David Vizard
February 1, 2007

It's Doubtful that it has slipped many Ford enthusiasts notice, but we are truly in the age of big-inch stroker motors. Any time extra cubes are part of the formula, the cylinder head's job of feeding sufficient air becomes that much more difficult. Sure, there are heads that work, but they can also be inconvenient to use. For instance, bolting on a set of Yates-style NASCAR heads might solve your airflow problem, but it would introduce a new set of problems. With the ports raised, it's likely most intakes and exhausts just wouldn't fit. The challenge then is not so much how to get airflow, but how to do it while retaining stock port locations and-this is important-doing it at a sane end-user price.

Jon Kaase, IHRA champion, two-time Engine Masters winner, and builder of many monster motors (800-plus inches) had some ideas on how a better cylinder head may be done, but for some years he just had too much to do to even make a start. But three or four years ago, we saw the proliferation of big-inch Ford small-blocks, and with them came the need for better heads. Ask yourself who builds a 302 anymore? Unless your budget is highly restrictive, or you race in a class with restrictive displacement, it just does not make sense to use a stock stroke when stroker crank kits are so cheap.

The 5.0 version of the Windsor is not the only game in town, though. Taking a 351 and stretching it is also popular. Even with a stock block bored 0.030-inch over, a 4.10-inch stroke crank can net 418 cubes. Throw a Dart block into the equation and you could be looking at as much as 480 inches. But all these inches need feeding, and one must presume, from his track successes, that Kaase knows a thing or two about feeding a hungry big-inch motor.

Kaase is now in a head-designing mode, but there's a problem here. Jon Kaase Racing Engines ships a lot of cubes, but they are contained in only a few engines. The bottom line is Kaase is not a mass merchandiser. He needed to work with someone who could deal with the sales of hundreds of sets of heads. Enter the good guys at Jeg's. A deal was made. Apart from being the potential sales arm of this operation, the com-pany also had some valuable input to help design a commercially successful head.

Intake Orientation - The biggest problem with any big-inch engine is getting the intake port and valve combo to flow enough air. But enough air does not mean a good airflow number at one lift point on a flow bench. No, enough airflow means having good numbers all the way throughout the lift range. When valve diameter is limited by bore size to some value significantly smaller than we would like, the importance of good flow in the lower valve lift range becomes paramount. As you might expect, Kaase is aware of this, so the starting point for the design of the new head was the intake valve.

To make the grade in an arena where good aftermarket heads are far from scarce, Kaase had to do something different, maybe even a little radical. As such, he made the decision to not only increase total flow at the higher lift values, but also throughout the lift envelope. In addition to this, such niceties as piston-to-valve clearance and valvetrain geometry had to be taken into account. But let's start with the airflow situation first.

From the airflow prospective, the design reasoning behind these heads was simple. If they were to really be high-performance street heads (with strong race potential), they had to deliver flow at street-type valve lifts. This means not fixating on stratospheric seven hundred thou-sandths or more valve lift figures. To reliably deliver a lot of power over an extended time period meant having a lot of flow at low and moderate lift values. Such a requirement also dictated the valvetrain had to have inherently good rocker geometry, otherwise undue side loads would wear out the guides in an unacceptably short time.

0702_mmfp_01z Cylinder_head_power Valve_angle
The new Kaase heads are not of a typical parallel valve design. By angling the valve and relocating its chamber position, big flow numbers have been achieved with stock port locations and regular valvetrain parts.
0702_mmfp_02z Cylinder_head_power Block
Using a block such as this Dart Windsor, displacements of 460 inches plus are easily achieved, and 480 inches is not out of bounds. Big inches need high-flow heads to feed them.
0702_mmfp_03z Cylinder_head_power Combustion_chamber
This shot of the combustion chamber shows how close the exhaust valve is to the chamber and cylinder wall. Moving it over like this gives more room for the intake to function effectively.
0702_mmfp_04z Cylinder_head_power Intake_port
The design concept of the intake port is one of both a larger and deeper-than-normal bowl being fed by a relatively moderately cross-sectional runner. This results in a longer-than-normal port of 247cc volume.

The logic to achieve the airflow goals went something like this: To get good low- and midrange flow, start with a bigger valve. The usual deal here is a 2.02-inch intake, although some of the current big-port street heads do sport intakes of 2.08 inches. Here Kaase elected to go to a 2.10-inch intake as a starter.

Now as good a move as a bigger-than-normal intake sounds, it could run foul of the negative effects of valve shrouding. The stumbling block here is that the bigger the valve used, the more potential there is for valve shrouding to cut into the bigger valves' potential gains. So is all lost? Not really, because shrouding of the exhaust valve by the cylinder bore is of far less consequence than it is for the intake. Because the valve is smaller, the close proximity of the bore produces a much lower percentage loss of flow. But there's more. At a lift value of about one-quarter of the valve's diameter, the flow pattern changes because the valve has moved sufficiently far from the seat to be close to leaving the field of influence of the valve head to the valve seat. Since the valve is only 1.6 inches diameter, it reaches this critical lift point at 0.400 inch instead of about 0.525 for the intake. Because this critical point takes place at a lower lift, a normal exhaust valve would spend more time in the near non-shrouded, higher-lift range. OK, so the exhaust situation is looking good, but it does not, as we shall see, end there.

Most of the engines on which we are likely to install a set of heads such as these will almost inevitably be relatively high compression. The higher an engine's compression ratio, the more exhaust flow can be traded for additional opening duration to compensate. In short, the higher the compression ratio, the more you can trade exhaust valve size and flow for intake size and flow. With the forgoing about exhaust shrouding and flow in mind, Kaase made a move that has often been shunned by other head designers. Namely he moved the exhaust valve closer to the cylinder wall so as to give room to move the intake towards the middle of the cylinder. This cut the intake valve shrouding, thus giving the intake valve a much better chance of flowing more air at low lift. As a last move, the intake was inclined at about a 5-degree angle so, as it opened, the periphery of the valve moved further away from the adjacent cylinder wall.

At this point all looks well on the flow side, but this had to be accomplished while retaining good valve-to-rocker geometry. This was achieved to the extent that not only was the need for piston-valve cutouts vastly diminished, but also any 1.6 or 1.7 Ford rocker using a 71/416 stud would work, except maybe those with a wide body.

The Ports - With a combustion chamber configura-tion that held great promise for strong flow figures throughout the lift range, it became obvious the intake port itself had better work well or all the chambers assets will amount to near zero. Kaase opted to make the port enter the head and sweep upward more than usual. This allowed for a deeper bowl and a bigger short-side turn (also called the short-turn radius). Both these moves contribute to improved flow in the mid- and high-lift regimes. It also produces a longer than normal port so the 247 cc this port has is not directly comparable to a more conventional head.

What we have here is a head that has about the same areas as a conventional one of about 220 or so cc's. That's still big, but the cross-sectional area is well utilized. Added to this, the high flow means that a lot of air is going through the port so that port velocity is more akin to a head in the 200-215cc range. Our flow tests showed, at an extremely credible 296 cfm, the highest as-cast figures so far seen. As such, our numbers are somewhat lower than those you will see in Jeg's catalog, but don't let that be a source of disappointment. The bench we use has the calibration checked with a Helgesen plate almost every time a project head is flowed. Flow figures from industry benches almost always run higher than ours.

0702_mmfp_05z Cylinder_head_power Exhaust_port
The exhaust port flowed well in as-cast form to the extent that it was one of the better ones we have tested.
0702_mmfp_06z Cylinder_head_power Valve_seperation
With the valves in place, the close separation of the intake to exhaust can be easily appreciated.
0702_mmfp_07z Cylinder_head_power Ported_intake
This view down the T&L-ported Jeg's/Kaase head highlights the port shape. The port floor rises more than most, and as it rises into a deeper-than usual pocket, the port spreads in width. This makes for a larger and more effective short side turn.
0702_mmfp_08z Cylinder_head_power Exhaust
The T&L port work on the Kaase head, even in its simplest form as a clean-up, delivered 236 cfm. Given a little more leeway, T&L quickly got this up to 245 cfm. That is something nearer the true potential of this stock-position exhaust port.

What can be said for sure is that this Kaase head design, as cast, has flow capabilities that approach the figures seen from some conven-tional parallel valve heads after they have been CNC ported.

On the intake, things are looking really good. But how about the exhaust? Remember, this has been pushed much closer to the cylinder wall than is often deemed wise. Also, unlike the intake, the exhaust valve has no inward cant. It appears, for all practical purposes, about as conventional an exhaust port as you might see in any number of other aftermarket heads. With 184 cfm at 0.600 and 188 cfm at 0.700, the exhaust flow did not appear to have suffered one iota by the move toward the cylinder wall. In fact, the good news here is that exhaust-flow numbers were typically up, if only marginally, over most of the as-cast heads tested.

In all, as a customer would receive these heads, we can say they flowed exceptionally well. The next move was to see what they would do when given a basic porting job. Basic, in the context meant here, is a porting job that can be done over a weekend by a complete beginner.

Ported Results - Our test porting job was done by T&L's chief head porter, L.J. McCleary. McCleary is well known for his porting skills, so we can hardly call him a beginner. That said, the instructions given were to clean it up and smooth it out only. No reshaping, just make it the way Kaase intended by following the existing casting form. When you are a pro porter, it is difficult to ignore all you have learned from experience, but inspec-tion of the heads after McCleary finished looked like he had followed our instructions pretty well although workmanship was probably a few hundred percent better than some first-timer's.

So how much extra flow did we see from this simple porting exercise? Usually, the better the heads are coming out of the gate, the harder it is to make much of a gain. The flow bench showed that the expected small increase just did not happen. Instead, a relatively big increase was seen, not just on the intake, but also on the exhaust side. Check out the flow curves in Fig 1. For the intake, this Kaase head with just basic porting came within a whisker of 340 cfm at the relatively low lift of 0.600. That is solidly in CNC-ported-head territory, and the exhaust was equally impressive with 237 cfm at 0.700 lift.

Dyno Time - We would like to have had a dedicated big-inch engine to determine exactly what these heads may be capable of in terms of power output. With the airflow they delivered, they certainly promised a lot, but, as we all know, promises do not always equate to horsepower. What we needed to really put these heads to the test was a big-inch, high-compression, big-cammed, big-carb (Dominator size), and big-intake-equipped engine. What we had was a T&L customer engine that, had it been equipped with conventional parallel (inline) valve heads with basic porting, would have cranked out about 625 lb-ft and 620 hp. It has to be said that these numbers are based on dyno testing similar engines in all respects other than the heads. However, dyno tests from other engines is hardly a true back-to-back test, so all we can do with the results here is make no more than a rough comparison.

Well, the dyno test did give more than an inkling of what these heads might deliver under ideal circumstance by producing, in the less-than-ideal circumstance here, 630 lb-ft and 632 hp from our temporary mule motor. How much less than ideal are we talking of here? Enough that any more manifold vacuum at wide-open throttle and the engine would have inhaled the entire carb.

One thing's for sure: For a cost of about $1,400 a pair from Jeg's or Kaase, these heads look to be among the most cost effective on the market today. We can hardly wait to try a set out on one of our own motors. If you want a ported set from T&L (and this includes porting and the seat job that goes with it), it will cost you $2,450. For this, you will get a pro porting job that will produce in excess of 345 cfm on the intake and 245 cfm on the exhaust

0702_mmfp_09z Cylinder_head_power Dyno_graph
As these flow figures show, the Jeg's/Kaase heads are excellent at passing air into a cylinder. The as-cast heads closely approach some of the CNC heads on the market today. In the most basic ported form, which is something that could be done at home, they can equal many highly respectable and relatively high-dollar CNC-ported heads.
0702_mmfp_10z Cylinder_head_power Finished_chamber
This is a finished chamber opened up to match a 4.03-inch bore cylinder. Note the amount of space from the left-hand side of the valve to where the bore would be. The reduced shrouding this design concept produces is partially responsible for the strong low and midrange flow seen.
0702_mmfp_11z Cylinder_head_power Ported_kaase_head
Here is the finished T&L-ported Kaase head. A set similar to this with over 700hp potential will set you back $2,450 direct from T&L.
0702_mmfp_12z Cylinder_head_power Dyno_test
We did a quick dyno test on this 460-inch Dart Windsor small block at T&L. The results left us wanting to scratch-build an engine specifically to utilize the Kaase heads' strong airflow assets.