Cylinder Head Vital Specs - Power Curves

We Measure All Vital Specs on 8 Cylinder Heads

Bob Mehlhoff Jun 19, 2006 0 Comment(s)
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We tested power curves of several key cylinder heads and recorded the results. Our criteria for this examination was straight-forward: Each set must be under$1,000 in any port size and made from either cast iron or aluminum. We then flow-tested each set, bolted them to the same engine with the same camshaft, and dyno-tested the combinations for horsepower, torque, and power curve.

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Meeting our requirements were five sets of iron and three sets of aluminum heads. The advertised port sizes ranged from 165 to 220 cc, and of the eight sets sent, the Trick Flow heads eclipsed our $1,000 mark by $25.95. Rather than banning them, we took the opportunitiy to see how well they would perform under our scrutiny. The engine of choice was our invaluable mule, a 383 small-block Chevy fitted with a Comp Cams Xtreme Energy 274H with 230/236 degrees of duration measured at 0.050-inch lift and 0.487/0.490-inch valve lift. Why not? After all, it is very represen-tative of a typical performance engine found in most Chevys today. In the end, we not only gained tons of data, but also found that all the cylinder heads we tested demonstrated power curves to match a variety of performance levels at different costs.

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For days we beat the heck out of this 383 small-block. Eight paris of heads in three days. That means the cylinder heads and intake manifold on and off 16 times, 272 head-bolt torques, and 128 valve adjustments.

To illustrate the difference between the heads, we placed them into three categories based on published intake-port size. Each category is matched to the engine's size and performance level. As an example, a moderately built 327 should perform well with cylinder heads from category I, whereas category III heads would be too large and should be selected for hot performance engines (typically larger than 400 ci). While greater port size does not guarantee increased airflow, properly matched port size and design promotes increased airflow without sacrificing velocity. This equals improved torque. Category I (179 cc and smaller) includes three heads: the Scoggin-Dickey upgraded Vortec 170, the Aerohead Racing 165, and the Edelbrock Performer RPM 170 head. Our Category II (180-199 cc) group includes three heads: the RHS 200, the Competition Products 180, and the Trick Flow 195. Finally for Category III (200-220 cc) we included World's Motown 220 and the Dart 215 cylinder head.On the following pages you'll see the specs for each head, including the true measured chamber and port volumes (as tested), valve size, weight of each head, and cost. Below that you'll find each cylinder head's airflow chart at a range of valve lifts. We've listed the torque and horsepower numbers for every rpm up to 6,100 and figured out the averages.

When surveying these test results, keep in mind the performance category you're trying to target. Your engine size, compression, camshaft selection, stall speed, and rearend gears each play a vital part in maximizing performance. Like all engine modifications, the cylinder heads you install, when matched to your engine's specifications, will help provide huge gains in power levels.

Quick Notes
We flog eight sets of cylinder heads
Five sets iron and three sets aluminum; advertised port volume range: 170-220cc
$1,000 or less


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