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Engine Change, Petrol to Diesel


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Hello,

You may have seen my post as a new member last night. Do any of you have views regarding changing from a petrol engine to diesel ? I caused many members of the Bayliner site in USA to question my descision last winter to remove the 5 litre V8 petrol engine and replace it with an Isuzu 2.8 turbo diesel. I am very pleased now, runnung costs are almost nothing when compared to the thirsty V8.

Regards, Paul

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It really depends on whether the boat still performs in the manner you want it to imho, if you want a planning boat and the diesel won,t get you over the hump, then it,s not good if you get what i mean :party::grin:

I'm not sure how the speed is yet, it's great on the river at displacement speed. I had to guess at prop size, but I got it wrong and can only get 2400 RPM, when the engine should rev. to 3600. I am hoping the boat will just plane when everything is sorted.

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Personally I’d have left the V8 in, apart from petrol being much quieter and smoother at river speeds I very much doubt that Izuzu will get your boat over the hump, assuming that’s what you want. I’m not too well up on Bayliners but your avatar looks like a 2556 wide body to me, the old 5.0L Mercruiser would have shoved out 200hp and even that was considered a bit underpowered for that boat.

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Hi Antares,

My boat is the model before the 2556. It's the 2450 Command Bridge, 8' beam with the Volvo engine and drive. My V8 was totally worn out, it would only achieve 1500 RPM with compression readings from 30 - 45 psi ! It seemed more sensible, as I had to change the engine, to go to diesel. The guys in the States say if I change to the duo-prop drive it will make a big difference.

Paul

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http://www.castlemarine.co.uk/pitch.htm

this might give you a pointer?? :wave

Thanks for the link, I have just done the calculation, with the resulting prop size 15.75" X 11.75" I have a 15.50 X 15 at present on the boat so it does explain the low revs and therefor lower power output, particularly from a turbo / intercooled diesel. The suggested max speed is 20.50 MPH, I will be happy with that.

Paul

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Ah, you didn't say the motor was screwed :grin: In that case anything would be better, I doubt a douprop would make a lot of difference to top end, though it would have better economy and holeshot. Don't forget that the old sterndrive would be geared for the higher revs of the old Chevvy V8 rather than a tourqey diesel lump and that will need to be factored into any prop calculations. Does the motor rev to max when off load?

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Ah, you didn't say the motor was screwed :grin: In that case anything would be better, I doubt a douprop would make a lot of difference to top end, though it would have better economy and holeshot. Don't forget that the old sterndrive would be geared for the higher revs of the old Chevvy V8 rather than a tourqey diesel lump and that will need to be factored into any prop calculations. Does the motor rev to max when off load?

The gear ratio I have is 1.61:1, which was suggested to me as ideal for the diesel, the V8's were not a high reving engine. I did use this ratio in the prop calculation, plus I bumped up the weight of boat ( to allow for the beer on board ) I have not checked the max off load revs. I will do it this weekend. The engine was re-built, injection pump serviced and calibrated etc. before installation. At 1100 RPM, 6-7 MPH, I'm using just over 1 litre per hour, that is quite amazing compared to the V8.

Paul

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A litre an hour is amazing however consider the following calculation. For every hour on the river 2x pints of beer or lager. That's another litre but at nearly £4 for that litre so it works ou the same as 4 more litres of fuel and bingo - your consumption is the same as Ians 5 litres an hour!

On a serious note, out old boat had twin Volvo 150hp petrols and even with both engines in our average mpg over the season (including a good deal of coastal travel at 25plus kts) was still 2.6 mpg which is good for the size of boat (27 x 11) so the question certainly now raises it's head - with the imminent loss of any duty allowances on diesel ad negating the premium paid for diesel engined boats, it suddenly appears that petrol engined boats may be making a bit of a re-emergance

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Would agree 100% Gav, but then I would wouldn't I.

All I can say is a wise old bird once said to me, while I was looking for a 310 statesman and was adamant I was buying one with diesels, seek out a petrol version with V6's in, that is the perfect boat for the type of boating you are doing (60% broads 40% sea).

Have to admit he was right, boat has been fantastic, never missed a beat, pretty economical and saved us 10-15k on the purchase price over the same boat with diesels in.

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Petrols are fine when at broads speeds, in fact nicer than non common rail diesels I reckon, or at economical planing speeds but when you have to plug it out at the in between stages, which is a lot of the time on the East Coast they drink it and don’t have the torque to punch like diesel. Then there is the question of getting the stuff. As for the rumoured loss of heating allowance duty reduction and 5% VAT discretion, I was at a workshop at the BMF in Egham today and I for one have no worries about that at all (I can say no more) You didn’t save 10-15k Ian you just lost the use of (and the scant earnings on) the 10-15k whilst you own the boat as the differential remains when you sell it.

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Hello,

It's very interesting to hear all your views re. petrol verses diesel. I chose diesel because I believed it to be better than petrol for low speed river use. I went down the route of marinising a vehicle engine purely on the basis of cost, but it was a lot of work for me over the winter. The fuel consumption I find quite amazing, but I am running just above tickover. I think the fuel useage will change drasticly when I try to plane the hull ! For this year at least, I expect 90% of my use to be on the river.

post-1207-136713817354_thumb.jpg

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  • 6 months later...

Maybe this thread has been resurrected by a potted meat enthusiast, (this may make no sense if the post at December 1st, 2011, 1:13 pm subsequently disappears !)

but I hadn't noticed the thread before, so I'm almost grateful for the "High School Diploma" Advert. :naughty:

Some interesting comments about V6 petrol engines over the past year or so, and their suitability for the Broads.

Also a very neat installation of the Isuzu diesel by Swordfish. Did you ever get it to plane with the new prop ?

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