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AFR Small-Block Heads - Calculatus Eliminatus

Testing AFR's New Eliminator Small-Block Cylinder Heads.

Dec 18, 2006
Sucp_0701_02_z Afr_small_block_heads Tony 2/16

This is how AFR's Tony Mamo spends his rainy days, locked away with a grinder looking for hidden horsepower.

Paraphrasing Dr. Seuss's magnificent Cat-in-the-Hat, "Calculatus Eliminatus is the best friend that you've got; the way to find the missing horsepower is to find out where it's not!"

As we all know, the process was quite effective in locating one missing moss-covered, three-handled, family whatever it was, but the same principle holds true when you spend that rainy day searching not for family feline brick-a-brack, but for absentee airflow. Just ask AFR's own Tony Mamo, the cat inside the hat so to speak, as his monumental task was to take an already impressive AFR small-block cylinder head and make it even better.

Given their impressive performance, it's hard to believe that the original AFR line of small-block heads dates way back to 1991. Available in port volumes ranging from 180cc to 210cc for the street heads and all the way up to the 227cc for the race versions (AFR also makes a 215cc raised port race head), testing has proven the complete AFR lineup to offer impressive airflow (especially given the port volumes).

Better yet, AFR has made sure all of the airflow offered by its small-block heads converted directly to horsepower. Big flow numbers are one thing, but big flow numbers that produce equally big power numbers are what distinguish a good head from a great one.

Sucp_0701_03_z Afr_small_block_heads Heads 3/16

Since it was time to retool, AFR took this opportunity to refurbish the existing line of small-block Chevy heads. As is often the case, the simple refurbish turned into a whole new head. The new Eliminator series offers a weight savings of 4 pounds (compared to the original AFRs), improved oil drain back and a sizable increase in airflow.

Despite the impressive power production offered by the existing line, AFR decided it was high time to up the power ante. Not surprisingly, revamping the lineup coincided with retooling the product line. Rather than simply retool to streamline the production process, the gang at AFR decided to use the opportunity to upgrade its existing SBC product line. This is obviously good news for enthusiasts, as we have managed to produce exceptional power numbers with the previous AFR small-block heads and having an upgraded version will help take any build (mild or wild) to the next performance level.

Revamping the product line sounds easy while standing around water cooler, but actually putting into action takes a great deal of hard work. That is where Mamo comes in, as he was the man responsible for creating the new Eliminator line of AFR SBC heads. This was no easy task given the already impressive performance, but with porting tools, knowledge and experience, Tony set to work on redesigning the ports, chambers and even valve train to modernize the 23-degree heads.

Having had such good success with its big-block Chevy and new LS-series heads (for the LS1, LS2 and LS6), they decided the original small-block deserved equal attention.

In fact, many of the improvement ideas came from the LS-head program, namely the valvetrain upgrades. Tony went looking for two things when reviewing the existing valvetrain package, namely improving flow and reducing mass. The additional flow is somewhat self explanatory, but a reduction in valvetrain mass will improve the rpm potential of the motor, thus allowing more power at higher engine speeds. There is nothing more frustrating than having valve float ruin a perfectly good power curve. Things are going well, the power is climbing and all of a sudden the engine note roughens and the power heads due south. While the typical cure is to increase the valve spring rate, another approach is to decrease the weight of the components that make up the valvetrain (i.e. valves, springs, retainers and keepers).

Sucp_0701_04_z Afr_small_block_heads Valve_springs 4/16

The new Eliminator heads were also treated to a valvetrain upgrade, including the use of smaller diameter (lighter) valve springs and retainers. Shown (from right to left) are the spring package used on the original AFRs, the standard and optional spring packages for the new Eliminator heads. The titanium retainers used on the optional springs offered a weight savings of 9 grams.

Valve control is a function of engine speed, spring rate and valvetrain mass. Valve control is proportional to spring rate and inversely proportional to engine speed and valvetrain mass, so a decrease in either will improve valve control. The downside to increased spring rate is an increase in friction losses and a possible reduction in power, thus maximizing control with the minimal spring rate is actually ideal. This is where a lightweight valvetrain comes into play, as not only does the improved valve control allow higher engine speeds, but it is possible to actually improve the power output by not resorting to excessive spring rates.

Tony went after every component on the valvetrain, including the valves, springs, and retainers. He even saved 3.5 grams (per pair) by upgrading the keepers. More than simply a weight savings exercise, Tony used the opportunity to actually improve keeper strength by replacing the standard square-cut keepers with bead-lock versions. The bead-lock keepers eliminate the point loading of the square cut keepers by spreading the retaining load over a greater surface area.Thus the new design is not only lighter, but also stronger.

The keepers were just the start, as Tony turned his attention to the spring package and valves. The spring package was upgraded with the new double springs from the LS1 heads. The smaller-diameter springs combined with a new retainer to drop the total package weight by a whopping 33 grams. While 33 grams may not sound like much on a 3500-pound car, the fact that this package must cycle as much as 100 times per second (or more) means an exaggerated relative mass.

Weight conscious individuals can further reduce valvetrain mass by 9 grams with the use of titanium retainers (used with the optional 8019 spring upgrade). The standard 8017 springs (135-punds of seat pressure and 320 pounds open) will accept up to .600 lift, but when nearing that maximum lift value, AFR recommends stepping up to the 8019 springs (155 pounds seat and 412 open), as the spring upgrade will also allow cams with up to .650 lift. Naturally AFR has a spring package for solid roller cams available for the new Eliminator heads.

Sucp_0701_09_z Afr_small_block_heads Intake_port 8/16

Naturally the intake port shape was altered to maximize efficiency.

In addition to the springs, retainers and keeper upgrades, the new AFR Eliminator heads also received new intake and exhaust valves. The key to the weight savings in the new valves was the use of 8mm steams (again, a la LS1) in place of the conventional 11/32ths valve stems. The valve stem upgraded netted 15 grams on the intake, while the exhaust valve weight was actually as wash (both checked in at 99 grams). The reason the new exhaust valve did not net any weight savings was that in addition to the 8mm stems, the valve upgraded also included a tulip head design with an undercut stem. The thicker valve head means improved valve life, but more importantly it means a significant improvement in flow. Remember, reduced valvetrain mass was only one of the goals, and the valve upgrade applied to the new Eliminator heads also improved flow.

The success of the new valvetrain upgrades can be seen in the supplied power curve, as the original AFR heads were run with a 145 lbs seat/315 lbs open spring package against the new Eliminator heads 135 lbs seat/320 lbs open. Despite slightly less spring pressure, the motor was able to run several hundred rpm higher before experiencing valve float.

The valvetrain upgrades would have been a worthwhile upgrade all by themselves, but Tony and the gang were just getting started. Naturally the trend to improving flow is to make the port bigger, but Tony is a huge proponent of maximizing airflow while minimizing port volumes. Port volume is a critical element is driveability (part-throttle response), not to mention average power production (throughout the rev range). Given the AFR lineup was available in a variety of different port volumes, Tony set out to improve the efficiency of the existing ports without resorting to increased volume.

Sucp_0701_10_z Afr_small_block_heads Valve_stem 9/16

The new Eliminator heads also received valve upgrades. The new valve not only offered undercut stems, but (more importantly) 8mm stems. Dropping down from the conventional 11/32nds stems to the smaller 8mm stems (stem size shared with the LS1 heads) on the intake valves knocked off another 15 grams.

While computer simulation and modeling are currently all the rage, the new Eliminator head ports and chambers were designed the old fashion way-with porting tools and a flow bench. Using his experience and knowledge base, Tony worked his porting magic on the Eliminator heads to the tune of an extra 23 cfm, upping the AFR 195 street heads from 262 cfm (at .600 lift) to 285 cfm. The higher-performance Competition package 195 heads were also improved, from 282 cfm to 300 cfm. Note that the new Eliminator street heads now outflowed the previous Competition version.

In true Calculatus Eliminatus fashion, the flow improvements came not from one area, but from eliminating tiny little restrictions everywhere, including the bowl, port and chamber. Even more impressive is the fact that the new Eliminator heads offer flow improvements at every lift value, not just at the peak.

While our testing here was on the most popular 195 cc heads, the Eliminator program was applied to the entire line up of AFR heads, from the street-oriented 180cc heads all the way up to the massive 220cc versions. Though work is still being completed on the larger heads, look for flow numbers approaching 320 cfm numbers from the 220cc heads. While the 210cc and 220cc heads will work well on high-horsepower and large-displacement stroker applications, enthusiasts with stock-displacement 350 c.i. performance street motors might do well to take a look at the new 180cc Eliminator heads.

Sucp_0701_11_z Afr_small_block_heads Combustion_chamber 10/16

AFR's Tony Mamo left no stone unturned in his search for additional airflow. The combustion chamber received a great deal of work, as it is a critical element in the quest for power. As with the previous AFR heads, the Eliminator heads will be made available in 64 and 76cc chambers.

Offering 275 cfm at .600 lift, the 180cc Eliminator heads now outflow the original 195cc heads-making for an impressive package. Remember, the best head offers maximum flow with minimal port volume, and the 180cc Eliminator head combines just that. Given the flow rate, we know the 180cc Eliminator head will easily support over 500 hp, yet offer impressive part-throttle response and a broad torque curve. If that doesn't sound like the ideal street motor, maybe we're in the wrong business.

In most instances, yours truly is at the helm when it comes to dyno time, but for this test we relied on the engine experts at American Speed. With a number of impressive small-block combinations to choose from, they had no shortage of test motors for the new AFR Eliminator heads. Given the impressive flow numbers offered by the new Eliminator profile, American Speed chose a 383 stroker to properly illustrate their power potential. The 383 test motor was configured with 9.6:1 compression, a hydraulic roller profile from Comp Cams that offered a 236/242 duration split. The 383 stroker also featured an Edelbrock Performer RPM Air Gap intake, 750 cfm Holley carb and Hooker long-tube headers. MSD supplied the ignition, which American Speed used to dial in 37 degrees of total timing (38 degrees with the original AFR 195 heads).

Running 15W-40 Lucas oil and 93-octane pump gas, the 383 produced 504 hp and 521 lbs-ft of torque with the original AFR 195 (street) heads. After swapping on the new 195cc Eliminator (street) heads, the peak power numbers jumped to 540 hp and 541 lbs-ft of torque. Out near redline, the valvetrain improvements allowed an additional 400 rpm (note on the graph how the original power curve fell off dramatically after 6000 rpm). Judging by these results, we'd say Calculatus Eliminatus was a smashing success.


Air Flow Research
Valencia, CA 91355



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