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.
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.
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.
We flog eight sets of cylinder heads
Five sets iron and three sets aluminum; advertised port volume range: 170-220cc
$1,000 or less
One of the bargains we tested was the Aerohead small-block Chevy head, featuring a larger com-bustion chamber than most tested. It should be noted that this netted a lower compression ratio. These reconditioned Dart Iron Eagle S/S heads pro-duced a healthy torque number of 475 lb-ft at 3,900 rpm and 430 horses at 5,700 rpm. With these heads you can gain power and save money.
The Edelbrock Performer RPM heads had excellent flow numbers, and they provided exceptional power and torque during our dyno testing. At 3,900 rpm these heads produced 491 lb-ft peak torque and 452 peak horsepower at 5,500 rpm, making them a great choice for many mild-to-medium street-performance engines.
The Scoggin-Dickey modified Vortec cylinder head was one of our price leaders at just $680 per pair. To allow the use of a 0.525-inch-lift hydraulic camshaft with these Vortec heads, Scoggin-Dickey adds high-performance late-model Z28 valvesprings with lightweight LT4 retainers and machines the valve guides for clearance. These heads produced an average torque number of 445 lb-ft, a large portion of it near the lower rpm band. Peak horsepower for this head ran in at 430, with an average of 392 at all measured points from 3,300 to 6,100 rpm. These heads make a great choice for a budget-built street car where good torque is needed. The use of these heads requires a special Vortec intake manifold and recommended head bolt kit. For our dyno run we used an Edelbrock Vortec Performer RPM Air Gap.
The RHS 23-degree cylinder heads come complete with high-quality Comp Cams components (valvesprings, retainers, and keepers). They unleashed 468 lb-ft of torque from the 383 small-block at 3,900 rpm and 422 horses at 5,500 rpm. This head incor-porated a larger 72cc cumbustion chamber, which produced lower compression on our test engine than the smaller 64cc chambers featured on many of the other heads.
At $880 the Competition Products cylinder head is the most economically priced aluminum head we tested, and the power numbers ran in at 470 lb-ft of torque at 4,100 rpm and 409 horsepower at 5,600 rpm. These heads produced good mid-range power.
This aluminum head from Trick Flow produced 496 lb-ft of torque at 4,000 rpm and 455 horses at 5,300 rpm. With its 195cc intake ports and 215-cfm flow numbers at 0.400-inch lift it was a good match for our 383 small-block test engine. Matched to a similar engine, you can have neck-snapping torque and big power. We went over our budget by $26, but at such a marginal cost, who are we to not test them? Besides, a week of brown-bagging our lunches made up the difference.
The World Motown 220 pumped out 478 lb-ft of torque at 3,800 rpm and 439 horses at 5,400 rpm. These heads, with their 220cc intake ports, are the biggest we tested, and it must be mentioned that the large port size would most likely work better on engines with more than 400 ci (such as the latest 427 and 454 small-blocks). Because our test engine was a smaller 383 we were not able realize the power numbers that these heads produce on big-inch small-blocks.
The Dart Iron Eagle heads pumped out 478 lb-ft of torque at 4,100 rpm and 450 horses at 5,600 rpm. The 215cc runners flowed 220 cfm at 0.400-inch lift and would be a good choice for larger small-block Chevys.