Big-Block Heads Shootout - The Big O Vs. The Big R

Oval ports and rectangular port heads

Richard Holdener Jul 18, 2012 0 Comment(s)
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Two issues back, we subjected a 468-inch big-block Chevy to a variety of different oval-port cylinder heads, ranging from stock peanut-port-style heads to full CNC-ported versions (see “The Big O”). In that story, we attempted to dispel the myth that any powerful big-block combination must include rectangular-port cylinder heads. Equipped with the right oval-port heads, the 468 easily exceeded 600 hp on the engine dyno. Most of the oval-port heads tested in part 1 offered airflow that would support another 100 hp on the right combination.

Contrary to popular opinion, our combination was limiting the potential of the oval-port cylinder heads, not the other way around. It is true that all of the factory performance big-blocks sported rectangular-port heads back in the day, but much has changed since the first muscle car era. Not only does a good set of aftermarket oval-port heads outflow the factory rec-port stuff, it does so with reduced port volume. Big, lazy ports are ideally suited for neither performance nor street use, while smaller, efficient ports offer the best of both worlds. Nowhere was this more evident than in the fact that a couple of manufacturers chose to supply oval-port heads once again on this larger (and more powerful) 496 test engine.

A common stroker displacement, our 496 was the result of combining a 0.060-inch overbore with a 4.25-inch stroker crank. Our BBC rotating assembly came from the experts at Scat Enterprises. The BBC combination featured a 4340 forged steel crank combined with a set of matching 6.385-inch, I-beam rods. We chose a Scat crankshaft design specifically for our late-model, one-piece, four-bolt, Gen-6 block. The Scat crank and rods were combined with a set of forged pistons from JE. Offered as part of their SRP line up, the JE Pistons featured 18cc domes to produce a static compression ratio of 10.0:1 with typical 120cc combustion chambers.

The short-block was built not to maximize power production, but rather to demonstrate what is possible for street use in a performance driver. We wanted all of our testing to be run on pump gas, so we kept the static compression at a reasonable level. L&R Automotive was responsible for machining and balancing of the combination, while Total Seal came through with a set of performance rings to ensure proper sealing.

The displacement ensured that our 496 would be more powerful than the 468 used in part 1, but we hedged our bets with the installation of a wilder cam profile as well. Balancing the street/performance theme, we chose a small solid roller profile from Comp Cams. The 300BR-14 offered 0.652 lift, a 255/262 duration split and 114-degree LSA. To work in the Gen-6 block, the cam was teamed with a set of 0.300-tall solid roller lifters and a double roller timing chain.

Since the cam and timing chain were designed for a Gen-4 block, it was necessary to eliminate the factory cam retaining plate in favor of a traditional cam button. The swap also required the use of a custom front cover (PN217) from Comp Cams to provide the necessary room for the double-roller chain (factory Gen-6 covers must be run with a single-roller chain).

Finishing touches on the test mill included an Edelbrock Victor Jr. 454-R intake, a Holley 950 HP carb and SFI-approved, neutral damper from Procomp Electronics.

Prior to running the test engine, all of the heads were treated to flow bench testing to correlate the flow potential to the power gains. In truth, heads like the Brodix BB-3 Xtra O offered over 400 cfm--enough to support more than 800 hp. We were just scratching the surface or their potential with our 496 street/strip combination. After bench testing, we subjected the heads to port and chamber volume measurements. Since the compression ration is a function of the chamber volume, chamber size has a significant effect on the power curve (to the tune of 3-4 percent per point). Measurements indicated that our test heads varied greatly, from a low of 107cc to a high of 123cc. Bear this in mind when viewing the power numbers.

It is again worth mentioning that though this was originally to be a rec-port-only head test (to follow the oval-ports tested in part 1), some of the manufacturers supplied oval-port heads for this 496. Don't look down you noses at oval-port heads, as testing from both stories suggests that if anything, oval is the new square.

Test 1: Stock GM 088 Iron


Prior to running any of the aftermarket heads we had to establish a baseline by running the stockers. We chose a set of 088 castings that featured 316cc intake ports, 121cc exhaust ports and 123cc combustion chambers. The airflow data suggested that the stock iron heads would support over 650 hp, but on this 496, the heads managed to produce peak numbers of 630 hp at 6,600 rpm and 577 lb-ft of torque at 5,300 rpm. While 630 hp would make a serious street motor, we would see that the right head choice on this application would add nearly 100 hp to that total.

  • GM rectangular port castings
  • Retail Price-NA
  • Intake Valve Size-2.19
  • Exhaust Valve Size-1.88
  • Intake Port Vol-316 cc
  • Exhaust Port-121 cc
  • Chamber Volume-123 cc
  • Peak Power- 630 @ 6,600 rpm
  • Peak Torque- 577 lb-ft @ 5,300 rpm
  • Avg HP (3,500-6,500)-532.4
  • Avg TQ (3,500-6,500)- 560.5 lb-
  • TQ @ 4,000 RPM - 562.7lb-ft
Flow Data: CFM @ 28-ins
Stock 088
Lift In Ex
0.0503227
0.1007756
0.200144112
0.300206142
0.400245166
0.500289188
0.600320192
0.700334197
0.800335201

Test 2: Summit Racing Iron


Many would dismiss the iron heads simply for the weight savings, but don't count them out, especially when you consider the price and performance. These rectangular port iron heads from Summit Racing offered surprising bang for the buck. The Summit Racing head upgrade improved the power output of the 496 from 630 hp and 577 lb-ft to 688 hp and 607 lb-ft. This was all the more impressive considering the fact that the heads cost just $750 bucks each, assembled. Toss in the fact that the Summit heads flow only marginally better than the stock heads and share the same combustion chamber volume. If you are looking for iron heads on a budget, look no further than Summit Racing.

  • Retail Price-$749
  • Intake Valve Size-2.25
  • Exhaust Valve Size-1.88
  • Intake Port Vol-309 cc
  • Exhaust Port Vol-127 cc
  • Chamber Volume-122 cc
  • Peak Power- 688 hp @ 6,600 rpm
  • Peak Torque- 607 lb-ft @ 5,400 rpm
  • Ave HP (3,500-6,500)-555.5
  • Ave TQ (3,500-6,500)-582.1
  • TQ @ 4,000 RPM-563.3 lb-ft

Summit Racing Iron
Flow Data: CFM @ 28-ins
Lift In Ex
.0503434
.1006969
.200146109
.300204155
.400264192
.500309223
.600340246
.700323262
.800330273

Test 3: Procomp Electronics Rec-Port CNC


The aluminum heads from Procomp Electronics combined the largest port volume and (nearly) peak flow numbers with the lowest retail cost. The intake port volume measured a sizable 369cc, while the exhaust checked in at 157cc. This head configuration would be much more at home on a larger displacement, higher horsepower application, but how can you argue with aluminum BBC heads that flowed over 400 cfm for around $600? Equipped with the Procomp heads, the BBC stroker pumped out 690 hp and 600 lb-ft of torque. We suspect the large port volume and sizable combustion chamber hurt torque and power on this application, as many of the other heads featured smaller chambers and port volumes. We'd like to see this head strut its stuff on a high-compression 572, but for our 496, it was likely just too big.

  • Retail Price-$625
  • Intake Valve Size-2.30
  • Exhaust Valve Size-1.88
  • Intake Port Vol-369 cc
  • Exhaust Port Vol-157 cc
  • Chamber Volume-123 cc
  • Peak Power- 690 hp @ 6,300 rpm
  • Peak Torque- 600 lb-ft @ 5,500 rpm
  • Ave HP (3,500-6,500)-554.2 hp
  • Ave TQ (3,500-6,500)- 581 lb-ft
  • Tq @ 4,000 RPM-568.3 lb-ft

Procomp Electronics BBC Rec-Port CNC
Flow Data: CFM @ 28-ins
Lift In Ex
.0503531
.1007067
.200152132
.300234175
.400294206
.500336231
.600364251
.700389267
.800403279

Test 4: Trick Flow Specialties PowerPort 360 Heads


Like the Procomp heads, the PowerPort 360s from Trick Flow Specialties were probably a tad on the big side for the 496. With intake ports that measured 357cc, the impressive PowerPorts would be more at home on a big-block exceeding 500 cubic inches. With peak intake flow numbers of 384 cfm, the heads we capable of supporting over 750 hp, but on our 496 manage 691 hp and 603 lb-ft of torque. The PowerPort heads shared the large (122cc) combustion chamber volume of the stock heads and came in at a cost-effective $1,229 (through Summit Racing).

  • Retail Price-$1229
  • Intake Valve Size-2.30
  • Exhaust Valve Size-1.88
  • Intake Port Vol-357 cc
  • Exhaust Port Vol-134 cc
  • Chamber Volume-122 cc
  • Peak Power- 691 hp @ 6,400 rpm
  • Peak Torque- 603 lb-ft @ 5,400 rpm
  • Ave HP (3,500-6,500)-555.3
  • Ave TQ (3,500-6,500)- 581.9 lb-ft
  • TQ @ 4,000 RPM-562.3 lb-ft

Trick Flow Specialties PowerPort 360 head
Flow Data: CFM @ 28-ins
Lift In Ex
.0503530
.1007261
.200148125
.300217168
.400275198
.500325227
.600360246
.700376261
.800384273

Test 5: Brodix BB-3 Xtra 332


The new Brodix BB-3 Xtra 332 heads were not quite a rec-port head nor were they a conventional oval (or peanut) port head. They were somewhere in the middle, more like a rectangular-port with rounded corners. In truth, use of the 454-R (rec-port) intake may have hindered the power potential of the Brodix heads more than others due to the port mismatch. One thing for certain is that the Brodix heads topped all comers in terms of airflow with peak numbers of 409 cfm. Capable of supporting over 800 hp, our 496 produced 705 hp and 624 lb-ft of torque. We would love to port-match an intake to these heads in an attempt to translate all that airflow potential into power.

  • Retail Price-$1840
  • Intake Valve Size-2.30
  • Exhaust Valve Size-1.88
  • Intake Port Vol-335 cc
  • Exhaust Port Vol-133 cc
  • Chamber Volume-115 cc
  • Peak Power- 705 hp @ 6,400 rpm
  • Peak Torque- 624 lb-ft @ 5,200 rpm
  • Ave HP (3,500-6,500)-574.6
  • Ave TQ (3,500-6,500)- 602.7 lb-ft
  • TQ @ 4,000 RPM-585.7 lb-ft
Brodix BB-3 Xtra 33
Flow Data: CFM @ 28-ins
Lift In Ex
.0503331
.1006669
.200147120
.300211173
.400273221
.500333256
.600380277
.700409286
.800403296

Test 6: Dart Pro 1 335


The Pro 1 name from Dart has always meant power and this test illustrates that the name still carries some weight. For our street/strip 496 BBC, Dart supplied a set of its CNC-ported 335 heads. With flow numbers that reached nearly 400 cfm, the Dart Pro 1s were another set of 800-hp heads in search of a motor. The Dart Pro 1 heads featured rolled valve angles and raised exhaust ports to improve flow and power, but remained compatible with stock accessories. Run on the dyno, the big-block produced 717 hp and 619 lb-ft of torque. Equipped with a smaller chamber shared by the AFR and Edelbrock heads, the Dart would likely be right in the hunt for maximum power.

  • Retail Price-$2021
  • Intake Valve Size-2.30
  • Exhaust Valve Size-1.88
  • Intake Port Vol-303 cc
  • Exhaust Port Vol-137 cc
  • Chamber Volume-122 cc
  • Peak Power- 717 hp @ 6,500 rpm
  • Peak Torque- 619 lb-ft @ 5,600 rpm
  • Ave HP (3,500-6,500)-568.0
  • Ave TQ (3,500-6,500)-594.3 lb-ft
  • TQ @ 4,000 RPM-572.5 lb-ft

Dart Pro 1 335
Flow Data: CFM @ 28-ins
Lift In Ex
.0503429
.1006961
.200148125
.300228181
.400294219
.500336249
.600376271
.700398281
.800399289

Test 7: Edelbrock E-CNC 355


Edelbrock has stepped up in a big way recently with new performance offerings and these E-CNC 335 heads are a perfect example. Proudly made in the USA, the E-CNC heads offered plenty of flow, peaking at 391 cfm on the intake and 285 cfm on the exhaust. Sporting the smallest combustion chamber of the bunch at 107cc, the Edelbrock heads produced the highest static compression ratio. Naturally this helped power, allowing the E-CNC heads to produce 723 hp and 627 lb-ft of torque.

  • Retail Price-$1,630 (required spring upgrade)
  • Intake Valve Size-2.30
  • Exhaust Valve Size-1.88
  • Intake Port Vol-353cc
  • Chamber Volume-107 cc
  • Exhaust Port Vol-135 cc
  • Peak Power- 723 hp @ 6,500 rpm
  • Peak Torque- 627 lb-ft @ 5,600 rpm
  • Ave HP (3,500-6,500)-573.5 hp
  • Ave TQ (3,500-6,500)- 599.9 lb-ft
  • TQ @ 4,000 RPM-574.0 lb-ft

Edelbrock E-CNC 355
Flow Data: CFM @ 28-ins
Lift In Ex
.0503329
.1007361
.200148132
.300224185
.400283226
.500334252
.600364270
.700385278
.800381285

Test 8 AFR Magnum 300 Oval


It takes more than just big flow numbers to make power, and these Airflow Research heads proved that. In fact, when asked to supply rec-port heads for this test, they opted to instead send over a set of oval-port heads. It new 300cc Magnum heads did not offer the highest peak flow numbers, topping out at 383 cfm (at .650 lift), but when combined with exceptional mid-lift flow and an efficient chamber design, the results were enough impressive. Power production is all about the combination of components working together and on this 496, the AFR Magnum 300 heads proved to be the optimum combination by producing 729 hp and 639 lb-ft of torque.

  • Retail Price-$1,559
  • Intake Valve Size-2.30
  • Exhaust Valve Size-1.88
  • Intake Port Vol-300 cc
  • Exhaust Port Vol-123 cc
  • Chamber Volume-110 cc
  • Peak Power- 729 hp @ 6,500 rpm
  • Peak Torque- 639 lb-ft @ 5,400 rpm
  • Avg HP (3,500-6,500)-584.1
  • Avg TQ (3,500-6,500)-611.4 lb-ft
  • TQ @ 4,000 rpm-587.0 lb-ft

AFR Magnum 300 Oval
Flow Data: CFM @ 28-ins
Lift In Ex
.0503432
.1007462
.200153126
.300233198
.400296237
.500345263
.600377277
.700371288
.800365296

Sucp_1208_14_oval_rectangular_port_heads_the_big_vs_r_ 38/38

21 The combustion chamber of each cylinder head tested was measured.

Sources

Air Flow Research
Valencia, CA 91355
661-257-8124
AirFlowResearch.com
Trick Flow Specialties
Tallmadge, OH 44278
330-630-1555
www.trickflow.com
Brodix
Mena, AR 71953
479-394-1075
http://www.brodix.com
Comp Cams
Memphis, TN 38118
800-999-0853
http://www.compcams.com
Summit Racing
Akron, OH
800-230-3030
SummitRacing.com
L&R Automotive
Sante Fe Springs, CA 90670
562-802-0443
www.lnrengine.com
Procomp Electronics
Ontario, CA 91761
909-605-1123
www.procompelectronics.com
Dart Heads
Troy, MI 48084
248-362-1188
http://www.dartheads.com
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