Volvo Penta Engines and Issues with Reverse RPMs

[mdsilvers]

OK. I need to cast a wide net on this issue and see if anyone can help. Here are the specifics on the setup for the boat:

Volvo Penta D2-40
MS115L-B 2.61:1 Transmission
Volvo 3 blade folding prop
--
Forward RPMs are around 3,000 full throttle
Reverse RPMs are around 1,500 - 1,700 at full throttle

The Volvo dealer said we should be getting similar RPMs in both forward and reverse. However, there seems to be conflicting information on this from others. I know that with the Volvo folding props, there is an impact to reverse 'bite', but not such a major impact to RPMs?

Does anyone have any ideas on this? I just can't seem to feasibly think that 1,500 - 1,700 RPMs in reverse is 'normal' - especially when you factor in the folding props being less efficient in reverse.

Any thoughts would be appreciated!'

Thanks!

Mark

[hogfighter]

My Volvo Penta has very similar specs......almost 3k rpm in forward, around 1,600 rpm in reverse.

[Tellie]

Why would you need full throttle in reverse?

[mdsilvers]

Originally Posted by Tellie

Why would you need full throttle in reverse?

At this point seems to be driven by the folding prop and needing more rpms. I have received different answers on this topic. One Volvo dealer in Miami said we should be able to get similar rpms in reverse and that would counteract the folding prop.

[moggie]

It's purely a geometry problem with your linkage from the quadrant, you don't get the same travel to the pump. You don't need it.

[DougR]

This is an old thread, and I dont know if you have solved the problem or not, but the issue which you are experiencing is due to different gear ratios between forward gear (right hand rotation) and reverse gear (left hand rotation) on your transmission.

The Volvo Penta MS15L-B transmission (ex Hurth, now made for VP by ZF) has a 2.63:1 reduction in forward and a 1.95:1 reduction in reverse. Thus your prop is sized to obtain the proper RPM in forward and the prop is too big when in reverse.

Of course you should make sure the throttle cable travel is 100% in both forward and reverse.

The VP folding prop isnt part of the problem.

Rgds.
DougR