Cams & Sprockets for Subaru Impreza GH

The camshaft sets when each valve opens, how far it lifts and how long it stays open, and its drive keeps it in step with the crankshaft. Here you will find camshafts and camshaft kits, followers, vernier pulleys, timing belts, and bolt and stud kits for cam sprockets and towers.

Duration is the number of crankshaft degrees a valve spends off its seat. More duration, and more overlap when intake and exhaust are open together, helps the engine breathe at high revs but costs low-speed torque and idle quality. The full-lift point is where the lobe peaks, in degrees from top dead centre. On the intake cam, moving it earlier shifts torque down the rev range, and later moves it up.

Solid followers need a running clearance so the valve still closes fully when hot. Ramps on the lobe take up that clearance gently, so it must be set to the profile’s figure. Hydraulic followers adjust themselves.

Camshafts are listed by engine and graded by use:

• Grade: the grades run from road to competition use. Quoted power bands, such as 2200–7500 rpm or 4000–8500 rpm, depend on profile and engine.
• Duration and full lift: intake durations run from 256 to 328 degrees, with full-lift points such as 102, 108 or 110 degrees. Intake timing such as 48–72 deg means opening 48° before top dead centre and closing 72° after bottom dead centre; their sum plus 180 is the duration.
• Valve clearance: mostly 0.20–0.30 mm on the intake and 0.25–0.35 mm on the exhaust, or hydraulic.
• Drive parts: vernier pulleys for fine timing adjustment, and timing belts listed by width, length and tooth count, such as 25 × 1272 mm with 159 teeth.
• Followers and fasteners: followers include solid ones such as 33 × 26 × 14 mm. Cam bolt, sprocket bolt and cam tower kits come in metric threads from M6 × 1.00 to M10 × 1.50 and imperial from 1/4-20 to 1/2-20.

Degree a new camshaft rather than trusting the marks: find true top dead centre with a dial gauge and degree wheel, then set the full-lift point to the cam card. A skimmed head or decked block shortens the distance between crank and cam and shifts the timing slightly; a vernier pulley corrects that. Check valve-to-piston clearance and spring travel with any longer or higher-lift profile.

Coat lobes and followers with assembly lube before the first start, and renew the tensioner with the belt. Plan for remapping, as a new profile changes idle vacuum and airflow.