Volvo Diesels 31L

[barryjl]

I am considering re-powering my Fairline Sunfury with two new diesels and have been offered a pair of brand new Volvo 31L's (130hp) at a very reasonable price. Now I don't want to open up a debate on the virtues of diesel v petrol or whether it make sense to re-power such an old boat with new engines (been there done that etc etc) but what I would I like to know is what you experts think of those particular engines - anyone got them? - and what level of performance I might expect from them in particular how the performance will compare with the twin petrols I have in there at the moment (Volvo 151 A's 150hp). Thanks in anticipation of some constructive advice.

<hr width=100% size=1>There's no problems..just opportunities

 

[miket]

Believe the L stands for liesure.

Not familiar with this particular engine but possibly cheaper because next generation of VP are now out D3, D4, D6 etc?

<hr width=100% size=1>

 

[Moose]

P stands for pleasure duty, L stands for Light Duty. I have always been told that the L engines are bullet proof considering the use they are likely to get.
I think (not sure though) that P duty means you are allowed to run the Engines at WOT for 10 mins in every 10 hours. I think L is 20 mins in every 10 hours.

<hr width=100% size=1>

 

[Wiggo]

Sounds a bit suss, Moose. I've got the AD31P's, and AFAIK, they're still 'leisure' rated, but crank out 150hp rather than 130. The P is allowed to rev to 3900 vs 3800 for the L, and is rated R5-R4, whereas the L is R5-R3. Anyone know what that means?

<hr width=100% size=1><-- insert witty sig file here -->

<A target="_blank" HREF=http://www.fairlinetarga29.info>Buy my boat!</A>

 

[Moose]

Yeah, thats right. I have 63P's (370hp) the 63l's are 318hp. A "P" is an uprated version of the "L"
Therefore the "L" is going to last longer as it is not working as hard, My 63P's in a truck would deliver about 160hp.

<hr width=100% size=1>

 

[[2068]]

An opposing view:

Some assumptions...

1.) Curves giving maximum power/torque are just that: run on a dyno (or whatever) at max throttle over the rev range. They do NOT show you how much power will be generated by the engine on any particular boat at any particular throttle setting - these curves will be specific to your boat.

2.) The AD31P and AD31L's are essentially the same engine, with different injection pump settings to control their maximum output.

Now consider two identical boats, one fitted with AD31P's and the other fitted with AD31L's. Assuming the same drive ratios and similar props, both boats side by side at the same constant speed over the same stretch of water, both the P's and the L's will be "working" equally as hard in terms of power generation. There can't be any other conclusion, because if this wasn't the case, one boat would be going faster (unless it was generating more heat or noise, which isn't the case). In fact, the L's will be probably be operating at slightly higher revs at this constant speed than the P's, because they will be running with a lower pitch prop to get the correct rpms flat out.

So in this case, my choice would be the higher output engines every time, on the basis that you can cruise at any given speed at lower rpm's. Just don't run flat out too often...

It would be a completely different story if the choice were between two engines that were of different capacities, for example the D4-210, which is comparatively high capacity, low revving, and a KAD43, which is smaller but produces more power at higher revs...



<hr width=100% size=1>