Text and Photos by Isaac Martin - Originally from Mustang magazine January 1989 edition.
If anyone tries to tell you that a 302 with stock cast-iron heads can’t make power, don’t believe him. How does 331 horses at 5,500 rpm and 353 ft. lbs. of torque at 4,000 rpm sound? If that’s not enough, and you want to spend extra, bolt on a set of the aluminum Ford Motorsport heads. Those numbers will be bumped up to 410 horses at 5,500 rpm and 404 ft. lbs. of torque at 5,000 rpm. Impressed? We definitely are.
All this power is available from Performance Automotive Wholesale’s (PAW) 302 Blower motor. It doesn’t involve any Ford performance buzzwords like Boss or Cleveland, but rather it uses Windsor components. Plus there’s nothing unusual about its assembly and it requires no extra machining or special tools. Try that with a turbocharger. Besides inspecting the parts and checking clearances at each step of assembly, it was strictly bolt together. This engine is destined to be installed in the B&M / Motorsport Mustang (an ’83 GT magazine project car - Fletch), but it’ll fit in ‘65-’73 ponies with ease (although a hood scoop is needed for carb clearance). So, if you would like a small-block with a healthy dose of power, read along and we’ll show how it’s done.
The key to the power output is B&M’s coordinated supercharger and Street Supercharger cam. Supercharging offers several attractive benefits. One, obviously, is more power. Since it is mechanically driven, the boost is always immediate, but more important, it’s street usable power that’s developed between idle and 5,000 rpm. The supercharger case displaces 144 cubic inches, making it well matched to the engine’s displacement. Like most other automotive components, bigger is not necessarily better. Since we’re dealing with a street engine, you don’t need a big blower volume or more boost. In fact, B&M doesn’t recommend running their blower beyond 7 pounds boost for street application unless the engine is specifically built for a higher boost.
A cam matched to the supercharger setup is included. It’s B&M’s Street Charger Cam (part no. 90770) which has 218 degrees intake duration (at 0.050-inch lift) and 228 degrees on exhaust. Valve lift is 0.471 inch. While these are modest specifications, the cam is specifically designed to make power in a supercharged application. Hydraulic lifters make the setup maintenance free.
Carburetion is a Holley four-barrel (Part number 0-3310) with a 750 cfm rating. Once again, this matches the engine’s induction needs.
As usual, this combination may not be legal for use on the highways where you live, so be sure to check with local authorities before dropping one into your car.
While the photos detail individual steps, we’ll concentrate on some of the critical engine details we learned during the building.
PAW supplies a complete engine kit that includes all the major parts. The other component needed for finishing is B&M’s supercharger adapter kit (part no. 90684 with A/C, or no. 90869 without). It’s designed to fit late-model 302s factory-equipped with a single serpentine belt accessory drive system. This kit won’t work on dual serpentine setups, such as those found on some ’85 Mustangs. In addition, the instructions have a list of parts readily available from Ford dealers in order complete the front engine dress.
It all starts with a two-bolt main, 302 casting; plain, but more than adequate for out goals. PAW fully machines the block, including a 0.030-overbore that our engine received. Crank is cast iron with rod and main journals turned 0.010 under.
Pistons are TRW forged units (part no. L2305F). These are flat tops, with valve reliefs. Since this a blower motor, there’s no need for high compression. They’re then fitted to 302 rods, with press-fit wristpins.
Ask most Ford enthusiasts, and they’ll say that a Cleveland-style head is the way to go for power. But that’s unnecessary, thanks to the supercharger maximizing Windsor head-flow capability by forcing more air/fuel mixture into the cylinder (that was also before the market was flooded with great aftermarket cylinder heads for small blocks that have made Cleveland-style heads forgotten - Fletch). Cylinder heads (casting no. prefix D8OE) are open chamber heads and chamber volume measures 63cc. The valves were enlarged to 1.94-inch intake and 1.50-inch exhaust. A three-angle valve job was completed, but otherwise the ports are left as cast (note - these heads have very little performance potential above stock heads without porting - Fletch). Compression is 8:1. Keeping with the high-performance nature, screw in rocker studs and guide plates are also fitted. The heads come completely assembled, including the valves.
Optional heads are available for more power and the selection depends on how much you would like to spend. PAW offers either ported cast-iron heads or Ford Motorsport aluminum heads (part number M-6049-J302). While ported cast-iron heads cost less, they yield only about 60-70 percent of the increased power gain compared to aluminum heads. On the other hand, the aluminum head is excellent in terms of breathing and power potential. But they are expensive, so you have to decide what your budget limits are.
Finally, the PAW kit is finished off with optional high-quality hardware. For example, some of the Milodon parts include the oil pump drive (part no. 22500), the oil pickup tube (part no. 18360), and the oil pan (part no. 31125). Instead of head bolts, a Milodon head stud kit (part no. 80155) was used.
A B&M steel harmonic balancer, designed for externally balanced engines, is included in the kit. B&M stresses the importance of following the correct installation procedure. Jim Davis of B&M explained the balancer is designed with an interference fit to insure against unwanted looseness or wobble. To sum up B&M’s installation instructions, you need to check the crank for burrs or rust, and correct as needed.
Now immerse the balancer in boiling water for 15 minutes, which will expand the balancer’s hub. Smear the crank snout with clean engine oil. Remove the balancer from the water and apply oil to the inside of the bore.
Wearing heat-proof gloves, place the balancer on the crank snout and index it to the key way. Quickly, utilizing a piece of aluminum to protect the face, drive the balancer onto the crank snout. Install the retaining bolt and washer and torque to 90-ft. lbs. If you don not follow these details and end up pounding the balancer into position, the crank snout may become bent. If you encounter any difficulty fitting the balancer, contact B&M.
After the one-day engine assembly, it was shipped to Dick Landy Industries for dyno testing. Once the results were determined, the computer plotted them on a graph including the blower pressures.
Blower Test Results Chart:
The horsepower and torque figure spoke for themselves. But Davis pointed out some interesting details related to the engine power charts, which are apparent, thanks to information learned during B&M’s extensive supercharger dyno development work. Look at the blower boost at the bottom of the chart. Check the chart for cast-iron heads at 5000 rpm and note how the boost climbs. As Davis explains, the blower isn’t necessarily producing more usable boost for more power. Rather, the increased boost is now backing up into the intake manifold.
Now, look at the numbers for the aluminum heads. He continues by noting that it levels off at 5000 rpm and stays there until 5500. Here, the aluminum heads breathe better, so blower boost doesn’t back up into the manifold until higher in the rpm band. This illustrates that more boost showing on the boost gauge doesn’t necessarily mean it’s reaching the cylinder.
Davis commented that the blower drive ratios differed slightly between the two engines. The cast-iron combination had a lower ratio (1.97:1), due to its standard crank pulley (6-inch diameter), which utilized a six-rib drive belt. The higher (1.99:1) ratio used on the aluminum head test occurred due to larger-diameter crank pulley (7 1/8-inch diameter) which in turn allows the use of a larger-diameter blower pulley. A 10-rib belt fits this configuration and provides for more total belt contact for less slippage. Since the top pulley is selected from the eight standard upper drive pulleys B&M offers, it’s difficult to get exactly the same ratio with larger crank pulley (7 1/8-inch diameter) as with the standard pulley.
Well enough theory. Let’s get this engine together, because the sooner you read how, the sooner you can put one in your Mustang.