The K06 Upgrade for Astra H VXR is an often overlooked conversion in favour of either a Garrett or Borg Warner EFR turbo, where the thinking is ‘the bigger the better’.
In a real world scenario, this is often not always the case, especially for fast road and trackday use where you want to retain driveability throughout the rev range, rather than wait for a huge hit of power right at the top end.
Here is a graph showing the comparison between a Stage 2 Astra H VXR (ECU Remap and full exhaust system) compared to a K06 conversion:
Astra H VXR K06 Conversion
In short the power gains of the K06 over the Stage 2 K04 are substantial, to say the least:
+20bhp @ 4,500 rpm
+30bhp @ 5,000 rpm
+50bhp @ 5,500 rpm
+70bhp @ 6,000 rpm
+90bhp @ 6,500 rpm
with much more mid range and top end torque as well, and still producing excellent power of 330bhp at 7,000 rpm and by 7,500 rpm still producing 320bhp, long after the Stage 2 car has faded by the wayside.
Notice also the power is still available from the mid range at 3,000 rpm, where a bigger ‘Garrett’ type turbo may not be fully on song until 4,000-4,500 rpm making the car less ‘on-road’ friendly for mid range road and trackday use.
So what exactly is involved?:
The full Stage 4 K06 conversion consists of a K06 turbocharger, a Courtenay Piper full stainless steel 76mm exhaust system, a Courtenay VXRacing full height front mounted intercooler, a Courtenay Klasen High Flow Inlet Manifold, steel rods, uprated arp rod bolts, new gaskets, exhaust valve spring shims, oil and filter, head bolts and a bespoke Courtenay ECU remap carried out and set up on the rolling road.
New pistons are not required due to the high quality nature of the factory fitted OE (Original Equipment) forged pistons, which are good for up to 500bhpm so they take this power easily in their stride.
The steel rods are fitted for strength, durability and safety. They also mean the engine can be revved much further, taking full advantage of the inlet manifold. Not fitting the rods simply means we have to turn the power down for safety!
The fully reworked K04 Turbocharger to K06 spec includes an uprated bearing pack and seals and billet K06 compressor wheel, meaning the turbo can produce and sustain more boost helped along with an uprated stronger actuator.
Our high flow Courtenay Klasen Inlet Manifold is designed to not only retain mid range power and torque (unlike some manifolds which sacrifice mid range power and torque for top end gains) but it also removes the restriction of the factory OE manifold at the top end. The improved flow means huge gains.
The full height intercooler keeps inlet air temperatures under control, and is available powder coated in stealth black, whilst the full 76mm exhaust system gives the required flow to obtain the maximum gains – a 70mm system will restrict power to 315-320bhp, due to its inability to flow at the top end as well as the 76mm system.
Finally the bespoke mapping and datalogging with map optimisation is carried out on the rolling road, making for a very useable, driveable fast road and trackday conversion not only retaining mid range power and torque but also increasing it.