The lowly 318, the Rodney Dangerfield of the small block V8 world

I've gathered some information from the internet about 318cui motor upgrades. Mainly the low buck solution. It's easy to buy some rods and pistons and new Edelbrock heads etc., if you have the money. But I think it's great to see what you can use from other engines to get yourself a nice low cost horsepower upgrade. It's even possible to create an incredible 400hp engine!

Some thoughts about upgrading the 318

Mild ported heads, adjustable rockers, 625 carb, .60 over short=block, 125 shot of nitrous, B-body 8 3/4 rear with 3.91 gears.

Car Craft did a 318 build a while ago, they called it the junkyard jewel.
Look for the article on their website. It made? over 400 hp. Heads are the big thing. You can go with Edelbrock aluminum heads or you can find a set of late '80s - early '90s 318 heads ending with the casting number "302". These are swirl port heads, similar to Chevy Vortec. With big valves and ported out alot they will make a ton of power.

Ah, the lowly 318, the Rodney Dangerfield of the small block V8 world.
Most people always lust for 340s or go for 360s, and think of 318s as dogs because nearly all 318s started life as low HP bread and butter motors. Fact is ALL LA heads start off with the same valve inclination angle used for better breathing in some of the so called race heads made for SBC, and the stroke (3.31) is only slightly greater than a 327 (3.25) with it's reputation for high winding HP. Admittedly you give up tenth of an inch of bore, but the slight stroke increase should more than make up for it. Most advice I've seen centers on find a pair of pre-magnum 308 heads from an early 90s Dodge pickup, adding in a Thermoquad carb and intake (GM Quadrajet would work) and decent cam/exhaust. Lockup 4 speed OD 518 trans from 91 or so helps, too. Go to moparaction.com and look in the tech section. Take the time to read the Q and A archives. Lots of info on the right heads, cam, etc., to wake that 318 up and these guys like the low budget approach.

the bore on 318 is is 3.19 in. - 273 is 3.625 - 340 is 4.04 - and 360 is 4.00 if your looking for factory hp locate a 4 bbl intake from the thousands of old police units around in junk yards - they breath well , cheap- I like cheap -these intakes came from factory from 1978 on. Headers free up the other end . Alot of mopar guys like the 273 crank (same stroke) stronger forged steal like the 340(same stroke) --- 400hp is not out of the queation and will maintain some milage- jaxx

Can you find a casting number on the heads? the late 80's 318's in the cars had the 302 heads, my guess is the vans did too. easiest bolt on HP is ditching the leanburn 2bbl for a 4bbl carb and intake, you'll need a new ignition to go with that. You can go mopar performace, FBO, or I bet if you search the moparts forum you can find how to make your own out of salvage yard parts. might also search the allpar forums, key word being leanburn. that way you'll find all the leanburn removal posts. there's plenty of performance parts available from places like summit, I know the cars got roller cams in 85, I think I heard the vans/trucks didnt until 89.

Hi Rick. I have a question. I have a 1971 Plymouth Duster 318 car that i and my father are planning on restocloning. My first question is, will the stock A904 transmission hold up to a mild 318? I have heard these trannys are aluminum and dont last long. My 2nd question has a lot to do with the last one, how much horse power and torque can I expect from the 318, here is what I'm planning on doing:

  1. 308 heads from a 360.
  2. .450 inch lift cam.... I cant remembr the duration.
  3. Hooker headers.
  4. single plane intake with a 625 cfm carb.
  5. and of course all the goodies like spark plugs, wires, viscous fan etc...
I just mainly want a good fun street car that may see one or two trips to the track every 6 months. (By the way it will have 3:55 gearing) Thanks Rick. Andy

Andy, so aluminum is weak, huh? Tell that to all those 8-seond super stock guys who run basically A-904 internals, lightened with even more aluminum stuff, in stock aluiminum 727 cases!
While a 904 will never last as long as a 727 in high-horsepower / high torque street applications, building a 904 to last 100,000 miles behind your relatively mild 318 is pie, even dead stock it should be OK for a while, just crank up the line pressure. Remember, even some 360 cars came with 904s.
Your buildup sounds pretty good. Longtime MA readers know that I generally like single plane intakes for virtually any performance application, but a 318 might -- repeat, MIGHT -- be the exception. With your gears, and, hoefull, a decent converter, it will probably be fine, but if it seems especially doggy at lower RPMs, you might want to do a re-think on the manifold. If you haven't bought the manifold yet, maybe initially try a dual-plane, even the stock 360-4 piece, though heavy, flows pretty damn well, add maybe a 1" spacer and you'll be home.

Colton Herzog, PA, 1973 Dodge Charger 318
I am wondering if you know any way to get a little more horsepower out of a 318 without spending a lot of money. I don't want to get into changing the crank or cam, or even boring it. So if there any thng small that I could do for horsepower, what could it be?

Colton, there's no magic. But "bolt-ons", as these "small things" are typically referred to, DO work. What you're trying to do is get more air in and out of the engine, so it can burn more fuel. If you pin me down, I'd have to say the first two places to start would be:

These two additions should add 30-40 HP, plus, as a bonus, the exhaust mods will improve mileage, and the carb swap will have almost no effect on MPG - if you can keep your foot out of it!

Josh Tracy, Kirkland, WA, 1969 Plymouth Sport Satellite
I've got the MP dual plane intake and a Holley 600 planted on top, now I am wondering if I can swap on a set of 360 heads? Will they bolt on and what else would I have to change if they do? New exhaust manifolds, any valve train issues? Stuff like that.....and what is the "gain / pain" ratio, will it be worth the trouble? Thanks, Josh

Basically, they will bolt on. You'll lose a tad of compression depending on exactly which year heads you use. The extra flow will more than make up for the reduced CR, although the exact gain will depend on which 360 heads you use! Best are the '89-92 "308" castings, next best are the early-'70s "J" heads (which, unfortunately, do not have induction hardened valve seats.)
Doing the heads alone will be a total bolt-on, but, while you're at it, a set of hi-po 340 exhaust manfolds or headers, and a mild (but upgraded) cam, will help you get the most from the least. With some careful planning, 260 - 280 HP is pretty easy.

Kevin Seifried, Kitchener ON 1974 Plymouth Satellite Sebring Plus 318
My Satellite is an all original car with the 318 727 trans and I belive 3:55 gears. My question is, how much HP would I gain if I swap the 2 bbl, 318 intake and heads for a 340 4 bbl set up?? Do I need 340 manifolds as well?? Or should I stick with the 318 set up and do a port 'n' polish on my heads, go with some headers and open the exhaust up a little? Any guidance on a mid budget HP boost aside from swaping motors (she's a #'s matching car), would be greatly appreciated. Kev-

Your Satellite is a pretty heavy ride. And, unless it has trailer tow, or the axle has been swapped, I'll bet it has more like 2.94 cogs. So you really need to keep the low-end torque up if the car is to have any 'snap' on the street. I'd go with a set of stock 360 head castings - even the worst smog-era ones will flow lots better than your heads (which are not very good.) Yes, you'll need matching manifolding, including, preferably, a dual-plane aluminum intake and a small 4-Bbl. Headers would help, too, but if you go that route use the smallest pipe ones you can find. Either way, a nice set of 2.25" dual pipes will help tons. The key to making this work is the cam. Briefly, don't go nuts! The wildest I'd even consider would be a stock 340 repro cam. Something with a few degrees more lobe separation (i.e., less overlap) would be even better. Call one of the major cam houses and tell them your combo, making sure that they know it's a 318 in a heavy car, has tall gears and a stock converter, and is a street driver. If they come up with something close to what I've described, pec-wise (i.e., not over 268/276 deg duration [at 0.008"], not over .4509 lift, less than 45 deg. overlap, I'd go with their recommendation. Otherwise, just a stock 340 repro cam, maybe installed 2 or 3 degrees advanced. With these changes, you should be adding approximately 40 to 60 HP - a difference that you'll really feel.

Jeff Schliep, Duluth MN , 1967 Plymouth Fury 318 2 barrel
I have a 1967 Plymouth Fury with a 318 2 Barrel that I am using for Enduro Racing. I am looking to get a little more out of her and have been told that by adding a 360 manifold w/2bl carb it would help more so than adding a 318 manifold with a 4 barrel. Therefore what I am wondering is if the 2BBl manifold of off a 318 is actually different than a 2BBl manifold off of a 360. If they are the same then I would just have to swap carbs, if not I would have to swap carbs and manifold.
Thanks for your help, Jeff

Yes, the 360 manifold has bigger ports, also a bigger carb mounting pad. A worthwhile swap, wild guess: +10 HP. if you port-match the heads (if this is legal in your class), opening up the heads to match the new manifold, you might increase this to 15 HP or more. But best of all would be the 4-Bbl. All factory 4-Bbl SB intakes had the larger 360 ports. Keep in mind, though, for what it sounds like you are doing with the car, mid-range torque, off the corners, is the key to winning. The upshot: Keep the 4-Bbl on the small side (600-650 CFM.)

And finally, you should read :
318cui Junkyard Jewel - how to build a cheap 400hp 318
This is an article taken from Hotrod.com and is very interesting reading!
318cui Junkyard Jewel - how to build a cheap 400hp 318.pdf