to how you know a 12x15 came from the factory. When I first got mine I had no prop.I wrote the factory asking what to use,they had no idea. There was nothing on the build sheet for mine.

I was just wondering. Back when I got mine I was at a loss and with no internet and of course no CCF to help me out either! I used a couple of old props my Dad had from his Chris Craft days to get me started,and had always felt they were lacking. Thanks to Reid who got me set up with a Federal 12x14 as a spare and an OJ 12x13 for everyday.

Some of that info is correct (explanation of diameter and pitch)... some of it is not.

You do not want your engine to turn 4800 rpm at WOT unless that is where it makes peak hp. What is called out in your manual as the "max operating RPM"? More likely, it will perform better and run faster if you prop it to turn 4400-4600.

Having a more powerful engine does not mean you need a prop with more pitch. Like I said above, its a game of matching WOT RPM's to the horsepower curve. Since the 302, 305 and 307 were all very close in displacement, they were all propped the same, as far as I can tell. Chevies in general tend to breathe a little better than the Fords, so they tend to make a *little* more hp, which peaks at a *slightly* higher RPM. So, in effect, you spin the same size prop for both powertrains- the higher hp one simply turns the same prop a little faster. A motor with larger displacement (350, 351w, etc), on the other hand, would require a prop with more pitch to keep the revs in check.

In regards to diameter, thats not really "fixed" as was suggested. What you need to watch carefully is the prop to hull clearance. 10% of the prop diameter is the general rule of thumb, but you can encroach on that a little bit. Having ~1" of clearance between the hull and tip of the blade on these hulls is about as close as you want to go. The 16' boats like the Mustang/Skier/Tique came with 12" diameter props from the factory, while the larger boats generally came with 13", or sometimes 14". A prop with a slightly different design (like an Acme, which will have aft-raked blades) will allow you to turn a slightly larger diameter prop (12.5" on the 16' boats is just fine) without encroaching on that minimum clearance.

storm34 wrote: If you're taking it to Nashville start asking if you can try some different props. I'm sure there will be some folks there who can either let you try one out, or may have them for sale.

I'm going to bring the 13x13 Federal that came on my '85 for him to try.
But that maybe to wide, I could bring the 540 from the '85 if you guys think it would work on his boat.

I thought they may be to wide.