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 . . .
When installing heads with...
When installing heads with pushrod guideplates, it is necessary to use hardened pushrods like these from Manley (PN 25627-16). These 4130 swedged end pushrods are 51/416 x 6.272 inches and feature 0.080-inch wall thickness.
Prior to installing the heads,...
Prior to installing the heads, the Capri was making 255 hp at the rear wheels.
Swapping heads is a straightforward...
Swapping heads is a straightforward procedure. Working with Glen Knell of Crazy Horse Racing, we got started by pulling out the distributor, the ignition wires, the fuel line, and the intake manifold.
Next, we removed the iron...
Next, we removed the iron cylinder heads. In addition to gaining flow, the aluminum heads will knock about 40 pounds off the nose of the Mercury.
Factory E5TE and E7TE cylinder...
Factory E5TE and E7TE cylinder heads sport small 1.78- and 1.46-inch valves. Combustion chambers are rated as being between 60.6 and 63.6 cc.
While the top end of the engine...
While the top end of the engine was removed, we thought it was a good time to replace the 130,000-mile roller lifters. To accomplish this, the metal retainer, commonly called the "spider" must be removed.
We pulled out the old lifters...
We pulled out the old lifters and installed a new set from Comp Cams.
It's virtually impossible...
It's virtually impossible to install the tie-bar improperly, as the topside reads "up."