Basic Sterndrive Configuration Questions

[tpenfield]

As this discussion about replacing the engine and outdrive evolves . . . I am wondering about the budget for such. Are we talking new power package? Used? Separate engine, then transom assembly and outdrive?

Just wondering what the budget is for all of this . . . can't remember if that has come up or not :noidea:

 

[76SeaRay]

I am not so much into speed but mostly interested in good cruising characteristics and handling. Are the 7.4L pretty close in size (volume) to the 5.7L in the marine engines? Wondering about fitment issues since this had the Windsor 351 in it from the factory. I don't have the engine cover for the boat and will have to fab one so mostly concerned with the fitment between the stringers and overall height. This is a tall transom boat though.

Thanks.

 

[Rick Stephens]

You can get dimensional drawings off this page. Really useful to spend some time measuring.

 

[76SeaRay]

Thanks for the link. That's great. I had the info on the 5.7L from others on here earlier but not for the 7.4L or sterndrives... Have a bit of reading to do now..

 

[HT32BSX115]

I am not so much into speed but mostly interested in good cruising characteristics and handling. Are the 7.4L pretty close in size (volume) to the 5.7L in the marine engines? Wondering about fitment issues since this had the Windsor 351 in it from the factory. I don't have the engine cover for the boat and will have to fab one so mostly concerned with the fitment between the stringers and overall height. This is a tall transom boat though.

Thanks.

If you want outstanding handling you'll definitely want a Bravo III.

I originally wanted a Bravo I but this "III" presented itself.

Now that I have it, I would never go back to a single prop drive on a boat over 20ft. At medium planing (cruising) speeds, you will absolutely use less fuel. IMHO, it's worth the extra money. I have bought all my propsets, (26p 3x3 and 24p 3x4) used off eBay for about $500 or so.

I removed the original 460/King Cobra and swapped it out for the 454/BIII .........Since the crankshaft HP was similar, the top speed difference negligible, but every other parameter (holeshot, low/slow speed and reverse handling was huge improvement!!

In any case, Alpha or Bravo, you will have to drill the "keyhole" in a position that places the propshaft at the correct depth (IAW the Mercruiser installation manual) and then work backwards from there to the engine mounts etc.

You will definitely be ok with a 300HP 5.7L MPI or a 383. But if you're going to that length, you should also do the Bravo III for the reasons indicated above.

A good running 7.4L engine will perform as good or better than any 300 MPI or 383 and will probably cost less to obtain. (and you can probably use a 454 "truck" engine fresh out of a wrecking yard........as long as you replace the dist, carb, starter and ALT with "marine" units of course!)

The best way will be to find a "pulleys-to-prop" package from a damaged boat....

Good luck!

Rick


)

 

[Scott Danforth]

The big block is about 1" wider (about 34" wide with manifolds) and about 2-1/2" taller for a carbed motor. Mounts the same width

 

[76SeaRay]

Great, thanks for all the info. To answer the earlier question about budget. I don't have an unlimited budget and will be retiring soon (that old fixed income thing). So, this is intended as a retirement cruising and a little bit of fishing boat with occasional overnighter. I don't want to cut corners but on the other hand I don't need a way over the top boat either.

I like the idea of getting a wrecking yard 454 and doing the rebuild myself. Engine rebuilds are no problem for me and I like knowing what goes into it in terms of part quality. Any reason for recommending a truck BB versus a car BB other than availability? Thanks for the list of changes to make it marine. I understand the need for the electrical safety of marine components. I read somewhere that there are other components like the "freeze plugs" that should be changed. Any junkyard rebuild of an engine gets complete disassembly, hot tanking, magnaflux and new freeze plugs in my car restoration world so the same would apply here.

So, since I am not finding much in the way of complete pulleys to prop set ups, I am more focused on finding the correct sterndrive unit right now and getting the transom rebuilt. The engine decision can come later unless something happens to fall in my lap (yeah right).

 

[HT32BSX115]

Any reason for recommending a truck BB versus a car BB other than availability? Thanks for the list of changes to make it marine. I understand the need for the electrical safety of marine components. I read somewhere that there are other components like the "freeze plugs" that should be changed.

I would replace the core plugs in anycase......Stainless steel and brass are available I believe.....

The "truck" engines are usually thought to have a camshaft that would allow for a somewhat lower max RPM. Max torque will be at lower RPM in truck engines.

And yes, there's probably FAR more pickups and Suburbans in the wrecking yards with 454 engines in them vs cars.....

Since you might be tearing it down, you could easily replace the camshaft with a "correct" Marine cam. Comp, Crane, Crower comes to mind, but if you can find an engine out of a truck or RV chassis etc, the stock camshaft is close enough for a (stock performance) marine application. You want all the HP and torque to peak below 5000RPM in general.

Also, once you get to that point, there are quite a few here that have "Been There, Done That" who will jump right in and have good suggestions on what cam to use if you want to get a "marine" type cam.....I think any truck 454 would be adequate as is.

Another way to do it would be to get an existing good boat if you can buy it cheap enough and swap everything ove......then part out the boat and trailer........

(In that case....you REALLY have to want to use that Searay though!) Here's an example........end of Summer there's always a LOT of boats everywhere for sale!! https://seattle.craigslist.org/sno/boa/d/1992-wellcraft-216-eclipse-21/6305965595.html

I gave $5000 in 2006 for the engine/transom/drive I have. I am not sure I would do it again though. Unless you can find a Super swinging-deal......it's not really worth it unless you REALLY like the boat you want to repower. It was a LOT of work, but at the same time a fun project ...... And I was lucky...... I was able to sell all the OMC "stuff" for about $3600 total (That was a LOT of work too!!)

 

[Scott Danforth]

the only reason to pick up a wrecking yard core for a rebuild is that you want to rebuild it, not because you want to save money. it will not be less expensive than finding a mid 90's boat with a rotten hull and a good running motor for $3k and then scrapping the rotten hull and selling the trailer. the later route gets you a full running power plant, with all the bits and ready to go for about $2500. just rebuilding a big block using cast parts is $2500. full forged internals with an internal balance job and upgraded heads with a port and polish job will be closer to $5k

buying a power plant already removed is a bit more like HX indicates, however you dont have to spend the hours removing it.

regarding wrecking yard big blocks, yes, cars quit getting the big block in the mid 70's. trucks, ambulances, and RV's continued to get them. if going this route, I would go with a gen VI motor (1996-2000). the Gen V and Gen VI are both 1-piece crank motors, however the gen VI is a roller motor with priority main oiling and doesnt have the steam hole design oops that the Gen V has.

 

[Rick Stephens]

I would absolutely recommend you go the rotted out donor boat route as it gets you every part you will need. Then you go through everything as you redo the stern of your boat to take the newly refurbished pulled motor and drive.

 

[76SeaRay]

Not having much luck finding any donor boats.

By the way, I see that a 5.7L with Alpha Gen 2 that the gear ratio should be 1.47 (1.50) to 1. Is the gear ratio engine dependent or drive/prop dependent. That is, would it still be 1.47 to 1 with a 5.7L in front of a Bravo drive? Likewise, would it be 1.47 with a 7.4L independent of the drive?

Thanks...

 

[Rick Stephens]

Alpha ratios are different from Bravo ratios. The Alphas, which I know best, have a fixed lower ratio and the upper gear sets are chosen to match the torque output of different motors. A low torque motor like a 3.0L gets the most gear reduction at 1.98:1 (later models were 1.94:1). A high torque motor like a 5.7L or 6.2L gets a lot less gear reduction 1.50:1 or a 1.32:1 with the goal being a prop pitch that is applying power at most efficient RPMs. Your pick of motor determines the choice in gear ratio. With a large boat, your only choice with an Alpha would be a 1.50 or a 1.32 Alpha paired with a 5.7 or larger motor, or a BBC and a Bravo.

Bravo drives have everything from 1.50 to 2.20 in upper gear sets and alternate lower sets can change ratios in a much wider range from a low of 1.20:1 on up for super high performance installs. Bravos are not something I have spent time working with, so there are undoubtedly a bunch more to it.

My advice on finding a donor boat is keep on looking. A little patience goes a long ways. They pop up regularly on CL. You need to take your time and find the right deal. It will come around. One thing about boats, there is always another one for sale.

 

[76SeaRay]

I will keep looking but don't want to pass over a good deal on a sterndrive unit or engine if I find one. I am leaning towards a 7.4L and Bravo 3 if I can find one, hence the question on gear ratios. Will need to see what Bravo 3 gear ratios to watch for with a 7.4L up front.

There is a boat surplus place in Colorado but its about 3 hours one way. Waiting for a good weekend to make a dry land outing of it. The old OMC block is coming out this weekend.

By the way, I just got the Clymer book on Mercruiser to spend some time reading now. Haven't check to see if they talk about engine/sterndrive match ups.

 

[Bondo]

By the way, I just got the Clymer book on Mercruiser to spend some time reading now. Haven't check to see if they talk about engine/sterndrive match ups.

Ayuh,..... That's an Ok knee pad,... little more,....

Ya oughta spend a few hours siftin' through Don'S Adults Only Section,....
The link is in my signature,....
Oceans of Info in there,.....

 

[HT32BSX115]

Will need to see what Bravo 3 gear ratios to watch for with a 7.4L up front.

my 7.4L + Bravo III came out of a 1998 24ft Bayliner Cuddy. It came stock with the 1.81:1 ratio and 24p props. The original owner told me he could get about 55 mph at 4600 RPM (max for a 7.4L, carbed for that year)

For a boat of your size, a 1.81 Bravo III will might work ok with 22 or 24p props..........

A 2.00:1 drive might be better though................. If you build up a 454 to turn 5000 RPM max, you'd probably be good with a 2.20:1 drive

 

[76SeaRay]

Ok, so after a lot of study on the question, I am planning to go the 7.4L/Bravo III route. Hopefully I can find the budget for it. So, the next question is on the engine itself. I see 7.4L listed as 73 to 90, 91 to 97, and 96 to 03. I plan to go carbureted at this point. I am guessing I should go with something from the 91 to 97 years. How do I identify the correct engine/block for what I should get? I see the following listed as casting numbers 182, 297, and 313.

Thanks.

 

[HT32BSX115]

Ok, so after a lot of study on the question, I am planning to go the 7.4L/Bravo III route. Hopefully I can find the budget for it. So, the next question is on the engine itself. I see 7.4L listed as 73 to 90, 91 to 97, and 96 to 03. I plan to go carbureted at this point. I am guessing I should go with something from the 91 to 97 years. How do I identify the correct engine/block for what I should get? I see the following listed as casting numbers 182, 297, and 313.

Thanks.

Not sure it matters all that much, as far as flywheel, housing and coupler is concerned. older engines have mounting for a fuel pump, some newer ones don't. If I was building up an engine from scratch, I would want to use an electric pump anyway so you can use the less expensive Bravo raw water pump.

Mine was from a 98 Bayliner and I believe it's a GEN VI engine

Here's some info on different generation BBC:

http://www.superchevy.com/how-to/456...e-generations/

http://www.chevyhardcore.com/news/re...sting-numbers/

You're also going to need to "remote" the oil filter and find an oil cooler.

Also, if it were me building up a "new" engine(and I DID do this on mine) I would install a San Juan Engineering Closed cooling system. It does add about $1k to the cost but IMHO, it's well worth it.

 

[76SeaRay]

Thanks for the info links. Great stuff there. By the way, what about the weight? By that I mean, this boat had an OMC 351 Windsor so I am guessing that a GM 7.4L is going to add about 150lbs more at the stern. Any issue with that messing up weight and balance or causing handling problems?

 

[HT32BSX115]

I don't think you'll notice much difference. My boat was available with the Merc/GM 350, 454 and OMC 460 V-8's. It's unlikely an additional 150 lbs would change it anymore than 2 adults would sitting in the back

 

[Scott Danforth]

the BBC is about 100# heavier than your motor

it the extra weight bothers you, go with aluminum exhaust manifolds on the Big Block such as EMI or Stainless Marine and you can get that weight back. 23# for aluminum vs 65# for the cast iron exhaust manifolds