AFR Small-Block Heads - Calculatus Eliminatus

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

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.




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