Marc Christ
Brand Manager, Modified Mustangs & Fords
August 19, 2012

The small-block Ford cylinder head market is flooded with options ranging from 160cc intake runners all the way to huge 240cc high-port race heads and everything in between. But bigger is not always better, especially for a street-driven Stang. The size of the intake runner dictates air velocity, and the smaller displacement an engine has, the less velocity the incoming air will have when using larger intake runner cylinder heads, especially at low rpm.

So what size cylinder heads should you choose? Well, the ideal scenario would be to have the increased runner velocity of a smaller intake runner while still being able to flow a large volume of air like larger intake runners. But you can't have your cake and eat it too, right? Maybe you can.

Airflow Research, known simply as AFR, recently revamped its entire SBF cylinder head line. The new versions, which have taken the place of the old line, are simply called: Renegade. Not to take anything away from the old AFR heads--these are simply in a different league than the elder versions. Utilizing the same part numbers and even price of their predecessors, the new versions are anything but re-massaged touch-ups of the old heads.

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"The new SBF program is a clean-sheet deal. Improvements were made everywhere" says Tony Mamo of AFR, who is the head of R&D and designed these new pieces. "And we've been working on the new Renegade stuff for over a year and a half." This is where the cake-eating begins. Grab the ice cream. "Our focus was to improve the efficiency of the previous Outlaw version, which even today are still at the top of the performance food chain" Mamo told us. "Through an extensive effort, we managed to improve flow on the Renegade line on average about 15-20 cfm. That's a huge improvement in airflow, one that leaves our 165 Renegade flowing similar to the 185 Outlaw, the 185 Renegade flowing similar to the 205 Outlaw, and so on.

"An added benefit being the obvious increase in air speed through the better shape port/chamber configuration needed to accomplish this, which improves air charge inertia and cylinder packing. It also helps reduce the negative effects of reversion from overlap in performance camshafts. It's a win-win design philosophy and these new heads should really pack a punch for the end user," Mamo told us.

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But to be sure this just isn't some clever marketing ploy dreamed up deep in a conference room, we put a pair to the test. Our subject: a mostly-stock five-speed '90 LX hatch owned by James Bickam of Orlando, Florida. Bickam's super-clean Fox already had a handful of bolt-ons, including underdrive pulleys, shorty headers, a catted H-style mid-pipe, a Magnaflow after-cat, Cobra intake and matching 65mm throttle body, C&L elbow and 73mm MAF, and a high-flow air filter in the stock airbox (silencer removed). Other than that, it has subframe connectors, 3.55 gears, and some performance springs, shocks, and struts. Heck, it's still rockin' the clutch fan.

Since we were dealing with a stock short-block, we knew that we needed heads with smaller intake runners, but weren't sure exactly which ones would maximize the potential of our 302. So we called Mamo himself for some guidance. He told us that our stock engine in naturally aspirated form would best utilize the 165cc versions. He also suggested a camshaft profile, which we passed on to Comp Cams for a custom grind.

Mamo suggested a 0.556/0.556-inch lift camshaft with 224/224 degrees of duration at 0.050-inch lift and a 112-degree lobe separation. Comp Cams ground the cam (PN 35-000-8; $297.78), and also sent us a set of aluminum roller rocker arms (PN 19044-16; $309.38), lifters (PN 851-16; $217.63), and hardened pushrods (PN 7619-16; $116.42). We also ordered a complete gasket set from Fel-Pro and fasteners from ARP.

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Our non-emissions 165cc heads (PN 1399; $1,560) feature 1.90/1.60-inch valves, fully CNC-ported combustion chambers and ports, 3/8-inch ARP rocker studs, and 5/16-inch pushrod guide plates. We did opt for titanium spring retainers, a $100 option. AFR also milled our heads down, bumping up our compression ratio from stock (about 9.2:1) to 10.25:1. The combustion chambers are usually 58cc on these, but ours are now 50cc. Since these were an all-new design, we wanted to see how they flowed on a flow bench. So we headed to Auto Performance Engines (APE) in Auburndale, Florida. There, Kevin Willis put the new 165s to the test. On a 4.030-inch bore on a Flow Pro bench, they flowed an astonishing 269.4/212.5 cfm at 0.500-inch and 278.5/216.9 cfm (intake/exhaust) at 0.600-inch lift! The intake flows over 200 cfm from 0.300-inch lift and above.

Willis was very surprised, and compared these to a pair of the previous AFR 185s that he tested, which flowed slightly better down low, but were surpassed by the Renegade 165s above 0.400-inch lift. He even had to re-check everything to make sure he did it correctly. For the install, we headed to Lamotta Performance in Longwood, Florida. There, Billy Eldert has been slowly modding Bickam's LX since the late '90s. To establish a baseline, we strapped it to Lamotta's Dynojet chassis dyno. It put down 222 rwhp and 272 lb-ft of torque.

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Eldert installed the cam and a new timing chain from Comp Cams. He then mocked up one cylinder head and checked piston-to-valve clearance. Everything checked out, and he finished reinstalling the rest of the components and added five quarts of Comp Cams Muscle Car and Street Rod oil. He also set the timing back to 10 degrees BTDC, where it was when we started.

Back on the chassis dyno, without any additional tuning, Bickam's LX spun the rollers. It made 285 rwhp and 309 lb-ft of torque--a 63hp and 37-lb-ft increase. Eldert then installed an SCT Performance chip with a canned tune from SCT. After making another pull, we were rewarded with 302 rwhp and 325 lb-ft of torque. We picked up 80 rwhp and 53 lb-ft of torque with a heads and cam swap--and we didn't sacrifice any power or torque down low. You actually can have your cake and eat it too, after all.

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On the dyno, Bickam's LX made 302 rwhp and 325 lb-ft of torque--up 80 hp and 53 lb-ft of torque from a heads and camshaft swap!