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outdrive ratio for diesel & prop size.

T

trophyone

New member
well ive been getting conflicting info so I figure ill post on a few sites & compile all the info. <br><br>Im repowering a bayliner 2460 trophy hardtop 1985 model. Was powered with a gas volvo 225 v8 & 280 single prop drive the prop is marked c350. I am repowering with a megatech m290. <br>specs<br>285 hp@ 3200-3600 rpm<br>weight 870lbs<br>2400 rpm 200hp<br>2800 rpm 260hp<br>3200 rpm 280hp<br><br>fuel consumption g/hph best at <br>157 @ 2400 to 2900 rpm<br>160 @ 3200 rpm<br><br>drive <em>I curently have for the project is a volvo dupoprop dp-c 1.95 ratio ive been told I nbeed a lower ratio ive also been told to go up 1 ratio with the duoprop. <br>qestions<br><br>1- will this drive ratio work?<br>2- Is it the best ratio for the diesel?<br>3- what props will I be wanting? I have a test set (aluminum b5's). <br><br></em><br><br><br>
 
Hi, I'm doing a similar repower as yourself( 24ft bayliner trophy hardtop 1988) I've taken out an OMC 5.7l petrol and a Cobra outdrive
I'm repowering with a GM V8 6.2l diesel and a VP 290 duoprop, the VP drive is 1.78-1 and apparently that is the correct ratio for the diesel I have
Dont know if thats of any use to you

Regards Nick
 
Trophyone, I think that I've made this similar suggestion to Nick.
You may want to consider this:

The Duo Prop ratios are pretty hard to compare to a single prop drive ratios.... prop dynamics are considerably different, etc.
Your 2460 Trophy is not all that large but the diesel is heavy.

The AQ225 gasser ratio was (or should have been) 1.61:1 in a single prop (that is the tallest available in that series drive). The 1.61:1 should also work with the diesel, depending on hull size.

The 285 hp @ 3200-3600 rpm diesel should have more torque, but you can see the limited rpm range compared to the AQ225 gasser.

Now look at hydro-propulsion and prop dynamics.
We don't want to spin a prop too fast per MPH, yet we want a ratio that brings the prop shaft rpm to within reason for the lower 3200-3600 rpm diesel.
I guess that another way of saying this would be that @ 3,200 engine RPM, we'd like to spin the props as though the engine was doing V-8 RPM.
The taller ratio should achieve this.

Something else to consider is the characteristics of gear teeth as ratios change. You may have a friend who is into Off-Road 4WD stuff. One of the first things the Novice does, is install Low Gears in both differentials. The other first thing that happens, is he breaks Ring/Pinions. Why? Less tooth contact with low ratio gear sets.

There are three Duo Prop ratios in this AQ series that will work for you.
2.30:1, 1.95:1 and 1.78:1.
Gear tooth contact increases slightly with the size of the "driven" gear, and is proportionate to the above ratios and in that order.
I.E.:
2.30:1 has the smallest drive gear, and largest driven gears.
1.95:1 drive gear is somewhat larger, the two driven gears are somewhat smaller.
1.78:1 drive gear is largest, the two driven gears are smaller.

This affects gear tooth contact at any given time, thus rendering the taller gear set a tad bit stronger than the lower gear set.

So you have more torque and lower rpm w/ the diesel and prop dynamics to consider.
I'm not an ultimate authority on this, but my bet is that the 1.78:1 will work best.
You may want to contact Volvo Penta and speak with Tech Support.

doubt that B-5s will work. There is a diesel set that you may want to look into.
As with any prop selection, we try a hand full of prop sets and do the WOT RPM test until we find one that gets us the WOT RPM.

Question: Since you now have the DP-C 1.95:1 (of which is correct for the AQ225) have you considered trying it?
You can install the lower unit only (shimming must be done) and the vertical shaft bearing race should be carried over with the DP-C lower unit.
It can always be installed back into the DP-C Intermediate housing later on.

You'll be surprised at what this will do for the 225.

.
 
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