ASTRA H VXR TUNING
The Astra VXR as standard produces 240ps and 320nm of torque (237bhp 235lbft). However with some bolt on parts and ECU mapping the Astra VXR becomes a very tunable car.
The Z20LEH engine found in the Astra VXR is a revised version of the LET engine found in the earlier GSi's. The LEH comes with forged postons good for 500bhp, uprated injectors, balance shaft delete, oil squirters and a new form of engine management.
At GCAP we have tried and tested tuning packages for this engine, below is a break down.
GCAP's bespoke custom ECU remaps will tweak the fuelling, boost, ignition timing, etc to boost the power to around 265-270bhp with up to 300lbft of torque without any hardware modifications. We advise at this stage the addition of a panel filter or cone filter to allow the vehicle to breath better.
The removal of the pre-cat, the first very restrictive part of the exhaust system, with a decat pipe, will open up more performance gains. There will not be much bhp gained over a stage 1 but will certainly help open up some more power.
At this stage we now address the exhaust system. By removing the restrictive system and fit a larger bored free flowing exhaust system, we again open up room for more power. The standard system is very restrictive, so by fitting a 2.5inch-3inch exhaust along with sports cat or decat system, followed by a ECU calibration and map, power is boosted to 275-289bhp and up to 320lbft of torque.
At this stage we focus on cooling the intake temperatures. At stage 2 the car will be struggling to keep the air cool via the standard intercooler, therefore after prolonged use the car's bhp will begin to fall. To ensure a consistent performance figure, we swap the standard intercooler for an uprated front mounted cooler. Combined with a map tweak we see figures in the 290-305bhp and up to 350lbft torque.
At stage 3 we also suggest customers fit an uprated actuator to ensure a more consistent boost in the higher rpms. We also recommend an uprated recirc valve. The factory ones begin to split at this power so an all metal bodied recirc is far more benficial. We also suggest customers swap their spark plugs for a higher heat tolerant plug.
At this stage we address airflow via the inlet system. The factory inlet manifold begins to struggle higher up the rev range to flow the amount of air requested. By installing an uprated inlet manifold, the engine will be able to breath far more efficiently from 5500rpm onwards, right up to the redline. This in turn will allow for a better stronger pull and will see around 35-42bhp gains at 6500-7000rpm. Peak figures tend to be around 305-310bhp and around 340lbft-350lbft.
At stage 4 we now remove the standard K04 turbo and replace with a hybrid alternative. The hybrid turbos take the K04 KKK unit and replace the internals with:
High flow Billet K06 large trim Compressor Wheel
Re-profiled compressor housing
Modified turbine wheel blades to reduce backpressure
Lightening of turbine wheel for quicker response
360 degree thrust kit
Unit fully blueprinted to motorsport tolerances
With this turbo we see power in around 320-360bhp. At this level of performance it is now important to upgrade the valve springs along with forged conrods. The factory pistons in the Astra VXR are good for 500bhp, so no need to upgrade these. This will allow you to run the power safely. For those who do not wish to forge the engine, the map will be set for lower boost parameters and thus keep the engine at a safe level of tuning.
The next upgrade will be the camshafts. The inlet and exhausts camshafts are swapped out for GCAP spec fast road cams allowing the car to flow air far better due to the opening of the valves higher and longer.
If you wish to go further down the power route, the next option is installing a Garrett turbo. These range in performance and see anywhere between 350bhp-500bhp+. One of our demo vehicles is running 514bhp.
We offer full engine forging the Z20LEH and Z20LET engines.
On the LEH engines found in the Astra and Zafira VXRs, we offer a full strip down and rebuild service using FCP, ZRP or PEC conrods. The pistons themselves are forged from the factory so these only need a clean up and new pistons rings installed. However, we can offer Wossner pistons for this engine.
Included in the rebuild are all new gaskets top and bottom end, plus a full head rebuild including valve lapping, new stem seals, full degrease and skim. Customers have the option of upgrading the valve springs and stem seals whilst this is done.
For the LET engines, the rebuild is the same as the LEH but we offer the choice of LEH or Wossner pistons, balance shaft delete and the addition of under piston cooling.
SUSPENSION & TRANSMISSION
We can offer a variety of suspension and handling upgrades spec'd to your exact needs, whether it be fast road or a full on track set up.
We can offer lowering springs, coil over kits, RARBs, FARBs, Uprated engine mounts and bushes.
We also offer a variety of clutch and flywheel set ups ranging from stage 1 - stage 3. Single mass flywheel conversion, uprated clutches, 4 and 6 paddle clutches and uprated covers. To help aid put the power dowe we also recommend the addition of a limited slip differential at any level of tune.
VALVE STEM SEALS
The Z20LET,LEL,LER and LEH engines all suffer from a problem with the stem seals. Like most engines, these have a valve stem which the valve runs in, which has the valve stem seal at the end of it to stop oil running down the stem. However, these engine's seals just push onto the end of the stem with nothing to hold them on but friction. Therefore high EGT'S, age and frequent hard revving results in them to pop off and cause leaky valve stems.
We offer 2 methods of repair, one with the head on, and one with the head off. With the head off you gain the extra service of valve lapping, new headgasket, skim and full head degrease and clean up.
We also offer uprated stem seal retainers. These are CNC machined from stainless steel, are 0.5mm thicker than the original spring seat for extra strength, plus they sit 1mm off the seals to allow for differences in stem fitments and are fatter in the base for a tighter tolerance fit in the head so they dont float around.