re-powering

bobyn · #1 10-22-2005, 09:03 AM

Hi, I have a 1973 23 foot CC I/O with a Mercruiser 165 hp 4 cylinder engine that is getting tired (second one), and am considering putting in a V8 of 250-280 HP for increased speed and effiency. Currently I cruise at 18-19 mph and 9-9.5 gph on Flowscan. I have an alpha one drive that is two years old that I would like to keep. Does anyone out there have any experience in this conversion or have any suggestions that would help me? Bob

ScottM · #2 10-22-2005, 10:37 AM

bobyn,
I don't have any experience with the repower, but I think you'll be very happy going to a V8, especially a 5.7 liter/350 Chevy block. That 165hp is probably working pretty hard just to give you the current cruise speed, whereas a 260hp carb'd V8 will give you a mid to high-20s cruise and probably burn the same amount of fuel (expect around 40 mph WOT). The Alpha One should hook right up to a V8 too, so you won't need to replace the drive.

Go one step further and opt for fuel injection and efficency should improve. Or, drop in a HO 6.0 liter (320hp) and Bravo III drive and you'd really be moving along. [img]/images/graemlins/cool.gif[/img]

Briguy · #3 10-22-2005, 11:55 AM

mmmmmmmmm good time for a diesel. Merc has a 170/200hp 4cyl package that burns under 5gph.........

http://www.cmdmarine.com/recreationalsterndrives.html

Fr. Frank · #4 10-23-2005, 05:49 PM

The gear ratio in the Alpha One drive you already have will probably not be the same as you'll need with a V8. This problem is easily solved by changing propellors. Unfortunately, you can't just "drop in" a V8. You will need to change everything from the gimbal housing upward. Same problem, by the way, for any engine that doesn't use that same Mercruiser big-block 4 cylinder.

That being said, that big-block four cylinder is available in factory versions up to 190 hp, and I have even see a Wellcraft Airslot 24' with twin "470" mercruisers that had been outfitted with Paxton superchargers. The owner had gotten them off a couple of factory supercharged AMC Gremlins. (No, I don't know why AMC offered a supercharged Gremlin} He claimed 220 hp from each engine, and said he had over 200 hrs since the install, running them "8% under-driven", whatever that means.

If cost is not a major issue, or at least not the overwhelming issue, I TOTALLY agree with Brian, go with the diesels.
Here's something people often overlook about diesels: At a given horsepower, a diesel will produce 20 - 50% more thrust/torque than an equal horsepower gasoline engine.

For instance (going aviation here) a Cessna 172 with a 180 hp six cylinder gasoline engine will have almost exactly the same performance characteristics as the same aircraft equipped with a new 120 hp four cylinder aviation diesel engine, and yet the diesel will use just about exactly half the fuel at cruising speeds, and about 15% less fuel at maximum speeds. That changeover to diesel power, while expensive, effectively increases the cruising range of that aircraft by more than 75%, from 720 nm at max weight, to over 1250 nm at max weight.The same principles apply for marine use.

The question you need to ask is, do you want to spend the up-front money for the repower with diesels.

Briguy · #5 10-23-2005, 10:39 PM

Just a far flung guess but the Merc Diesel package will probably cost 12k-14k with outdrive. I know Merc sells the 120hp with drive for 9k. A diesel package in a SC is my wet dream. [img]/images/graemlins/wink.gif[/img]

bobyn · #6 10-24-2005, 09:16 AM

Fr Frank, Scott and Brian, thanks for the replies. You have given me something to think about- especially the diesel option-with gas so high, it is food for thought. If I choose that route, do you think a Mercruiser diesel pkg would fit the existing transom cutout? Or is surgery required in your opinion? Again thanks for the feedback, Bob

Tarpun · #7 10-24-2005, 10:25 PM

These days diesel fuel is more expensive than gas by about ten percent.In fact in my area it's been more for the last three years. Thats at the service station. I'm not sure about marina prices. Diesel routine maintainence runs more also with generally twice the oil capacity and more expensive oil and fuel filters. Plus the greater initial cost. All that being said the increased torque, safety, and better range make it a tough choice. Another plus for the diesel is that a lot of it's increased initial cost may be recouped by an increase in resale when you sell. For me it would boil down to the amount of use. The more hours I put on in a season the more I'd vote for diesel.

nestorpr · #8 10-25-2005, 01:05 AM

Besides the Cummins-Mercruiser outfit check out the Volvo Penta and the GM offers.

Briguy · #9 10-25-2005, 04:34 PM

Bob,

Only Mercury can tell you if a new motor/drive will fit without cutting. Diesel is $20c cheeper a gallon where I buy fuel.

Fr. Frank · #10 10-25-2005, 10:58 PM

The transom cut-out is the same. Engine mounts may have to be fabricated, though. Not a big deal. The current Mercruiser/Cummins or larger (240 hp & up) Mercruiser/Yanmar combo's are supposed to be "bolt in" replacements. (Just for the record, though, there really ain't no such thing.)
Volvo Penta has 16 different diesel sterndrives ranging from 130 to 350 hp, and ranging from $18.7K to $33.4K
For Mercruiser package prices look here:
http://www.dougrussell.com/Products/...=70&Category=6
Doug Russell Marine Diesel sterndrive package pricing