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.
Add it up: The Edelbrock heads have the advantage of being made of lightweight aluminum; they have new bronze guides; new stainless 2.02-inch intake/1.60-inch exhaust valves; a high performance valve job; high performance valve springs; are machined for and fitted with positive valve stem seals; the ports and bowls have already been opened-up and reshaped for high flow; and the chamber is redesigned to a closed configuration for quench. Unlike starting with a set of junkyard heads, the Edelbrock heads, being new, are clean, have flat decks, aren't cracked, have equal valve heights with no sunken valves, and carry hardened valve seats all around. Unless you own a machine shop and can port like a pro, you'll have a hard time approaching all of these features with a set of cast iron stockers for the price.
Even so, we still couldn't help ourselves and performed some minor modifications to the out-of-the-box Edelbrock heads (see Sidebar 1), enhancing flow even further.
Induction UpgradeAlong with the Edelbrock heads, we felt a change in intake manifolds would be required to get the most from the combo. Our baseline engine was set up with an Edelbrock Performer manifold, which works well with the stock 318's small ports. The standard Performer has relatively small runners, matching the small size of the ports in the 318 heads. Going to the Edelbrock heads, with their larger port openings, would require an appropriate upgrade in the intake manifold for a well matched combo. Edelbrock recommends their high performance, two plane Performer RPM manifold for use with these heads, so that's what we went with.
Unfortunately, the Performer RPM comes only in a square flange carb configuration, meaning that we would be unable to run our spreadbore Thermo-Quad carburetor. We used a Federal Mogul/Carter 750 CFM Competition Series AFB carb, which proved to work very well in this application. Edelbrock offers similar Performer Series carburetors, based on the AFB, which would likely produce comparable results.
Nuts & BoltsTo sum up, our changes from the last test came down to swapping the production heads to the Edelbrocks, switching from the Performer to the Performer RPM manifold, and shelving our beloved Thermo-Quad carb for a 750 AFB. Our 318 was already running closed chamber heads with a volume of 62.5 cc's, so the Edelbrocks' 65cc chambers would have slightly lowered the compression ratio in this application. We kept the compression ratio constant at 8.88:1 by substituting Mopar Performance's thin .028-inch head gaskets in place of the thick Felpro gaskets we used with the iron heads. Ideally, we would like to have run a half point or more additional compression with the aluminum heads, but we didn't want to touch the shortblock, or mill the new heads.
The head swap turned out to be less work than the cam swap done previously. With the top end off, we had a chance to have a look at the 318's bores. With 40,000 miles since the overhaul, we didn't know what to expect, although low blow-by and negligible oil consumption suggested the rings were sealing. Once daylight hit the cylinders, we found the cylinders looked great. Using the unscientific method of feeling the ridge at the top of the bore with a finger, the bores had hardly worn at all despite the mileage since the hone and rering. Credit the bore-friendly moly rings.
Bolting on the Edelbrock heads is no different than installing a stock set, except for requiring four, rather than two, long head bolts. Edelbrock supplies two long bolts-quality ARP pieces with a reduced hex head. Since we were just reusing stock headbolts anyway, we just grabbed two spare long stockers from another engine, so that all of the head bolts go in with the same socket. Since the heads are aluminum, and a lot softer than the steel headbolts, hardened washers are needed to keep the bolts from digging into the heads. Omitting the washers will cause damage to the heads, as well as throw off the torque readings. We just got some 11/42-inch hardened washers from the hardware store, which fit the bolt spot-face on the heads like a glove.
The top-end swap was completed by reinstalling the valvetrain from last month-Comp's Pro Magnum stainless steel roller rockers, and Isky pushrods. With the stock 318 heads, the tight valve-spring-installed height of 1.65-inches really compromised spring choice, limiting the rpms with the Xtreme Energy cam's aggressive profile, and relative heft of the rockers. The Edelbrock heads have a base spring installed height of 1.8-inches, which allows a much stouter spring to be installed without running into coil bind problems. The Edelbrock springs that come with the heads proved to be more than up to the task, controlling the valve action to well past 6000 rpm. With the valvetrain in place, and adjusted to zero lash, the engine was capped with the Performer RPM manifold, 750 AFB, and we were ready to run.
Dyno TimeBack at K&N to spin the 318 against their Dynojet chassis dyno, we'd get the hard numbers to see if all this thrashing on a lowly 318 was worth it. Man, it felt strong, giving a surge of power as the rpms climbed. We knew that physical realities dictated that getting big power from a small engine meant it had to scream up top. Scream it did, and given the changes, that wasn't surprising-but the low-end performance seemed no worse than before, actually somewhat better. Now the standard magazine mantra is that big valves and bigger ports, combined with small displacement, kills bottom-end power. We chose the combination of cam, induction, and heads carefully, with street performance in mind. Would it work on a 318? The Dynojet wouldn't lie.
While Paul, the dyno operator at K&N, was strapping the Dart to the rollers, he looked over and asked, "What'll it make this time?"
Some quick Calculus had me thinking; (...hmm, we had 215.7hp last time, the Lexus we're gunning for cranks 237, a '96 six speed LT-1 350 registered 256...) "I don't like to make predictions, but it'll make 275," came the reply. It wasn't long before the Dart's tires twisted the rollers, and we had the answer-273.6 at a reasonable 5800 rpm. My seat-of-the-pants guess was good to 1.4hp, or about 11/42-percent. Paul wondered why I had wasted my time coming in for the test, since I had the output judged to within the accuracy of the Dynojet, but, as I explained, we needed something a little more scientific to publish.
That's over 340hp at the crank-from a smooth idling, regular gas drinking, scrap-pile refugee 318. Down low, the big valves and substantially increased port size, defied the predictions and actually belted out more low rpm power and torque than either of our previous combos. What's that translate to in performance? We haven't put the Dart to the track yet, but we did have a chance for some testing with a Varicom Performance Analyzer, which showed a 14.36 ET at 104.3 mph. The ET was limited by the open 2.71:1 differential, but the mph numbers show that we are running solidly with the best of the factory big-inch, big block musclecars. Where's that kid in the Lexus now?
Detailing Edelbrock's Aluminum Small Block HeadsWhile the Edelbrock heads are already manufactured with performance in mind, we spotted a few areas where production line realities put the crimp on theoretical flow potential. After dyno testing for Part One of this article, we had a spare afternoon at David Vizard's flow lab, so we decided to scrutinize the heads before bolting them on. Studying the intake port from the valve seat into the bowls and around the guideboss, the form was beautiful-just the way we would have carved them if we could port the perfect set of iron heads. Looking at the other end, we noticed that at the pushrod pinch, the port window could be increased noticeably without unduly thinning the casting wall.
Another area that caught our eye was along the straight-side wall, where a noticeable bulge was necessitated to cast-in the center headbolt hole. It didn't look like much work to modify these two areas, so we baselined the heads on Vizard's Quadrant Scientific flowbench, with the figures given in Column 1. Next, we broke out the cutters and modified the ports as shown in the photos. The result is shown in Column 2. A significant improvement for minimal effort.
With the gains on the intake side, our attention turned to the exhaust side. There were no obvious areas that caught our eye, but the sound of the air when baselining the port (Column 3) provided a hunch that a mild change in the shortside radius could show an improvement. The shortside was re-cut as shown in the photos, with the result given in Column 4. Again, a meaningful gain in flow for minimal effort, bringing the intake-to-exhaust flow balance back into proportion. We weren't looking to make radical mods to the heads, but just trying a few simple tweaks to get the most out of them for a minimal amount of time spent. For us, it was worth the extra effort.
|EDELBROCK HEADS |
|Tested on quadrant scientific flowlab 580 at 28-inch pressure drop |
|LIFT ||STOCK INT. ||MOD. INT. ||STOCK EXH. ||MOD. EXH. |
|.025-inch ||13.1CFM ||14.3 ||11.9 ||12 |
|.050-inch ||27.4 ||29.1 ||22.9 ||24 |
|.100-inch ||57.9 ||61.1 ||49.6 ||51.4 |
|.150-inch ||84.3 ||88 ||76.5 ||79.6 |
|.200-inch ||112.5 ||118 ||99.8 ||102.8 |
|.250-inch ||136.6 ||144.7 ||117.8 ||121.5 |
|.300-inch ||155.6 ||169.5 ||129 ||133.3 |
|.350-inch ||175.9 ||194.7 ||141.4 ||145.8 |
|.400-inch ||190 ||214.3 ||149.6 ||156.6 |
|.450-inch ||200 ||229.2 ||154.5 ||163.2 |
|.500-inch ||207.2 ||238.5 ||158.5 ||168.2 |
|.550-inch ||211.2 ||230.6 ||161.5 ||171.7 |
|.600-inch ||213.2 ||231.3 ||164 ||175.6 |
|.650-inch ||214.3 ||233.9 ||165.8 ||177.4 |
|.700-inch ||215.4 ||237.5 ||166.8 ||NOT TESTED |