318-3 Motor Conversion

[RandyB]

I am working on a 318-3 motor that dropped a valve and destroyed a head. I am trying to get it rebuilt and add some power. I've heard that you can use regular 318 or 360 heads if you change the intake too. That eliminates the water crossover port but lowers compression because of chamber size. I can offset that with some KB pistons. Intake runner size and valve size are also different and I am trying to get the just right camshaft and flow to pull extra horsepower out of this old Mopar. Does anyone have any input to build this for 80 extra HP?

[Drew M.]

I used 360 "J" heads (2.02/1.60 valves) on a 318 years ago. Killed the lower end torque but was great once reved up. While fun with a 3000rpm stall converter for drag racing with my 1969 Baracuda (Holley 650 dp, 284 dur/.484 lift cam, 3.91 ratio sure-grip) - it would be a lousy setup for a truck.

Why? #1 the 360 head has a larger valve recess than the 318 head and will drop the engine's compression. #2. the 360 head flows much better - and ruins the 318's low rpm vaccuum response = boggs down.

What to do? Use the 318 heads as it. Swap in the 1.80 intake valves off the 360 and install in the 318 heads be better flow while keeping air velocity high.

Do some research on the web for this idea - the complications from this simple sounding swap are many.

There is no substitute for cubic inches. That said, why are you looking to mess with a 318 when 360's are common and build more hp/torque than the 318 for far less cost? The 360 just has the annoying external balance issue - which is easily fixed if you have an auto by welding on the appropriate bal weight to the 318's original torque converter. Used 360 flywheels are tough to find.

[RandyB]

I did find a lot of information on 360/318 swaps, head chamber sizes are bigger and it is the intake runners that kill the 318 performance. I can fix the compression issue with KB pistons, but the last thing I need is a truck that bogs on the low end where we want pull. Using a slightly better cam can help. With the smaller displacement, one that was recommended was actually a stock cam for a 340. I think I can get the best characteristics of worlds here. One big concern is that we are eliminating the water port under the carb and on a regular 318 that port uses exhaust gas to warm the base of the carb. Does anyone know if that will create overheating or cooling system problems..Thanks alot for your help. Lots of good info in here.

[Drew M.]

You sure look hard for ways to complicate things. You are willing to buy pricey KB pistons to end up with a 318 frankenstein rather than bigger cubes even after doing some research.

I am sure your next project will be along the lines of making 200hp with your lawn mower engine. :)

BTW: Where were you a few weeks ago? I offered my std 360 block FOR FREE on the donation forum. You can pick up a running 360 for $100 easily in PA- which was why I had so much trouble finding a home for the block.

[RandyB]

you are right, and crackin me up. here is the deal. Best friends motorhome. 70 vintage, he drove it home 400 miles, had a hole about the size of your fist in the piston but it still ran and got him home The 318-3 has a steel crank and bushed pistons. Also has one of those wierd timing covers that mounts the waterpump way up. Is that to center it with that huge radiator and big fan? The block is in the shop and bored 30 the crank is good with .001 under. The heads became a problem. No one around here had those heads 57cc with the water port. To do the 360 we need to replace balancer, flywheel, converter, and our 8 qt oil pan wont fit because the rear journal is a different size. I havent ordered parts yet or ruled out the 360, the 318 is getting expensive, I will have to see how much he really loves that little motor

[Drew M.]

OK, let's tackle them 1 at a time . . .

To do the 360 we need to replace balancer - no. Just file an offset bolt hole into the crank pulley to use the old 318 crank pulley with the 360 balancer (the crank pulley bolt spacing for 1 bolt hole changed by ~1/4"in 1971)

flywheel, converter, - which is it? You don't need both. Flywheel is for a std trans and converter is for an auto. Both the 318 and 360 use the same flexplate with an auto trans. 360 converters for the autos are everywhere! Or, reuse the 318 and weld the 360 balance weights on it - cost under $20 last I checked. Most trans shops dont' do them anymore - so you'll have to do it yourself or buy another converter. 360 flywheel will run you $50-100 used typically.

And our 318 8 qt oil pan wont fit because the rear journal is a different size. True. 3 options:
#1 buy a 360 truck pan. They run $20-25 or so on Ebay regularly.
#2 modify a 360 pan if not big enough by widenin the lower pan section while keeping the pan depth the same (so oil pickup works) or swap motor home oil pickup to the 360 oil pump and build pan dimensions to match or cut off MH pan section and weld to he 360's pan - this is why God made MIG welders. BTW: Why do you need a 8qt pan anyway. Nice, but not needed. If going off road - add oil baffles to that pan and a windage tray!!! 8qt is a lot of resistance against the crank assembly if it suddenly sloshes while the engine is at high rpm.
#3 get a 360 pan off a motor home.

[RandyB]

Im thinking you should change your name to MoparSpock, your logic seems flawless. The cost of this modification is begining to exceed the cost of buying a completely rebuilt 360. While we have a sentimental attachment to the 318, our objective is to have the power we need to get this machine to move down the interstate with traffic. Besides the cost of the engine itself, we need to changeover the timing cover, buy a balancer and torque converter, add a four barrel and intake, make sure our pulleys line up, possibly and electric fan to eliminate the high mount fan, and I seem to remember something about one of the motor mounts being different, and of course the oil pan issue. Then of course, the core charge for the engine itself. They dont seem to be laying around like I thought in my area. I would possibly have the core charges for the heads on the 318 anyway. What do you think about the cooling system??? The engine sits way low in the cradle compared to the radiator. I realize that I am starting to obsess and go off in left field so your straight line logic is appreciated. Im not doing anything else until I finish cost analysis. Do you know anyone looking for a fresh bored 318-3 block?

[Drew M.]

Randy,

I am interested in the intake manifold water outlet from your 318 engine. Shoot me an email if you feel like parting with it. I am sure I have something you'd be interested in for trade and/or +-$ (360 std bearing sets, motor mounts, gasket sets, truck oil pans, Dodge 4bbl q-jet, intake & exhaust manifolds,alum timing covers . . .)

Where are you located? Your profile is blank.

Cooling - any small block Mopar rad will be fine with either the 318 or 360 when using the factory fan shroud and clutch fan. The exception is boring the block out too far w/o verifying the cylinders did not have core shift resulting in a thin wall when over bored and causes a spot that super heats the coolant. The AMC 360 is notorious for having his happen when bored out 0.060".

Live long and prosper.
-Drew M.

Good luck on selling the 318 - there are fewer and fewer people messing with these old engines anymore. Post here the Mopar forums (cars) and Ebay with a copy of the machine shop receipt and hope for the best. I would be surprised if you got over $100 after spending at least $225 to clean and bore the block.

[wayfarer]

Just wondering if you even looked at all of the available 're-man' / 'crate' engines on the market...I have seen 360 assemblies priced at about $1000. It is real hard to get to that price point on a one-off and if all you want to do is 'get it to run down the road' then something from Jasper or one of the many others is the best way to go.

Gary

[MoparNorm]

...The exception is boring the block out too far w/o verifying the cylinders did not have core shift resulting in a thin wall when over bored and causes a spot that super heats the coolant. The AMC 360 is notorious for having his happen when bored out 0.060"...

Just to avoid confusion, the AMC 360 has no relationship to the Mopar 360 LA Series block. Two completely different animals with a common displacement.

[Drew M.]

RandyB - the person who got my std bore 360 LA (Mopar :)) block will not be using it. I doubt he will charge for it being I gave it away and it is now cluttering up his limited space garage. The block was cleaned, includes mains, and the cam bearings were removed in preparation for rebore. It is in central PA if you want to come for it.

IMHO - stick with the 318 you started with. If you get stuck on a needed part - give me a holler. I might have what you need and prefer you get it than the dumpster. For instance, I prefer the iron timing cover for a M37 V8 swap. That is why I bought mine for $75. If you need an alum cover - you have have my old one for free + shipping cost.

[RandyB]

finally got the combo

Here is what I ended up doing. Using the stock 318-3 block, found set of '74 heads casting #2843675 for $75, from boneyard, one head has all new valves 60cc chambers vs 57cc original, used stock mopar pistons, cast with 4 valve reliefs, approx 8.5 to 1 comp. vs stock 8.0 flat tops. Saving a ton on engine kit by NOT buying high dollar pistons to bump compression. The bottom end of this engine is very durable so the money saved is going into the head work. thats the weak point. mild porting and stock but new valves. positive rotators from original heads. Adding electronic ignition, small bump cam for RV use, 4bbl and looking for a good set of headers. I can build any engine for loads of power, some at great expense, but after re-thinking the fact that this engine is constantly under load, (11,000lbGVW) I thought building it for longivity would be smarter. It may never have the power to snap your neck on acceleration, but, hopefully it will pull the hill, maintain interstate speed and not need a valve job every 25k miles. Should have it built by mid April. thanks for the useful suggestions and will let you know if there are any parts I dont need.