Honda K-series tuning is one of the deepest rabbit holes in the kingdom of car modifications. There are several way to slice that pie, with turbo K24s making easy supercar power, or high-revving K20 builds that make over 300 hp. 4Piston Racing is one of the tuning houses that makes those K-series dreams possible, and they’ve come out with a unique K24-based 400 hp naturally aspirated race engine made for the storied USAC Midget rule set.
Powerful K-series engines are 4Piston’s specialty, making some of the best ones you can buy as complete packages. You can also buy their specially-developed parts separately, which include camshafts, pistons, rods, oil pumps, and ported cylinder heads, to make your own extra-spicy engine. This engine was built to fit the USAC Midget rule set, which has historically been occupied by de-stroked and de-bored four-cylinder versions of racing V8s.
The ruleset generally stipulates a 2.5-liter displacement and 9,600 rpm rev limit for the Honda K-series, with a maximum stroke of 99 mm. All engines must be naturally aspirated and have dry sump oiling, have non-billet cylinder heads, have fixed camshaft timing, and complete engines must be reasonably available for competitors to purchase. Otherwise, you can pull every other trick to make power, making national-level USAC Midget an engine builders competition.
4Piston went to town to make 400 horsepower out of 2.5 liters. What’s interesting was the usage of the stock CR-V crankshaft and a sleeved CR-V block as the basis for the engine, with 4Piston trusting the stock parts to work well in a racing application. The head, being cast aluminum as per the rules, has aggressive cams and meticulous porting and machine work to allow the most airflow possible. With an astronomical 15:1 compression ratio, which is not uncommon for a race engine running race fuel, the engine makes 400 hp through Kinsler mechanical fuel injection with individual throttle bodies.
This is a nasty race motor, which can potentially make more power according to 4Piston. But as it is, for $39,915, this engine will run for 15 USAC national events before a $6,500 service. It could run longer as 4Piston learns about and develops the engine, but it could certainly be a real competitor for folks looking to get serious in USAC.
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