BOAT = Break Out Another Thousand. So I got myself caught up in the restoration of a '74 Conqueror SuperBee III. Long story short, the original 340 is shot, looks like from detonation. Having a hard time finding anyone who knows anything about this engine. I'm tempted to just drop a common 318 back in but know I'll regret not keeping the 340 in it. I need some piston recommendations for this 340. I don't want high compression, hopefully something around 9:1. I've never owned a small block. Are all the heads the same? Thanks for any info. Mike

In 1972 Mopar lowered the compression ratio on all car 340 motors to 8.5 to 1, that is in blueprint specification. Mopar never blueprinted any production motors so the average car motor had less than that spec. My message is to go ahead and buy good quality replacement piston for the 1972,73 car motors and check the deck hieghts, combustion chamber volumes and see what true compression ratio you get use the head gasket thickness to help achieve the compression ratio you want IHTHs

Agree with Cab

As to your other question, No, all the (SB) heads are Not the same. (Click on Link below for Hot Rod Mag article on SB Heads)

http://www.hotrod.com/how-to/engine/mopp-0607-mopar-cylinder-head/

I am fairly new to Mopar SB's too. Just bought my first one, an LA 360, in the '74 Dodge Power Wagon I bought last November.

If the block doesn't check out to be good, do a stroker 318, not so common.

By late 72 340's had a very sturdy cast crank, forged went away. 340's, and 360's, have bigger port/valve heads than a 318.

But, since you said "restoration", do the 340.

If you're wanting to be out on the water for what is left of the summer months what about dropping in the 318 to get you up & running then we can help you get the 340 rebuilt/setup for high rpm longevity. (simply) Sounds like the PO didn't use enough octane.

Boats are under constant load, like pulling a trailer uphill in a vehicle all the time...

that jogged my memory & once I worked on an inboard 318 speedboat & it was reverse rotation! took awhile to figure that one out (firing order)

This one seems normal rotation. The firing order runs clockwise. The numbers on the side of the block is 2780930-340 and there's a larger # 7 cast near that. The head #'s seem to be 2843 and I think 678 but might be 578 or 576 - 21

I have always thought why didn't boat manufacturers reverse the rotation on the props made to accomodate standard rotation engines??

Twin engine shaft drive boats usually had one regular rotation engine and one reverse rotation engine. At least that is how I remember them.

The prop on many single inboard engine boats turns clockwise(CW/reverse/right hand rotation) to help trim the boat.
When a boat is operated by only one person sitting on the starboard (right) side, the operators weight creates a list to the right. If the prop turns CCW (std automotive rotation), the torque it produces will also create a list to the right. So by turning the prop CW, it's torque now creates a list to the left, which will help counter the list on the right caused by the drivers weight. Hopefully the two are near equal so the boat will trim up level.
When more than one person is in the boat, they can shift their sitting positions to help with trim, one person doesn't have that possibility.

A bit of trivia, Chrysler Marine V8s didn't use the AVS's, almost all used a AFB's modified for marine use.

If you do change to a newer style engine, I'd suggest 360 to better match torque and power of the previous engine. With the same prop and gearing, it should run a little easier vs the 340. A 318 would have to run hard unless you reduce prop pitch.

Excess load from too much pitch can contribute to detonation. With full throttle the engine should max out around 4300-4500 RPM. Less than that means too much pitch, more means not enough.

Most Chrysler Marine motors have special oil pans and timing cover, so if he went with a 360 he'd have to locate them.

If it were me and if I'm buying new pistons, might as well get new rods and a 4" crank to go with them and throw them in a 318 block. What's a plus .030 318 with a 4" arm? 390"? That should do it.

Yes, boat motors have a load on then all the time they are cruising. If it has the original dist, notice there is NO vac adv pod. It's easy for a prior owner to jack up the timing to auto specs and causing detonation. Check the owners or shop manual for total timing, it will far less than automotive, 10* less, maybe more.

First thing I'd do is verify that the 340 is a RH/CCW/standard rotation. Internal parts will be the same as automotive.
If it's LH/CW/reverse rotation, careful with the cam and dist drive gear. There are new ones available for the SB and pricey but at least you can get them, only choices for the BB is used.

TY for the prop rotation comments above...

Just to make sure... when checking for clockwise or ccw are we looking at the front of the engine or referenced from the rear? Thanks

Looking at the engine from the front, like where the crank was on antique cars.

R.

Can't do it, one engine would be pushing forward the other would be in reverse.

Any pictures of that boat you are restoring?

If the boat was raw water cooled, there's a good chance that the block is thin from years of rusting in the water jackets.

Find a good replacement block that had antifreeze in it.

Also, you really need to find a shop that builds marine stuff. There are LOTS of subtle differences that will bite you. (Carb setup, piston to wall clearance, valve guide clearance, oiling, cam selection etc........) don't think you can just drop in an automotive engine and be good to go.

First, let me correct my post.
"First thing I'd do is verify that the 340 is a LH/CCW/standard rotation.""

From the rear or like you're in the drivers seat.
Standard rotation is CCW or Left Hand.
Reverse is CW or Right Hand.