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4 Piston's K-Series Billet Cylinder Head

The next level of performance for the high-powered K-crowd

Mark Gearhart
Apr 8, 2019

Images by 4 Piston Racing

If you're looking to go full tilt on your next K-series build, 4 Piston Racing's gorgeous billet cylinder head should be at the top of your parts wish list. Designed for max-effort, naturally aspirated, alcohol drag race engines, the 4 Piston's billet head is designed to increase power beyond 11,000 rpm. Yeah, you read that right! For big boosted engines that are approaching 100 psi of boost, 4 Piston is already hard at work on a standard port version that will offer racers increased rigidity and reduce deflection issues.

4 piston racing k series billet head Photo 2/31   |   4 Piston is known the world over for its record-breaking cylinder head and engine building services. The company has taken everything it knows about naturally aspirated Honda drag racing and put it in its new billet K24 head.

"The billet is not going to fit 80 percent of the applications; that's just the reality," says Luke Wilson of 4 Piston Racing. "Most applications are going to want a standard K-series casting with a good CNC port job."

4 piston racing k series billet head CNC grooves Photo 3/31   |   4 Piston Racing K Series Billet Head CNC Grooves

While the OEM Honda castings offer sufficient performance for smaller-displacement endurance and drag race engines, they limit power when trying to turn stratospheric engine speeds. The OEM casting and its water jackets have been scrutinized and tend to be the limiting factor in making more than 500 hp in 165- to 170-plus-ci race engines. This is where 4 Piston's billet head really shines.

"To continue carrying rpm, we needed to work without the constraints of these water jackets," Wilson explains. "So, we designed this billet piece to give us the freedom to put whatever port shape we wanted into the cylinder head. The valve angle is changed, which allows us to not only have a better approach angle with the port, but it also gives us flexibility with camshaft centerlines that we don't have with the OEM cylinder head. The rigidity of the head also allows us to have a better head gasket seal with bore sizes that push the limits with the OEM casting."

4 piston racing k series billet head valveseats Photo 4/31   |   4 Piston Racing K Series Billet Head Valveseats

Valve diameter comes standard in 40 mm, though 39 mm is an option for those who want to try more aggressive cam centerlines. Exhaust valve sizing is 30 mm and titanium valves are typically requested to keep the weight out, while stainless is also an option. The seats used are copper beryllium on the intake and the exhaust side, however, a nickel aluminum bronze option is also available.

4 piston racing k series billet head CHE valveguides Photo 5/31   |   4 Piston Racing K Series Billet Head CHE Valveguides

CHE valve guides are situated at the nucleus of the custom-spec PSI valvesprings. A Ferrea retainer, seat, and lock combination holds the valvespring in place and spring pressures are dictated by end-user camshaft selection.

4 Piston currently has just one port package, but it can customize the head however the customer desires. The valve angle change is based around one port design for naturally aspirated drag racing, but a turbo port without the valve angle moved is also available. The head is currently offered without water jackets, and the crew is working on a design with water on the exhaust side.

Is this sexy billet head the right fit for your bolt-on K-swap that sees local meets and the occasional car show? Probably not the case, though it's certainly show-worthy. If you're looking for the most efficient, naturally aspirated K24 head on the market, or perhaps you're tired of trashing head gaskets regularly on your big-boost setup, this may be your answer.

4 piston racing k series billet head 4 piston racing valvecover Photo 6/31   |   4 Piston Racing K Series Billet Head 4 Piston Racing Valvecover
4 piston racing k series billet head 4 piston racing carrott Photo 7/31   |   4 Piston's house hatch—dubbed "Carrott"—has served as an R&D platform for its billet head program. Real-world testing brings about real-world results.

Intake valve size options:
38 mm - 420 cfm at .650
39 mm - 438 cfm at .650
40 mm - Proprietary

Exhaust valve size options:
30 mm - 280 cfm
31 mm - 290-plus cfm

Combustion chamber:
47 cc - 52 cc available

4 piston racing k series billet head CNC grooves Photo 8/31   |   4 Piston Racing K Series Billet Head CNC Grooves
4 piston racing k series billet head engine Photo 15/31   |   4 Piston Racing K Series Billet Head Engine
4 piston racing k series billet head Photo 25/31   |   4 Piston Racing K Series Billet Head


4 Piston Racing
Pittsboro, IN 46167
By Mark Gearhart
22 Articles



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