Pete, i have a 34SF with (2) mercruiser 5.7's, zf 2.5:1 and 18x22 props...my WOT is 4600prms at 23knts cruise is 3200rpms at 13knts...very good gas efficiency with this set up...its for sale BTW...i need a smaller boat
On Aug 29, 1:17 am, john hamilton <[email protected]> wrote: > I joinedwww.boatdiesel.comfor a year when I was rebuilding the engine my 27 > Express Cruiser. They have a couple of chat rooms that really sharp guys > weigh in on regularly and they have an excellent prop calculator that was > instrumental in my getting my prop perfect for my boat when I went from 260 > hp to 410hp. > > I agree with Victor's points. If the maximum rpm is low you will generally > need to reduce the pitch and possibly even the diameter as well, although > that costs lift. I'm gussing there won't be a ton of difference between > 18x17 and 17x18. 17x15 or 18x13 should make more of a difference. You > didn't mention your top speed and rpm with the old engines. Did the boat get > up onto full plane with the 270 horse motors? How fast was it at top speed, > and at what rpm? One of the things I read in my research before I > finished my job is that very shallow props are less efficient than steeper > props. Beyond a certain point, the prop calculator recommended a lower > transmission ratio and steepr prop rather than a higher ratio and shallower > prop. > > I spent hours on the calcultor plugging in different transmission ratios, > prop diameters, number of blades and pitch amounts. The price for a year's > subscription was something like 25 or 50 bucks and more than worth it to me. > I found a great place for a new stuffing box on that site reading the chat > rooms. > > Whatever calculator you use, it will need a displacement figure and a > waterline length and that particular one onwww.boatdiesel.com has a hull type > as well. > > One place I disagree slightly with Victor on is rpm range. I think most > stock marine engine camshafts have a designed top end around 4400 to 5000, > not the 5500 Victor mentioned. A high performance version might go that high > but you probably wouldn't put high performance motors in a big cruiser unless > you are somebody that likes fiddling in your engine room a lot (like me). > You might decide to go with high performance small blocks instead of low > performance big blocks but most folks would probably go the other way, as you > did in this case. If you can get your engines to at least 4400 rpm you > should be good. In my case, I took a small block and made it big > displacement, sort of splitting the difference. The cam I had specially > ground for my desired cruising rpm (3400) has a top end of 5000rpm. > > It seems unusual to me that you could only get 4400 rpm out of your engines > when you had the 2.57/1 transmissions in it. The engines might not be > putting out their full horsepower potential and if they aren't, you will > never be able to get the thing propped right. I think I would do a > compression test and double check the basics like timing and carb > settings before I did any more work on the prop selection. It's cheap, easy > and will give you more confidence when you do pick a prop combination that > you have it right. I choked on the price of one new prop. You're buying two. > > You are increasing your horsepower by about 30%, which sounds like a lot but > might not give you as much of a performance imporvement as you think. I > increased my horsepower by 60% and got 20% more cruising speed, 25% more top > speed and 28% more fuel economy. Great results to be sure, but not as much > as one might think with that much extra power. The one thing that > everybody who seems to know what they are talking about agree on is > this. Whatever prop pitch, diameter and transmissionration ratio you settle > on, it's critical that your engines will reach the maximum rpm the > maunfacturer lists for that model with a full load in the boat. Anthing less > will dramatically shorten the life of the engines and severely limit the fuel > efficiency you can obtain. Good luck, and let us know how it comes out! > > John > > --- On Fri, 8/28/09, Love and Luck <[email protected]> wrote: > > From: Love and Luck <[email protected]> > Subject: [UnifliteWorld] 34ss with 454's > To: "UnifliteWorld" <[email protected]> > Date: Friday, August 28, 2009, 5:49 AM > > Hello Everyone, > > I posted a message last year but never got any responses. I'm looking > for information once again on my engine upgrade. First a little > background.... I have a 1982 Uniflite that used to have 270 hp > crusaders, 1.91:1 Velvet drive Transmissions, and 18 x 17 inch props. > My boat would only cruise between 12 and 15 knots. I decided to > upgrade my tired motors and put in a pair of used 350 hp crusaders. > The motors I bought came with 2.57:1 Transmissions so I initially > installed these into my boat. I borrowed a pair of 18 x 22 inch props > from a friend and the boat would cruise at 9 knots and top out at 4400 > rpm. At this point I spoke with Sea-cure technologies to find out how > 34 ss was set up from uniflite. They told me those uniflites came > with the 1.52:1 Transmissions and 17 x 18 props. So, thanks to > craigslist, I found a pair of 1.52:1 Velvet Drives and put them into > my boat. Took the boat out for a cruise with the 18 x 22 props, > topped out at 2000 rpm and 10 knots. Next I took off the 18 x 22's > and put back on my original 18 x 17's. Took her out for a run and she > did 14 knots topped out at 3200 rpm. So, my question, will going to > the 17 x 18's bring my rpms up and my cruise speed up? Is there > anyone else out there with a 34 uniflite with 454's? > Thanks > Pete --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "UnifliteWorld" group. 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