I know some of you might scoff at the article but many years ago Hot Rod built a 400 horse 318. Guess what heads they used? #302's. Now I don't give a damn if there's better heads out there. There are, but these heads aren't a bad choice for a mild street 273 or 318. Now they did grind on those heads to make them better like most would do to any head. There's some highlights.
Compression
An inspection revealed the stock pistons to be 0.058 below the uncut factory decks, so the first order of business was to consider the cylinder head possibilities to deliver some compression. With the small cubes and excessive deck clearance, our 318’s compression ratio with junkyard 360 heads would fall to the kerosene-burning range of 8.0:1. We needed heads with two criteria: ready availability and small chamber volumes. The ’85-and-up swirl-port 318 two-barrel heads (casting number 302) filled the bill on both counts; they come stock with modern, heart-shaped, 59cc chambers and are commonly available on such exotica as ’85-’91 318-two-barrel-equipped Chrysler Fifth Avenues, Diplomats, Grand Furys, pickups, and vans. With large, flat Milodon valves filling the chambers, plus a 0.050 cut on the mill, our final chamber volume was reduced to a compact 52cc, bringing the compression ratio to a whisker under 10.0:1 when combined with thin head gaskets from Mopar Performance (PN P4349557).
Cheap Head Flow
The milled No. 302 heads offer compression on the cheap, but fall short on the flow side of the equation. These heads carry the common 318/two-barrel valve sizes of 1.78/1.50-inch and in stock trim flow about 135 cfm stock on the intake side. Our plan was to find flow by porting the heads and upping the valve diameter to 2.02/1.60 with a set of Milodon street valves. The valve spacing on all small-block Mopars is the same, so these valves will fit in the 302 castings the same as with any 318/340/360 heads. Valve shrouding isn’t any more of an issue than with other small-block Mopar heads, since as part of the valvejob the chambers were cut concentric to the valve out to near the line of a Fel-Pro gasket. This makes the chamber quite a bit wider than the 318’s stock 3.91-inch bore in the area adjacent to the valve. To address this, the bores were chamfered (notched) to minimize shrouding by the shelf left where the chamber meets the bore. Contrary to popular misconception, 2.02-inch intake valves fit the 318’s bores without a problem; in fact 2.08-inch intake valves won’t hit.
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The intake port runners were opened to a 360 gasket size, quite an enlargement from the stock 318 dimension. This move allows the runners to mate nicely with a performance intake manifold (which are typically based on the larger 360 port dimension) or to a stock 360 intake. The exhaust runners were opened to the dimension of a Fel-Pro header gasket. At the other end of the passages, the seat area was prepped with a Serdi-machined cut of the chambers out toward the head gasket line to minimize chamber shrouding of the valve. The oversized seat form was cut, along with a 75-degree bottom cut, which greatly opened the port bowls. After machining, the hand-porting involved blending the machined cuts into the as-cast bowls, streamlining the valveguide bosses, then blending and widening the short turn to a smoothly rolled form from the port floor to the valveseat, eliminating the various factory humps in the corners of the turn. The fully ported No. 302 heads with larger valves installed showed an intake flow improvement of nearly 60 percent to a respectable 215 cfm at a peak of 0.500 lift.
Are these low-buck heads? Getta grinder and learn to use it, and the answer is yes. There’s no such thing as a free lunch; sometimes the trade is time and effort for cubic dollars.