Merc 470 to SBC 305ci?

[95ImpySS]

Well, I purchased my first boat. Spent many weeks fixing it up and after I purchased it learned of the dreaded 470's issues. Well I gave it its first sea trial today. Needless to say, its in sad shape. Needs a starter, flywheel, alternator (evil 470 regulators), head, head gasket, shift cable bellows, and maybe u joints this list goes on. Anyway, I'm an avid chevy mechanic and am curious if I could pull the 470 out for scrap or a nice outdoor foot rest and replace it with a carbed 305ci small block chevy.

*I am pretty sure I heard that the alpha one gen one has the same bellhousing bolt pattern as a SBC. Is this correct?

*Also I would like to do ported heads and a cam on it. Could the alpha one take about 350 hp reliably?

*And final question, could I use any SBC if the bolt pattern works? I would like to use one out of a car since they are very plentiful. Any ideas on what I would have to do to convert it over to work in a marine application?

BTW the boat is a 1989 Wellcraft 192 classic cuddy.

Thanks

 

[Bondo]

Re: Merc 470 to SBC 305ci?

Ayuh,.... Welcome Aboard,... Short answer is,.. Sure, Anything is Possible...
The long answers start with the fact that about Everything in your hull will have to be replaced with other parts....
No,.. You don't want ported heads,+ a Hot cam...
And,..
Yes,.. an SBC is a SBC....

 

[gcboat]

Re: Merc 470 to SBC 305ci?

Oh boy! Well, let's start with the room factor - would you have enough to install a SBC, even the 305? It would be a lot of work changing out the entire exhaust system if nothing else.
I do question the strength of your present drive unit though. That would be a question the pro's should answer - not me.
As far as placing a car motor in a boat - go ahead. Just don't expect it to last very long. Look at it this way. When was the last time you took your car and ran it peddle to the metal? That's the way most boats are operated. Of course that is an extreme statement but I hope you get my drift. Marine motors are engineered with different internal parts. Cams for one. They also have sparkproof starters, alternators and all sorts of required marine equipment.
Guess I'm just from the old school and like to see things done right.
If nothing else take a look at using a 4.3. You'll get a lot more power, the lower unit will probably handle it and it won't cost you an arm and a leg to do a retrofit.
My $.02

 

[95ImpySS]

Re: Merc 470 to SBC 305ci?

Ahhh I love this forum, lightning quick reply's. Well I'm laying out the financial costs. Could prolly make the room since I want to pull up the deck (soft in a few spots) and upgrade the fuel tank (25gals jut not enough IMO). I have seen a 454 in a 182 classic basically the same boat just 1ft shorter. I would use the heat exchanger and upgrade it to at least 4 inch (go bigger for more ci I assume) so the engine itself would see a 50/50 antifreeze/distilled water mix. I also understand the RPMs that the engine would see. Yet I see many boats with regular v8's in them. Thoe I have no idea of their life expectancy and can only assume by the amount I see that it must be good. I will rebuild the engine before I put it in and am obsessive with maintenance. Judging by the way this 470 is build, (lack of cam bearings and no hyd roller lifters) I think a regular fresh SBC would outlive it any day. I'm sure I could find a marine starter and other marine specific parts to make it legal in that sense. And after owning this engine, I will stay away from all merc products. I cannot believe the lack of engineering that has gone into this engine and can only assume merc cut corners in their other power plants. Now what will make or break the deal is if the alpha one cannot bolt up or handle the added power from the v8. The motor mounts are already rotted out and will have to be changed.

 

[Don S]

Re: Merc 470 to SBC 305ci?

would you have enough to install a SBC, even the 305?

A 305 and a 350 are identical on the outside.

No an Alpha will not handle 350 hp, especially since I can see how you want to run it. FAST and Hole shots to Fast. It might handle it if you want to baby the throttle, but I don't see that happening.

You would also need a differnt gear ratio for the drive or your problems will be even worse.

Hooking up the exhaust would be a problem if you can't find the proper Y pipe. You would also need all the V8 exhaust parts (New manifolds and risers) coupler, bellhousing (470 won't fit a SBC), engine couple (470 won't fit a SBC), along with the marine starter, alternator, distributor, carb, fuel pumps, etc. as mentioned above.

Can it be done? Yes, all it takes is money.

 

[95ImpySS]

Re: Merc 470 to SBC 305ci?

I was afraid the exhaust would be an issue. I have seen boats the put the exhaust through the transom with what look like custom headers that also have the liquid cooling. To be honest, I'm new to boating and speed and quickness are not my main priority. Mastering maneuvering and speedy ramp launches and retrievals. (after today, I see how people take forever and its very aggravating) I am used to repairing these chevys and figured why not put one in the boat if it would bolt up to the drive and delete this power plant. I would like to change it, but if I have to change the drive also, I may just cut my losses and sell the boat.

 

[95ImpySS]

Re: Merc 470 to SBC 305ci?

Trust me, Id love to keep this boat. I have well over 100 hrs in rewiring it and repairing all the riggs that were done by the previous owner. But I refuse to put another 470 or mercury product in. help...

 

[Don S]

Re: Merc 470 to SBC 305ci?

Your best bet would be to find a doner boat with a good engine and drive, then install it in your boat. Or, you might want to consider a new engine and drive combination. Here is just one example http://www.marinepowerservice.com/BoatingStore/browse_detail3.cfm/productID/23392.cfm

 

[Bob_VT]

Re: Merc 470 to SBC 305ci?

Keep your eyes open for a project boat with a 4.3 mercruiser on craigslist. It would be easier to change everything motor and outdrive then to try and make things fit. If you do find a project boat with a 4.3 you could freshen it up before you install it.

There are many boats out there.

Don summed it up..... it's all about money.

 

[TilliamWe]

Re: Merc 470 to SBC 305ci?

Impy, if your boat was perfect, I'd say go for it. But you have rotten stringers and a rotten floor. Sorry, but you are throwing good money away. You bought a bad boat.
As far as Mercruiser cutting corners, well, they confined most of their mistake to 470. They don't actually make any of their other I/O engines, those are all supplied by GM (they did use Ford in the past).
Installing a SBC can be done, but you will have t fabricate front motor mounts in the stringers (your 470 has that crescent shaped thing), and you need to see if there are any width restrictions. You better be a carpenter/fiberglass man in addition to a mechanic, cause you have a lot of work ahead of you.

Lastly, when it comes to building Marine engines, you can not put in a real high lift or long duration camshaft. You have to have power available at 1500rpm, and overlap leads to the posibility of water reversion through the exhaust. Mercruiser and Volvo Penta outdrives seem to get limited to about 5200 rpm, so you can't build a 6000rpm high horse/low torque engien and expect it to perform well in a boat.

Good luck.