According to Dart, the new Pro 1 CNC heads come with healthy 210cc intake ports and 76cc exhaust ports. Naturally, the size of the ports ultimately affects the flow potential, but size is not the sole determining factor (bigger is not always better). To put the 210cc intake port into perspective, the stock 5.0-liter Ford casting (model E7TE) measures just 127 cc. The disparity carries over to the exhaust port as well, with the Dart Pro 1 measuring some 32 cc larger than the stock 44cc exhaust port. The valve sizes are equally large on the Pro 1. With a (Chevy-sized) 2.05-inch intake and a 1.60-inch exhaust, the Pro 1s are significantly larger than those in a stock Windsor casting (1.78-inch intake/1.46-inch exhaust). The combination of the sizable runner volume, precise CNC porting and impressive valve sizing adds up to just one thing—big airflow. The intake ports on the Dart Pro 1 CNC heads flow 140 cfm more than the stock 5.0-liter heads, a considerable feat considering that the stock heads flow 160 cfm. To put these numbers into perspective, the Dart heads flow a whopping 88 percent more than the stock heads. The exhaust flow is even more impressive, with the Pro 1 heads coming in at 221 cfm compared to just 112 cfm for the stock heads, a gain of nearly 100 percent.

While the Dart Pro 1 CNC head certainly has a ton of impressive features and appears to offer exceptional airflow, how does that translate into horsepower? Actually, there is a formula to convert maximum intake airflow into potential horsepower. We will explain in a moment just what we mean by “potential” horsepower, but for now let’s take a look at the airflow/power formula. The formula states that horsepower is equal to the maximum airflow times 0.257 times the number of cylinders, or: 

HP = Max Airflow x 0.257 x Number of Cylinders

This airflow/power formula can be used to calculate the power potential of any cylinder head on any engine configuration. If we plug in the airflow generated for the new Dart Pro 1 CNC head, we get the following: HP = 299 cfm (max intake flow at 0.650-inch lift) x 0.257 x 8 (cylinders) or 615 hp. The formula suggests that the airflow will support up to 615 hp in normally aspirated form. Pretty impressive considering that the power potential offered by a set of stock heads is just 329 hp (160 cfm).

While the power formula can be used as a guide, the reality is that the eventual power output of any engine is not solely determined by the flow rate of the intake port on the cylinder head. Obviously, adding these Pro 1 CNC heads to your stock 302 would never result in over 600 hp, regardless of the flow rate of the heads. The remainder of the combination (displacement, cam and compression) will obviously affect the power output, as will the exhaust flow. Suppose you had a head that offered big-time intake flow but suffered with a poor exhaust port design. You can’t expect that head to offer as much power potential with a poor exhaust port regardless of the intake flow. With 221cfm exhaust ports, the Pro 1 heads offered an impressive 74 percent intake-to-exhaust flow relationship, so the exhaust ports were not going to hold the power potential back on these heads. In fact, these Dart Pro 1 heads actually exceeded the power potential suggested by the power/airflow formula, something that is rare but certainly possible given a solid combination of components.

Rather than simply provide our readers with airflow numbers and call it a day, we decided to see just how close we could get to the numbers suggested by the power formula. Knowing we were looking for over 600 hp, we built an engine capable of utilizing every bit of airflow offered by the new Dart Pro 1 heads. The short block came from Coast High Performance and featured a 351 Windsor block stuffed to the gills with a custom stroker kit that upped the displacement from the standard 351 ci to a full 418 cubes. The displacement change came primarily from the increase in stroke from 3.50 inches to 4.10 inches. The block was bored 0.030-inch over, but that was responsible for only 5 extra inches. The big-inch Windsor featured 12.0:1 compression thanks to a set of forged pistons from Probe Racing. The 418 stroker also included custom-length forged connecting rods. Knowing we needed a healthy cam to produce over 600 hp, we selected a solid-roller profile (from its oval-track offerings) that offered a 0.688-inch intake lift, 0.672-inch exhaust lift and a 264/268 duration split at 0.050 inch. The aggressive roller cam also featured a tight 106-degree lobe separation angle. The Dart heads were topped off with an Edelbrock Super Victor intake and a 950hp Holley carburetor. Also present was a set Hooker Super Comp headers, an MSD ignition and a CSI electric water pump.    

After installing the heads using Fel-Pro 1011-2 head gaskets and 1/2-inch ARP head studs, we installed the intake and carb and warmed up the 418-inch beast on the Westech engine dyno. After bringing the engine up to temperature, we allowed 30 minutes of break-in time for the new combination. A few steady-state loads at 4,000 rpm told us we were on the right track, as the stroker thumped out some impressive torque numbers of over 525 lb-ft. Naturally, we were anxious to see how long the curve held above 525 lb-ft, as our calculations told us that a torque reading of 525 lb-ft at 6,100 rpm would put us very near our power formula target of 615 hp. The initial torque readings of 525 lb-ft were actually just the beginning, as the Dart-headed 418 thumped out a peak reading of 564 lb-ft at 5,100 rpm on its way to exceed the targeted 615 hp suggested by the power formula. After some minor jetting and a few degrees of timing, the engine finally produced 625 hp at 6,600 rpm, exceeding the formula number of 615 hp by a solid 10 hp. Obviously, the 418 combination responded well to the new Dart Pro 1 CNC heads.

It should be evident that the power/airflow formula is an indication of potential power and not a determination of actual power. In this case, we were able to exceed the power potential thanks to a well-matched combination of components, but this engine is actually the exception rather than the rule. In most cases, readers will be installing heads capable of much more power than they will eventually produce. This is certainly the case for most mild street combinations, as street engines do not typically run around with oval-track roller cams and 12.0:1 compression. Given the port volumes and flow figures, these Dart Pro 1 CNC heads would not be the ideal choice for an otherwise stock 302, as the mild engine could not take full advantage of the power potential of the heads. A well-built supercharged 302 with more cam timing and rpm ability, or, even better yet, a stroker 347 or 408, would be the perfect choice for these heads. The head-port volume and airflow potential must be matched to the engine combination to produce optimum results.