Mercruiser3.7L/170 4 Cyl Repower to 4.3L V6 Pros/Cons

erwinp

Recruit
Joined
Feb 24, 2013
Messages
3
Hi everyone,

I've been doing a lot of reading on the pros/cons of either rebuilding/replacing the 3.7L 4 cylinder with a 4.3L 6 cylinder. A couple of weekends ago, the engine lost power, started making a metallic banging sound, then died. The sound doesn't happen when cranking though. It's in a 1986 Hurricane Deckboat.

I did a compression test and got the following.

Cylinder #1 80 PSI
Cylinder #2 110 PSI
Cylinder #3 0 PSI (Yes Zero)
Cylinder #4 80 PSI

So there's something wrong with cylinder #3. I haven't pulled the head off yet to figure out what the cause is, but I know I'm looking at putting some funds into it to get it back up and running.

I've been able to find 4.3Ls a little easier and cheaper than the 3.7L; including a blown 4.3L that was complete that I could transfer parts from.

The decking and 1 stringer is soft from the PO bringing tubes in and dumping water just in front of the rear seat, so I'm already looking at doing a stringer repair (probably with the composite stuff like seacast). So adding new mounts wouldn't be too much trouble. Would there be an issue with mating to the transom (i.e. are the engines mounted on the same angle or clearance)? I know they have the same bolt pattern and the gear ratio is correct (1.84).

I'm also aware of the exhaust y-pipe. One question I'd have on this, is whether it would makes sense to provide dual exhaust? Can the single exhaust opening be closed off?

So my main question is this... for anyone who's done the engine swap, how did you like the results? I've looked and didn't find horsepower and torque curves between the 2 motors and I'd be interested in seeing any differences.

Another question, how much of a weight difference is there between the 2 engines? How much lower would it make the rear of the boat?
 
Top