Petrol to diesel conversion, stay with me ....

julians said:
My old 5.0 v8 mpi 260hp used to burn 35 litres per hour at 25knots, my current boat, volvo d4 260, burns 25 litres per hour at the same speed. So that's 10 litres per hour more, that about £13 per hour more at road fuel prices. So £26 per hour more for twin engines. Over a 100 hour season thats an extra 2600 quid on fuel. I guess if you don't do many hours then it's not a big deal.
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That being the case...you must have been seriously underpowered or under propped. My V8MPI even with its cam injectors and exhausts burns 18/19 litres per hour at 25ish mph cruising. It is safe to say it is around a litre a mile or just under.
Last I looked it used less than a 260hp VP diesel easily. All be it the diesel is cheaper.
 
julians said:
My old 5.0 v8 mpi 260hp used to burn 35 litres per hour at 25knots, my current boat, volvo d4 260, burns 25 litres per hour at the same speed. So that's 10 litres per hour more, that about £13 per hour more at road fuel prices. So £26 per hour more for twin engines. Over a 100 hour season thats an extra 2600 quid on fuel. I guess if you don't do many hours then it's not a big deal.
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Cavalierbond said:
They are Volvo Gi if that’s any good
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Ok so the GI is a tbi efi. No where near as efficient as the mpi or gxi. Still good though.
 
My Volvo aq130 is from the mid seventies I have presumed it will not like the new unleaded e10 and opted to use super unleaded.one question I can’t seem to find an answer to is is it safe to run without lead additive
 
simonfraser said:
I am still looking for a 26ft mobo, hard top, diesel, with a good rear seating area - some of facing towards the stern.
NO rear fishing area, plastic tub MF etc.

Not many about, the only ones i can see, Aquador 26 HT, are quite old.

So, just thinking, why not 'just' find an old petrol boat like the above, suggestions please, and re-engine it.
Yes that will take a lot of time / money, but a totally new Cancun 260 is 100k+ and has a fabric 'hard top'

Shoot me down.
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I’ve done it twice.
In both cases I was better off financially. As long as you don’t price your labour.
In stern drive boats the swap is not that difficult but more work than you think.
Buy right, preferably something with a blown petrol engine.
When sourcing the donor engine and drive make sure it is absolutely complete.
Small parts can be eye wateringly expensive.
 
Rusty1953 said:
My Volvo aq130 is from the mid seventies I have presumed it will not like the new unleaded e10 and opted to use super unleaded.one question I can’t seem to find an answer to is is it safe to run without lead additive
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Have you asked Volvo? Is it car based? If so owners club?
 
QBhoy said:
That being the case...you must have been seriously underpowered or under propped. My V8MPI even with its cam injectors and exhausts burns 18/19 litres per hour at 25ish mph cruising. It is safe to say it is around a litre a mile or just under.
Last I looked it used less than a 260hp VP diesel easily. All be it the diesel is cheaper.
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Pointless quoting “at a certain speed” though. Only relevant to quote at a certain rpm when the engine is correctly propped to give max speed at max rpm. So your very light small boat may do 25kts at 2000rpm and be capable of 60 at 5500 rpm - but a 3000kg cruiser with the same engine, correctly propped will need 4500-5000 rpm to achieve the same speed.

Put the same engine in 3 completely different boats and you get 3 different figures for the same engine.

25kts is 1/3 throttle on some boats and flat out on others.

So to say at 25kts the other boat was “wrongly propped” isn’t possible as we don’t know what that boat was, and 25kts could easily be flat out for that boat.

There is a much simpler rule / small and light is probably a petrol type boat. Big and heavy will suit a diesel better.

The cut off / crossover point to my mind is about 1600-1800kg - certainly anything over 2000kg will probably be better on diesel as petrol will just get unrealistically expensive to run.
 
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ontheplane said:
Pointless quoting “at a certain speed” though. Only relevant to quote at a certain rpm when the engine is correctly propped to give max speed at max rpm. So your very light small boat may do 25kts at 2000rpm and be capable of 60 at 5500 rpm - but a 3000kg cruiser with the same engine, correctly propped will need 4500-5000 rpm to achieve the same speed.

Put the same engine in 3 completely different boats and you get 3 different figures for the same engine.

25kts is 1/3 throttle on some boats and flat out on others.

So to say at 25kts the other boat was “wrongly propped” isn’t possible as we don’t know what that boat was, and 25kts could easily be flat out for that boat.

There is a much simpler rule / small and light is probably a petrol type boat. Big and heavy will suit a diesel better.

The cut off / crossover point to my mind is about 1600-1800kg - certainly anything over 2000kg will probably be better on diesel as petrol will just get unrealistically expensive to run.
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Not sure I get what you are saying. A 25ft cruiser would never see nearly 70 mph at any rpm with this engine, haha. My point was around propping a boat well to achieve the best from it. Then I have an example with some figures. The litres per hour will remain the same on any boat with this engine at a certain rpm
 
QBhoy said:
Not sure I get what you are saying. A 25ft cruiser would never see nearly 70 mph at any rpm with this engine, haha. My point was around propping a boat well to achieve the best from it. Then I have an example with some figures. The litres per hour will remain the same on any boat with this engine at a certain rpm
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Correct which is why quoting speed as you did doesn’t tell us anything.

You have a consumption (18/19l per hr) at 25 kts - which is fine, but only for your boat. The same engine in a heavier boat will use more fuel to achieve 25 kts.

Had you said “my boat burns 18/19 l per hr at (for example) 2100rpm which (on my boat) is 25kts “. that I would have agreed with.

My point was quoting fuel burn at a speed is no use to us, quoting it at an rpm knowing the boat is correctly propped to max out at max rpm IS useful.
 
ontheplane said:
Correct which is why quoting speed as you did doesn’t tell us anything.

You have a consumption (18/19l per hr) at 25 kts - which is fine, but only for your boat. The same engine in a heavier boat will use more fuel to achieve 25 kts.

Had you said “my boat burns 18/19 l per hr at (for example) 2100rpm which (on my boat) is 25kts “. that I would have agreed with.

My point was quoting fuel burn at a speed is no use to us, quoting it at an rpm knowing the boat is correctly propped to max out at max rpm IS useful.
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Ah. Ok. To be fair, I thought I’d included the rpms. Fair play. Just read it back. Had no idea I hadn’t.
Anyway. Was getting into the boundaries of a pointless back and forth, I’d say. My point was that a well propped set up, would be the ideal situation.
 
AQ130 is a B20 car engine.

Heads, timing and other details were adapter to e.g. US market to meet their petrol qualities and even on the Swedish home market many have converted heads to unleaded. Unfortunately no simple answers.

I think enthusiast sites for vintage Volvo's would be the place to ask. Preferably Sweden...
 
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