Kaase’s P-38 cylinder heads: Greatest Windsor news since 1962

Kaase’s P-38 cylinder heads: Greatest Windsor news since 1962

Kaase engine, P-38 windsor, By Sam Logan:


The Chevy faithful like to tell us that their small-block engine is cheaper and easier to build than the Ford counterpart—but it’s a myth.

First, the cost of aftermarket high-performance and competition parts is similar whether they are Ford or Chevrolet. And with regard to the simpler engine build, the small-block Ford is probably the all-time easiest engine to build.

In street form, the head bolts—of which there are only 10—don’t penetrate the water jackets, unlike the SBC, thus their threads don’t need sealer applied. In addition the Ford engines don’t have mirror-image pistons and ports, so they don’t have a right and a left piston—all the pistons are the same. Further, the Ford distributor is clamped directly to the block, unlike the SBC distributor which is located by the intake manifold. Therefore the height of the SBC distributor can alter if the heads or the intake manifold has been milled. Washers are often used to correctly position the Chevrolet’s distributor, allowing its gear to mesh correctly with the camshaft. On the Ford you can remove the intake manifold without touching the distributor. Moreover the Ford distributor is located at the front of the engine, thus more accessible for setting the timing compared with the rear mounted Chevy unit. Lastly, the SBC uses a cam thrust plate—a little bearing that pushes against the timing cover—that prevents the cam moving fore and aft when using roller tappets.

When Kaase first conceived the P-38 cylinder heads for Ford’s small-block Windsor engines, they were created with high performance in mind. They were also obliged to be user-friendly.

p38 engine, kaase motor

Kaase’s P38 heads fit the 302-347 and the 351Windsor blocks as well as Dart’s successful 427cu in aftermarket unit

canted valves, p38 cylinder head valves,

As the large canted valves open they move further and further away from the cylinder wall, achieving better cylinder filling. Improved port velocities and deeper bowls with sweeping short turns in the intake and exhaust tracts bring further rewards

cylinder heads, kaase heads, p38s

When laying out the combustion chamber and valve arrangement of a new cylinder head design, Jon Kaase’s first thoughts are likely to focus on bore size—the bigger the bore, the bigger the intake valve. To avoid restricting the entry of the incoming gases he’ll carefully place the head of the opening inlet valve at least .200in from the cylinder wall.

Porting to original locations

If you raise the induction and exhaust ports in the Ford Windsor cylinder heads from their standard position and give the gases a straighter, less impeded route to and from the combustion chambers, you’ll have a race head producing optimum power. But they will not be user-friendly and they won’t fit most applications.

Jon Kaase took a different approach: he left the port openings in their original locations and instead changed the valve angles, reworked the internals of the ports, and was rewarded with back orders of 50 head kits soon after the P-38 was announced.

Windsor intake manifold, P-38 conversion

Virtually any Windsor intake manifold, including EFI types, can complete the P-38 conversion as these cylinder heads use the original port locations. So far the Edelbrock Super Victor and Victor Jr have been the most effective. For all-out power Wilson Manifolds.

stud style rockers, extra clearance, canted valve rockers

Narrow stud-style rockers are useful for providing a little extra clearance for the canted valve layout. However, most rockers work fine; those that don’t quite fit can be adapted by a slight touch-up on the ends of the fulcrum shafts with a hand grinder

valve springs, p38 valve springs

With a solid roller camshaft, the valve springs have an installed height of 1.950-inches and generate seat pressures of 240lb. Open pressure is 500 to 600lb. As the action is quicker on a mechanical roller system, greater spring pressure is required to maintain contact between the roller tappet and the cam lobe. In contrast, seat pressure for a hydraulic roller system might be 145 to150lb.

Combining efficient heads with the correct cam and valve gear

“The two key things that invest the Windsor engines with additional power,” says Kaase, “are the cylinder heads and the camshaft with its attendant valve gear.”

To coax the best power from Kaase’s P-38 heads, he’ll suggest combining them with a high-lift camshaft, solid roller lifters, and stronger valve springs. The camshaft will probably provide lift of 0.600in to 0.700in., the valve springs provide seat pressures of 240lbs with open pressures of around 550lbs, and as a result engine revs will probably peak around 7,500 to 8,000rpm. Valve spring specifications usually depend upon the weight of the valve gear selected. Big-block engines, for example, need heavier valve springs because the parts are heavier. Though selecting solid lifter valve gear produces optimum power, the engine probably won’t run quite as well on the street and the solid lifters will wear quicker because the spring pressures are higher.

The second reason the solid roller lifter doesn’t last as long as the hydraulic roller arrangement relates to the mechanics of valve lash. As a result of taking up valve lash, the action of the rocker operating on the valve stem tip is harsher—a bit more slapping about as Jon puts it. In contrast, a hydraulic roller lifter, which runs fairly tight against the cam, lasts hundreds of thousands of miles, even though they are often made from inferior materials compared with its solid roller counterpart.

mighty demon carburetor, p38 carb

With a Mighty Demon carburetor, a modest camshaft, an Edelbrock Jr. intake manifold, and just under 9:1 compression ratio the 302 with P-38 heads will easily produce 500hp at 7,500rpm. The bigger 427CID engine using the Dart block and Demon carburetor made 717hp at 6,900rpm (1.68hp per cu in).

Jon kaase, engine builder

An unfamiliar arena: much to Kaase’s surprise, short track oval racers have embraced the P-38 for its power and lightness.

valve pocket cutter, p38 valve modifications,

Because the P-38’s valves are positioned at different angles from the original, some alterations are required to the inlet valve pockets on the piston crowns. Kaase supplies this simple cutting tool, if required, to trim along the edge of the existing pockets.

To coax the best longevity from Kaase’s P-38 heads, he’ll suggest combining them with hydraulic roller lifters, which operate with lighter valve springs. Even with solid lifters, if you reduce the valve spring pressures, they will last a lot longer, though the engine won’t generate quite as much power. The biggest change in Kaase’s hydraulic roller setup lies in the profile of the camshaft lobe itself. Of course the hydraulic lifters won’t rev as high as the solid types because the hydraulic type loses some of its oil during actuation; therefore, the valve doesn’t lift as high and consequently the engine doesn’t rev as high.

When laying out a combustion chamber and valve arrangement of a new design, Kaase’s first consideration is usually bore size. “You want the biggest intake valve you can get and the bigger the bore the bigger the valve. Also you don’t want the inlet valve opening close to the cylinder wall or it will restrict the entry of the incoming gases. I usually position it at least .200in away from the cylinder wall. The higher the engine operating speeds the more critical it is.”

Valve spring specifications usually depend upon the weight of the valve gear. For this P-38 layout Kaase selected valve springs with seat pressures of 240lbs and open pressures of around 550lbs. As a result engine revs will probably peak around 7,500 to 8,000rpm.

Valve spring specifications usually depend upon the weight of the valve gear. For this P-38 layout Kaase selected valve springs with seat pressures of 240lbs and open pressures of around 550lbs. As a result engine revs will probably peak around 7,500 to 8,000rpm.

valve cover, kaase p-38 valve cover

As a canted-valve construction, the arc of at least one of the rockers on the P38 interferes with the conventional rocker cover. Kaase’s exclusive cast aluminum covers eliminate the problem. As a clean-sheet design, it was also easy for him to increase clamping power: the rails on the P38 head are configured for eight (rather than the usual six)

installing camshaft,

The two essentials for making power in the Windsor are the cylinder heads and the camshaft with its attendant valve gear. Use a high lift cam, solid roller lifters, and stronger springs for optimum power. Use appropriate cam with hydraulic roller lifters, and lighter springs for longevity.

Valve-to-piston clearance

Because the valves in the P-38 heads operate at different angles from the original equipment Windsor heads, some additional relief is needed in the inlet valve pockets of the existing pistons. The exhaust valve-to-piston clearance, however, is usually not an issue.

Though Diamond and others provide pistons with suitable valve pockets, Kaase supplies a simple, optional cutting tool to relieve the existing inlet valve pockets.

engine builder, jon kaase, jon kaase racing engines

A Cleveland, Ohio native Kaase moved to Atlanta, Georgia in 1977 to work for Dyno Don Nicholson. In that year he won the NHRA Pro Stock title, followed in the decades since by a string of IHRA titles, and the Engine Masters Challenge title four times.

The cutter is installed in each combustion chamber by slipping its stem through the inlet valve guide and operating it with a hand drill. It features a stop that comes to rest on the top of the valve guide, indicating the valve pocket has been machined to the correct depth. As the inlet valve is positioned high in the combustion chamber roof only a relatively shallow pocket is required to accommodate the valve head—about 0.150in and mostly achieved by a slight trimming along the edge of the existing pocket.

When performing this operation it’s advisable to seal the gap between the piston and the cylinder wall to prevent debris falling down by the top ring. This is simply done by bringing the piston to TDC and, with everything clean and dry, sealing the gap with small squares of masking tape all the way around. Next, fit the head with a few bolts and spin the cutter with a hand drill while sucking out the small chips via the exhaust port with a vacuum cleaner hose.

These are most of the steps that will tax the brain during the installation of the P-38 head kit. But the Kaase group is a conscientious bunch and your work will be well compensated by the gains in performance of the finished product. Aim for a remarkable piece of work, as Kaase’s efforts have you off to a grand start!

Jon Kaase Racing Engines
Tel (770) 307-0241



  1. Your new Ford head would be neat to try on a 410 sprint car deal!! The World of Out Laws have a rule the valves must be straight in line. (checked with a straight edge) Would your head some what meet this, hard to tell in the picture. Here in WI they leave us alone until your in the top 5 then they check it out!!!

  2. Hello,
    What is the true compression ratio on the 427 engine with the Kaase heads that is making 717 hp? Also curious what CC’s the heads are and camshaft spec’s was being used to make these HP figures along with what type of fuel please. Seems comparable to an engine I built with high port heads and 438 cubes on 93 octane pump gas.
    Thank you in advance.

  3. Tim,

    Unfortunately the P-38 cylinder heads would not be legal under those rules as the valves have been moved from the inline position.


    That engine was exactly 10:1 compression with a 60cc combustion chamber. The cam was a proprietary grind from Comp Cams specifically for us.


  4. What is the part number for the pistons for a 351W 0.030in over, stroking to 408 and using P-38 heads?

  5. I’m building a 369 stroker with a Dart 8.2in block, forged internals, 9.5cc dish pistons and Comp Cams extreme energy efi cam. Would these P-38 heads work with this build and how do they do on boosted applications?

    • James,

      A few things. First, if you have already purchased pistons you will need to determine what type of cylinder head the piston is designed to be used with, as the valve reliefs may not be in the proper location or depth to work with different cylinder heads. With that said, we have actually discontinued our small-block cylinder head program to concentrate on our core big block and race engine business. We would suggest checking with AFR, Brodix or Dart to see what they would recommend for your combination.

  6. Good day,

    I was inquiring if you still produce your P-38 cylinder heads and, if so, where can a pair be purchased from?

    • Steven,

      No, we are no longer producing the small block cylinder heads. Your only option for P-38 heads would be finding a set on the used market place. We would suggest checking with AFR, Brodix or Dart to see if they offer a head that would suit your specific build.

  7. Kaase! How could you desert our poor small-block fellows? At least sell the tooling to someone else who could continue supplying these perfect SBF cylinder heads? We’re back to where we started. Nobody that bought them would part with them. Sorry Jon but I don’t have the room for a big block! Love you guys and keep the blue oval flying! Lol.

    • Truman we appreciate your comments and would have been thrilled to continue selling our P-38 heads, but unfortunately sales did not justify the investment. The small-block market is primarily driven by price and less so by innovation, making it infeasible for us to continue.

      • Hello, I just wanted to tell you I absolutely love my P-38 heads. I run them on a Dart block 427 with solid rollers in my bracket car, and I’m so glad I got them when I did!


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