Make note of it, bigger is better isn't a mantra for the weak-hearted and such is the case when it comes to cylinder head technology. For years, Airflow Research (AFR) has been synonymous with big-steam powerplants with their line of conventional 23 degree heads. And these days, AFR is still a very progressive company, making serious strides to stay ahead of the competition.
Until recently, the shining star for AFR's small-block lineup has been the 227cc piece. These bad boys flow big numbers and are available in your choice of Race Ready or Competition versions with fully CNC'd ports. The Race Ready version has been flow tested, revealing 309/233 cfm on the intake/exhaust ports at 0.650 lift while the Competition series flow 321/243 cfm on the intake/exhaust ports at 0.700-inch lift.
As impressive as the 227s are, AFR has just released their latest 235cc small-block offering, which is even more impressive and has the potential to eclipse the 725-horsepower barrier on the motor alone. If you're wondering how, just look at the flow numbers they're able to extrapolate from them (see Flow Specs sidebar). We're talking 18 degree performance out of a standard 23 degree head!
If you're already contemplating a set for yourself, there are a couple of things you need to know. Foremost, if you have anything less than 400 ci, then these aren't for you. This may be bad news for some, but something that can easily be rectified if you plan ahead. The good news is that you aren't limited to a shaft-mount rocker system since the 235s will also accept conventional roller rockers. On the other hand, if you already own a set of 227s then you'll appreciate the fact that this upgrade features a similar geometry, enabling you to transfer over your current rocker arms, be it conventional or a shaft-mount system, including stud girdles (note AFR recommends 0.050 offset stud mount rockers although in a pinch standard rockers could be utilized).
The original AFR 227 configuration...
The original AFR 227 configuration generated 610 horsepower at 6,600 rpm and 530 lb-ft at 5,200 rpm. For the follow-up 235cc test session, we left the combination intact, utilizing the same camshaft, manifold, and rocker ratio for a true apples-to-apples comparison.
Out of the box, you have a choice between 70cc and 80cc chambers. If you're looking for something in between, know that AFR can accommodate your needs with flat milling options. To do the math, expect 0.008 inches per cc for angle milling and 0.006 inches per cc for flat milling. When it comes to valvesprings, the 235s are outfitted with a dual 1.550-inch diameter spring with 225 lb/in on the seat and rated to maximum 0.710-inch lift. Again, if you need something more aggressive, AFR has a spring good for 0.800 lift that's 260 lb/in on the seat (AFR PN 8001).
To see how the 235cc Eliminators performed, we were lucky enough to find a local bracket racer who had recently procured a set. Using a Dart Little M block with forged internals, his mill wasn't shy or fresh by any means with well over 400 quarter-mile passes. Even so, the leakdown test revealed a happy short-block with 5 to 7 percent. To be fair, as potent as his 11.5:1-compression, 400ci small-block was, it still wasn't the ideal combination to showcase the maximum performance of these heads per Tony Mamo, head of AFR's R&D department. The cam was a bit light on lift to really take the most advantage of the big airflow upstairs, and adding a bit more compression with a larger intake and a 4500-series carb would have helped immensely because its the upper portion of the powerband that will shine with these deep breathing heads. Nevertheless, the timing was right as Tony was just putting the finishing touches on the new 235 program; we all felt this was the ideal situation to see the type of gains to be had from simply swapping over to the 235s from the 227s-even on a milder combination (with the obvious potential to show even larger gains on a more aggressive application).
If you didn't already know...
If you didn't already know this, AFR now offers trick-looking valve covers for both small- and big-block applications. These are priced at $169 while the big-block variants can be had for $237.
Wasting little time, Mamo...
Wasting little time, Mamo and Brulé of Westech Performance swapped over to the 235cc castings and sealed the heads with a pair of Fel-Pro 1014 head gaskets that feature a 4.200-inch bore with a 0.039-inch thickness. Prior to installing the manifold, a fresh bead of silicone was laid on opposite ends of the lifter valley and a fresh set of Fel-Pro 1266 intake gaskets were laid into place. These are designed specifically for 262-400ci small-blocks and feature a 1.34x2.21-inch port size with a 0.120-inch thickness.
1. Spent gasses expel via...
1. Spent gasses expel via Hedman 1 3/4-inch long-tube Hustler Hedders.
2. Carburetor of choice is a Holley HP series 950.
3. 400ci Dart Little M block, 4.125 x 3.750 bore/stroke.
4. Ported Edelbrock Super Victor manifold.
5. 1.65:1 ratio T&D shaft-mounts actuate the valves.
6. AFR's 235cc heads feature a 2.125/1.600-inch intake/exhaust valves.
7. Keeping the rotating assembly in check is an 8-inch Fluidampr.