Ford Engine Tuning Efficiency - An Easy Route To Super Engine Efficiency - Tech

To give you an idea of what air weighs, figure a typical school gym contains between 20 and 30 tons of air. Surprised? Most people are. If that air moves fast, we can utilize the kinetic energy it contains to not only ram into the cylinders at high speed, but also reduce flow reversion at low speed. Getting the port area and shape just right for the engine combination being used means more power at the top end where a previously air-starved engine can now breathe as well as the low end. That's the end of the power curve we use 95 percent of the time on the street, so it should at least be a realistic priority.

Another item on the agenda is swirl. Without good mixture motion, the combustion process is compromised. If a head has good swirl, it helps improve combustion quality, especially at low engine speed. In a nutshell, good swirl often equates to good low-speed torque.

The last factor we'll consider is compression ratio. This is as important for a street-driven machine as it is for an all-out race car. The compression ratio has a considerable influence on the size of the cam that can be used before low-speed output becomes unacceptable. The higher the compression ratio, the more cam that can be used. Also, more compression equates directly to more mileage-something that can't be overlooked these days.

Getting Started
With the carb and ignition dialed in, our 302 mule engine produced the numbers (rounded to the nearest whole number) listed here.

Even with stock heads, it's a pretty stout unit. This can be largely attributed to the improved breathing capability imparted to the heads by the significantly greater valve opening area produced by the cam and supported by the 650 Demon carb and Performer intake combination. Because we are minimizing potential restrictions elsewhere in the induction system, any superior character-istics the new heads have should pay off big with significant results.

Test 1
The first head change was to a set of as-cast 170cc Dart Pro 1s. The intake port volume on these was measured at 165 cc and the exhaust 62 cc. So you have a reference point-the stock heads are typically in the low-to-mid-120s on the intake and low-to-mid-50s on the exhaust. The 170 Pro 1 heads are intended to be used as a direct replacement on an engine that has an otherwise stock bottom end. That means they must have valves that are not too big to be accommodated by the stock valve cutouts in the pistons. To do this, the intake valve is sized at 1.94 inches. That's up an appreciable amount from the stock 1.78 but significantly less than the typical 2.02-inch normally used when aftermarket pistons are in the engine.

Flow curves for the entire lift range are shown in the sidebar. So, we can make a comparison quickly and easily by looking at two reference points that will, for all practical purposes, define the heads' ability to get the job done.

These two points are the flow at 0.250 lift and the flow at peak valve lift as delivered by the cam and valvetrain used. In our case, that's 0.560, but to make life easier we'll use the 0.550 lift point because it's close enough. At these two key lift points, the intake on a stock head delivered 121 and 155 cfm, respectively. On our freshly calibrated flow bench, the 170cc Dart Pro 1 delivered 151 and 255 cfm. To put that into perspective, at as low a lift figure as 0.250, the Dart heads delivered flow numbers almost as good as a stock heads at maximum lift. At the peak valve lift point, the Dart Pro 1 head produced a full 100 cfm more than stock.