Rectangle vs. Oval Port Big-Block Head Test

Ccrp 1211 Rectangle Vs Oval Port Big Block Test 12

Ccrp 1211 Rectangle Vs Oval Port Big Block Test 07

After minor jetting and timing sweeps, the iron heads produced peaks of 541 hp and 513 lb-ft of torque. Torque production with the rec-port heads exceeded 500 lb-ft from 4,440–5,500 rpm.

After minor jetting and timing sweeps, the iron heads produced peaks of 541 hp and 513 lb-

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!

AFRs Tony Mamo (left) and Westech’s Steve Brule discuss the potential of the AFR 265 heads while removing the Team G intake and factory heads.
AFRs Tony Mamo (left) and Westech’s Steve Brule discuss the potential of the AFR 265 heads
Named for their intake port volume, the AFR 265s were more than 40cc smaller than their rectangular counterparts. They were also equipped with sufficient spring pressure to ensure proper operation above 6,500 rpm.
Named for their intake port volume, the AFR 265s were more than 40cc smaller than their re
The AFR 265s also featured a 2.19/1.88 valve combo, but the 112cc combustion chambers increased the static compression by roughly seven-tenths of a point (responsible for about 2.5 percent of the power increase—approximately 13–14 hp).
The AFR 265s also featured a 2.19/1.88 valve combo, but the 112cc combustion chambers incr

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 testing indicated a peak flow of 332 cfm, but the AFR 265s outflowed the rec-port heads by as much as 53 cfm at 0.400 lift. The exhaust flow was equally impressive, as the AFR outflowed the stockers by over 80 cfm. Average flow gains are what create horsepower.
Airflow testing indicated a peak flow of 332 cfm, but the AFR 265s outflowed the rec-port
Off came the stock iron heads to make way for the new AFR 265s. Aluminum BBC heads are so much easier to work with than their hefty iron counterparts.
Off came the stock iron heads to make way for the new AFR 265s. Aluminum BBC heads are so
The AFR 265 heads required a dedicated intake manifold designed to match the oval-port openings in the heads.
The AFR 265 heads required a dedicated intake manifold designed to match the oval-port ope

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.

AFR supplied a single-plane Edelbrock Victor Jr. intake that had been port-matched to the oval-port 265 heads. The single-plane intake was designed to maximize power production higher in the rev range.
AFR supplied a single-plane Edelbrock Victor Jr. intake that had been port-matched to the
Run with the same Holley 950 HP carburetor, the AFR-headed 468 pumped out 622 hp and 569 lb-ft of torque. Not only were the peak numbers up, but the oval-port heads improved power production through the entire rev range.
Run with the same Holley 950 HP carburetor, the AFR-headed 468 pumped out 622 hp and 569 l
The final test involved installation of an Edelbrock RPM Air Gap intake manifold. The dual-plane intake improved low-speed torque production by as much as 42 lb-ft, but dropped peak power from 622 to 602 hp.
The final test involved installation of an Edelbrock RPM Air Gap intake manifold. The dual

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