Well I'm prepared to take some abuse on this thread. The whys? waste of money/time? etc...

I have been researching turbo's for a year before considering this dumb idea....

I have a 19'.5" bowrider I am thinking about installing a turbo system on, I have all the fabrication ability, I have worked in the after market automotive industry for 12 years so I have hard parts knowledge, I have worked on turbo applications before just never put a turbo on something that was never intended to have one. I don't mind spending money as long as I learn something so I am prepared to spend some cash doing something really dumb.... I also know that marine generally means a different animal.

I was thinking I would have to remake the dog house because of the extreme heat, possibly use some type of scoop to draw air in the top to cool the turbo along with using a old Rayjay water cooled housing, I have seen another member weld his existing water cooled manifolds and redirect water out of the back of the manifold back through the riser and sterndrive.

Existing engine

- 4.3L (no I dont want to put in a SBC I probably should but would like to dig into this turbo idea a bit more )
- 97 "REAL" Vortec heads with kidney bean chambers, exhaust port work and CNC bowl and floor work done to take advantage of 2.02/1.60 valves
- Camshaft hydraulic roller 210°/214° @.050" .478/.487 112 lobe sep (no I didn't get water inversion ran the engine all year)
- GM/Merc 4 barrel single plane intake manifold for Vortec heads with 1" spacer
- Edelbrock 1409 Marine carb with 1485 calibration kit for 4.3L engine
- Stock rods, crank and pistons
- Merc Thunderbolt IV ignition amplifier/ distributor with MSD 6A box and Blaster Coil


I'm going with a set of forged dished pistons with the same cam, same intake, same heads but know I will have to get a blow through carb.

My questions..

What size turbo would you recommend? I was thinking I would need to keep it smaller than an automotive app because there is not a lot of room for turbo lag and I need power from 1500-5000rpm
I have 2 turbos but willing to buy another.

1) Rayjay ( cant find any info on this)
Part # SE70010
Serial # 42481
A/R .80

2) Garrett (from 85-87 Daytona Shelby Z)
4105800
PE13360P
A/R .42

Should I go back to the stock Merc cam? (stock cam 202°/213° @.050" .403/.409 lift, 108°/116° lob sep)

any recommendations on turbo size and the water cooled exhaust manifolds?

Ok... ready to take the abuse from 99% of the people and hoping the other 1% will give me some usable information.

 

Have a look through here , it might give you a few ideas.
https://www.theturboforums.com/smf/index.php?topic=111257.msg1093653#msg1093653

 

That was definitely inspiring makes me want to "adjust" a few engine parts.

 

Turbo number 2, way to small. Go ahead and pull the ray jay apart and take some measurements. Start by pulling off the compressor housing and measure the compressor wheel size.

 

You need to identify your goals to start with.
What are you trying to achieve ?
Do you have the best hull and engine to achieve your goals ?

You don't want to get a lot of time and money invested and have to rethink the project.
Many times your efforts to improve the HP of something will decrease it's value.

If you need to have a cover over the engine everything carrying exhaust will have to be water jacketed.
The water jackets around the whole exhaust system will decrease exhaust heat and also decrease the efficiency of the turbo.

Another consideration, turbos make torque, I/O's are not able to handle much torque.
I boat with several guys with BEEFED UP Bravo drives and they are breaking them on a regular basis. They all have had the drive off for repairs during this season.
They all have spare drives. The repair parts are extremely expensive.

 

Another consideration, turbos make torque, I/O's are not able to handle much torque.
I boat with several guys with BEEFED UP Bravo drives and they are breaking them on a regular basis. They all have had the drive off for repairs during this season.
They all have spare drives. The repair parts are extremely expensive.

This is another valid point a Bravo out drive will handle a lot more power than a Alpha Gen II, if I can recall the Alpha Gen II will only handle 300l ft bs which I would assume even the simplest Turbo build would make. In fact I wonder what kind of power I was making with my previous engine?

 

Don't see where you are coming from on this one... I tune the odd boat .. those outdrives are just as tough as anything ,, if the right man puts them together.

 

Water jackets on the hot side are not going to effect anything on the cold side. It just decreases the heat that drives the turbine wheel.
The heat differential from before the turbine to after is one of the things that give a turbo setup high efficiency.

#ad

 

I ended up getting a Vortec S-trim kit should be an interesting project now.

 

Sell out! J/k I'm sure it will work out great, should be a good match to the 4.3.

 

I would have loved to have used one of these turbo's!

If any one is interested I could post pics, I know its not a turbo build, but I would rather share the build with anyone from this forum than the Pompous "marine" forum guys that make marine engines and boats in general out to be strange space ship type vessels that are crafted of unobtainium.

 

You're uninformed with that statement.
No matter who puts it together there is a limited size of the gears and shafts that will fit into the Bravo case.

 

I'm not uninformed at all ... doesn't matter what size gears or shafts you run .. I have seen them explode ...just not mine.. thank you very much . If the boat guys spent half the time setting up a gear set as the automotive side nobody would whine about any gear case.
good day.

 

Are you suggesting that a Bravo 3" +- diameter gear "properly" setup will be as strong as an automotive rear end gearset ? like a Ford 9" maybe ?

What's the most hp you have ever seen put to a Bravo outdrive once it was "properly" set up ?

If I would have known this information a few years ago my friend could have kept his Bravo outdrive, got it "properly" set up and saved the 35k he spent on a #6 outdrive to hold his 1400 hp turbo motor.

 

^^^ lol , I'm not talking 1400 hp .. more like 450-600 hp... allot of people read first and think they are beat before they start because they have X gear case and not Y ... All I'm saying is most marine shops in this area spend very little time setting up outdrives / lower units because they aren't spending the time they should have or just weren't trained on them. I wasn't trying to start an argument over which is better or what should be used .... I was just trying to say that the drives are overlooked in a build until they grenade and then shit on because of the year , make and model ... rebuilding or maintaining them when adding power is often the last thing anyone thinks of until it's to late. You have to admit that the average person who is adding power doesn't take the drive into consideration when the build starts and is only thinking of how much mph he is going to pick up. To me this is when people start pointing fingers and calling stuff junk without truly understanding why. It may be different in your area but I'm only going on my experience.

 

No one has mentioned the out drives RPM limits. 600 HP isnt that bad on a Bravo drive if its kept at 5200 and under. The # drives can handle a lot more RPMs and torq. Much depends on how the boat is driven. If your drag racing from a dead stop its different than a running start on plane. One friend of mine was always blowing drives with a stock big block. He ran at full throttle all the time. Another guy I know of has # 6 drives. 2000 HP engines and kept blowing 2 speed transmissions needed to get on plane. He built his own transmissions. Wish I could afford a pair but 10K a peace is pricy for me.

 

there is some good info on the last few posts.

 

, that's barely above stock HP then.
When you said "those outdrives are just as tough as anything" I knew there was something missing.

They start to have problems at the 800 hp level and it's downhill from there.

 

what kind of power levels do you guys think a gen II alpha will handle 300hp/300 ft lbs?