Differences in Volvo penta 280 lower units?

[jerama88]

Hi, I have a few questions. I have a 165hp AQAD40B powering a 280 leg- 1.61 ratio. It is in really bad shape.

I have a very nice condition 280 leg that is spare but it is a 2.15 Gear ratio model. Can I swap the drives completely and achieve the same speed/ torque by simply changing the propeller size? (pitch increase maybe?)

Also I am wondering if the 2.15 ratio is as strong as the 1.61? I am aware that the 1.61 is for v8's or inline 6's and the 2.15 is for 4 cylinders..? will the 2.15 give up on me quicker? Have they weaker parts?

 

[captmello]

Re: Differences in Volvo penta 280 lower units?

no difference in part strength, just gear ratio. the 2.15 will work but don't expect optimal performance. It will get you from point a the point b. IF it was just a matter of propeller, they wouldn't have so many different gear ratios.

 

[Maclin]

Re: Differences in Volvo penta 280 lower units?

Your power plant is a diesel which has a much different power band and recommended top RPM range than gasoline engines. Diesels top rpm is usually 3500 or so, which is why they are usually a ratio like the 1.61. The HP rating on a diesel is deceptive when compared to a gasoline engine becasue diesels do not rev as high. But diesels make up for that with their much higher torque available at the lower rpm's when compared to gasoline engines. If you change to a 2.15 from a 1.61 your engine will be in serious over-revving territory and your top speed will be way way slower at the top recommended RPM of the diesel.

 

[Maclin]

Re: Differences in Volvo penta 280 lower units?

In my earlier post I only considered single prop units. A DuoProp unit is different ratio. If the spare unit is a DuoProp then the 2.15 may be ok (but I think the only DuoProps end up being a 1.95 or a 2.35).

Let's say you have a 1.61 single prop unit. Swapping in a DuoProp lower would make it a 1.95 because the gearing in the lower is different and the final drive ratio is affected by the gearing in the lower unit as well as the upper.

 

[jerama88]

Re: Differences in Volvo penta 280 lower units?

Thanks heaps for your help, I was hoping I would be able to change my propeller to alter rev/ top end/ tourque. I was going to go from 16x 16 to 16 x 21. Increasing the pitch would be counteracting the ratio change? I am not sure if there is any thing I am not thinking about? Any more advice on this move..

 

[captmello]

Re: Differences in Volvo penta 280 lower units?

It's my understanding that even though you may be able to counter the change in gear ratio with the change in prop, that the overall performance is affected. However, assuming you are not operating this boat for water sports and/or trying to achieve maximum hole shot or top speed, I see nothing from stopping you from giving it a try. Finding the best prop will be most likely take some trial and error, but what the heck... You've already got the drive! Let us know what happens.