Theres more to this article ...machining the 318 and the 360 , using headers and ignition, great article!
see:
http://www.allpar.com/mopar/4bbl.html
(by Keith Indy)The 318 is a good, solid and dependable engine. I will be the first to admit and try to sell that. Secondly, the 360 is an outrageously great engine because it has so much potential, greater than a Chevy 350 or Ford 302/5.0. The SBChevy guys have a little advantage because all the heads and intakes all bolt on without major changes other than combustion chamber and valve sizes. MOPARs have two sizes of runners and various valve sizes.
What you have to do is make the determination of what you really want to do. A 318 can be built rather easily using stock components and be very reliable and strong, the 360 you can do the same thing with a lot more aftermarket options. About the only things that are different between the two other than the heads/intake, are motor mounts (right side, actually), harmonic balancer and torque converter (being external balance on the 360) and rear main being smaller on the 360 means oil pan will not interchange. The 318 does have the advantage of a steel crank stock, so power and rpm limitations are minimal.
If you are on a 'budget', your best choice is to 'freshen' the 318 and only replace or machine items as necessary.
There are some differences between the 318 and the 360, but many parts interchange. It is easier to get raised or decent compression pistons for a 360, not as easy for the 318. Another common thing is there is no replacement for displacement. 4 inch bore is always good as opposed to the 3.91 inch bore for the 318, but you can still get whatever valve you want into the head so that is not an issue either.
There is no better source than either the MOPAR Engines or MOPAR Chassis 'Speed Secrets' books available through your nearest dealer.
I always advocate that anyone who lacks experience and/or technical training and wishes to 'build-up' or 'modify' an engine, should talk to engine builders, ask lots of questions and read and learn. Read and talk to a reputable machine shop, talk to MOPAR people at car cruises and swap meets in your area and find out who they recommend in the way of a machine shop and go talk to them about a hi-po 318 build.
First performance enhancementThe first performance enhancement you do on a stock 318 is to install the (factory) 340/360 H.P. cam (or equivalent). With stock heads, 2Bbl carb and even 2.76 gears this is already a 'fun-package'. Even with 4.11 gears (and street tires), the FIRST 5 feet that the car travels is the most critical. Over carburetion or a non-functioning accelerator pump will pretty much have the same effect, the car may indeed 'fall on its face'. You will benefit from a quicker advance curve in the distributor and enough initial lead to give about 36 degrees max. A dist with 13 inside will double to 26 degrees on the crank then you can set the 'static' to 10.
HEADSThe 360 heads and Intake swap will fit on the 318, but the compression will be around 7.2:1, which is not very good for performance, which is not to say that the heads cannot be shaved .050 and intake be rematched to fit, adjustable rockers added to offset the rocker geometry, and away you go.
The book says the 360 to 318 works well, but, take the 318 heads, shave .020 off the head, install 1.88 intakes vice 1.78, port the heads and you would have a better combination, especially on the bottom end response and will still rev as high as you want and float the valves before the power falls off (how can you beat that?). It can be done, but, if you have a 360, which is physically the same dimensions externally as the 318 and 273, why not go the least expensive route?
Keep in mind that the 318 runs about 8.5:1 compression and will be about 8:1 or as low as 7.5:1 with the J heads of the 360. This is going to drop the compression pretty low, which is great for cheap gas, but bad for the performance side, thus most 318s are rated at the 185hp, which is a shame. If the engine is out and heads are off, do some measuring to determine what the compression is going to be. Some of the pistons can be as much as .080 below deck just to start with. I am not trying to squelch your combination, but, as many others have done with similar combinations, if it is a dog, don't be surprised.
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Now, there is a solution to this problem. Last month's Hotrod mag had an excellent article similar to yours, but the heads were with smaller chambers. They shaved theirs .050 to raise the compression, whereas you may have to do the same. When removing that much metal from the heads, the cork gaskets front and rear of intake may be too thick, so be cautious during installation of the intake.
Here is the thing about the 318 heads compared to the 360 heads. The intake valves are smaller on the 318, but the stock 360 valves put into a 318 head (1.88 vice 1.78) and then the bowl tuliped, vice opened up all the way, really makes the head flow in the chamber side. The pushrod pinch on the intake port is the same for the 318 and 360 head, so there is no gain there, but the height of the port is taller than the 318, and the port mismatch can have detrimental effects. Port matching can be done on most castings; some are close at the top of the gasket.
Here is the hard thing to deal with on the 318 head of 1969: The exhaust valves will be sunk within a couple years because the seats are not hardened and need the leaded gas to survive. Figure you can get approximately 25,000 miles out of the heads before they are affected completely by sunk valves. Have the 360 heads shaved .020 or get new pistons is the best solution because the cost of the work on the 318 heads will be a couple hundred dollars and the porting time, if you do the porting yourself.
Another solution is to hit the junkyards. I had several sets of 318 heads that were closed chamber that I have had in 73-74 Plymouth engines. Don't know the casting number but they do exist. Then put the 360 valves in the heads and port them. These heads already have the hardened exhaust seats.
Intake valves are not affected. Did it on two sets of heads and have had wonderful results in the power increase world. I originally ordered stock 318 valves and ended up with stock 360 valves. Cut the seats, ported the heads, and really noticed the breathing and torque increase. It was fun!
You can indeed 'shave' the (360) heads 20 or 30 to raise the CR but that should still keep it under 9.0 to 1 and allow the use of (cheaper) 87 octane. The power potential is already there, but everything has to work together; the timing, the intake and exhaust flow, the distributor curve, the plugs and wires, the cam specs, the carb itself, and even the type/grade of engine oil to make any 360 dependable, efficient and a pleasure to drive.
The 340/360 intake is a larger runner than the 318/273 heads. This is like taking a 3/4 inch pipe and running it into a 1/2 inch pipe. They have to be port matched, or, if that cannot be done, find a 318 specific Streetmaster type dual plane intake.
The amount of shaving to get them down to the 318 size, so as not to lose compression (takes it down to about 7:1 vice 8.5:1). An old favorite, and extremely helpful thing to do is have 1.88 valves from a stock 360 installed. There is a requirement to tulip the intake port to do this, but the small amount of work is well worth the effort and money. This also prevents having to change out the intake manifold to fit. If you do go with the stock 360 heads, you have to stick with a 360 intake, for the 340/360 heads and 318 intake do not match, and vice versa.
Edelbrock makes a really nice aluminum head, with the smaller chamber size, if they are anything like the big block aluminum heads, would be fantastic, along with headers/dual exhaust and a 4 bbl and 600cfm carb (or police 4bbl), would add in the neighborhood of 100 hp/ftlb torque.
Go out to the salvage yard and find a set of closed chamber heads. Anything past 1973 will have hardened exhaust seats for added durability. The closed chamber heads add compression and simplifies the need to shave so much off to raise compression. Get a set of 360 valves (1.88inch) and get the intake seats cut for them. Port the heads to gasket size and tulip the bowl to the valve size, but don't just bore the bowl out to the bigger valve. The less you shave the heads, the less likely you will need adjustable rockers. (big bucks to add).
If you can't get a set of heads that are closed chamber, only shave the heads .020 so as not to throw the geometry for the rockers off any more than necessary. Get a set from the salvage yard and get them prepped and ready instead of waiting a week with your car down. Port match and bowl work is the best. Do not switch everything over to 340/360 heads and intake. It really kills your compression and stock ported heads run higher velocity for the 318, which you need.
You suggested replace the stock 1.75 (or 1.78) /1.50 valves with the 1.88/1.60 360size. Other people recommend this as well. Now I know that the 318 heads are better that 360 for compression. My question is, would the 0.10 increase in valve area make that much difference on a slightly modified 318 (4bbl, duals, & quick bolt-ons)? Wouldnt it be easier & less expensive to increase the intake flow with a 252 (stk 360) or 260 (Crane) cam? Or 1.6 rockers?
Id imagine for competition youd want larger valves, but for a daily driver, would the effort & machine shop fees be worthwhile? And what about increased fuel consumption? Im thinking of installing late 80s #302 swirl port heads on a 318. (about 500cfm & duals, no headers) Has anyone done just this upgrade alone, that could verify performance gain & MPG difference?
I did just this to my 74 Barracuda 318 when the wrong valves were sent to me and I was not in a position to wait for them to be replaced. The difference between 1.78 and 1.88 is 100 thousandths of an inch. That's one tenth of an inch.
Mileage did not decrease, it actually increased because the added efficiency with the small runners breathed better, not worse. I was using the Crane .444 cam and it was superb. I could feel the difference from stock and it worked well. It was coupled to a Streetmaster dual plane and Hedman headers, ported heads, balanced stock rods and pistons, and Holley 650 double pumper, 2.71 rear 8 3/4 rear. Oh, exhaust valve change is not necessary.
All the machine shop has to do is cut the valve seats, which I simply ground with the standard 45 degree stone cutter, then tuliped the cut to the edge of the seat diameter (i Marked the edge of the seat with the new valve, properly ground at 45 degreese, by doing a quick lap job on they dyed valve seat so I could tell how much material needed to be removed). Do not hog out the whole pocket because that just defeats the purpose of the tulip design. The charge enters the pocket, expands to the outward direction, as the valve is opened and then closed, the velocity in the runner remains packed and at a higher velocity, but the valve closing compacts a larger charge in the tulip area for higher charge to wait and enter for the next valve open motion. The idea of a higher lift cam will drop the vacuum and velocity of the charge and then you have no bottom end power.
Going with the 360 heads, unless you are running high rpm and higher compression domed pistons, are pretty dead on the bottom end because of the size of the intake runners and drop of compression to low to mid 7:1. The bore is too small and the stroke is too short to get good bottom end draw on the 318.
Magnum heads, although good, have poor pushrod geometry, so I don't like that idea too much. They work, but I fear bent pushrods because of the poor angles. 1.6 rockers, other than not being able to work stock on the early heads, and are around $450 with pushrods in the aftermarket. (extra cost). If you can go with a complete Magnum block to go with the heads, that would be the best thing.
I could routinely wind this motor up to 7500 rpm without it dropping out, and one time slipped a gear on the highway to move quickly to avoid an accident and hit first doing 55(7500 rpm) and shifted at 75 before I really realized what had happened (panic mode to avoid the accident). I figure I hit 8400 rpm and not only did it not float or bend a valve, but was still picking up rpm and power before I could correct my mistake. A stock 1.78 definitely would not have been able to do that.
It's your decision, just some good solid personal experience with this set-up. Need more info or help, just ask.
Buy a set of 1.88, stock valves for a 360. I have personally found PAW to be an excellent mail order company. They have never steered me wrong and they have all the good stuff. You can find ads for them in all the car mags. At the machine shop, ask that the intake seats be ground to the size of the 1.88s, have the valves (new) redressed (just lightly ground to check them; little or no material is removed to verify factory tolerance and angle), and have the machine shop let you have the heads to do the seat position and port work yourself, then, when you have ported the heads as described, porting up to about 20 thousandths to the inner edge of the valve seat you have verified the valve will sit. Return the heads for assembly. If you have a friend, this goes a lot smoother, and can be accomplished in one day. Explain to the machinist what you want to do, and he will tell you how much it will cost. Valve grinds are usually around the $100-150 price range. Enlarging the seat may be slightly more.
45-degree angle, by the way, is the stock angle for about 95 percent of factory heads. For the three angle valve grind, there is a 60 degree angle cut on the inside edge of the 45 degree seat that is about 30 thousandths inch, and then a 70 degree angle cut into the chamber. This isn't necessary if you are porting and especially with this tulip design porting.
