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Ford Capri AFR Cylinder Head - King Capri
In this final installment, we try AFR's new 165 Competition cylinder heads on this '85 Capri.
To A 5-liter owner, getting a set of aluminum heads is like hitting the lottery. The factory chunks of cast iron don't flow diddly, and that's a big problem if you're trying to make horsepower. Thankfully, aluminum heads are plentiful and affordable. Unlike the modular powerplants, which have pretty good heads in stock form, the 302 engines from 1979-95 weren't big breathers, so one of the keys to unlocking power comes from swapping the heads.
Knowing this, 5.0 owners will normally go for a set of aftermarket heads, of which dozens are available. Aftermarket aluminum casts prove beneficial because they save weight and increase airflow to the engine. For around $1,200, anyone can increase performance of an otherwise stock 5.0, and with a few extra bolt-ons, the increase can be doubled. That's the point we're trying to prove in this article.
Often, owners subscribe to the "bigger-is-better" theory, but this just doesn't work when trying to select the most efficient set of heads for a mostly stock 302. It's far more important to select heads that have intake and exhaust ports (and valves) sized for your intake, cam, exhaust, and gearing, or the combination won't be efficient. In many applications, smaller ports create better airflow velocity in the low and mid-lift range. This helps fill the cylinders, which translates into great torque and excellent throttle response. Some will still want the big flow numbers up high, at 0.600-inch lift, but for most street/strip applications, you'll see better results when you focus on average power.
To that end, we decided to swap heads on the '85 Capri we've been fooling with. In the past two issues, we've taken the mildly modded 302 and added a Weiand Stealth intake and Demon 575-cfm carb, an S&B free-flowing air filter, and a Holley fuel pump. We also added a Lunati cam (PN 510A2LUN) with 0.525-inch lift and Comp's 1.6 Magnum rockers. For our effort, we were rewarded with gains of almost 50 rwhp, from 207 to 255. Now it's time to swing for the fences.
We originally selected Air Flow Research's popular 165cc heads for this article, but the folks at AFR turned us on to their latest 165 Competition Package heads with 1.90- and 1.60-inch valves. The Comp Package uses the standard 165 casts, albeit with a different porting profile.
"We run a different porting program with a different shape in order to flow more air," says Rick Sperling of AFR. "[The program] takes a few more hours to run, but it picks up 7-10 cfm across the board, from 0.200- to 0.600-inch lift on the intake and exhaust.
"The Comp heads are for the guy who can't use a 185cc head with the larger 2.02-inch valves because they would hit the pistons in a stock short-block. For the size, these heads offer excellent flow with small valves and ports, and we've seen them make 10-12 hp over our standard 165s."
Swapping heads on a 302 is not difficult, but there are things you should know. First and foremost, you'll need a set of gaskets. We used Fel-Pro 8548 head gaskets, as well as new head bolts from ARP in our 130,000-mile engine. While AFR offers the heads with pedestal rocker mounts, we ordered ours with stud mounts because of the the Magnum rockers we're using. The stud-mount heads come with pushrod guideplates, and this requires hardened pushrods, which we got from Manley (PN 25627-16). We also slipped in a new set of hydraulic roller lifters from Comp Cams because the stock lifters looked beat up
If we hit it right, the package would produce awesome power from idle to redline. While we didn't want to make any predictions, we were secretly hoping the 302 would eclipse the 300-rwhp mark.
With parts in hand, Glen Knell of Crazy Horse Racing worked with us on the 302 from morning to evening. In that time, we had the heads and most of the components bolted to the 302. At this time, we also realized the 302 was not equipped with stock '85 heads, but a set of E7TE heads that had the emission bumps removed from the exhaust ports. The following day, we buttoned up the engine, added the coolant, fired the engine, and checked for leaks. All seemed well, so we strapped the Mercury to the Dynojet to get the results.
Chris Winter of CHR jumped in, cracked off the engine, and got the fluids up to operating temperature. Then he slid the T5 through the gears and into Fourth, hit the green button, and matted the gas. There was a totally different sound emitting from the pipes as the 302 charged toward redline. The engine revved really hard, and we watched the tach needle fly past 6,000 on its way to 6,400, where Winter cut it off.
We cocked our necks to see the computer results, and in a moment the screen showed a graph revealing 306 hp and 318 lb-ft of torque. Two more pulls (with no changes) resulted in a best of 310 hp and 321 lb-ft of torque, thus proving the heads alone were worth 55 hp over the E7 castings. Had the iron heads been totally stock, we might have seen a gain of 60 hp or more.
Thinking there would be power in a larger carburetor, we tried a 650-cfm and a 750-cfm Speed Demon. Amazingly, the smaller 575 proved to be the champ on this engine. The 650 was down about 12 hp, while the 750 made 310 hp, but with less torque. We were shocked at the results, so we placed a call to Doug Schriefer, head of technical services at Demon Carburetion, for some answers.
Schriefer explained that Demon does not rate its carburetors using the standard cfm rating system, so we can't simply compare a Demon to another brand based solely on flow rating. "When it comes to carburetion, you have to give the engine what it wants," Schriefer says. The cfm rating doesn't always matter. Our ratings are based on an average airflow for the specific application; it's not a total airflow number."
Based on our results, we concluded that the 575 was flowing enough air to satisfy the needs of the 302-and that you simply can't say this engine or that engine will need a 650, a 750, or an 850, unless you have experience with a particular brand of carburetors.
Schriefer recommends that anyone in the market for a new carburetor contact the manufacturer before making a purchase. He says, in this case, "your buddy" may be your worst enemy because he knows what works on his car, and he's only guessing what your car will need. In contrast, Demon offers a dedicated tech line (706/864-8544) to help you select the most efficient carb for your specific applications and driving needs.
Needless to say, we're excited about the results of this project. We spent about three days working on the Capri and were rewarded with over 100 hp at the wheels, or about 120 at the flywheel. Best of all, power is there all the time, and we lost about 40 pounds from the nose of the car. This should translate into an e.t. drop of more than 1 second in the quarter-mile. It's equal to a basic nitrous kit or a blower kit, which has us thinking . . .
|AFR 165 Flow Comparison*|
|AFR 165 Comp Pkg||AFR 165|
|*Figures provided by the manufacturer|