To recap from last month, our quest for 318 power was inspired by necessity. We had a super-cheap backyard-built 318 in our daily driver Dart. The Dart was respectably quick, running low 15s at over 90 mph, even with the freeway 2.73:1 gears out back, and was economical enough to run every day in LA traffic. Things were good, and we were satisfied-until that baggy-pantsed kid in a new Lexus GS-400 blew our Mopar's doors off and had us scraping 'em off the pavement. It was kind of humbling, but looking at the stats, not surprising. The $48,000 Lexus has a 300hp rated, double overhead cam, fuel injected V8. Delivering 0-60 performance in the high five second range, that's enough to handle most big block muscle cars. Our Dart had a hand-honed and reringed 100,000-mile 318, a set of valve-jobbed '85 318 two barrel heads, and was mildly sprinkled with aftermarket parts. As mundane a combo as it was, we figured that with some mods, our 318 could be built to more than handle that rice rocket the next time around.
To find out where we stood, we took a trip to K&N Engineering to use their Dynojet chassis dyno. The Dart cranked out 200.7 rear wheel horsepower at 5400 rpm. Not too bad for our low compression 318. In fact, looking at some of the other dyno tests K&N has on file, our 318 bettered the new Magnum 5.2 truck motor (175hp), a 5.0 Mustang (196), and even a "300hp" Goodwrench 350 crate motor (192)-but was short of the Lexus GS-400, tested at 237.7hp.
Our plan was simple-we would go with slightly more cam (the modern Comp Cams Xtreme Energy hydraulic in a daily driveable 268/280 degree duration) and upgrade the heads and induction. The cam swap was outlined in last month's issue, and upped the output of our 318 by 15 rear-wheel horsepower. This was a respectable gain, adding 711/42 percent more power to the 318 over our baseline combo. Considering that the engine already had a high performance cam not much milder than the Comp stick, the cam change alone was worthwhile. However, the cam swap was just a preliminary step for what was coming next-a set of high flow Edelbrock heads to replace our small-valve '85 318 stockers.
Head GamesAs we covered last month, our 318 was built-up using the parts from two junk 318s-a 100,000 mile '84 police block with acceptable bore wear, and a set of pistons and heads from a worn out '85 block. The '85 318 heads (#302) were a radical departure from previous 318 heads, featuring compact fast-burn closed combustion chambers and swirl ports. These heads retained the small 1.78-inch intake/1.50-inch exhaust valve sizes used in all previous 318 2Vs. The output we were getting with our engine through such small valves suggested that these were decent castings. Mopar Performance has done tests using these same castings, modified with bigger 1.88-inch intake/1.60-inch exhaust valves from the 360, and found they outperformed a 360casting on their mild 318 test motor. In our case, with the small valves, we figured the heads were the main limiting factor in getting performance out of our 318.
While not new to the market, the Edelbrock aluminum heads have become a popular upgrade on small block Mopars. With a price tag of about $1,200, they're not dirt cheap, but not outrageously expensive either. If it's performance you want, stepping up in cylinder heads is the main place to get results. Sure, excellent performance can be achieved with modified production castings, but with full rebuilding and then the required porting, the costs can quickly escalate to meet, or exceed, the cost of the brand new Edelbrock castings.