changing outdrive question-gctid398101

[Guest]

I am new to the stern drive family. I have a 1989 2655 Sunbridge. I love the boat and got it for $3000 and have a little money to upgrade it. I cruise at 3600 rpm/ 21 mph(gps) and WOT at 4400 rpm/25 mph(gps) with a 15 x 13 prop. I am also having problems with reverse and have heard that OMC Cobra outdrives are limited to 300 HP. I am thinking of changing the OMC Cobra outdrive to a King Cobra or possibly a Volvo-Penta DuoProp or a Mercruiser Bravo III. What all do I need have to change? Will a King Cobra or Volvo bolt up to my transom plate? I will be installing a 320 HP 383 this winter and would like to change the outdrive at the same time.

All advise would be surely appreciated.

[Rocky_Road]

This is the only place that I know that offers a conversion for the Cobra outdrive:

http://www.sterndrive.cc/

They have a strong following and a 'no-fault' replacement warranty.

Happy boating!

[2850Bounty]

The SEI conversion takes you from one dog clutch drive to another!

There is another option.

.

[Download_Complete]

Your options are somewhat limited.

1. Change to a King Cobra : I wouldn't do this. The Dog Clutch KC will bolt up (I think), and yes it will hold more power, but the shifting issue is a shift cable issue, not a drive issue. Volvo and OMC share transom shields (at least up to a few years ago) so in theory, VPs are mostly bolt-on.

2. Change to Volvo Penta: Big bucks, but ultimately the way to go

http://www.marinepartsexpress.com/cobraconversion.htm

3. Switch out to an SEI Merc clone - the cost effective way to go...but still limited to 300 hp.

What I would do: Find a junk boat with a VP outdrive, and piece together the swap. Or chase down the parts from the link I listed in option 2 above.

Great boat, but needs a repower.

[itsabowtime2]

What's your budget?

[Guest]

My budget is about $3000-$4000. i see that the OMC to Volvo SX kit starts at $770. Will this allow me to put a DP on this kit? if so, that sounds do-able. if not, then what?

[2850Bounty]

only3000 wrote:
My budget is about $3000-$4000. i see that the OMC to Volvo SX kit starts at $770. Will this allow me to put a DP on this kit? if so, that sounds do-able. if not, then what?

Yes....... but the DP-S or SX only!

DP is synonymous with Duo Prop, of which can be either the AQ series or the Gimbal system V/P drives.

.

[Guest]

So, if i buy the conversion kit, what year SX upper gear case do i look for and what gear ratio? My OMC Cobra is a 1.41 and everything i am reading show that the DP are 1.95. Being new to the Stern drive but being USAF Flt Eng i am mechanically inclined. Does my 5.7L have enough torque to turn the 1.95 DP?

[Download_Complete]

only3000 wrote:
So, if i buy the conversion kit, what year SX upper gear case do i look for and what gear ratio? My OMC Cobra is a 1.41 and everything i am reading show that the DP are 1.95. Being new to the Stern drive but being USAF Flt Eng i am mechanically inclined. Does my 5.7L have enough torque to turn the 1.95 DP?

I will defer to Rick on this, but when I had a VP AQ, the DP was a bolt on to my middle and upper gear case, and I was running a 1.61:1 ratio, which was the VP SP ratio for 5.7L V8s. The 1.95:1 is the DP ratio I would need to upgrade, and I was running a 1986 5.7L V8 with 260 hp.

So, long story short, yes, you should be fine, but you will want to check that with a mechanic to be sure. Another question I would have before running out and buying one is, what is your maximum RPM at wide open throttle?

[Guest]

I am running a 260 hp 5.7L with a 15 x 13 prop and WOT is 4400 rpm.

[Download_Complete]

only3000 wrote:
I am running a 260 hp 5.7L with a 15 x 13 prop and WOT is 4400 rpm.

I will go out on a limb here and say you are likely fine.

[Guest]

Funny but to me the prop seems wrong for that boat. Have same out drive with 351 ford on 2455 and have found that the 15 x 17 seems to be best with the 15 x 15 being ok. The 15 x 17 planes the boat well at 3200 at 22 knt on GPS.

Before changing the out drive if its working good you might try a diffrent prop first.

[Guest]

only3000 wrote:
My budget is about $3000-$4000. i see that the OMC to Volvo SX kit starts at $770. Will this allow me to put a DP on this kit? if so, that sounds do-able. if not, then what?

That'll get you the SEI, the Cobra is a beefier drive and better built than the SEI and the Alpha... you'll have a better chance of handling 300hp from the Cobra.

The "kit" may start at $770, but that's just to mount the drive. Then you need a seawater pump and associated bracketry/hoses, and the drive. If you're able to find an inexpensive, functioning SX and do the conversion for $3000-4000 you're a lucky guy in good shape. Hopefully your budget was not for engine AND drive

Something sounds up, my 2855 which was much larger had the 5.7 Cobra and would hit 29-30mph IIRC, at the very least 28mph for sure.

[2850Bounty]

The additional sea water pump should not be a deal-breaker. The Johnson F5B-9 can be found on sale for as little as $149 or so.



The plumbing of this pump should be fairly simple and easy.

Closed Cooling system:



Open or Raw Water cooled system:



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The SX or DP-S conversion is without doubt more expensive.... no questions about that.

Perhaps find a good used SX or 1.95:1 DP-S drive!

Here's what many do not consider:

• Smooth cone clutch gear engagement. No meshing of rotating dog clutch teeth into one another, and then released from one another.
• No more two shift cables. This now becomes one 33C style cable from the throttle/shift unit directly to the drive.
• No more ESA shift linkage system on/at the engine. This is completely eliminated.
• No more ESA. This too is completely eliminated.

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BTW, if you are building a 377/383, you may want to research an alternate Q/E piston selection for this engine build.

You'll be able to find several threads on this topic here.

Also, MichiganMotors is willing to provide a Q/E build on a custom order basis.

If you go with a well built 377/383, you may be able to take advantage of the greater engine torque and use the 1.78:1 Duo Prop drive.

.

[Chief_Alen]

No one mentioned bravos wonder why ? The cobra cutout is the same as mercs. Bbc mated to a bravo 3, out of a bad hull boat.

Maybe you can get your hands on a donor boat. Or sell the one you have and buy a boat with the package you want in it.

So stay with me a second here... you want to spend around 4,000... keep that money in a account your wife doesn't know about, sell the boat you have and then get what you really want.

There is no replacement for displacement.

Bbc Volvo duo or a bravo 3.