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TOPIC: Engine swap from Mercruiser 5.7L V8 to Chevy 6.5L V8 Diesel Turbo.

Engine swap from Mercruiser 5.7L V8 to Chevy 6.5L V8 Diesel Turbo. 29 Sep 2017 22:45 #1

  • GTO_paul
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Hi Everyone,

I have removed my Mercruiser 5.7L v8 petrol engine with Alpha 1 drive to fit a Chevy 6.5L v8 Turbo Diesel.

I have a few things to modify and alter.

My first issue is the outdrive, it always causes arguments. so here goes. This is my theory:
The Diesel has less RPM at WOT than the petrol so top speed will be reduced. I think the leg will cope if I don't change the prop size. Same load.
If I change the prop size to a larger one to gain my speed back, the outdrive WILL fail.
Also the momentary cut out switch to get out of gear, will not work with this diesel but my understanding is coz the lower idle speed of the diesel, getting out of gear is ok.

The engine is going to run a closed loop cooling with a belt driven pump for the salt water flow through the heat exchanger.
Exhaust and salt water exiting through a flap at the rear.

I can't make my mind up whether to take water in through the hull or outdrive. Comments please.

Flywheel and bell housing from petrol bolts straight on and fits fine. Done it already.

ALL THESE THINGS SEEMED TO BE WORKING OUT OK TILL I FOUND A BRAVO 2 WITH GIMBLE HOUSING.

So now all changes.

I am not familiar with the bravo 2 drive so I need some help with these questions please:

1. Is the input shaft to the bravo 2 outdrive the same diameter as an Alpha 1 and splines?
2. I believe there is no impeller on a bravo 2, will a belt driven pump suffice?
3. Are the engine mounting positions on the gimble housing in the engine bay in the same position as an Alpha 1?
4. I believe the bolt holes line up but 2 extra holes need to be drilled for gimble housing. Is this correct?
5. Can you think of anything other than prop sizes that could cause an issue?

Answers on a postcard or a piece of toilet paper please :)

Thanks for your comments in advance, please be gentle.

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Engine swap from Mercruiser 5.7L V8 to Chevy 6.5L V8 Diesel Turbo. 30 Sep 2017 03:01 #2

  • builderdude
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What are the hp and torque ratings of the 6.2?? Even though it will idle at a lower rpm than the gasser the torque curve of the diesel may not be nice to the alpha. IMO the Bravo drive hands down, make sure the gear ratio is correct for your new set up. Personally I think pulling water through the leg would work fine, helps cool the drive but a seperate through hull with strainer can be added.

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Engine swap from Mercruiser 5.7L V8 to Chevy 6.5L V8 Diesel Turbo. 30 Sep 2017 03:37 #3

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I don't think the Alpha will hold up to the torque of the diesel.

Bravo uses a different coupler, don't know what the difference is.
Yes a belt raw water pump will work as long as it flows what is required for the diesel. All Bravos use a belt driven pump.
I believe you are correct on the transom assembly, two additional bolt holes. Not sure about the rear mount location between them.

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1997 Maxum 2400 SCR 5.7LX Bravo II

Mike

Engine swap from Mercruiser 5.7L V8 to Chevy 6.5L V8 Diesel Turbo. 30 Sep 2017 04:13 #4

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Bravo!

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Engine swap from Mercruiser 5.7L V8 to Chevy 6.5L V8 Diesel Turbo. 30 Sep 2017 05:45 #5

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GTO_paul wrote: Hi Everyone,

I have removed my Mercruiser 5.7L v8 petrol engine with Alpha 1 drive to fit a Chevy 6.5L v8 Turbo Diesel.

I have a few things to modify and alter.

My first issue is the outdrive, it always causes arguments. so here goes. This is my theory:
The Diesel has less RPM at WOT than the petrol so top speed will be reduced. I think the leg will cope if I don't change the prop size. Same load.
If I change the prop size to a larger one to gain my speed back, the outdrive WILL fail.
Also the momentary cut out switch to get out of gear, will not work with this diesel but my understanding is coz the lower idle speed of the diesel, getting out of gear is ok.

The engine is going to run a closed loop cooling with a belt driven pump for the salt water flow through the heat exchanger.
Exhaust and salt water exiting through a flap at the rear.

I can't make my mind up whether to take water in through the hull or outdrive. Comments please.

Flywheel and bell housing from petrol bolts straight on and fits fine. Done it already.

ALL THESE THINGS SEEMED TO BE WORKING OUT OK TILL I FOUND A BRAVO 2 WITH GIMBLE HOUSING.

So now all changes.

I am not familiar with the bravo 2 drive so I need some help with these questions please:

1. Is the input shaft to the bravo 2 outdrive the same diameter as an Alpha 1 and splines?
Yes
2. I believe there is no impeller on a bravo 2, will a belt driven pump suffice?
yes
3. Are the engine mounting positions on the gimble housing in the engine bay in the same position as an Alpha 1?
yes
4. I believe the bolt holes line up but 2 extra holes need to be drilled for gimble housing. Is this correct?
5. Can you think of anything other than prop sizes that could cause an issue?

Answers on a postcard or a piece of toilet paper please :)

Thanks for your comments in advance, please be gentle.


Truck engine or is this a peninsula engine?
Chevy 6.5 turbo should put out about 215 HP, but modified to 320HP even more.

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Engine swap from Mercruiser 5.7L V8 to Chevy 6.5L V8 Diesel Turbo. 30 Sep 2017 14:27 #6

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GTO_paul wrote: Hi Everyone,

I have removed my Mercruiser 5.7L v8 petrol engine with Alpha 1 drive to fit a Chevy 6.5L v8 Turbo Diesel.

I have a few things to modify and alter.

My first issue is the outdrive, it always causes arguments. so here goes. This is my theory:
The Diesel has less RPM at WOT than the petrol so top speed will be reduced.
Yes!

I think the leg will cope if I don't change the prop size. Same load.
What is the gain if so?

If I change the prop size to a larger one to gain my speed back, the outdrive WILL fail.
Most likely!

Also the momentary cut out switch to get out of gear, will not work with this diesel but my understanding is coz the lower idle speed of the diesel, getting out of gear is ok.
That would be the SA (shift assist) or SI (shift interrupt) depending on the language used.
The slightly lower idle speed will make little difference re; coming out of gear easily.
You need a B drive for several reasons....... 1 for the greater strength...... and 2 for the cone clutch!

.

The engine is going to run a closed loop cooling with a belt driven pump for the salt water flow through the heat exchanger.
Exhaust and salt water exiting through a flap at the rear.

I can't make my mind up whether to take water in through the hull or outdrive. Comments please.
The A drive requires the seawater path for upper unit cooling.
I am not certain about the B drive.
The Cone Clutch B drive cannot use a lower unit located Seawater Pump.


Flywheel and bell housing from petrol bolts straight on and fits fine. Done it already.

ALL THESE THINGS SEEMED TO BE WORKING OUT OK TILL I FOUND A BRAVO 2 WITH GIMBLE HOUSING.

So now all changes.

I am not familiar with the bravo 2 drive so I need some help with these questions please:

1. Is the input shaft to the bravo 2 outdrive the same diameter as an Alpha 1 and splines?
Since the engine drive coupler alignment tool is the same between drives, I would say "yes"!

2. I believe there is no impeller on a bravo 2, will a belt driven pump suffice?
You mean seawater pump? If so, yes..... that is correct!
(with upper gear unit cone clutch gear selection, the vertical shaft only rotates with gear engagement...... therefor a cone clutch drive cannot operate a lower gear unit seawater pump.


3. Are the engine mounting positions on the gimble housing in the engine bay in the same position as an Alpha 1?
The B drive's inner transom plate, alone with the correct Flywheel Cover (what you are calling a bell housing) will take care of this.

4. I believe the bolt holes line up but 2 extra holes need to be drilled for gimble housing. Is this correct?
Correct!

5. Can you think of anything other than prop sizes that could cause an issue?
Yes..... the correct over-all gear reduction that will allow the lower RPM engine to turn a prop that is not overly aggressive.

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Rick E. Portland, Oregon
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Twin 270 HP 5.7's w/ Closed Cooling
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Engine swap from Mercruiser 5.7L V8 to Chevy 6.5L V8 Diesel Turbo. 02 Oct 2017 16:21 #7

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Adding my 2 cent. My preferred drive is the Bravo III 220 ratio, as for fitting the Bravo ii yes it will all fit you may need a spacer on the bell housing to clear the steering on my set up the exhaust going to the turbo was tight. Did you change the motor mounts? Water intake through the hull is better 1.5 inch intake, from the drive it is restricted to 3/4 at the drive. What is the marine conversion - exhaust, heat exchangers and so on?

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