Astra J VXR

WGM Astra J VXR Engine Tuning 

The all-new engine in the Astra J VXR shares no similarities to its well-known predecessor, the Z20LEH. The J’s engine is known as the A20NFT, or LHU. The duplex timing chain system; balancer shafts, and high pressure fuel pump with direct injection (DI) system result in an impressive 276bhp (280ps) as standard. Running a square bore/stroke at 86mm, the DI engine runs a compression of 9.3:1 from the factory. This, along with the Variable Valve Timing (VVT) and twin scroll turbo, all combine to provide a very respectable 400Nm (295lbft) of torque.



Most standard cars typically put out around the 276bhp (280ps) quoted by the manufacturer, which is exactly what our development car saw, however we have seen outputs as low as 260HP also. Having said this, generally the torque on most vehicles are outputting  around 320-335lbft, which is above standard quoted figures of 295lbft (400nm).

WGM Stage 1

Our ECU remaps will transform the power of this car, bringing it to life with a massive increase of torque in the mid-range, gaining 30-40lbft and peaking between 300-310bhp.

astra j vxr stage 1

Rabbid Remaps ECU software only upgrade transforms the mid range punch from the ko4 twin scroll turbocharger, by optimising boost, AFR and ignition timing gaining 40-60lbft with peak increase of 25-35HP, resulting in 300-310bhp/365-375lbft.

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WGM Stage 1.5

The next stage of improvement for this car is to remove heat from the engine by extracting exhaust gases more quickly. The first catalyst, also known as the main cat, is the biggest restriction on the exhaust system. Fitting a decat downpipe (leaving the secondary cat still in place so as to pass UK emissions testing) will dramatically improve turbo spool, throttle response and low-end pick up, producing an extra 8-14bhp across the complete rev range, and 15-20lbft at peak. In addition, a secondary decat or sports cat can gain a further ~5bhp/lbft. We also install a high flow panel to allow increased airflow to the turbocharger.


The stage 1.5 package all comes together with Rabbid Remaps ECU Software including CAT code deletion, optimising Ignition, boost and AFR to create 315-325bhp and 385-400lbft

  • Option secondary cat bypass or sports cat section

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WGM Stage 2

With the Astra J being well equipped from the factory with a 2.75” bore exhaust, we believe it is not necessary to upgrade the exhaust system at this stage. With the A20NFT engine, we found that improving the intake system alone gave very impressive gains across the complete rev range, seeing 10-15bhp/10-15lbft.

Adding a 3″ cat back system gains only a few bhp/lbft over the normal Level 2.

With ECU calibration for Level 2/2+, including optimising ignition timing/boost, we expect to see 320-330bhp and 400-410lbft. Note: torque is limited to for standard clutch

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WGM Stage 3

The next constraint to tackle is the intake temperatures. Having increased boost levels, the standard intercooler is now at its limit. Adding a more efficient intercooler with larger pipe work helps keep power more consistent in hot weather and throughout prolonged hard usage. Resultant cooler intake temperatures maximises the power from the standard Ko4 turbocharger.

wgm stage 3


With the uprated intercooler installed, the air charge entering the engine is cooler and more dense, therefore the ignition timing and boost are optimized, with the engine now running more efficiently,  gains of 330-345bhp 400-410lbft are expected (torque limited, as above).

  •  3″ Cat back exhaust system required for optimal HP gains

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WGM Stage 4

The factory size mass air flow-meter (MAF) housing maxes out around 12,000Hz or 256g/s, which equates to approximately 350bhp. Therefore, before increasing the power any further, it is necessary to install a larger 90mm MAF housing. This gives the ECU scope to read air flow up to ~360-370g/s, which equates to 450-480bhp.

To gain any more power at this stage, a modified turbocharger (known as a hybrid) must be fitted. To do this, we take a standard turbocharger and upgrade the internals, clip the exhaust wheel, and most importantly fit larger Billet compressor wheel. This is all done to motorsport tolerances.

Installing a hybrid turbocharger transforms the car, giving a peak gain of ~35bhp over the previous stage. More importantly, the hybrid continues to produce power beyond 5500rpm, with gains of 60bhp at 6000rpm, 80bhp at 6500rpm, and the power remains strong all the way up to 7500rpm.

We have found the standard cat back exhaust system to be restrictive at this point, to which we install our free flowing 3″ cat back system to see these peak gains.




With ECU calibration for Stage 4, including optimising ignition timing/boost and MAF calibration, we expect to see 355-375bhp and 400-410lbft (torque limited, as above).

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WGM Stage 4+

  • Currently in development


WGM Stage 5

Our Stage 5 Packages are well known for pushing the limits, with new turbo kits Currently under development – we will be offering Motorsport Turbos with Beautiful Tubular manifolds , along with supporting modifications also avaible now- such as : Uprated Clutch / Flywheel packages, Uprated Engine Mounts, Camshafts, Valve Springs, Oil Coolers.

The Sky becomes the limit.

We recommend to forge the engine internals for this stage, replacing the weakest component – the factory cast pistons with superior forged Items

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WGM Level Packages info- 

– All Power / Torque Gains can very car to car, this is an approximate guide of what would would expect +/-5
– For Optimal Results, we recommend the Use of Tesco 99 or Shell Nitro – any other ‘Super unleaded’ could lead in lower results than Expected
– 95 Ron / Supermarket Fuel should never be used, Even on the Standard Map from the Factory
– Torque is limited for Standard Internals / Clutch to around 400-410TQ
– Although PEAK Torque gains are Limited, overall under curve Torque will increase making a ‘flatter’ torque curve
– Rabbid Remaps Software is Custom and can be adjusted to your car for optimal gains