Cylinder Head Comparison Test - Volume Control

Are the stock heads really that bad? No. In Ford's defense, the factory 5.0L (E7TE) heads were never designed to support 400 hp (or more), but it's amazing what the proper heads can do to wake up a 5.0L or stroker combination. In the past, we've tested nearly 30 different sets of cylinder heads on different test motors based primarily on their port volume and market competition. Basically, the bigger heads were run on bigger and more powerful engine combinations. This testing left some important questions. How would the smaller heads fare on the bigger motors, and vice versa? Are the larger heads really out of place on a milder combination, and just how much does a small (but efficient) port hurt a wilder combination?

We suspected that the larger CNC 225 heads would offer more power than the smaller as-cast 170cc heads on our wilder 363 stroker, but we were curious to see how well the only slightly smaller 210cc heads would fare. The same can be said for the as-cast 190cc heads, as they flowed enough to support the intended power output of the 363 stroker, but would they offer the same power as the larger CNC versions? How would the milder 302 combination respond to the four different head configurations? Would the additional airflow offered by the CNC heads add power, or would we see a loss in low-rpm torque from the change in port volume?

Our 363 SHP came from directly from Dart and featured a Dart four-bolt block combined with a forged crank, rods, and pistons. The SHP short-block combined a 4.125-inch bore with a 3.40-inch stroke to achieve the 363ci displacement. The big bore improved breathing potential of the combination, allowing our stroker to take full advantage of the free-breathing CNC-ported Dart Pro 1 heads. The 11.0:1 short-block was stuffed with a solid-roller cam from Cam Research Corp, featuring 0.692 lift (with the 1.6 rockers) combined with a 256/260-degree duration split (at 0.050) with a tight 105-degree lobe separation angle.

Prior to running the different Dart Pro 1 heads, we took the liberty of checking the pushrod length and made certain to have adequate spring pressure for both combinations. As we planned on running a solid-roller cam in the wilder 363, we configured our test heads with a spring package suitable for the roller application. The 195 pounds of seat pressure might be a tad on the high side for a hydraulic roller application, but this much pressure eliminated any trace of valve float. As it turned out, all heads required the same pushrods on the hydraulic roller 302. The solid-roller cam required slightly longer pushrods.

The cylinder head test was run on the 363 stroker in descending order, starting with the largest 225 CNC Pro 1 heads. The Pro 1 CNC heads offered impressive statistics, including 225cc intake ports, 87cc exhaust ports and a 2.08/1.60 valve combination. Peak flow numbers checked in at 325 cfm for intake and 235 cfm for exhaust.

Equipped with the 225 Pro 1 CNC heads, the 363 produced 568 hp at 6,700 rpm and 489 lb-ft of torque at 5,300 rpm. Torque production exceeded 450 lb-ft from 4,200 rpm to 6,600 rpm. For this testing, we loaded the motor all the way down to 2,800 rpm to ensure we could register any loss in low-speed power with the larger heads. The air/fuel ratio was adjusted using conventional jetting on the 950 hp. To find the ideal timing value, we tested the motor with total timing from 30 to 36 degrees. The 363 produced best power at 35 degrees, while the air/fuel curve was optimized at 13.0:1.

Using the same procedure, we ran timing sweeps and were eventually rewarded with 566 hp at 6,800 rpm and 484 lb-ft of torque at 5,200 rpm. From 4,200 rpm to 6,800 rpm, the larger 225 heads offered slightly more power (as much as 8-9 hp), but the curves were identical above and below those engine speeds. Like the larger 225 heads, the 363 pumped out over 450 lb-ft of torque from 4,200 rpm to 6,500 rpm. Either Dart Pro 1 CNC head would be an excellent choice for the 363 stroker, but the larger 225 did offer slightly more power with no loss in low-rpm torque.

We quickly swapped over the larger 1.550-inch springs from the CNC Pro 1 heads to accommodate our Cam Research roller cam. Though the airflow data suggested these 195 heads would support nearly 600 hp, the peak power numbers dropped on our 363 test motor to 528 hp at 6,500 rpm and 482 lb-ft of torque at 5,200 rpm. Note that peak torque occurred at the same engine speed as the larger heads, but peak power dropped by 200-300 rpm (to say nothing of the loss of roughly 40 hp). The smaller 195 heads did manage to offer more power from 3,700 to 5,200 rpm, but we suspect the smaller 13/4-inch headers had something to do with the shift in the power curve.

Interestingly enough, the 170cc heads offered less power than the 195 heads, even down at 2,800 rpm. The two produced equal power from 3,200 rpm to 3,600 rpm, but the larger 195 heads pulled strongly away thereafter. On this 363 test motor, the larger heads demonstrated a clear advantage, though the difference between the 210 and 225 heads was 8-9 hp.

The forged 5.0L short-block was augmented with a Comp XE274HR hydraulic roller cam. The XE274HR cam featured a 0.555/0.565 lift split, a 224/232 duration split and a 112-degree lobe separation angle. In keeping with our mild (but powerful) street application, we topped the 302 with an air-gap-style, dual-plane Qualifier intake manifold (from Pro Comp) and Holley 750hp carburetor. Also present was 13/4-inch Hooker Super Comp headers, a ProComp billet distributor, wires and valve covers, and a Meziere electric water pump. Having already run this motor, we filled the stock oil pan with Lucas 5W-30 synthetic oil and we were off.

For this testing, we loaded the motor all the way down to 2,700 rpm to ensure we could register any loss in low-rpm power with the larger heads. Dialing in the Holley HP carburetor was easy using the Percy's Adjust-a-Jet system. As with the 363, we tested the motor with total timing values ranging from 30 to 36 degrees. The 302 produced best power at 35 degrees of total timing, while the air/fuel curve was optimized at 13.0:1. Though seemingly oversized for the application (since the 225 Pro 1 heads will support over 650 hp), the 302 managed to produce 315 lb-ft of torque, even at 2,700 rpm.

It must be pointed out that both the 225 and 210 heads were run with larger 17/8-inch step headers used to fit the wider 3-inch exhaust bolt pattern, while the smaller 195 and 170 cc heads were run with Hooker 13/4-inch Super Comp headers. The headers themselves are partly responsible for changes in the power curve lower in the rev range, but the difference between the 210 and 225 heads was strictly port-volume and flow dependant.

After running the 210 heads, they made way for the first of our pair of as-cast heads. The as-cast, 20-degree heads featured 195cc intake ports combined with 65cc exhaust ports. Though the 195 heads lacked CNC-porting, the peak flow numbers were impressive. Given the peak flow numbers of 288 cfm, even the 195 heads were capable of supporting much more power than our 302 could dish out. Equipped with the smaller 195 as-cast, Dart heads, the 302 produced 390 hp at 6,100 rpm and 373 lb-ft at 4,300 rpm.

The final set of 170cc as-cast heads were actually never run on the 302, as catastrophic failure occurred before we could finish the test. While swapping the heads, we developed an intake leak. The author is to blame for not ensuring the intake gaskets were sealed for the final installation. Water leaked into the adjacent intake port, which unfortunately had an open valve prior to start up. Having water fill the cylinder resulted in a hyrdo-lock situation that actually snapped a connecting rod after start up!

Though the motor ran, an inspection revealed that the piston in No. 1 cylinder had left the party. Thus, we are left to speculate even further about the 170cc head results on the 302, but we know that it would produce less power than the 190cc heads despite the fact that they offered more than enough flow to support our 400hp small-block. It would have been interesting to see if it improved torque production down low compared to the 195cc heads, but judging by the results of the 363 test, it seems unlikely.

On the 363, basically more flow equaled more power, despite the increase in port volume. Stepping up to the largest 225cc heads improved the peak power numbers by just 2 hp and 5 lb-ft of torque over the 210 heads. The reason is that the 210 heads offered more than enough flow to support the power needs of the 363, but the increased flow offered by the larger 225 heads did improve the power output by 8-9 hp and lost no power to the smaller 210 heads anywhere in the curve. On the right application, bigger really is better.

Looking at the 302, we see a similar pattern, as the 195cc heads produced 9 hp less than the larger 210cc heads. It is important to look at the entire curve, as the 195cc heads offered more power from 3,800 rpm to 5,600 rpm, but lost out to the larger heads above and below that rpm spread. Some of the improved mid-range might be attributed to the 13/4-inch headers being a better match for the mild 302 application than the larger 17/8-inch headers run on the larger CNC-ported heads, but the 195-cc head is an excellent choice for this mild application.

This was reinforced when we installed the largest 225cc heads from Dart. Though the 225 heads certainly flowed more than the 210 heads, they offered no power gains. Minor differences of 2-3 hp below 3,700 rpm were registered, but oddly enough it was the larger 225 heads that offered the small power gains lower in the rev range. It should be pointed out that the 225 head lost no power down low compared to the 210 (or 195) heads, though the results would be different at part throttle. The larger ports would certainly be a tad more sluggish on the milder application at part throttle. Had we run the smaller 170 cc heads, we suspect that they would have offered less power than the 195 heads, but the difference would not have been as dramatic as the test on the wilder 363 (probably 10-12 hp at most with a small but consistent loss registered through the second half of the power curve-from 4,000 rpm on up).

Horsepower Numbers