Jon Kaase’s career as an engineer and engine tuner has a depth few contemporaries have achieved. On Monday, October 15, he celebrated his sixty-sixth birthday, and a few days earlier, he won his ninth award at the Engine Masters Challenge in Cleveland, Ohio. He felt privileged to have a chance to compete again and grateful for the new-found enthusiasm for the contest. More recently, he introduced a new big-block Ford cylinder head, the SR-71, his first in 10 years.


Kaase SR-71 Cylinder headsRaised intake entry ports

• 100% CNC-machined in-house on 5-axis Hurco

• Compatible with Super Cobra Jet intake manifolds

• Fits all conventional engine bays


According to engine builder Jon Kaase, his company’s new SR-71 cylinder head will out-power any conventional big-block Ford head.

Extensive dynamometer tests have demonstrated average gains of 50hp and similar peak gains over best existing cylinder heads. In addition, the usable engine speed range is increased by a minimum of 500rpm. Kaase assures that the SR-71 heads will fit the conventional engine bay, and when installed on a maximum-effort 598cid engine, will produce over 1100hp and rev to 8,000rpm.


Kaase SR-71 cylinder heads

Despite placing the intake port entries half-inch higher than customary, all Super Cobra Jet intake manifolds fit the new heads. Clearly, higher intake ports are desirable, providing straighter, faster paths for the air-fuel mixture to reach the valves. Raising them while preserving compatibility with conventional intake manifolds is achieved by extending the port entry face toward the valley area—the head is wider. On the exhaust side, dimensions are stock Super Cobra Jet / Kaase P-51. The entire CNC-machining process is performed in-house on Kaase Racing Engines’ new 5-axis Hurco equipment.

Deeper bowls

The SR-71’s intake and exhaust bowls are deeper than stock, 0.450in and 0.250in respectively. In addition, the intake and exhaust short-turn cross-sections—known as windows—are considerably larger than stock. Kaase refers to the porting system “Ported as Cast”, which means the ports are shaped and sized to their best known contours. “We’ve done our utmost to reduce the bother of further porting,” he explains, “and deeper bowls combined with easier flow around gentle short turns have improved high-rpm performance.”

Kaase SR-71 Cylinder headsThe intake and exhaust valves are of stainless steel, measuring 2.375in and 1.760in respectively, with valve shapes designed for maximum flow. Also worth noting, these new cylinder heads have adopted stronger rocker-stud bosses. Similarly, high quality CHE bronze guides are employed, and the valve seats are of a unique alloy from Durabond. The CNC-machined combustion chambers provide a capacity of 70cc.

Kaase SR-71 Cylinder headsAnother factor that might catch the attention of the astute observer is the centrally located spark plug position. Convenient though less visible is the revised mounting position of the valve cover, which is slightly modified to provide more exhaust spring clearance.

Kaase’s China Wall spacers raise the intake manifold above the cylinder block, aligning manifold ports with head ports.

Roller cam heads use Manley valve springs, part number 221443.

Finally, Kaase Racing Engines will again display their wares at this year’s PRI exhibition in Indianapolis, Dec 6-8 at booth 2233, and earlier in the week, Jon will address the AETC conference.


For further information contact:

Kaase Racing Engines, Inc.
735 West Winder Ind. Parkway,
Winder, GA  30680,
Telephone (770) 307-0241 or email: