Swapping in Bravo unit in Place of Alpha

My-SS · Jan 21, 2008

I am going to put a 500 Cu.In. Gen III in my boat.
Now has a 5.7 w/Alpha 1.
I bought a Bravo III complete unit.
I have been told I can change the lower unit to a Bravo I
and have a really stout outdrive.

Anyone ever do this?

Bondo · Jan 21, 2008

Re: Swapping in Bravo unit in Place of Alpha

I bought a Bravo III complete unit.

Ayuh,......
Does that include EVERYTHING from the rear motor mounts Back,..??..??

Anyone ever do this?

Ayuh,...... Piece of Cake........ You Might have to drill 2 more holes,.... Maybe....
It depends on the vintage of Alpha you're removing......

My-SS · Jan 21, 2008

Re: Swapping in Bravo unit in Place of Alpha

Got "everything"
motor to prop

HT32BSX115 · Jan 21, 2008

Re: Swapping in Bravo unit in Place of Alpha

Yeah...it's actually pretty easy. I swapped a 460 King Cobra for a 454 (Gen VI Bravo III in my Four Winns Liberator.

Like Bondo said you'll need to drill 2 more holes at the top of the gimbal mount.

You won't be using anything from the alpha except maybe the trim pump...but your Bravo should have come with that too.

You may have to move the front engine mounts if the Big Block mounts are in a different place than the Small block.

Other than that it's pretty easy. You will LOVE the cone clutch shifting and the additional thrust and low speed/reverse handling of the Bravo III.

What size boat is it going in, what ratio is the drive and what props do you have now?

Mine is a 1.81:1 drive and 26p props.

At 4600RPM(rev limited to 4700) I get about 58mph.

My brother bought this boat new in 1987 with the 460 King Kobra.

He had the engine somewhat tricked out when had it rebuilt 5 years later.

I took him for a ride in the boat last OCT when he was up here in the NW and he told me that with the 454/Bravo III it comes out of the hole TWICE as fast as it EVER did when new or when he had the 460 tricked out!!

Cheers,

Rick

Don S · Jan 21, 2008

Re: Swapping in Bravo unit in Place of Alpha

Take out your old engine, transom shield (aka gimbal housing) down to a bare transom. Drill the 2 extra holes needed at the top of the opening, install the new stuff. You should have an installation manual in the paperwork for the new engine. If it's a new engine.
As I recall, you may have to change the side motor mount pad heights some, but nothing major.
Why do you not want to use the Bravo III drive?
If you don't have an install manual and it's an older engine, what is the SN of the 500?

DJ · Jan 21, 2008

Re: Swapping in Bravo unit in Place of Alpha

I can vouch for the "slickness" of the Bravo III. I have one behind a 7.4L. It shifts beautifully.

As mentioned, I can't see why you do not want to use the B III other than they are a little slower-top end. I wouldn't give up the holeshot and handling for that.

HT32BSX115 · Jan 21, 2008

Re: Swapping in Bravo unit in Place of Alpha

I have been told that the Bravo I is a little "faster" than the III.

I suppose that could be true. maybe 3 MPH or so.....but whats 3 mph at WOT? who runs for any length of time at WOT?

I'd try it if I found a "B-one" lower for free.....but I wouldn't waste any money on it If I had to buy one.

Don S · Jan 21, 2008

Re: Swapping in Bravo unit in Place of Alpha

Unlike the Volvo DP's, the Bravo III's excell over 50 mph. That is where they actually start coming alive.

JustJason · Jan 21, 2008

Re: Swapping in Bravo unit in Place of Alpha

ht32bsx115 said:
I have been told that the Bravo I is a little "faster" than the III

Well... sorta...
The B3's extra prop is going to add more drag overall, more drag means slower boat.

However, The bonus is no torque steer, better handling all around, better accelleration.. etc.
Unless your building a boat to run with a chopper prop.... stick with the B3, you'll be glad you did.

My-SS · Jan 21, 2008

Re: Swapping in Bravo unit in Place of Alpha

Ok, I started this, so I'm gonna open the door for the
bashing I;m fixin' to get.

19' Celebrity.
currentyly 5.7 w/alpha 1
top speed now 62 by gps.

Building (not a big block) LSX Gen III late model 500 cu.in.
w/LS7 heads & carb. (injection too expensive and too much hassle)

Why? Same bore as a big block, head ports flow outragous #'s
and lighter than a small block. And make horses so easy it's ridiculous.

Everyone I know around here tell me a Bravo 1 is the way to go for
the lower unit.

I'm looking for 80 to 90 mph hotrod..

I know, I'm sick.

And don't worry, I'm a service manager, so I can take the abuse!!

So, it's bash time...I'm ready for it.

HT32BSX115 · Jan 21, 2008

Re: Swapping in Bravo unit in Place of Alpha

Uh....ok. We're all a little sick in one way or another!

so what's the drive ratio on the B III and what RPM do you expect that thing to turn?

If you use this Prop Slip Calculator

and use 1.81:1 ratio, 6000rpm, and 30p props you get about 95mph theoretical speed. (no slip)

If you add about 8% slip(for a Bravo III...which is only a wild azz guess and probably low for that speed) you get about 87mph.

I don't know if you can safely turn a Bravo III at that RPM for long.....

If you go to a Bravo I, at around 1.5:1 ratio, 5500 rpm, 30p prop and 15% slip which again may be low, you get about 87mph.

Trust me. if that boat was not designed to go that speed......It's gonna be fairly dangerous to go that fast. But you probably know that!!

Is this in a closed engine compartment or is it open? (you're using carb or marine EFI + a blower?)

Mkos1980 · Jan 21, 2008

Re: Swapping in Bravo unit in Place of Alpha

Hope your hull can take it. Theres a few guys on other sites that have added a ton of power to some boats to find out the hull is not stable and they even get scared. You best get a full Hyd steering too if you planning those speeds. Some K planes

Mkos1980 · Jan 21, 2008

Re: Swapping in Bravo unit in Place of Alpha

I know that the LSX blocks also house stock SBC mounting pad provisions, but will their be a problem mating the two together?

Your going to need more then a Bravo III for what your doing. Probebly a bulletproof upper Bravo one and a shorty custom lower unit with a clever prob. With hardley any weight in that boat, its going to be hard to control.

180shabah · Jan 22, 2008

Re: Swapping in Bravo unit in Place of Alpha

Are marine parts(starter, cooling and ignition) available for that block?

Mkos1980 · Jan 22, 2008

Re: Swapping in Bravo unit in Place of Alpha

I would imagine so as I have seen Indmar produce from LSX motors. I know the Malibu Corvette Boat Uses an LS7 Dry Sump system.

180shabah · Jan 22, 2008

Re: Swapping in Bravo unit in Place of Alpha

Thought they might be, just wasn't sure. Thanks.

My-SS · Jan 23, 2008

Re: Swapping in Bravo unit in Place of Alpha

180shabah said:
Are marine parts(starter, cooling and ignition) available for that block?

Besides the block, everthing else is the same.

"http://www.gm.com/explore/technology/gmpowertrain/engines/specialized/marine/2008_6000_LS2_Marine.pdf[/url]

achris · Jan 23, 2008

Re: Swapping in Bravo unit in Place of Alpha

I think your new speed figure is a little optimistic. You currently have 260hp and make 62 MPH. The LS2 makes 390hp.... I have just changed from 180hp to 220hp and picked up 1.3 knots increase. That 40hp to make 1.5mph. I think you'll get a top speed of around 70 mph...

Interesting fact I hear on a TV show the other night. They were test driving a Bugati with a 1001 hp engine

. The presenter said that the top speed of the car was 253mph... and later proved it... and that to get to 150mph took just 250 hp, the next 100mph took the extra 751 hp....

Same with a boat, to increase speed with something a bit slow is easy. As the speed rises the amount of power required to further increase speed rises exponentially.

Just my 0.02

Chris....................

My-SS · Jan 23, 2008

Re: Swapping in Bravo unit in Place of Alpha

I guess this was all a fantasy...sold the complete BBC and Bravo 3.
Money going into house repair.
Now my 350 block is cracked, my manifolds are cracked...
my spare 350 has a spun brg.

Life is wonderful!!!

I'll just have to roll up my jeans and wade on the shore this summer.

achris · Jan 23, 2008

Re: Swapping in Bravo unit in Place of Alpha

My-SS said:
...Money going into house repair....

Ouch!!! That's gotta suck!!! Condolences...

Chris..............

Swapping in Bravo unit in Place of Alpha

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