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Mopar 318 Engine - Cheap as Dirt
Inside, the engine still had its fill of 20-50 conventional diesel oil used for break-in. We figured the little Mopar mill had gotten over the critical flat tappet cam break-in period by now. There was the potential for a little more power with the oil change, so we switched to Lucas 5-20 full synthetic oil for our next series of runs. The synthetic offers a lower viscosity, and presumably lower friction, which we hoped would result in some additional power by a reduction of parasitic drag. The oil change proved to be a positive step, with output now reaching 412 hp at the exact same power peak. Dyno operator Steve Brule suggested we might gain some additional power by swapping the 1-inch open spacer for a tapered combination spacer. We grabbed a 4150-sized HVH SuperSucker spacer from our shelf, and made the change. The SuperSucker provides a tapered entry from the carb into the plenum; with some combinations this can add incrementally to the output. It proved to be the case with our 318 Mopar combination, taking peak output to 415 hp at 6,300 rpm, which would prove to be the best numbers of the day. Our 318 cam delivered a rated 0.525-inch lift with 1.5:1-ratio rockers. Under the valve covers we were running the stock Mopar hydraulic rocker valvetrain, which we just cleaned and re-used, including the stock solid bar 5/16-inch pushrods. Although this non-adjustable valvetrain looks crude, test after test has proven it to be remarkably capable in hydraulic cam applications where adustablility is not strictly required. These stamped-steel rockers are lighter than anything from the aftermarket, and the ingenious shaft-mount system lets the rockers ride with virtually no clearance on broad bearing surface at the lower half of the rocker, sliding on a film of oil much like a main bearing. Friction at the shaft is virtually nil, and the stability is excellent. Still, we wanted to see if a little more lift could be added with a higher rocker ratio, so we swapped to a set of aluminum 1.6:1 roller rockers. This would get us to 0.560-inch lift. The rocker change didn't work out, and in fact, the engine's effective rpm range dropped dramatically, down to 6,100 rpm, as compared to the easy and clean 6,700 rpm ceiling (the limit of our test range, not the engine's rpm capabilities) with the factory stock 1.5:1 rockers. We tried setting the lash to zero, to curb lifter pump-up, but it didn't help. What went wrong? In my experience, there are definite limits to how much intensity can be used with a hydraulic lifter, be it a flat tappet or roller. We were over that line with our overall combination. With the super-quick 0.904-inch cam lobe profile, even with the 1.5:1 rockers we were already reaching a very high lift when considering the overall duration. As previously noted, these "0.904-profile" lobes are about 8 percent faster than high intensity 0.842-profile lobes, and the high-ratio rockers add another 7 percent. At the resultant 0.560-inch lift on a 231 @ 0.050 lobe, with only 275 rated seat duration, the valve action is well into the range of a very aggressive solid roller, far faster, in fact, through the early stages of the valve event. The result is valvetrain instability, which the hydraulic mechanism of the lifter cannot cope with. We've been through it before, and increased spring load will do little to help the situation. Besides, with longevity in mind, our COMP No. 972 springs were at the limit of loads we'd run in a street flat tappet application. If hunting for the far reaches of hydraulic cam intensity and rpm, the direction has to be mass reduction throughout the valvetrain, including lightweight valves. The 3/8-stem street valves and now heavier rockers just weren't gong to cut it with this combination. Should we be disappointed that the higher ratio rockers didn't work? Maybe not, since it told us that the factory stuff, when combined with the fast COMP lobe profiles, is in the upper range of the potential available. While more would definitely be possible with trick lightweight components like valves, these items are somewhat out of the budget nature of this build. It also reinforces the value of the stock Mopar valvetrain. It represents a significant cost savings compared to other makes of engines where a valvetrain swap is virtually mandatory for survival with a high performance cam. Thinking about the results, we were pretty happy with the 415 streetable hp and 6,500-plus rpm capabilities we got from Chrysler's neglected 318, especially considering how much of this engine consists of nothing more than mundane factory production parts.  It won't make you a lick of...  It won't make you a lick of power on the dyno, but the best thing you can do to your small-block Mopar's lubrication system for the street is to add a pan baffle. We made this one, and welded it to the stock pan. If you don't want to fab, buy a baffled pan, or you will rash the bearings on slicks. |  Meet Mr. Ugly; this ThermoQuad...  Meet Mr. Ugly; this ThermoQuad flows 850 cfm, and with enough patience and tuning will run with anything on a combo like this. Pluses include metering that is extremely sophisticated, a plastic body that keep fuel much cooler inside, and you can get them at an average of twenty bucks a throw. Minuses include laborious tuning. We used an 850-cfm TQ, on top of the excellent Edelbrock Performer RPM AirGap. |  For hassle-free dyno duty,...  For hassle-free dyno duty, we stabbed an MSD distributor, which works with the Dyno's MSD box, along with MSD wires and Denso plugs to complete the ignition. A blue and a silver spring and the thick black bushing dialed in the timing curve for max power. |  For exhaust, we went with...  For exhaust, we went with TTI's excellent small-block Mopar step headers, and went the full exhaust route with a pair of Hooker Max-Flow mufflers. The mufflers didn't cost any horsepower. |  Right off the bat our mongrel...  Right off the bat our mongrel 318 clicked off 400 hp at 6,200-6,300 rpm, despite the TQ running too rich. Not bad, huh? |  There is no debate that a...  There is no debate that a Demon carb is easier and quicker to tune than the TQ, and time was ticking. We made a quick swap to a 750 Mighty Demon atop a Wilson spacer, and within a couple of jet changes had 406 hp at 6,200- 6,300 rpm. |  An oil change to Lucas 5-20...  An oil change to Lucas 5-20 synthetic, and a swap to a HVH tapered combo spacer helped power even more, allowing this "lowly" 318 to tag 415 hp. That's not a bad number for a simple and dirt cheap street combination, and more than we've seen some bigger street builds make. |  Hollywood Steve "Stevie" Brule...  Hollywood Steve "Stevie" Brule added a set of 1.6:1 aluminum rockers, and even set at zero lash, the rpm capability crashed. We had as much spring as we were willing to run on the street, so this is a dead player with the high-velocity cam, at least without serious attention to lightening the valvetrain. Some 8mm or hollow-stem valves, Ti. retainers, and beehive springs may have allowed the hydraulic lifters to cope. |
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