350 MAG mpi 300hp/CM 225hp diesel

[Matt13]

How economical are these engines? I think I know what my next boat will be but there are two options I could go for, the boat is 25ft and has this engine or I could wait as there could be another one coming on the market with the V W 225hp diesel which is lighter and supposed to be quiet for a diesel and well thought of as an engine. The diesel one is out of my budget at the moment unless I can get it for a good price.

My questions are, will the diesel be underpowered? How economical compared to the Mercruiser would it be. If you had to choose one which would you go for, I keep hearing that you are more likely to make or get close to your money back with a diesel when you come to sell.

thoughts most welcome !

[markanddawn]

Hi Matt

For me, diesel every time but I do not know about power differences. What I do know is that diesel's give much more torque, so pulling ringos etc should be ok. I am guessing but the 350 mag will drink much more fuel (which you could add to your boat buying budget) and may give some more top speed and acceleration. Without a shadow of doubt, the diesel will have better residual value, albeit a relatively "unknown" installation in the marine world.

I keep banging on about it and although mine is petrol, I would much rather have 76 gallons of diesel under my feet than petrol for obvious reasons.

I am sure you will love it regardless. Are you going to spill the beans on what it is?

[Gazjen]

Yes diesel is better safer more economical cheaper on the water etc but diesel engines have a narrow power band really suited to gearboxes which of course boats don't have a 350 mag would be my choice of motor in my new boat, but the only way to know for sure is to take it out and see what its like, I know for a fact the mpi models are more frugal than there carb'd equivalent. I did look at diesel engined cuddies for about 10 mins then wrote them off because if the power limitations plus the diesels will cost a lot more if they go wrong, I can't imagine a Turbo or a diesel pump is cheap for a marine engine. I am a petrol head though so my opinion may be biased

I did find a 1990 bayliner with a 7.4 MPI

[Matt13]

This is the info regarding the VW engine which has now been taken over by Cummins/Mercruiser

I read on a forum elsewhere that parts are not that expensive and quite easy to get hold of, wether that is true or not I dont know.

http://www.cmdmarine.com/Product2/3.0L/3.0L.html

[Capn Jack]

Here's something to upset the apple cart!

Diesel is always a better choice for longevity as long as it's torque and power are at relatively low revs, which is the main reason they last so long. Lorry/ship engines usually rev to approx 1500rpm where the torque is at max. and they have very small rev bands, usually 300rpm. Very big ship engines only rev to 800rpm....

Similarly crusiers rev to approx 2,500 - 3,500max, so they have long life and good economy.

So when balancing your choice you have to be objective with the statistics and specs. The VW engine produces it's BHP max at 4,200 revs. However I cannot find any information which gives it's max torque and at what revs. The economy will be better than the 350 mag, but the power will be less and the longevity will depend on quality control and design.

For me, a little more information would help here. I think with the information available I would think again.

[Matt13]

Does this help, I dont know what it means though!

http://www.cmdmarine.com/Product2/3.0L/ ... _225-6.pdf

Cap'n Is the concern over diesel engines in general or just this particular one? I understand what you say markanddawn but how many petrol boats blow up in the UK, its not something I am too concerned with.

I'll try and find some more info on the engine

[markanddawn]

I understand what you say markanddawn but how many petrol boats blow up in the UK, its not something I am too concerned with.

A fair point Matt, but I guess it is considerably more than diesel boats. Safety aside, I run a diesel car that is absolutely astonishing performance wise. 0-60 6 secs and limited 155mph all for 41mpg (in stock form). I'd never go back to petrol unless I ever get my dream 911.

I didn't consider it anything to do with gearboxes and power bands. Incidentally, why don't boats have gearboxes, or is that a stupid question?

[Matt13]

I understand what you say markanddawn but how many petrol boats blow up in the UK, its not something I am too concerned with.

I didn't consider it anything to do with gearboxes and power bands. Incidentally, why don't boats have gearboxes, or is that a stupid question?

Your asking the wrong person, I got a nose bleed just posting in the technical section!

[markanddawn]

Ditto

[Matt13]

Cap'n this answers your question, for the 225hp rpm @ max torque is 2000. Is that good?

http://www.cmdmarine.com/Product2/3.0L/ ... csheet.pdf

Can any of the engine bods shed some more light on this engine?

[Gazjen]

I understand what you say markanddawn but how many petrol boats blow up in the UK, its not something I am too concerned with.

A fair point Matt, but I guess it is considerably more than diesel boats. Safety aside, I run a diesel car that is absolutely astonishing performance wise. 0-60 6 secs and limited 155mph all for 41mpg (in stock form). I'd never go back to petrol unless I ever get my dream 911.

I didn't consider it anything to do with gearboxes and power bands. Incidentally, why don't boats have gearboxes, or is that a stupid question?

335d??

[Gazjen]

Cap'n this answers your question, for the 225hp rpm @ max torque is 2000. Is that good?

http://www.cmdmarine.com/Product2/3.0L/ ... csheet.pdf

Can any of the engine bods shed some more light on this engine?

That motor looks very similar to the std Automotive 3.0 v6 TDI not going to be cheap though is it. I also know that engine can be tuned quite successfully

[Matt13]

Cap'n this answers your question, for the 225hp rpm @ max torque is 2000. Is that good?

http://www.cmdmarine.com/Product2/3.0L/ ... csheet.pdf

Can any of the engine bods shed some more light on this engine?

That motor looks very similar to the std Automotive 3.0 v6 TDI not going to be cheap though is it. I also know that engine can be tuned quite successfully

Hi Gaz no it's over budget but I think I could get it for less. What are your thoughts on the engines performance. I take it there would be plenty of power to get on the plane?

[Ed]

Very big ship engines only rev to 800rpm....

Very very big ship engines only run to 100 rpm

[Ed]

Cap'n this answers your question, for the 225hp rpm @ max torque is 2000. Is that good?

http://www.cmdmarine.com/Product2/3.0L/ ... csheet.pdf

Can any of the engine bods shed some more light on this engine?

That motor looks very similar to the std Automotive 3.0 v6 TDI not going to be cheap though is it. I also know that engine can be tuned quite successfully

Be very cautious tuning a diesel boat engine. Even in vehicles some cannot take sustained power for long periods of time, diesel turbos for example IMO of course tend to be too small so they have good mid range punch, but it puts the turbos on their limits at the top end. Perhaps in reality its not a problem. Depends how much you want to risk it I'd say.