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Oval Port Big-Block Chevy Cylinder Heads - The Big O

The best way to illustrate the power potential of performance cylinder heads is on the dyno.

By Richard Holdener, Photography by The Author

The heads from Dart and Procomp Electronics were as-cast with no additional machining of any kind. Heads supplied by Brodix and Trick Flow Specialties both featured port matching, but the Brodix head carried it one step further with CNC work on the combustion chamber. The AFR, Edelbrock, and 049 heads from Dr. Js all combined full porting and chamber work.

As expected, the level of work applied to the heads resulted in differences in flow and power. Take note that the combustion chamber volumes varied from 110 cc to 121 cc, resulting in a difference in static compression of 1 full point. This alone was worth 3-4 percent in power, so bear this in mind when reviewing the results.

The one upgrade we would like to see on many of the heads is more valve spring pressure. At the top of the power curve, some suffered slightly due to inadequate spring pressure.

Power and price usually go hand in hand, but check out the retail prices to determine how your favorite does in the all-important bang-for-the-buck category. Next month, we'll be testing some popular rectangular port heads on a larger-displacement Rat.

Test 1: Chevy Peanut-Port Heads

Our intention was to run a set of stock peanut-port heads and a set of stock oval-port heads, but our oval-port heads fell through. The stock peanut-port heads featured a 2.06/1.72 valve combination with 118cc combustion chambers. Closer inspection revealed that even our "stock" peanut-port heads had been milled sometime in their long life. The small valves, port volume, and flow numbers made them less than ideal with this healthy hydraulic roller cam, but they surprised us by exceeding 500 hp with peak numbers of 512 hp and 514 lb-ft of torque. Looking at the graphs, the peanut-port heads actually ran neck and neck with the aftermarket heads up to 4,500 rpm, which makes them ideal for intended low-speed truck applications. With a little porting, they make good heads for a mild street BBC, especially a small-displacement 396.

  • Notes: Out-of-the box 360 castings
  • Retail Price- N/A
  • Intake Valve Size-2.06
  • Exhaust Valve Size-1.72
  • Intake port vol-253 cc
  • Chamber Volume-117 cc [milled]
  • Peak Power-512 @ 5,800 rpm
  • Peak Torque-514 lb-ft @ 4,800 rpm
  • Avg HP [3,500-6,300]-453.4 hp
  • Avg TQ [3,000-6,500]-489.9 lb-ft
  • Tq @ 4,000 RPM-508.5 lb-ft

Flow Data: CFM @ 28-ins

LiftInEX
.0503324
.1005751
.20011794
.300185128
.400233158
.500247179
.600250297
.700250211

Test 2: Airflow Research 265

The AFR 265 heads didnt produce the highest peak power and torque numbers of the test because of peak flow numbers. In fact, every aftermarket head we tested actually offered better flow number numbers at 0.700 lift (and many at 0.600 lift) than the AFRs. Even the ported 049 heads outflowed the AFRs at 0.700 lift, but our 0.580-lift cam never made it to 0.700 lift. Besides, power doesnt come from peak flow, it comes from maximizing flow in the usable lift range. Since the valve must open up to the maximum lift value, then close down, it spends twice as much time in the rest of the lift range as it does at the peak. Using the additional mid-lift flow offered by the AFR 265s, the 468 BBC produced 613 hp and 559 lb-ft of torque. The spring package provided by AFR allowed the hydraulic roller motor to rev cleanly to 6,500 rpm. In terms of average power production from 3,500 rpm to 6,300 rpm, the AFR 265s produced 501 hp and 536 lb-ft of torque, while knocking down 520 lb-ft at 4,000 rpm.

  • Notes: Fully ported, chambers worked
  • Retail Price- $2,238
  • Intake Valve Size-2.19
  • Exhaust Valve Size-1.88
  • Intake port vol-266 cc
  • Chamber Volume-112 cc
  • Peak Power-612 hp @ 6,400 rpm
  • Peak Torque-559 lb-ft @ 5,300 rpm
  • Avg HP [3,500-6,500]-501 hp
  • Avg TQ [3,500-6,500]-536 lb-ft
  • Tq @ 4,000 RPM-520.3 lb-ft

Flow Data: CFM @ 28-ins

LiftInEX
.0503730
.1007363
.200164141
.300241196
.400298239
.500332260
.600331273
.700316280

Test 3: Brodix Race Rite Oval 270

The Brodix Race Rite oval-port heads featured 270cc intake ports that flowed just shy of 340 cfm--enough to support nearly 700 hp on the right application. Obviously, our mild combination could not take full advantage of what the Brodix heads had to offer, but they performed exceptionally well on the 468 nonetheless. Unlike the AFR or Edelbrock offerings, the Brodix Race Rite heads relied on CNC porting only in the combustion chamber. The intake ports received a minor gasket match, but the cutter was not allowed to do any serious work. The lack of CNC porting didnt seem to hurt the flow rates, as the intake and exhaust ports of the Brodix heads flowed 336 cfm and 270 cfm, respectively. This allowed the Brodix-headed 468 to produce 591 hp and 553 lb-ft of torque. The BBC averaged 492 hp and 528 lb-ft of torque while thumping out 512.8 lb-ft at 4,000 rpm.

  • Notes: CNC'd comb. chambers, intake ports
  • Retail Price- $2,796
  • Intake Valve Size-2.25
  • Exhaust Valve Size-1.88
  • Intake port vol-269 cc
  • Chamber Volume-111 cc
  • Peak Power-591 hp @ 6,100 rpm
  • Peak Torque-553 lb-ft @ 5,100 rpm
  • Avg HP [3,500-6,500]-492.7 hp
  • Avg TQ [3,500-6,500]-528 lb-ft
  • Tq @ 4,000 RPM-512.8 lb-ft

Flow Data: CFM @ 28-ins

LiftInEX
.0503430
.1006964
.200149127
.300220163
.400275193
.500315225
.600336254
.700333270

By Richard Holdener
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