rectangle or oval port, a non-issue based on mis-information


Staff member
most of us have heard this issue discussed for decades, back in the late 1960s everyone wanted the larger rectangle port performance heads and when the high performance 427-454 chevy engines were produced they all had rectangle port heads, but as guys experimented its been found that theres a whole lot more factors that come into play in engine component selection , than the old ,rectangle or oval port, debate which is a non-issue based on mis-information.
as a general guide oval port heads with 260cc-290cc ports tend to best match the 396-454-500 cubic inch and smaller displacement engines that will be operated in the 2000rpm-6000rpm power band, naturally the larger displacement combos will have higher average port speeds and reach port stall at a lower rpm where the cylinder heads cross sectional area becomes a limiting factor in how well the engine can fill its cylinders,and depending on the particular application,oval ports can still be a valid choice on larger combos but generally by the time your displacements in the 496- 540 cid range youll be looking at a 315cc-335cc port size or larger, in most cases if you intend to spin the engine into the rpm ban that maximizes it power potential.
but be aware the intake manifold,design and intake runner length and cross section, engine compression ratio, cam lift and duration, drive train gearing,and exhaust scavenging all have a significant effect on the results youll see.
The truth is that its the application, the cylinder heads will be used on that determines which head design is superior, and the relationship between the port cross sectional area , valve size, curtain area,and the engines cam timing, compression ratio, displacement and intended rpm band , and rear gearing that will have a huge effect on your parts selection.
if you have a basically stock 396-427 in your street driven muscle car, that you just stuck a hydraulic or mild solid lifter performance cam,into with an aftermarket intake ,expecting to have built a great deal of horse power, yet you stuck with the stock drive train and gearing and maybe added headers but kept the stock exhaust , in the car youll generally find oval port heads, are going to produce the best torque curve, because they keep
thats not going to be the case if you built a serious race combo and gear the car to spend most of its time in the 4000rpm-7000rpm power band, like a 13:1 compression 496 stroker big block engine and a cam with .700 lift with about 255 at .050 lift or more duration, simply because the stock or smaller port oval port cylinder heads will be nearly hopeless at supplying the required air flow that the displacement and cam timing can potentially require.
look thru the links there are calculators links to allow you to accurately calculate the correct port length and cross sectional areas,
this is NOT a GUESSING GAME the correct combo is fairly easy to accurately CALCULATE





most intakes require gasket matching to maximize the flow potential

simply open the ports to match and transition too the heads and blend back any change in cross sectional area up the runners at least an inch or more

don,t forget the plenum and runner entrance needs smoothing ... lock_test/ ... /A-P3.html














ID suggest you select from heads from these sources
Jegs; 800/345-4545;

Summit Racing; 800/230-3030;

Scoggin-Dickey Parts Center; 800/456-0211;

TRICKFLOW ... 4294867081
1-330-630-1555 • 1-888-841-6556


Dart Machinery; 248/362-1188;

toll free: 877-892-8844
tel: 661-257-8124

Patriot Performance
Patriot Performance; 888/462-8276;

Toll Free: 877-776-4323
Local: 901-259-1134

EDELBROCK ... main.shtml
Edelbrock; 310/781-2222;

BMP (world products)
Tel: 631-737-0372
Fax: 631-737-0467



Last edited by a moderator:


Staff member
Re: rectangle or oval port, a non-issue based on mis-informa

this is well worth reading thru, Ive always been a guy that preferred to build a big block, and this infos useful, but keep in mind oval ports have a distinct place as do rectangular port heads, and you can and should calculate the required port cross sectional area, cfm flow and valve curtain area, valve lift etc. your particular application requires, don,t make random guesses
Also of note they included a rough way of figuring out your cylinder head flow requirements for your hp level....
double the maximum airflow for your hp 300 cfm would support a 600hp,while thats hardly exact its a rough guide motor




viewtopic.php?f=69&t=189 ... blockchevy


obviously you will need to carefully port match some intakes to some head ports due to the wide variation in sizes and shapes ... ewall.html
Ask a big-block enthusiast what they need to make 600 hp and chances are they will point to some sort of rectangular-port head. No one in their right mind would select an oval-port head to make that kind of power, let alone one with a diminutive 265cc intake port, right? Well, big-block fans, times have changed and so has that well-defined line between the pedestrian oval-port and rectangular-port performance heads.

Back in the day, all the factory high-performance Rat motors were sporting rectangular-port heads and the street/strip crowd followed suit. But that was then and this is now. The aftermarket has stepped up in a big way and produced oval-port heads that not only out-flow any factory rectangular-port version, but do so while dramatically reducing port volume. The combination of more flow and less port volume makes these oval-port heads a much better choice for your street/strip motor than their rectangular-port counterparts. For motors up to and even beyond 600 hp, especially small-displacement big-blocks (under 500 inches), the hot setup today is more than likely an aftermarket oval-port.

With oval-port heads taking the street/strip market by storm, we decided it was a good idea to take a long hard look at them and thoroughly check out the performance potential. This meant gathering a number of different oval-port cylinder heads and putting them through their paces, both on the flow bench and the engine dyno.

First up, we needed a suitable test motor. We decided on a 0.060-over 454 equipped with a forged crank and forged rods from Procomp Electronics matched to a set of forged pistons from Probe Racing. The pistons feature an 18cc dome to help provide a streetable static compression over 10.0:1 with the 110cc chambers employed on a couple of the oval-port heads.

Many of these heads offered combustion chamber volumes below the 120cc range used on most rectangular-port heads. The smaller chamber (relative to factory rec-port heads) improved power by increasing the static compression--always a plus. The test motor also featured a healthy hydraulic roller cam in the form of an XR300HR from Comp Cams. It a 0.560/0.580 lift split, a 248/254 duration split, and a 110-degree LSA. All testing was run with an Edelbrock Victor Jr. intake fed by a Holley 950 HP carb.

Before being run on the engine dyno, each of the heads had to be mocked up to determine not only the appropriate pushrod length, but also the correct head bolt/stud combination. Our 2.25-inch dyno headers presented a problem for the heads equipped with stock port locations and required use of head bolts in the lower holes to provide adequate clearance. A few of the heads required different middle stud lengths, but ARP helped cure the situation. All we had to do was juggle the necessary bolts and studs to properly secure the heads. Thanks also goes out to Fel Pro for supplying the necessary head and intake gaskets for our test.

The test Rat was finished using a set of hydraulic roller lifters, timing chain, and a couple of different sets of pushrods from Comp Cams. Comp also supplied the aluminum roller rockers (1.7 ratio) for our head shootout.

The finishing touches included a Milodon oiling system, an electric water pump, and balancer from Procomp Electronics. Prior to their time on the test mill, each head was given the once over on the flow bench, then set up to measure port and chamber volumes.

The heads supplied for the test shared the oval-port configuration, but that doesn't mean they were all the same. We started with a factory oval-port head to establish a baseline, in this case the peanut-port variety. We hoped to include a traditional oval-port head as well, but it fell through at the last minute.

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.










Staff member
Re: rectangle or oval port, a non-issue based on mis-informa

this article (LINK POSTED BELOW) is a blatant example of one narrow view point being promoted to "prove" a point by IGNORING all the facts through carefully omissions in your options
yes the current 265cc oval port AFR heads produce 80 plus hp more than stock rectangle port heads, that were designed 50 plus years ago, IN THAT PARTICULAR APPLICATION, but what they are not bothering to point out is that there are similar improvements in the rectangle port head designed recently.
IF they had taken the effort to swap a set of the later design rectangle port heads on to the engine and swapped to a cam that that had the required lift and duration, and a matched intake manifold design, that would have allowed the far higher flow potential of the larger, port rectangle port heads to breath, efficiently at the upper rpm range, they are designed to operate at,the rectangle heads would once again show a marked advantage, this articles result is ms-leading, a bit like comparing a 20 year old Olympic athlete racing,, on a 2 mile sprint along a paved road, on roller skates and declaring the roller skates faster ,than the 65 year old fat guy with bronchitis they put in the race, on the bike, as a comparison, but forgetting to mention the bike tires were flat and the chain on the bike came off! during the race.... yet proposing the results are valid simply because there were TWO ADULT MALES RACING and IGNORING the fact that if a 20 year old Olympic athlete were placed on a fully functional racing bike,the result of racing would be far different.
Id also point out that the better, modern designs of rectangle port heads tend to work better and show the true potential on engines of at least 540 cubic inch displacement and with at least 11:1 compression, that are designed to spin over 4200 fpm in piston speed, and use cams with over .630 lift, only then do the better oval ports usually start to show a marked flow restriction in comparison to the newer rectangle port head designs

stock88.png ... ort-heads/




lets do a bit of math, and keep in mind that a correctly designed header and exhaust system, if matched to the correct cam timing can significantly increase the engines potential power/rpm band
port cross sectional area can be measured and the stall speed , accurately calculated, as can the required matching header configuration, and cam timing, yeah! it takes some reading but the infos readily available


just a bit of info on intake gaskets sizes to match port cross sectional areas


Calculating the valve curtain area
The following equation mathematically defines the available flow area for any given valve diameter and lift value:
Area = valve diameter x 0.98 x 3.14 x valve lift
Where 3.14 = pi (π)
For a typical 2.02-inch intake valve at .500-inch lift, it calculates as follows:
Area = 2.02 x 0.98 x 3.14 x 0.500 = 3.107 square inches
SO lets do a bit of math
a cylinder head with a 2.02' intake valve and a cam with a .450 lift at the valve with a 1.5:1 rocker will in theory produce a valve curtain area of 2.79 sq inches, swapping to a 1.6:1 ratio increases the lift to .480 lift 2.98 sq inches, increasing the available port flow potential at least in theory by about 6%, but keep in mind the port can only flow at full valve lift for the limited time the valve remains at full lift and if the narrowest section of the port cross sectional areas less that the valve curtain area that not the valve restricts flow


if you were to look at a performance big block chevy cylinder head your largest standard intake valve size is either a 2.19" or in a few cases the larger 2.3" valves
a bit of math shows that you won,t reach the max potential flow until valve lift reaches or slightly exceeds about .575-.600 inches of lift with a big block chevy
and a bit more math suggests a minimum of 4.2 square inches of port cross sectional area would be about ideal to match that potential flow,
if you built a 496 BBC stroker that 4.2 SQ inch port would max out at about 6000 rpm and would be best matched with a single plane intake and a cam with a tight 105-106 LSA



viewtopic.php?f=52&t=10705&p=46582&hilit=calculate+port+cross#p46582 ... cc-bbc.php

viewtopic.php?f=52&t=148&p=34936&hilit=calculate+port+cross#p34936 ... cc-bbc.php

Big-Block Heads Shootout - The Big O Vs. The Big R
Oval ports and rectangular port heads
Richard Holdener Jul 18, 2012 1 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.

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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
0.050 32 27
0.100 77 56
0.200 144 112
0.300 206 142
0.400 245 166
0.500 289 188
0.600 320 192
0.700 334 197
0.800 335 201

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
.050 34 34
.100 69 69
.200 146 109
.300 204 155
.400 264 192
.500 309 223
.600 340 246
.700 323 262
.800 330 273

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
.050 35 31
.100 70 67
.200 152 132
.300 234 175
.400 294 206
.500 336 231
.600 364 251
.700 389 267
.800 403 279

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
.050 35 30
.100 72 61
.200 148 125
.300 217 168
.400 275 198
.500 325 227
.600 360 246
.700 376 261
.800 384 273

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
.050 33 31
.100 66 69
.200 147 120
.300 211 173
.400 273 221
.500 333 256
.600 380 277
.700 409 286
.800 403 296

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
.050 34 29
.100 69 61
.200 148 125
.300 228 181
.400 294 219
.500 336 249
.600 376 271
.700 398 281
.800 399 289

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
.050 33 29
.100 73 61
.200 148 132
.300 224 185
.400 283 226
.500 334 252
.600 364 270
.700 385 278
.800 381 285

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
.050 34 32
.100 74 62
.200 153 126
.300 233 198
.400 296 237
.500 345 263
.600 377 277
.700 371 288
.800 365 296

21 The combustion chamber of each cylinder head tested was measured.
Last edited by a moderator:


Staff member
Re: rectangle or oval port, a non-issue based on mis-informa



rectangle port heads generally work best on 500 or larger displacement engines
with at least 10:1 compression and cams with at least 245 duration at .050 lift and valve lifts over .600 to take advantage of the potential port flow rates








While the heads you select are critical to making power in the intended rpm range , your HEADER DESIGN, exhaust back pressure, rocker ratio(s), cam lobe separation angles,valve shape and seat angles, valve diam. engine compression ratio, port and runner cross sectional area,runner length, the drive trains gearing , tire diam. all will effect the way the engine breaths and where in the rpm band powers most efficiently made, or restricted, and each can be used to further extend or restrict that power band.
swapping cams can easily result in a wild mis-match that costs you or potentially if correctly matched makes you 60 plus hp, intakes can be a plus or minus 30 hp choice, headers easily make or cost you 30 plus hp.



Last edited by a moderator: