Some engines have always been considered performance lightweights. You know, the pushovers that never get any respect. Count among this group the 307ci and 305ci Chevy, the 400M Ford, and the 318ci Mopar. Some guys would rather lie than admit to having one of these mills under their hood. In the case of the 318 Mopar, there are rabid fans, but more as admirers of its anvil-like durability than breakneck performance. For most of its production life, the 318 was a bread-and-butter two-barrel economy offering. The 318 debuted in 1967 but was not blessed with a four-barrel until over a decade later in 1978. By then, deep in the smog era, it was too late even for the 318, rated at a meager 175 hp, while its 2V cousins cranked out a lame 120 hp.
Sure the motor is displacement challenged, but the bore/stroke relationship at 3.91/3.31 is pretty good. Sure the bore is a little under the "magic" 4.00-inch mark, but not by much, particularly after a rebuild. Stacked in the motor's favor is an excellent rod ratio of 1.84:1, and like all small-block Mopars, it carries factory 18-degree valve-angle heads with an advantageous spark-plug position at the top of the combustion chamber.
The real hamstring on the 318 isn't the design at all, but rather the way the production engines were offered. Beneath the restrictive intake, small valves and port heads were the norm on the 2V engines, with valves measuring 1.78/1.50-inch intake/exhaust. Four-barrel 318s were simply assembled with the top-end from a 360 4V, but the larger chambers crippled the already pathetically low compression. Most 318s featured pistons deep in the bore, putting the hurt on building power by conventional bolt-on means. The final insult was a paltry camshaft, usually with 0.373-inch intake lift. It's no wonder 318s never flexed their muscle.
Our '68 Barracuda had a well-worn 318 in need of some attention. With a four-barrel and dual exhaust, we measured 196 hp at the rear wheels, but as witnessed by the plumes of blue smoke at the top of the chassis dyno runs, the engine was just worn out. We figured this tired 'teen could be built to show its true potential, but we had to pull this off as a budget deal. The package had to bolt together with common off-the-shelf components, providing a recipe that anyone could duplicate.
With a full rebuild, we had the opportunity to correct some of the little motor's deep-seated problems. At the top of this list would be a piston that we could zero-deck to add compression and make quench effect actually work for us. We addressed this with a set of KB 167 hypereutectic pistons and a judicious milling of the decks that set us up for a desirable zero deck clearance. We elected to go for a 0.040-inch oversize, opening the bore dimension to a respectable 3.95 inches (324 ci). The other side of a decent quench quest is the cylinder heads, but the majority of small-block Mopar heads are of the open-chamber design, limiting our choices in production heads. The notable exception is the swirl-port 302 casting from the mid '80s, but small ports and valves make them next to useless from a serious performance standpoint. The late Magnum head, however, offered an intriguing possibility, with a quench chamber, generous 1.92/1.625-inch valves, and respectable flow in stock form. Available at a bargain price of under $600 a pair, complete, from Mopar Performance (MP), we were game. As an added bonus, the MP heads are already fitted with performance valvesprings and quality stainless steel valves.
The Magnum head is a simple conversion but requires pushrod oiling for the 1.6:1 valvetrain. Most aftermarket hydraulic lifters have this covered, so the only custom component required is a set of pushrods at the required 7.650-inch length. The closed 59cc Magnum chambers with our zero-deck KB pistons yield exactly an ideal 10:1 compression ratio with the appropriate 0.040-inch-thick head gasket. Intake choices are limited, but Mopar Performance offers either a dual- or single-plane manifold to cater to induction needs. We favored the high-rpm potential of the MP M-1 single-plane, since our track-bound A-body already had stout gears and a converter. With that, we killed the 318's three major demons, blessing it with compression, quench, and airflow.
Delving deeper into the works, we found the camshaft was primarily determined by the heads. Magnum heads offer an excellent intake/ exhaust-flow ratio, which favor a single-pattern cam. The stock valvetrain is cheap, but highly effective. It's also nonadjustable, so we went with a hydraulic grind. Retainer-to-guide clearance becomes a limit at 0.525-inch lift, so we opted for a Comp 280H, coincidentally part of their "Magnum" line of camshafts. With a stock 1.6 rocker ratio, gross lift worked out to 0.515 inch, and duration at 0.050-inch tappet lift was a generous but not outrageous 230 degrees. Lobe separation is 110 degrees, promising a drawn-out torque curve for prolonged high-rpm pull. The standard Comp 822 lifters allow for valvetrain oiling.
With the power plan settled, we chose Federal-Mogul for rebuild components and shuttled our block to the craftsmen at Precision Speed and Machine for machining. Assembling the little Mopar was textbook simple, and we went from a pile of parts to ready-to-run after a single day. Next it was on the truck and off to Westech's dyno facility where the numbers would finish the story.
Dyno DerbyCompleting the package, we trimmed out the 318 with top-quality components throughout. An MSD distributor and wires handled the spark, while an amply sized mechanical-secondary Mighty Demon carb administered Unocal pump gas to the captured air. We bolted TTI stepped headers to the port exits, because we know that they make power, fit, and don't leak. With the 318 complete and bolted to the dyno, we wagered over how much power it would make. One guess was 385, while dyno operator Brul was less generous at 370. Our hopeful estimate of 400 was seen as easy pickings.
With the ignition timing set at 34 degrees and 84 jets all around, Brul loaded the engine against the brake for a partial pull, and we saw 374 hp at 5,600. Upping the rpm a couple of hundred at a time to find the peak, we found the top at 382 at 6,200 rpm, and we hadn't yet started tuning. Pulling the timing back hurt power, so we added advance to 36 degrees and found 385 at 6,200 rpm. Another 2 degrees was only good for a 1hp gain, so 36 degrees it was. Running through a jetting loop next, we found a better curve leaning the jets to 82s, but no higher a peak number. We noted that the oil pressure was quite high with the 20-50W oil sloshing in the sump at more than than 95 psi. It looked like a power drain to us, so we changed to a 10W30 Royal Purple synthetic that netted us a fat 394 hp at 6,100. We were so close to 400 hp that we could taste it, so we shuffled a Wilson 1-inch tapered spacer under the carb and the 318 responded by dealing up a 400 hp dyno curve, with peak output at 6,100-6,200 rpm.
Satisfied? We know we were, with a production iron-head 318 at near 1.23hp per cube with a street hydraulic cam. The engine had over 10.5 inches of vacuum at a 900-rpm idle, but just enough rump to get noticed. With 400 hp on tap, it's got some bite, and comes with the satisfaction of dishing out the hurt with just a little old iron-head 318.
Dyno Results Mopar 318 RPM HP TQ 3,000 190 332 3,500 241 376 4,000 286 376 4,500 321 375 4,{{{900}}} 357 382 5,000 363 381 5,500 388 371 6,000 398 348 6,{{{200}}} 400 339 6,500 393 318 Price List Labor Source Price Bore and hone Precision Speed $175 Deck Block Precision Speed 160 Line hone Precision Speed 156 Resize Rods Precision Speed {{{100}}} Balance Assembly Precision Speed 130 Press Pistons Precision Speed 78 Grind Crank Precision Speed 85 Total Labor $884 Parts Brand Source PN Price Pistons Keith Black Flatlander KB 167 $248 Rings Federal Mogul PAW E178K {{{57}}} Cam bearings Federal Mogul {{{Summit}}} 1451M 32 Main bearings Federal Mogul PAW 4923 39 Rod bearings Federal Mogul PAW 8-2130CP 35 Gasket set FelPro PAW KS2108 57 Oil pump Sealed Power Summit SLP-224-4166V 46 Timing chain Sealed Power Rock Auto KT 3160S 37 Windage tray Mopar Perf Glendora {{{Dodge}}} P4529790 64 Camshaft Comp PAW 20-232-4 121 Lifters Comp PAW 822-16 79 Pushrods Comp Summit 7960-16 137 {{{Eight}}} rocker pairs Mopar Perf Glendora Dodge P4876050 60 Intake manifold Mopar Perf Glendora Dodge P5007380 258 {{{Magnum}}} heads Mopar Perf Glendora Dodge P5007086 570 Head bolts Mopar Perf Glendora {{{Dodge}}} P4876759 15 Basic Components Subtotal $1,855 Valve covers Mopar Perf Glendora Dodge P5007617 160 Carburetor Demon PAW DEM-540201GC 499 Headers TTI TTI TTI 340A 510 Tapered spacer Wilson Wilson 03111 130 Distributor MSD {{{Summit}}} MSD-8534 183 Subtotal $1,482 Subtotal- Machine Work $884 Total Cost (as tested) $4,221 Cam Specs Camshaft Duration Duration Lift Lobe (Advert.) (@ 0.050) Intake/Exhaust Separation 280H Comp Cams 280 230 0.512/0.512 in 110 Lift is calculated using a 1.6:1 rocker ratio