Bayliner Engine conversion

Hi, I have a seized Cobra 5.7 litre with a cobra outdrive.
I am intending on using the boat inland and want to change the engine for something economical.. I am thinking a diesel..
What engines are compatible with the Cobra outdrive and transom plate?

This info seems impossible to find out after searching forums... so any advice is appreciated Thanks

Dave78 said:

Hi, I have a seized Cobra 5.7 litre with a cobra out drive.
I am intending on using the boat inland and want to change the engine for something economical.. I am thinking a diesel..
What engines are compatible with the Cobra outdrive and transom plate?

This info seems impossible to find out after searching forums... so any advice is appreciated Thanks

Click to expand...

First off, you would need to find a diesel engine that lends itself to a Cobra flywheel cover (bellhousing in the automotive world) bolt pattern.
This will allow the diesel engine to mate up to the Cobra drive components.

Next...... the Cobra drive coupler must be made to work with the diesel engine flywheel.

Then you will have front engine mounts to deal with. (are the stringers in the right location for this?)

After that...... you will need to determine which over-all reduction suits the lower RPM diesel engine. More torque/less RPM = a taller gear ratio.

Then you will need to figure out how the exhaust system will work. Will it be on the Port side, or will it be on the Stbd side?

Now, after all of that is said and done....... you would need to figure out a means of connecting the equivalent of an ESA system.
The gasoline engine (with a Cobra Dog Clutch drive) must be equipped with an ESA so that a shift from gear back into Neutral can be accomplished.
The ESA uses the spark ignition system for this.
With a diesel engine, there is no spark ignition system that can be momentarily stumbled for this shift from gear back into Neutral!


Honestly, it would be less expensive and less hassle to over-haul the 5.7L and run it.
It would take you years to recover from the cost of the diesel engine conversion.



Another option would be to go with an AQ series Volvo Penta cone-clutch stern drive with a diesel engine.
The AQ series lends itself to the Borg Warner components.
Quite a few diesel engines are Borg Warner capable.
No ESA is required with cone clutch gear engagement!

But again...... it would be less expensive and less hassle to over-haul the 5.7L and run it.

The money saved by NOT doing a diesel conversion could be used for your gasoline expenses.


.

Thanks for your advice. Just to explain a little bit of my logic...
My concern is the boat would always be tick over on the river and might be harder to handle we calculated the feul cost could be £26 per hour to run so a days cruising or a week away would be expensive.

Someone suggested the merccruiser 3.0l as a direct
swap for the larger V8 and this would be runnnng at £16 per based on feul costing £1.34 per litre as it currently is...

..................

Dave78 said:

Thanks for your advice. Just to explain a little bit of my logic...
My concern is the boat would always be tick over on the river and might be harder to handle we calculated the feul cost could be £26 per hour to run so a days cruising or a week away would be expensive.
Contrast this with the expense of a diesel conversion!

Someone suggested the merccruiser 3.0l as a direct swap for the larger V8 and this would be runnnng at £16 per based on feul costing £1.34 per litre as it currently is...
Are you discussing the Merc 3.0L, of which is a gasoline engine?

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Hi yes 3.0 gasoline I’m guessing would be more economical than the V8 5.7 cobra. Our rivers are also smaller and the cobra is a big engine...

Dave78 said:

Hi yes 3.0 gasoline I’m guessing would be more economical than the V8 5.7 cobra. Our rivers are also smaller and the cobra is a big engine...

Click to expand...

Actually,... Nope,..... Any gasoline motor, whether a 3.0l, or a 7.4l will burn 'bout the same amount of gas, at the same speeds,......

At 5 mph, they'll all burn the same amount of fuel,.....

You will never recoup the money in fuel savings that you will spend on this.

Without any idea as to the SIZE of your boat and your proposed operating speed and the boat's hull type, any detailed response is pure speculation...
Facts: Diesels are about 20% more fuel efficient than gasoline for the same shaft horsepower output.
Gas engines burn about 1 gal per hour per 10 HP actual operating output. True for a 10 hp outboard or a 300 HP engine.

Small engines burn less gas because they put out less HP.

sandkicker said:

Without any idea as to the SIZE of your boat and your proposed operating speed and the boat's hull type, any detailed response is pure speculation...
Facts: Diesels are about 20% more fuel efficient than gasoline for the same shaft horsepower output.
Gas engines burn about 1 gal per hour per 10 HP actual operating output. True for a 10 hp outboard or a 300 HP engine.

Small engines burn less gas because they put out less HP.

Click to expand...

The boat is a Bayliner 2155 Ceierra Sunbridge
I am also being advised the boat will be difficult to handle on a river because of the engine?? As I am new to boating it’s a tough one. But the engine does need replacing ...

RE: "difficult to handle on a river because of the engine" Sounds like BS to me... I have a 5.7 on my 23 ft deep V. Handles well in anything from a "No wake" zone here in NJ (at engine rpm from 650 to 900 RPM), trolling speeds (1000 to 1200 rpm), up to wide open. Any handling "difficulty" is due to hull design and the tendency for certain drive and hull combos to "wander" at slow speeds. This slow speed wander is not related to the size of the engine, but the hull design and to a lesser extent prop pitch. What kind of speeds are you anticipating on the river?

Thanks that’s good to know.
i believe the River speed limits are between 5 to 7 mph
I would say 90% of the time it will be on the river 10% would be sea / bay once I’ve completed the course.

whats your feul cost like?

The one and only time I checked fuel consumption in a controlled way I got a burn of about 7.5 gallons per hour. This was with the hull just on a full plane, i.e. that point where a deep V climbs its bow wave and the nose just drops. Not a good comparison to your hull, as mine is a deep V and has a 22 degree dead rise ( gas hog range) and the dry weight is 4000#. It is however a minimalist cuddy cabin with a bimini top. Given I have to transit several NO-Wake areas to get anywhere, its difficult to calculate fuel burn. I take that back... I did some patrol work for "Bay Day" at my YC last month and ran my boat for several hours at 900 to 1100 RPM (abt 5kts) sandwiched in between a run out and back of 10 mins each way @ 3100 rpm and only burned about 10 gal of fuel total (per fairly accurate dash gauge). When I first got into boating MANY YEARS ago, an "Old Timer" told me... "Don't obsess with gal per hour, look at gallons per boating day...and resist the temptation to lean on the throttle...It's hours on the water that counts, not miles."

sandkicker said:

............... When I first got into boating MANY YEARS ago, an "Old Timer" told me... "Don't obsess with gal per hour"

Click to expand...

I fully agree. Gallons per hour are meaningless without knowing the distance traveled.

If I burned 10 gallons in one hour, I would rather have traveled 10 miles in that hour, than to have traveled only 5 miles in that hour.

Hi yes 3.0 gasoline I’m guessing would be more economical than the V8 5.7 cobra[FONT=&quot] more​

. Our rivers are also smaller and the cobra is a big engine...​

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