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Oval Port Heads vs Rectangle

By Richard Holdener, Photography by Richard Holdener

First up were the stock rectangular-port heads (088 casting number). The open-chamber, rec-port heads featured 119cc chambers, a 2.19/1.88 valve combination and a valvespring upgrade for use with the hydraulic roller cam. As luck would have it, both the stock and AFR castings utilized the same (8.70/7.75-inch) pushrod combo. After dialing in ignition timing and air/fuel ratio, the rec-port 468 eventually pumped out 541 hp and 513 lb-ft of torque. Torque production exceeded 500 lb-ft from 4,400 rpm to 5,500 rpm, and the 119 cc intake ports offered 489 lb-ft of torque at 3,300 rpm. The maximum airflow of 334 cfm offered by the rec-port heads suggested they would support well over 650 hp, but the dyno doesn’t give a rat’s ass about airflow numbers and potential power. That’s why airflow numbers only provide a small part of the performance equation. With nearly identical peak intake flow numbers, how would the AFR oval-port heads fair on the big-block?

Installation of the AFR 265 oval-port heads went without a hitch. The heads were supplied with sufficient valvespring pressure to allow the test motor to rev cleanly past 6,500 rpm without concern for valve float or bounce. Some will point to the change in compression ratio, and some to the port-matched intake manifold, but the reality is that the AFR 265 heads simply kicked the crap out of the stock rec-port heads. How much power was the head swap worth? Equipped with AFR’s 265 oval-port heads, the 468 produced 622 hp at 6,400 rpm and 569 lb-ft of torque at 5,200 rpm. Where torque production exceeded 500 lb-ft from 4,400 rpm to 5,500 rpm with the rec-port heads, the AFR head swap extended this range from 3,200 rpm (possibly lower) to 6,500 rpm. Measured peak to peak, the AFR heads improved power output by 81 hp and 56 lb-ft of torque, but the gains exceeded 90 hp higher in the rev range. Toss in the fact that cast-iron BBC heads weigh a metric ton, and the choice is a no brainer. Euclidians be damned—round is the new square!

Not one to pass up an opportunity on the dyno, we couldn’t help but cater one test toward the street end of the spectrum. Man does not live by the dragstrip alone, and since most driving is done in the lower third of the rpm range, we wanted to see how much power would be sacrificed with the installation of a dual-plane intake. Off came the Victor Jr. and on went the Performer RPM Air Gap. As expected, the peak power dropped to 602 hp, but we expected the torque to increase. In point of fact, the peak torque was down slightly with the dual-plane to 564 lb-ft, but the Air gap did outperform the single plane up to 4,700 rpm. The choice comes down to where you put the emphasis on power production. For daily street use, the extra torque offered by the dual-plane (as much as 42 lb-ft over the single plane) would offer some serious grins, but those who live by e.t.’s and trap speed will be better served by the single-plane. End

Airflow Numbers

Flow Data: CFM at 28 inches

088 Rec Ports AFR 265
Lift Intake Exhaust E/I Intake Exhaust E/I
0.050 32 27 84% 37 30 81%
0.100 77 56 73% 73 63 86%
0.200 144 112 78% 164 141 86%
0.300 206 142 69% 241 196 81%
0.400 245 166 68% 298 239 80%
0.500 289 188 65% 332 260 78%
0.600 320 192 60% 331 273 82%
0.700 334 197 59% 320 280 87%

Note how much better the exhaust-to-intake (E/I) improves with the AFR heads. This is where much of the added power originates, along with the AFR’s better mid-lift intake flow.

Power Numbers

Stock Rec-Port versus AFR 265 Oval-Port

088 Rec Ports AFR 265 Air Gap manifold
RPM HP TQ HP TQ HP TQ
3,300 307 489 317 506 343 547
3,600 339 495 361 526 383 558
3,900 370 498 393 531 418 563
4,200 398 498 425 543 449 561
4,500 431 503 455 564 481 562
4,800 466 510 516 569 513 561
5,100 498 512 552 566 543 559
5,400 522 508 582 556 569 553
5,700 532 490 603 556 588 542
6,000 534 468 617 540 599 524
6,300 541 451 622 518 601 501
6,600 521 415 620 493 594 473

Sources

Airflow Research; 661/257-8124; AirflowResearch.com

Edelbrock; 310/781-2222; Edelbrock.com

Comp Cams/FAST; 901/795-2400; CompCams.com

Holley/Hooker; 270/782-2900; Holley.com

L&R Automotive; 562/802-0443; LnRengine.com

Probe Racing; 310/784-2977; ProbeIndustries.com

Procomp Electronics; 909/605-1123; ProcompElectronics.com

By Richard Holdener
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