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.

Richard Holdener May 18, 2012 0 Comment(s)
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Test 4: Dart Pro 1 270 Oval-Port

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The Pro 1 name from Dart has always meant power and this new 270 oval port cast was no exception. The Pro 1 was one of only two full as-cast heads to be tested. All others featured some sort of CNC porting, chamber work, or port matching. Obviously the designers were earning their money, as despite the virgin aluminum, the as-cast Dart Pro 1 offered impressive flow numbers. It's always easier to improve the flow with porting, but getting the results from a casting takes real talent. With enough airflow to easily support our test motor, the Dart-headed BBC produced 593 hp and 554 lb-ft of torque. The 111cc combustion chamber makes the Dart Pro 1 a perfect candidate for head swapping on a 7.4L truck motor. Yank a wrecking yard mule, stuff in a cam, and ditch the peanut ports in favor of a set of Dart oval ports and you have one serious street motor. The smaller chambers on the Dart head (compared to a typical 119cc chamber on peanut-ports) add both flow and compression to further increase power. The Dart Pro 1s showed the power of oval ports by averaging 494 hp and 529 lb-ft of torque and offering 509 lb-ft of torque at 4,000 rpm.

  • Notes: Totally unported, as-cast
  • Retail Price- $2,995
  • Intake Valve Size-2.25
  • Exhaust Valve Size-1.88
  • Intake port vol-274 cc
  • Chamber Volume-111 cc
  • Peak Power-593 hp @ 6,100 rpm
  • Peak Torque-554 lb-ft @ 5,300 rpm
  • Avg HP [3,500-6,500]-494.0 hp
  • Avg TQ [3,500-6,500]-529.0 lb-ft
  • Tq @ 4,000 RPM-509.8 lb-ft

Flow Data: CFM @ 28-ins

LiftInEX
.0503634
.1007169
.200158117
.300235159
.400290204
.500323234
.600324252
.700325267

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Test 5: Dr. J's Ported 049 Oval

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Popularity, availability, and cost all make a factory oval-port head appealing. Because so many enthusiasts not only have heads, but decided to massage them, we opted to include a set of ported 049s in this test. The factory 049 heads came from Dr. J's and were treated to their typical valve upgrade, full porting, and even a slight milling to get the chamber volume down to 118 cc. It is all but impossible to get the chamber size down to the 110cc range offered by the aftermarket heads, but the flow numbers were certainly right in the ballpark. The drop in compression caused by the larger chamber volume hurt power slightly through the entire rev range, but the ported 049s demonstrated why so many BBC owners insist on porting the stock stuff.

Equipped with the Dr. J heads, the 468 produced 576 hp and 538 lb-ft of torque. Torque production exceeded 515 lb-ft from 4,500 rpm to 5,800 rpm, while the BBC averaged 481 hp and 515.8 lb-ft of torque. Down at 4,000 rpm, the iron-headed big-block produced 504.7 lb-ft of torque. The one problem with iron heads is obviously the weight.

  • Notes: Reworked factory heads
  • Retail Price- $1,599 (porting customer-supplied castings)
  • Intake Valve Size-2.25
  • Exhaust Valve Size-1.88
  • Intake port vol-267 cc
  • Chamber Volume-118 cc
  • Peak Power-576 hp @ 6,000 rpm
  • Peak Torque-538 lb-ft @ 5,100 rpm
  • Avg HP [3,500-6,500]-481.4 hp
  • Avg TQ [3,500-6,500]-515.8 lb-ft
  • Tq @ 4,000 RPM-504.7 lb-ft

LiftInEX
.0503334
.1007371
.200152120
.300228162
.400282188
.500320215
.600336238
.700329246

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Test 6: Edelbrock RPM Xtreme

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The name Edelbrock has been around since the dawn of hot rodding, but it still has a few tricks up its collective sleeve. Case in point: Its RPM Xtreme heads, which offered the highest peak airflow of any of the heads we tested. Unfortunately, our test Rat, or more specifically our cam choice, was not able to capitalize on the available airflow, as it occurred at 0.700 lift, though the RPM Xtreme heads flowed nearly as much at 0.600 lift. These heads featured CNC porting through the intake, exhaust, and combustion chamber, and the power numbers reflected the extra work. Only the Edelbrock and AFR heads allowed the 468 to exceed 600 hp, as the Edelbrock-headed BBC produced 601 hp and 552 lb-ft of torque. The average power numbers also reflected the port work, with average horsepower and torque checking in at 498.2 hp and 524.1 lb-ft, respectively. Down at 4,000 rpm, the Edelbrock heads managed 514.9 lb-ft of torque and averaged over 515 lb-ft from 4,100 rpm to 6,100 rpm.

  • Notes: CNC porting throughout
  • Retail Price- $2,597 (porting customer-supplied castings)
  • Intake Valve Size-2.25
  • Exhaust Valve Size-1.88
  • Intake port vol-303 cc
  • Chamber Volume-111 cc
  • Peak Power-601 hp @ 6,200 rpm
  • Peak Torque-552 lb-ft @ 5,300 rpm
  • Avg HP [3,500-6,500]-498.2 hp
  • Avg TQ [3,500-6,500]-524.1 lb-ft
  • Tq @ 4,000 RPM-514.9 lb-ft

Flow Data: CFM @ 28-ins

LiftInEX
.0503529
.1006361
.200133125
.300210186
.400280225
.500327257
.600351277
.700353285

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