Mercrusier 4.3 with OMC 2.3 Outdrive

[jjones0377]

Long time listener, first time caller.

I have a MerCruiser 4.3 L engine and it has a OMC cobra outdrive 2.3 L.

The guy I bought the boat from said he had the outdrive re-geared for a 4.3.

2 questions
1) is this possible to do?

2). Will this affect my performance of the boat at all? Speed? Wear and tear on anything else if it truly is geared for a 2.3L

 

[Bt Doctur]

The V6`s like a 1.62-1 ratio but a 1.84-1 will also work

 

[jjones0377]

Anyway to tell if my outdrive was re-geared?

 

[Bt Doctur]

remove the drive, mark a prop blade, turn input shaft untill the marked blade make 1 complete revolution Number of input shaft turns to 1 prop turn
1.50 1.68 1.84, etc to 1

 

[Scott Danforth]

I like to make 10 full prop revolutions. I find it easier to distinguish between ratios that way.

I have to ask, why did you buy a boat with a Frankenstein setup

 

[jjones0377]

Eh. Considering this a learning boat for wife and I. It runs well. So wasn't to concerned with it. And only paid 2500 for it. Water ready. I do wish it had a little more top speed. Haven't done gps test on it yet. But gauge reads about 37mpm as top speed while we are WOT. 1988 Rinker Captiva 206

 

[Maclin]

If 37mph is close to accurate then that speed is in the ballpark for a 20 footer with a 4.3, so ratio could have been changed as the seller said. Does the tach work? Can you post the RPM"s it can get to at WOT? What pitch is the prop?

 

[jjones0377]

I think the RPMs get up to around 5-6k range. Can't remember. Not 100% of tach is right or not though.

Prop is 20 pitch. 14". It has a 1" long, 1/2" deep gouge on one of the 4 blades. It's getting rebuilt this week though.

 

[Maclin]

Using a prop calculator I have changed my guess to : The ratio was not changed as the seller said.

A 20p prop at 37mph with 15% slip and 1.6 ratio would be 3700 rpm. A 2.0 ratio would be 4500 rpm. So if your engine truly is wound out and has no more at the 37mph and is in good state of tune I would have to guess that the ratio is a 2.0, not a 1.6, so still has the 2.3l ratio. But that is respectable speed for a Rinker of that size with 4.3 I would say. If it comes out of the hole well then I say "Sir, Go Boating!".

 

[jjones0377]

We had a blast last year. 37 was while pulling tube with 280lbs on it. Maybe a little more without the tube. Maybe I'll buy a new outdrive and sell this one.

Just as long as there is no harm to engine running this. I'm ok with it as is. And a rebuilt prop hopefully will help extend life a little more by putting less wear n tear on lower end.

 

[bruceb58]

Make sure the tachometer is correct and then don't go over 4500 RPM. My guess is that the tach is still set for a 4 cylinder engine which is why it is reading so high.

 

[jjones0377]

Ah you're killing me! Ha. How do I verify the RPMs?

 

[bruceb58]

Ah you're killing me! Ha. How do I verify the RPMs?

Get a shop tach.

 

[jjones0377]

Ok that's what I figured you'd have me do. Didn't know if there was any other way. I may have one at work I can borrow.

 

[jjones0377]

I will also note. The RPMs always stay around 3k during idle. And stay there for a while as I open throttle. Then itll start jumping to the 5k mark.

 

[bruceb58]

That sounds more like a bad tach.

 

[jjones0377]

Ok I'll look at replacing. It all looks original. I need a new sending unit for the trim. may order together somewhere. Anywhere you guys recommend parts like these besides eBay? Or is ebay my best bet?

 

[Bondo]

Anywhere you guys recommend parts like these

Ayuh,... Right here at iboats of course,....

 

[jjones0377]

Duh! Ha. I didnt even look. Ill look around for compatible gauges and what not. I always found iBoats just for the forums in google searches. Never paid attention to the other parts of the site. Thanks!

 

[Scott Danforth]

so you missed the big banner on top of the page with links to parts for sale?