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).

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).

When the smoke finally cleared from the dyno cell the results of the new heads were impressive to say the least. Even on this 400ci pump gas build, the engine picked up an average of 2 lb-ft in spite of the larger runner, a gain in peak power of 11 hp, and a whopping 26 hp at 7,500 rpm, which is close to the ideal shift point in both combinations. In fact, the 235 combo would likely need around 7,700 rpm for the best results. In short, the swap to the 235s showed no loss of bottom end whatsoever; increased the peak power noticably, moving it 600 rpms higher; and simply hung on to those gains to produce an extremly fat power curve; boosting the average high rpm horsepower numbers signifiantly. And true to their words, the 227 valvetrain transferred over with no issues whatsoever.

Our testing isn't complete by any means and the next time we present the 235s, we'll have our own combination together, showcasing what an all-out effort can produce-we have no doubt that we'll be tickling well over 725 horsepower. Until then, follow along as we unveil AFR's newest heavy hitter!

Quick Notes
What Is It
235cc small-block cylinder heads
What We Did
Check the gains over a set of AFR 227s
Price (APPROX)
$2,225 for the pair, $219 upcharge for titanium retainers

DYNO DETAILS
AFR 227
ADVANCE 37 degrees
JETS 98/98
MAX TORQUE 530 lb-ft @ 5,200 rpm
MAX POWER 610 hp @ 6,600 rpm
AVERAGE TORQUE 492 lb-ft
AVERAGE POWER 517 hp
POWER 1.53 hp/ci
AFR 235
ADVANCE 34 degrees
JETS 96/98
MAX TORQUE 529 lb-ft @ 5,300 rpm
MAX POWER 621 hp @ 7,100 rpm
AVERAGE TORQUE 494 lb-ft
AVERAGE POWER 517 hp
POWER 1.55 hp/ci

BUMPSTICK
MANUFACTURER Isky Racing Cams
TYPE Solid-roller
DURATION AT 0.020 302/306 degrees, intake/exhaust
DURATION AT 0.050 268/272 degrees, intake/exhaust
VALVE LIFT 0.705/0.705-inch intake/exhaust (1.65:1 rockers)
LASH 0.028/0.028 inch, intake/exhaust
NET LIFT 0.677 inch
LOBE SEPARATION 106, installed at 105 ICL

FLOW SPECS
227CC COMPETITION
LIFT INTAKE CFM EXHAUST CFM
0.200 153 120
0.300 214 167
0.400 265 214
0.500 297 230
0.550 308 234
0.600 314 238
0.650 318 241
0.700 321 243
*17/8-inch pipe on a 4.125-inch bore

235CC COMPETITION
LIFT INTAKE CFM EXHAUST CFM
0.200 159 120
0.300 221 175
0.400 270 214
0.500 305 235
0.550 316 242
0.600 324 247
0.650 330 251
0.700 334 254
0.750 337 255
0.800 340 256
*17/8-inch pipe on a 4.125-inch bore

SOURCE
T&D Machine Products
Carson City
NV
775-884-2292
www.tdmach.com
Dart Machinery
353 Oliver Street
Troy
MI  48084
248-362-1188
http://www.dartheads.com
Fel-Pro/Federal Mogul
Detroit
MI
800-560-1400
www.federalmogul.com
Holley Performance Products/Brands
1801 Russellville Rd.
Bowling Green
KY  42101
270-781-9741
www.holley.com
Air Flow Research
28611 W. Industry Drive
Valencia
CA  91355
661-257-8124
www.airflowresearch.com
  • «
  • |
  • 1
  • |
  • 2
  • |
  • View Full Article