Bourne HPP Drop-In K20/K24 Camshafts for RSX/TSX/Civic Si

Bourne HPP 21S Drop-In Camshafts - K20/K24 (RSX Type S, TSX, Civic Si)

Camshafts are where a K-series engine really wakes up, because they control how far the valves open and how long they stay open, which is to say how well the engine can breathe. The factory cams are ground for emissions, economy, and a smooth idle, so they leave power on the table. The catch with most aftermarket cams is that chasing that power usually drags a whole project behind it: stiffer valve springs, head machining, a rough idle, and a car that's miserable below VTEC. The Bourne HPP 21S is built to skip all of that. It's a genuine drop-in cam that frees up real, usable power while staying friendly enough to run on your factory setup.

A True Drop-In, Not a Project

This is the whole appeal, so it's worth being clear about. The 21S is a mild enough profile that it doesn't ask for the expensive supporting work aggressive race cams require. There's no cylinder head machining, it runs on standard valve springs, and it works with your OEM valvetrain. You pull the stock cams, drop these in, set your valve lash, and you're running. That makes it one of the few real power upgrades on a K-series you can do in a weekend without opening your wallet for a full head build.

Where the Power Actually Shows Up

Peak horsepower is the number everyone quotes, but it's not the whole story. In independent testing against leading competitor profiles, the 21S has made up to and over 260 BHP, though how close you get depends on your supporting mods and intake setup. The part that matters day to day is the mid-range. The 21S is ground to make stronger mid-range torque than OEM JDM cams and other drop-in options, so you're not just gaining a top-end spike you only feel at redline. You get real grunt coming off corners and a wider, more usable power band, which is what actually makes a car feel fast on the street or quicker through a lap. On the cams themselves, expect in the range of 20 to 30 horsepower and 15 to 20 lb-ft, with the bigger numbers coming once you add intake, exhaust, fueling, and a tune.

Streetable Every Day

A cam that makes power but turns your daily into a cold-blooded, lumpy-idling headache isn't worth it for a street car. The 21S keeps a stable idle and good cold-start behavior, so the car still behaves in traffic and on cold mornings, while giving you a noticeable gain in throttle response and torque across the rev range. Whether it's a fast road daily or a regulated race car, the power delivery stays smooth and predictable.

Chill Cast Iron, Built to Last

Power means nothing if the cam wears out, and the lobes take a beating every revolution. Bourne grinds the 21S from chill cast iron blanks, which is the industry standard for a reason. The chill casting process gives the lobe surfaces exceptional hardness and wear resistance, which is what fends off the lobe pitting and degradation that kills a soft cam over time. Commuting or at redline on track, these are built to take it.

Getting the Most Out of Them

The 21S runs on your stock supporting hardware, but if you're chasing the top of its range, a few parts help it breathe and rev. A tune is the single most valuable addition, since it dials in fuel and cam timing for the new profile and is how you safely unlock the bigger numbers. Larger injectors keep up with the added airflow, upgraded valve springs are worth it if you're spending real time at the top of the rev range, and matched valves round out a freshened valvetrain. Bourne HPP offers injectors, valve springs, and valves developed for the K20 and K24 to pair with these cams.

Technical Specifications

• Intake duration / lift: 260 degrees / 13.46mm
• Exhaust duration / lift: 252 degrees / 12.19mm
• Valve clearance (intake / exhaust): .008" / .012"
• Usable RPM range: 1,500 - 9,000 rpm
• Horsepower gain: 20 - 30 hp
• Torque gain: 15 - 20 lb-ft
• Material: chill cast iron
• Part number: BHP-HK-21S
• Best for: street / fast road

Fitment

These cams are designed specifically for the K-series engines that run VTEC on both the intake and exhaust camshafts:

• 2002-2006 Acura RSX Type S (K20A2, K20Z1)
• 2004-2008 Acura TSX (K24A2)
• 2006-2011 Honda Civic Si (K20Z3)

They will also fit the K20A3, K24A1, K24A4, and K24A8. These engines use an i-VTEC design where VTEC acts on the intake cam only, so the 21S wasn't ground specifically for them and may need some additional supporting modifications to get the most out of it.