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TFS-R Cylinder Head Install and Test - Trick Flowing Casts - Tech
Testing The New CNC-Ported TFS-R Cylinder Heads On A 674hp 7.0L Stroker.
If the "Ultimate Guide to Cylinder Heads" article showed us anything, it demon-strated that power production is a function of many things. In the case of cylinder heads, it's obviously linked to airflow. Advertisements, Web sites, and even word of mouth continues to tout peak airflow numbers, but there's much more to a good set of heads than just peak flow. Much like peak horsepower numbers, peak airflow numbers can be meaningless when not combined with additional data. The old adage that if 200 cfm is good, then 300, 400, or even 500 cfm must be better, is just not true.
The peak airflow offered by a cylinder head is but one of many factors that determines the worth of the head. Just as with the entire engine package, it's the combination of components that make a decent cylinder head. The big peak flow numbers combine with average flow figures, port volume and shape, and the valve job to produce a desirable head package. Let's not forget the combustion-chamber design and volume, the valvespring package, and even small things like valve seals, as these can make or break the performance of a motor.
To understand the importance of average (as opposed to peak) head flow, we can liken it to the average power production of a motor. After all, it's the average airflow that determines the eventual power output. We all like to talk about big peak power numbers, but the reality is that this maximum value is rarely used.
Think about it for a minute. How often does your motor see the peak power rpm at wide-open throttle? Even assuming you're a serious leadfoot and flog your car at every opportunity, the motor sees maximum rpm for only a brief second or two. Only during top-speed runs (or the Silver State Open Road Race) does a motor run for any length of time at high rpm. Where the motor spends most of its time is revving from low-to-medium engine speeds at low-to-medium throttle angles. The same can be said of your cylinder heads, as the valves spend the vast majority of time running from zero to peak lift and back again, spending almost no time at the maximum lift value. This is not to say that peak numbers aren't important; they simply should not be the sole criteria for head selection. Obviously, power production is very high on the scale, which is why we tested the many heads in our "Ultimate Guide to Cylinder Heads" on both the airflow bench and the engine dyno. It's true that power and airflow are related, but as the head testing demonstrated, the highest peak flow numbers did not always produce the highest peak power numbers. In the case of the TFS-R heads tested here, the high-performance aluminum castings offer much more than big peak flow numbers.
Racers and street machines alike have run the TFS-R heads in confidence, as the design has always proven powerful. A portion of the credit for the impressive power production goes to the Twisted Wedge combustion-chamber design. Rotation of the intake and exhaust valves over the center of the bore helps to unshroud the valves, thereby improving the respective flow rates. The attending central location of the spark plug facilitates complete combustion by minimizing the required distance traveled by the flame front.
In addition to the altered valve angles, the R heads offer sizable port volumes and valve sizes. While Ford suggested we make do with a 1.78/ 1.46 valve combination in the stock E7TE heads, the TFS-R heads offer 2.08-inch intake valves and 1.60-inch exhaust valves. Naturally, the TFS-R offerings were of the stainless steel variety and, when combined with 61cc combustion chambers, 206cc intake ports, and raised exhaust ports, it resulted in the all-important peak flow numbers of 305 cfm for the intake and 222 cfm for the exhaust.
While the 0.700-lift airflow figures were impressive, the reality is that most enthusiasts run cams of less than 0.700-lift. Not a problem, as the TFS-R heads offered much more than big peak flow numbers. At a slightly more realistic lift of 0.600, the out-of-the-box heads flowed 296 cfm, which means they worked perfectly well with smaller 0.600-lift cams. Having tested TFS-R heads time and again, they have never failed to produce exceptional power. Even more impressive is they respond so well to porting, with TFS literature indicating that a simple cartridge roll can unearth an additional 20 cfm on the intake side and 30 cfm on the exhaust.
With the TFS-R heads working so nicely right out of the box and responding so well to porting, it was only natural that TFS offer a ported version of its own head. Maybe it got a look at the results of the tests we ran on the ported R heads from Total Engine Airflow, but whatever the reason, TFS now offers CNC-ported versions of the famous R heads.
Using the same 2.08/1.60 valve combination, the porting has improved peak flow from 305 cfm to 341 cfm. Since man does not live on peak lift values alone, the porting performed by TFS improved the flow rate of the heads from 0.300-inch on up, with only a slight trade-off at 0.200-inch lift. The CNC program also opened up the combustion chamber volume from 61 cc to 65 cc, but this can be adjusted by milling. The exhaust flow took a serious jump as well, from 235 cfm to 271 cfm, with sizable gains offered throughout the lift range. Naturally, the port volumes increased as well after porting, from 206 cc to 225 cc on the intake and from 92 cc to 100 cc on the exhaust.
While we all want heads that flow 341 cfm on our stock 302, the reality is the larger port volumes are best suited to larger-displacement motors or very high-revving ones. The often-used calculation for the relationship between airflow and horsepower is:
Horsepower = Peak Airflow x 0.257 x Number of Cylinders
This equation shows maximum power available from a given amount of airflow. Obviously this formula is helpful for determining the power potential of a set of cylinder heads, but it is not a predictor.
The airflow formula does not take into account the other engine components that may affect the power output, nor does it consider average airflow. Just for grins, we applied this formula to predict that the new CNC-ported TFS-R heads can support 700 hp in normally aspirated trim and a great deal more if equipped with forced induction. Again, just because you run these heads on your 302, 331, or even 351 stroker, it doesn't guarantee that your combination will produce anywhere near the 700hp potential offered by the new R heads. While we didn't go all out on this build, we did equip them for use with a solid roller cam. TFS offered the CNC-R heads with valvespring packages for either hydraulic (up to 0.680-lift) or solid (up to 0.720-lift) roller cams. We chose the latter.
To illustrate what the new heads had to offer, we installed them on a 428 stroker. What better combination could there be for the impressive head flow and large port volumes than a large-displacement stroker? The 7.0L motor started out as a Dart Windsor block equipped with 4.125-inch bores. This motor was further bored to 4.128 inches to accept the forged reciprocating assembly from Coast High Performance. The CHP stroker kit included a steel 4.00-inch stroker crank swinging a set of forged I-beam rods and flat-top pistons. The pistons featured dual valve reliefs for use with both inline and TFS valve locations. The combination of the 4.128-inch bore and 4.00-inch stroke produced a final displace-ment of just over 428 ci. The 428 was equipped with a custom solid roller cam that offered near 0.680-lift and a duration split of 246/251 degrees at 0.050 with a 109-degree lobe separation angle. The roller cam featured aggressive ramp rates to maximize opening time of the cam relative to the duration figures. The Comp cam was combined with a double roller timing chain, 1.6 ratio roller rockers, and custom-length pushrods to work with the R heads and roller lifters.
The remainder of the stroker included the CNC-ported TFS-R heads installed using Fel-Pro gaskets and ARP 11/42-inch head studs. The R heads were topped off with an Edelbrock Super Victor intake, a Holley 1,050-cfm Dominator carb, and a Wilson adapter. Also employed were 131/44-inch Hooker headers, an MSD ignition, and a CSI electric water pump.
Since the short-block had been run previously, there was no need for a break-in period, and we immediately filled the crank-case with Lucas 5W-30 synthetic oil. The 428 sounded plenty stout with its 12.0:1 compression crackling through the open headers and collector extensions. After tuning the Holley Dominator carb and adjusting the ignition timing, we were rewarded with peak power numbers of 674 hp and 589 lb-ft of torque. You'll remember that the airflow/power formula suggested the heads were capable of sup-porting 700 hp, and we see no reason why this motor wouldn't produce 700 hp with a more aggressive cam profile, a ported intake, or even by experimenting with something as simple as carb spacers. Where the as-cast TFS-R heads were impressive, the new CNC-ported versions from TFS take them to a whole new performance level.
|AIRFLOW DATA: CFM AT 28 INCHES |
Compared to the as-cast TFS R heads, the CNC version improved the peak airflow by 36 cfm on the intake and a like amount on the exhaust. More importantly, the flow numbers improved throughout most of the lift range, with the exception of 0.200 valve lift on the intake side. While more peak lift flow is good, more average flow throughout the lift values is of greater importance. Using the power versus airflow formula (Horsepower = Peak Airflow x 0.257 x Number of Cylinders), the CNC porting improved the power potential of the R heads by nearly 75 hp over the as-cast heads.