Because the valve angles and port layout are different than typical Windsor heads, it's probably a better idea to look at intake port cross-sectional area instead of volume for comparison purposes. This figure is determined by measuring the most constricted point of the intake port in both height and width. Usually, this is just inside the port entry where the intake port must clear the pushrod. By multiplying height by width of the port, this creates a cross-sectional area in square-inches. We measured 2.74 square-inches for the Jeg's/Kaase head, while an AFR 180cc intake port Ford head, for example, measures only slightly smaller at 2.55 square-inches. Generally speaking, the larger the cross-sectional area, the greater flow potential the head will offer. But this larger area also slows the speed of the inlet mixture.
Speed is another crucial component to cylinder filling, so the cylinder head designer plays a very careful game of balancing cross-sectional area and port flow to come up with a strong cylinder head that will make power.
One of the other important concepts about port flow numbers is that peak flow numbers are less important than they might first appear. Especially for street engines that rely on camshafts with valve lifts of 0.550 inch or less, a cylinder head that emphasizes flow numbers between 0.200- and 0.400-inch valve lift will generally offer the best power potential both with excellent overall torque as well as great peak horsepower. There's much more to this concept than we can get into here, but be assured that if you find a head with excellent 0.300- and 0.400-inch flow numbers compared to other cylinder heads, that head is worthy of serious consideration.
Toward this end, the Jeg's/Kaase head offers outstanding flow numbers both in the mid-lift and peak-lift numbers. All our flow numbers were generated on the Superflow 600 flow bench at Westech Performance where we had access to several other Ford heads that have also been tested by sister Primedia magazine Muscle Mustangs and Fast Fords. In a quick comparison, none of the other multiple small-block Windsor heads tested came close to the Jeg's/Kaase small-block heads on the intake side at both 0.300- and 0.400-inch valve lifts. On the exhaust side, there are a couple of heads that appear to be as good at the upper valve lift areas, but the Jeg's/Kaase head still offers an increase on the low-lift side
Kaase has also tested these heads on a high-mileage 100,000-mile production-based 302 yanked from an aging '89 5.0 Mustang. Running the engine on the dyno just as it came out of the Mustang, the EFI-fueled 302 managed a respectable 251 hp and 317 lb-ft of torque on Kaase's dyno. His first change was to add a 218/228-degrees-at-0.050 hydraulic roller cam that represented about 20 more degrees of duration over the stock 302 roller cam. This bumped the power up to 268 hp and 330 lb-ft of torque, which is a great gain for such a simple swap. Next up, Kaase bolted on the new Jeg's/Kaase heads along with a Holley SysteMAX intake and the power stormed to 381 hp and 373 lb-ft of torque, a gain of 130 hp over the stock motor with the better cam!
Kaase could have stopped there, but he wanted to see what a bigger cam would do since the heads were barely taxed with the relatively small cam. So out came the little hydraulic roller and in went a monster 256-degrees-at-0.050 mechanical roller cam that offered 0.620-inch lift numbers. This monster cam also required a swap to an Edelbrock Victor intake and a Holley 750-cfm carburetor. It required spinning the little 302 to 7,800 rpm, but the Jeg's/Kaase heads also delivered an amazing 511 hp from the otherwise-stock short-block.