Volvo Penta 8 1 Gi Workshop Manual
Re: Volvo 8.1 Gi Well a couple of things to consider here: 1) The simplest way to get more horsepower is more RPM with the same fuel flow per firing event. Just make that event happen more often i.e. More RPM 2) I believe each (Merc and Volvo) did their own fuel mapping (the actual fuel rates that the injectors squirt when you tell them to). Merc may have had a bigger budget for the higher rating, so they spent more time on it. 3) They really aren't that different.
The Merc 375 is rated at 4400 - 4800 and their 425 is rated 4600 - 5000 4) This is prop-shaft hp and maybe the Volvo drive is less efficient to turn internally (requires Duoprop) so it eats a little power requiring a higher RPM to get 5 less php. What's the specific concern? It seems to me that a boat with a motor turning lower RPMs will be slower out of the hole than one with the same horsepower, but with higher RPMs.That is true for prop selection purposes. But as far as comparing two of the same engines, with the same hp rating, but one rated at a slightly higher RPM really doesn't tell you anything about the hole shot. The one with the most torque at the point that the boat has to struggle to get up and out, will have the better hole shot. This assumes all other things are equal, boat, weight, drive, props etc.
Re: Volvo 8.1 Gi Most here will disagree with me, and most have more experience with Marine applications, but based on the words in the manuals that I have read along with my understanding of wear after 27 years in the engine biz, propped @ 4200 WOT with your max load would probably be the longest lived as she will be turning less RPM at all speeds as well. That's my take on it. With that said, IMHO unless you are in a commercial application, longevity is not really even a discussion if she is maintained properly. Personally I would prop it to 4600 or as close as I could get.I agree for flexibility. I was trying to be specific as far as the question of longevity is concerned.
I mentioned that most would disagree. Most mention valve seat wear and/or tuliped valves and holes in pistons.
If that's true, then I don't understand why OEMs would put the low end of the range in print. I think one thing that you and I agree on Don, is that the manual(s) is your best friend. Not looking for a debate here.
Volvo Penta 8 1 Gi Workshop Manual Pdf
I just wanted to 'splain myself.