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high duration reverse rotation cam

politicallycorrectcraft

politicallycorrectcraft

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Well my correct craft is going to be in the shop for the rest of the season. I've got some bum stringers and a delaminating floor. So in between nightmarish grinding and cutting sessions I've been dreaming about listening to this girl idling in the water. I would love to hear a lopey cam sound come through the straight exhaust I'll be running. My question is does anyone know of a mild cam upgrade that would work well in a reverse rotation 318. I'm planning on ditching my afb for a 1409 edelbrock. Any suggestions?
 
Oooowwww! I like the way you think!

About the best you can do is get a custom reground cam. I got one made for me by Herbert Cams. Be forewarned that valve springs and greater valve travel need to be addresssed as well.

Jeff
 
That maybe your only choice. Marine Parts Source still has the original CCW cam but no one will be able to tell
you what the specs are, even the standard rotation for that matter. Just remember the higher the 'lump' the higher the lobe the lower the torque. You want all your power off idle not 2500 rpm. I'm changing over to a 340 and passed up on a basically stock 340 purple shaft street cam P4452782 for a 197/199 @ .50 410/411.
The thing that concerned me about the Purple Shaft was the cars they were put in required a slightly higher stall converter to make them idle correctly , about 700-800 rpm or so which is too high for most drives.

Jack
 
Love the lope but, unfortunately, without other upgrades, you might not get a whole lot out of the money you spend for a custom grind.

To expand on Jeff's point about the valves, in addition to springs and lift, the valve sizes and ports are a real choker on the 318 heads (nice for torque not so nice for extracting the higher rev HP that you get from a bigger cam). In other words, even if you get those valves open further and longer, there's only so much breathing those heads are capable of in stock form. Moving up to 340 or 360 heads are a great upgrade for a 318 but require some milling for compression and also comes with the torque sacrifices that Jack mentioned.

However, in an application like your Correct Craft (vs. a big cruiser), you might be able to make that compromise.
 
I've got 360 heads available. How much machining would be needed? Would the bigger heads compensate for the higher lift? Keep in mind this is still all dreams that I'm seeing in clouds of fiberglass dust....
 
Hi Folks,

The one item you must remember is the camshaft in your boat was designed to keep water out of the exhaust. This by using a small overlap time when both valves are open that gives us that sound we all love. Best thing for you to do is contact the camshaft grinder yourself. I do not have any ties to any one camshaft grinder. Over the last 45 years I have used with good sucess, ISKY, ELGIN, HERBERT most of teh ones who have been around and know reverse rotation and std. rotation engine.

Yes I have built Marine engines with TOO MUCH CAM! Remember trying to dock for gasoline on a windy day and when you shift from forward to reverse the engine dies every time because of the BIG camshaft. Not a pretty sight. Sounds good but cannot dock it Ha

Hope this helps you decide.

Lauching........

Mike Caruso
 
Technically, the 360 heads will bolt right on to your 318 but the larger combustion chamber would cause the already-low compression to fall off the map. That's where the machining comes in. You need to mill the bottom of the head to increase compression. Since marina gas isn't always the best thing going, you wouldn't have to cut them all that much.....really just enough to bring you back to the 318's compression ratio (or a tad higher if you want to pull a little more out of it). Using the casting numbers off the heads, you should be able to figure out the ratio of the 360 heads.

Mike is correct about water reversion with a big cam.....but I don't think you're looking to go big enough to worry a lot about that. Reversion is most often seen on high compression/performance marine engines with very big cams and, in most cases, headers.

I know where you're coming from when it comes to the quest for more power. However, since you brought up the dreams in fiberglass dust, pick your battles. Boats are funning things when it comes to adding power. Gearing, prop specs, impellers (in jets) are all variables in how your added power will (or won't) translate into performance.
 
It can happen on small std. engine too!

I have customer that takes care of fishing and pleasure boats and installs factory new engines.
Using GM Mercruiser 1996-2006 4.3L engines and is having problems with the latest engine he installed. If you stop the engine while at idle it sucks water back in to it. From the water cooled exhaust manifolds on the rear two cylinders on one bank and the two front cylinders on the other bank?
The new engine uses a different camshaft and ran very well. It would even idle at a lower rpm than the old engine like 500 rpm and shut it off and it will suck water back into the cylinders!!!
The rear of the new camshaft is ink stamped the number 691-19f-8276.
The heel diameters (base circles) are close the other cam with-in .010-.020"
Both engine use hyd rollers tappets and have the same tappet bank angle of 22°.

The GM marine dealer will not give my customer any info if the new cam is a marine cam or a cam for a passenger car. All that they would say is that they identify the cams by color and were not sure why the new camshaft had a different color painted around the core by the front journal.

This new engine camshaft specs are;
Checking Intake to Exhaust 111° lobe centers
Checking @.008” tappet rise 248° Intake, 250° Exhaust
Checking @.050” tappet rise 191.9° Intake, 195.6° Exhaust
Checking the lobe lifts are .2768" Intake, .2856" Exhaust

The camshaft run in the older engine never had any of these problems..
The older engine has camshaft specs are;
Checking Intake to Exhaust 112° lobe centers
Checking @.008" tappet rise 256° Intake, 270° Exhaust.
Checking @.050” tappet rise 202° Intake, 214° Exhaust.
Checking the Lobe lifts are .2678” Intake, .272" Exhaust.

The answer is below.

These two Merc camshafts have 50% less overlap and is why the other camshaft pulls water back into the engine.
GM # 14097342 Mercruiser # 431-824327 (steel material) or # 431-803186 (sadi material)

Checking Intake to Exhaust 112° lobe centers
Checking @.008.
Checking @.050” tappet rise 204° Intake, 214° Exhaust.
Checking the Lobe lifts are .269” Intake, .273" Exhaust.

Mike
 
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