Ford 302 Engine Build Up - Modern Motivation
Real 302 Power for the Street
From the January, 2007 issue of Popular Hot Rodding
By Richard Holdener
When it comes to carbureted small-block Fords, a few notable candidates quickly come to mind. The early 271-hp (high-performance) 289s are naturally high on this list. Their high-revving nature allowed them to creep very close to the then-magical number of 1 (gross) hp per cubic inch. When Carroll Shelby came along and turned his performance wizards loose on the little Ford motor, they managed to up the power number to an impressive 306 hp from the little 289. Stepping up in displacement to the slightly larger 302, there is but one high watermark-the big bad boss himself. Though rated by Ford at just 290 hp, the real output of the legendary Boss 302 was thought to be considerably higher by racers and other performance enthusiasts in the know. Equipped with the free-flowing Cleveland-style cylinder heads, the Boss 302 was the small-bock Mustang to own and continues to be sought after by true Blue Oval enthusiasts.
As great as those early performance motors were, they simply can't compete with what is available today. Remember, it has been more than 30 years since Ford introduced the Boss and even longer since the heyday of the Shelby GT350 Mustangs. Technology has marched on in the form of high-flow aluminum cylinder heads, powerful camshafts and even more efficient carburetors (to say nothing of fuel injection). Benefiting from this infusion of technology are Ford enthusiasts. What this means is that the average early Mustang owner no longer needs to long for the performance offered by a HiPo, Boss or Shelby. Instead, you can whip up a performance street 302 using a select few aftermarket parts that would literally run circles around the best small-block Ford ever offered. In fact, thanks to modern technology, you can build a daily driven street motor that will out-perform even the FIA race motors used in the legendary Cobra Daytonas! How's that for impressive?
The key to all of this usable performance is in what we refer to as the power producers, namely the camshaft, cylinder heads and induction system. The aftermarket has made great strides in the last 30 years, so it should come as no surprise that we are able to surpass the power levels of yesteryear. Where 1 hp per cubic inch was the holy grail of power output for the manufacturers, it is now commonplace, at least for any performance street motor. In fact, if you built a performance 302 that only made 302 peak hp, you should consider your project somewhat less than successful, unless your buildup was more of a rebuild using primarily stock components. That we can now build a 302 that exceeds the power output of the early performance (and even race) motors should not be surprising, but that it can be done so easily and with excellent street manners is all the more impressive. Not only can a 302 be built that exceeds 375 hp, but such a motor can also be built for use as a daily driver. Such a motor offers not only impressive peak power numbers, but also a broad power band (torque curve) and acceptable idle quality. After all, who wants a temperamental race motor while they are inching along in bumper-to-bumper traffic?
Building a successful performance street 302 requires a game plan. Before choosing the necessary components, you must first decide on the intended application. Will the motor be used primarily for street with an occasional trip to the strip, or will time slips rule the buildup? Your choices will be different depending on how you answered these questions, but we chose the milder route, with an emphasis on street. Though our emphasis was on drivability, we didn't want to undermine performance altogether. One criterion that always enters into the picture is cost. If cost is no object, it is much easier to achieve your goals. I don't know about the rest of you, but I have never had the opportunity to build a cost-is-no-object motor. Realizing that the majority of these motors are built by cost-is-definitely-an-object enthusiasts, we made every effort to keep costs down. The cost factor also eliminates any exotic parts that tend to reduce reliability right along with the size of your bank account. Trick, exotic hardware may impress the folks at the local drive-in (do they still have those anywhere?), but try getting a replacement at your local parts store. A true daily driver means something that can be repaired with a quick trip to the your neighborhood parts store.
In keeping with the driver theme, our buildup began life with a stock 5.0L 302 block. The stock (late 5.0L) 302 block had many desirably qualities, including being set up to accept a hydraulic roller cam and attending valvetrain. While early 5.0L blocks came equipped with forged pistons from the factory, we decided to upgrade the stock short-block with a set of rods and pistons from Coast High Performance. While the factory components are more than adequate for this power level, for rock-solid reliability we stepped up to forged aftermarket rods and pistons. We retained the cast crank, since we had no intention of running the motor much past 6,000 rpm (certainly not more than 6,500 rpm). Given the short stroke and strength of the internals, the 302 short-block should be able to run to 6,000 rpm almost indefinitely.
The Probe Racing forged pistons combine with our TFS Twisted Wedge heads to produce a street-friendly static compression ratio 9.2:1. The relatively low compression allows easy use of 91-octane premium unleaded for maximum performance but will likely tolerate all the way down to 87 octane (regular unleaded) for the daily commute. The near flat-top pistons help optimize flame travel (requiring less initial timing) while the aluminum heads help dissipate combustion heat to further suppress detonation. With the CHP 5.0L short-block providing a solid foundation, the key to the performance of this street 302 was in the induction system. The critical elements to power production are the cylinder heads, camshaft and intake system. It should be noted that similar results could be obtained by using an early hydraulic flat-tappet 302 block. The flat-tappet cam would also allow a few more revs before valve float, as the hydraulic roller valvetrain is considerably heavier than the early flat-tappet system.
It wasn't long ago that the only choice for cylinder heads was the factory offerings. In the old days, your choices for topping a 5.0L or early 302 basically consisted of stock (E7TE) 5.0L casting, early 289 HiPo heads or the cream-of-the-crop 351 Windsor heads. Actually, none of these offered much performance, at least not compared to anything currently available from the after market. Early Mustang owners should thank their lucky stars that the late-model 5.0Ls became so popular, as performance parts abound for Windsor-based Fords, including cylinder heads.
Though many excellent heads are now available for the 302 (and 351), we chose a set of TFS Twisted Wedge aluminum heads for this street buildup. The choice was based on the fact that the TFS heads are offered by Summit Racing for around $1,000 complete and ready to bolt on. Looking at the flow numbers supplied by Trick Flow, the Twisted Wedge heads easily out-performed anything ever offered by the factory. Even more impressive is the fact that the TFS heads achieve their superior airflow not so much by excessive port volume, but by superior port shape. Anyone with a hand grinder can make something bigger, and bigger will usually flow more. The trick to getting an engine to produce more power is to maximize airflow while minimizing port volume. Basically speaking, you need to flow the maximum amount of air through the smallest possible hole. This creates something called velocity, which is critical to cylinder filling.
The TFS heads produced exceptional airflow through a rather small (compared to other aftermarket 5.0L heads) 170 cc intake port. The exhaust port is also relatively small at 66ccs, yet the intake flows as much as 251 cfm (@ .600 lift) and the exhaust flows 193 cfm at the same lift. These are big-time flow numbers, but the peak flow is only the tip of the iceberg. The TFS heads offered significant low and mid-lift flow numbers to match their high-lift flow. Basically, they represented a well-rounded package for our street 302. As we mentioned earlier, the TFS heads were also cast in aluminum. As such, the TFS heads provide a significant weight advantage over the factory cast iron heads. In terms of the all-important power-to-weight ratio, less weight is exactly the same as more power. The TFS heads weigh some 40 lbs less than the stock heads. Once you work with aluminum small-block heads, you will never want to lift a set of iron heads again. While the stock (5.0L E7TE) heads offered a diminutive 1.78/1.46 valve combination, the TFS Twisted Wedge heads come with sizable 2.02 intake valves and 1.60 exhaust valves. Given the substantial jump in valve size and port flow, it is easy to see why the TFS heads represent a major improvement over the factory castings.
Twisted Wedge heads get their name from the change in valve orientation. The TFS Twisted Wedge heads rotate (or twist) the valve orientation away from the inline-valve orientation employed on most traditional small-block Fords. As mentioned earlier, the aluminum heads also help dissipate heat much better than their cast-iron counterparts. This helps eliminate hot spots that can initiate detonation. Less weight, more power and reduced chance of detonation, what more can you ask of a cylinder head?
With our heads bolted in place, it was time to choose a suitable cam. The cam and intake manifold actually decide the effective power band of the motor. Match the two and you get a motor with a broad, usable power band. Mismatch them and you wind up with a cam that wants to make power after the rest of the components have signed off. The result is less power everywhere. Since impressive street performance (with daily drivability) was the design criteria, we selected a rather mild cam that provided exceptional power. Selecting from COMP Cams' Xtreme Energy line up, we chose the middle of the road XE266HR cam. There are smaller and larger varieties available, but the XE266HR provides an ideal combination of power and idle quality for this daily driver. Since the TFS heads flow well up to 0.600-inch valve lift and are equipped with sufficient spring pressure and clearance to accept this mid-0.500 lift cam, the XE266HR seemed to be an excellent choice. We have had nothing but success with the Xtreme Energy line of hydraulic roller cams, from the XE258HR all the way up to the XE282HR. The aggressive ramp rates employed on these Xtreme Energy cams allow them to produce exceptional power.
In keeping with the street nature of the buildup, we chose an Edelbrock Performer RPM Air Gap intake for the 302. Though a single-plane Victor will make slightly more peak horsepower, the dual-plane Performer RPM offers significantly more power up to 5,500 rpm, where the vast majority of the driving is done. Even on the track, the Performer RPM would offer better overall acceleration, as the Victor Jr. intake only out-performs the RPM by the slimmest of margins from 5,700 rpm to 6,000 rpm. The RPM delivers as much as 25-30 additional lb-ft down at 3,500 rpm, and carries that advantage all the way to 5,500 rpm. We obviously tested the 302 with the Victor Jr., but the dual-plane RPM is the better choice. Credit the longer runners in the dual-plane design for the additional torque production. Also credit the match between the XE266HR cam and the Performer RPM Air Gap. The efficient operating ranges of the cam and intake match perfectly, producing an exceptional power curve that exceeded 320 lb-ft from 3,000 rpm all the way to 6,000 rpm.
The finishing touches on our 302 included a 650 Speed Demon carburetor, an MSD ignition and a set of Hooker 1 5/8-inch long-tube headers. The headers were used in conjunction with a set of 3-inch MagnaFlow mufflers on the dyno, resulting in a free-flowing exhaust system not unlike something that might be found on the car. The ignition consisted of a billet MSD distributor, plug wires, and Blaster coil. Since the compression checked in a 9.2:1, there was no need to opt for the expense of an ignition amplifier. The carburetor chosen for the 302 dyno test was a 650 cfm Speed Demon. While a 750 carburetor might have produced a few more horsepower (or maybe not), the smaller carb is certainly the best choice for street use. The BG 650 Speed Demon carb would certainly offer improved the low-speed throttle response with little or no sacrifice in top-end power. The final performance component used in the buildup was a set of 1.6 ratio roller rockers. These stainless steel rockers from COMP Cams were used to ensure accurate valvetrain geometry. TFS heads require an adjustable valvetrain, so we opted for one of the best rocker sets available for the 302.
Once everything was bolted together, we installed the motor on the SuperFlow dyno at Westech Performance. There was no need to subject the motor to any break-in procedure, as the short-block had been run previously for another test. The motor was run with five quarts of 5W-30 Lucas synthetic oil. After bringing the fluids up to temperature, we began some low-speed power pulls. With some minor jetting and timing changes, an acceleration test was run from 3,000 rpm to 6,000 rpm. The results were indeed impressive. The little street 302 pumped out 396 hp and 377 lb-ft of torque. We have tested 302 strokers that don't make that kind of power! Not usually known for impressive torque production, this little 302 exceeded 320 lb-ft of torque from 2,900 rpm all the way to 6,000 rpm. In the sweet spot between 3,700 rpm and 5,800 rpm, the 302 thumped out over 360 lb-ft of torque. That's what we call an impressive mid-range, especially for a short-stroke 302. At 396 hp, this 302 will easily outrun any of the performance Mustangs of yesteryear, including most of the factory big-blocks. The best part about this buildup is that you can produce these kinds of power numbers with nothing more elaborate than adding the right cam, heads and intake to a mild (or even stock) 302 short-block.
The first thing you should notice is that the 302 produced impressive torque, exceeding 310 lb-ft all the way down at 2,500 rpm. Check out what happened to the torque curve as the motor came up on the cam. Starting at 3,100 rpm, the torque curve reached 340 lb-ft and motored up to the peak of 377 lb-ft at 4,400 rpm. Despite the short stroke, the torque output exceeded 360 lb-ft from 3,700 rpm to 5,800 rpm. A streetable 302 that produces 360 lb-ft of peak torque is impressive, but this one managed to carry 350-plus-lb-ft over a range of 2,100 rpm. In looking at the power curve, it appears that some additional valvespring pressure may have cured what we suspect was a minor valve float problem and allowed this motor to exceed 400 hp. Even at 396 hp, this 302 will easily outrun any stock Boss 302. At just 225 hp and 300 lb-ft of torque, an early 5.0L Mustang is an easy 14-second car. Just imagine another 170 hp and 70 lb-ft of torque in a lighter '65 Mustang. This motor should propel a 3,000-lb early Mustang into the low-13s, maybe even 12s with slicks.
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