Marinette Boat Forum

With all this talk about 318 stroker motors, has anyone ever tried swapping their 318 heads for “302” casting number heads?

This coming winter, I’m thinking about refreshing the top end of the motors (heads, lifters and pushrods) on our 32. Basically, the wet/dry compression is good on both motors. Leak down tests were ok. There's a little leakage but nothing horrible. Vacuum on both motors is a strong 15 PSI throughout the RPM range. The motors are mechanically sound. Simply want to prolong the life and increase my confidence in the motors.

The two major issues with 318’s are the below deck pistons and poor flowing heads. The below deck pistons lower compression and the low flowing heads reduce power. “302” casting number heads have heart shaped 59cc combustion chambers and hardened valve seats. These heads can be port matched to a 340/360 iron intake manifold. A thin head gasket will bump the compression by about 1.0 point. Since the pistons are below deck, there is no concern with valve/piston clearance.

With no other changes, the combination produces 300+ HP depending on the tune. This is a low end torque and HP combination. The power comes on below 3,000 RPM right in the range needed by a boat. Total cost is under $500 per engine. I’ve found the heads for $70 a set. Intake manifolds are $50 or so. I’ll pay a machine shop to clean up and deck the bare heads. I’ll do the port match. Largest cost is new valves and springs.

Many Mopar guys use this combination in their “daily driver” 318s.

Anybody done it in their boat?

I doubt if your motor will make 300 hp with those super mild stock cams.

Jeff

I will have to check, but I think I have a set of those heads.

Also, if everything checks out good on your engines, I would leave them alone. Cracking into a known good engine that doesn't click, tick or smoke is the easiest way to decrease reliability.

I believe that the 302 heads came out in the mid 1980's. My father in law had a 28' big M at the time with a tired 318. We pulled the motor, freshened up the bottom end with a .030 over bore, balanced, upgraded rod bolts and the "302" heart shaped combustion chambered heads. The upgrade was spectacular and the boat flew. I would recommend this conversion as it works well.

Sounds like I need to put this on my radar..

Even an extra 50 hp is huge on a 318

There are a number of articles written about this swap. Hot Rod, Car Craft, Mopar Muscle. Check out the Mopar chat rooms. There are plenty of people that have done this in 318 cars. Best results are achieved with machining the block to a "zero" deck or putting in Keith Black KB167 pistons, an aftermarket cam and a Holley carb. With that combination, the 318 will produce in excess of 370 HP. I'm not interested in that much power.

An extra 40-50 HP per motor for $1,000 or so would be a nice addition.

To repeat, the stock cam will not make great hp regardless of the heads and intake setup. It's dead mild.

Jeff

I need one head for a 1978 318. Any ideas where I might find one.
Fred in Louisville KY.

Any idea where I can find 1 head for a 1978 318?
diFrenzi in Louisville.

try Jasper engines