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1966-1977 Ford Bronco Engine - Stroking A Bronco
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While the stroker is pretty much a home run as an upgrade during a performance 302 buildup, particularly when weighed against the cost of reconditioning the original parts, other areas of the engine can also use some improvement. The stock heads are generally lacking when performance is the goal, and with an increase in displacement, this shortcoming will become even more acute. A hot 302 is definitely struggling for air with factory iron heads, so it only stands to reason that a 347, with 15 percent more displacement to feed, will be suffocating. Here it isn't too difficult to eclipse the OEM heads, which flow in the neighborhood of 155-160 cfm on the intake and about 110 cfm on the exhaust. With the variety of serious race hardware available, the temptation here is to go wild, but remember, we're not building a drag-race engine.  Assembly began with the crank...  Assembly began with the crank and cam, and then the piston/rod assemblies were coaxed into the bores using a tapered ring compressor. The engine was assembled with quality engine oil on the bearings, rings, cylinder bores, and piston skirts.  Keeping with the bulletproof...  Keeping with the bulletproof theme, the bottom end was assembled with high-quality fasteners. The Scat rods come with ARP bolts already installed, but we did add beef by going with a set of Milodon main studs to solidly clamp in the crank. Torque the fasteners to specs using moly lube on the bolt threads and under the heads of the fasteners.  Component strength won't mean...  Component strength won't mean much if lubrication isn't up to the task. This engine was built with a Milodon high-volume oil pump and pick-up, along with a Milodon windage tray to ensure oil delivery. The windage tray separates the oil in the sump from the rotating crankshaft, something your engine will appreciate as the oil tries to splash around the crankcase while bashing around off road. Milodon's 81157 main stud kit is required to mount the tray. Within those constraints, we were looking at heads with a moderate port size, and strong flow within the lift range of the cam. Huge cfm numbers mean nothing if they happen well past the highest valve lift the cam will deliver. We selected Holley's SysteMAX No. 300-575 heads, which have a moderate intake port volume of 165 cc and flow 228 cfm at 0.500-inch lift-just about at the upper reaches of the cam. The heads represent a flow improvement of 43 percent over the stock pieces, more than enough to satisfy our goals. For cost, ease of field diagnostics, and simplicity, we wanted to retain a carbureted induction. Here the first choice revolves around the manifold. There are manifolds of every imaginable configuration for 302 Ford-based engines, but for this type of application a single four-barrel is the natural choice. The major manifold decision is between a single or dual plane. In the rpm range of this engine, dyno testing consistently proves the dual plane to be the right configuration, with the long runners and 180-degree firing separation really being an advantage through the bottom and mid range. A Weiand Stealth manifold is a nice piece to do the job.  Milodon's No. 30501 deep sump...  Milodon's No. 30501 deep sump pan adds capacity, and also adds distance between the spinning crank and the oil, which helps reduce windage losses and oil aeration. This pan is designed for the early Bronco application, though Milodon catalogs pans for most popular rigs.  One of the key decisions in...  One of the key decisions in any engine build is the camshaft selection. We decided to go with a hydraulic roller, the No. 35-424-8 from Competition Cams. A hydraulic roller offers reliability and low maintenance, and a performance increase over a comparable flat-tappet hydraulic. The cam specs out with 224/230 duration at 0.050-inch tappet rise, and 0.513/0.513-inch lift, enough for some bite up top, while preserving driveability and torque.  The cam was installed with...  The cam was installed with a Milodon No. 15008 double-roller timing chain. The Comp cam is ground on a 110-degree lobe separation angle, and was installed with 4 degrees of advance, at a 106 degrees installed centerline as recommended by Comp. The advance is ground into the cam when it is manufactured, though the Milodon timing set can be advanced or retarded if correction is required.  Holley SysteMAX No. 300-575...  Holley SysteMAX No. 300-575 aluminum heads will help take weight off the front end of the Bronco, and add tremendously to the performance compared to the wheezy iron stockers. The SysteMAX heads flow 228 cfm at 0.500-inch, which is close to the maximum lift we will see with our hydraulic roller cam. The Holley heads feature 63cc combustion chambers, and the large 2.02/1.60-inch valves are set at a 17-degree angle. The moderate 165cc intake port volume helps to preserve torque in our application. These heads come fully assembled and ready to run. Speed-O-Motive bolted them on with FelPro gaskets, using a Milodon No. 80155 head stud kit.  Comp Cams supplied the complete...  Comp Cams supplied the complete valvetrain, including the 5/16-inch hardened pushrods and the 1.6:1 ratio Pro-Magnum roller rockers. The rockers mount on 3/8-inch studs and are adjusted to 1/2-turn past zero preload with the cam on the base circle of the lobe being adjusted. Polylocks make the adjustment easy and lock the rockers securely.
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