Rabbid Remaps explains why we do it the way we do!

So over the last couple years I’ve been working for myself providing bespoke remaps and providing services to WG Motorworks and I’ve probably seen every mod on the market for the VXR and between Warren and myself we’ve cherry picked what we have found works well. I’ve seen many people bolt on any old bit and sometimes feel down that the car didn’t achieve good results.

So I thought id share a couple of cars with you all and say a bit about what we believe makes the cars work so well and why, and how to build yourself an absolute monster of a car.

Big Power Astras

One of the first customers I had was local member Charlie G, his car started off with a few mods on and got in touch originally regarding cruise control. We talked and he agreed to help me develop some of my original base maps. At Stage 3 we achieved 296bhp, rolled at Surrey Rolling Road which is Dyno Dynamics, a good stage 3 typically comes in around 285-290 on one of these machines.

Today his car has had a couple more bits chucked on and a bit more tinkering with the map and rolled 481bhp on Hampshire Rolling Road which is also an analog Dyno Dynamics. This is with a mere 24 psi of boost.

I have to admit that Charlies build is one of the tidiest ones I’ve seen, he’s put a lot of time and money into it but more importantly a lot of time and effort to do things right and the hard work really paid off.

The key spec points with this car:

  • Z20LEH with forged rods and valve springs
  • Nortech Turbo kit with Garrett GTX3071R turbocharger
  • WGM Fast Road spec camshafts manufactured by Piper cams
  • Airtec Intercooler, Scorpion Exhaust, Pipercross cone
  • 90MM MAF with 875cc Siemens Deka IV injectors, Aeromotive Pump

Adam is a customer of WG Motorworks who tasked Warren with fitting his Garrett conversion, Adam was alot more concerned about reliability so we kept the boost down at a mere 1.3 bar or 19/20psi, but despite this we were still able to get just shy of 450bhp from the car.

  • Z20LEH with forged rods and valve springs
  • Nortech Turbo kit with Garrett GT3076R turbocharger external screamer
  • Uprated cam shafts
  • Airtec Intercooler, Scorpion Exhaust
  • 90MM MAF with 875cc Siemens Deka IV injectors, Aeromotive Pump

Both the cars above could easily crack 500, don’t be surprised if Charlie’s ends up with another 1psi within next few weeks and does so. Adams has even more chance with a slightly bigger a turbo on it to do so also at similar boost levels to Charlie he would probably see 500.

Big Power Corsas

Most of you probably have seen Adam and Jon’s Corsas before, but there are several more on their way to the road in the next few months, 2 or 3 hopefully within the next 4-6 weeks, with plenty more planned.

  • Z16LER with forged internals and valve springs
  • Nortech Turbo kit with Garrett GTX2867R turbocharger
  • Uprated cam shafts
  • Airtec Intercooler, Full Exhaust
  • 90MM MAF with 630cc Bosch injectors, Aeromotive Pump

Jon’s was our original 400+ Corsa VXR, while a very capable car some changes in the approach were made with Adams proving a higher compression engine could work to make more power with less boost.

With more cars on the way we have even more improvements to the specifications of the pistons and cams as well as some customers going for slightly smaller and much larger turbos.

How to Build One of These Cars

Astra engine builds:

In terms of the engine builds we’ve been recommending to use standard pistons. Reasons being not only are they up to the job in terms of strength but they perform better than many lower compression pistons on the market. Maintaining a higher compression makes more power natually, but lower compression actually leads to more detonation. If you have to lower timing to prevent detonation you’re losing even more power.

They’ve been proven in Klasens 700hp vx220 and in time attack by Bo.

Corsa engine builds:

Corsa VXR engines despite being a pretty infamous engine for piston 4 issues, once forged with valve springs are absolutely aweseome engines. Raising the compression up from the standard pistons and then adding a decent set of cams to complement the forged internals will lead to an engine capable of delivering huge power and high reving all the way up into 8500rpm perhaps even beyond.

These engines dont easily suffer from detonation issues and can easily run far more ignition than the astras, meaning they’re able to be much more efficient and can actually produce more power from the same sized turbo than if it were fitted to a Z20LEH. Even with boost turbos higher compression works well. I see no reason to fit anything less than standard compression on these cars.

Adams at high compression can make as much power running 1.7 bar 25psi of boost than a low compression car running over 2.2 bar or 32/34psi of boost.

Fabricating the bits:

When it comes to fabricating Nortech are well known for providing high quality manifold kits to numerous cars and the quality speaks for itself. Everything from the quality of the material to the construction and welding. You can rely that these manifolds are unlikely to crack, and fit well as expected saving time and hassle.

Cam specification:

While they’re piper cams they’re not your typical off the shelf product. WGM specs have been tested and refined for different applications. Many people only sell one cam, but just like the stock cam, one cam doesn’t fit all situations. WG Motorworks can supply several cam specifications depending on the requirements. Charlie’s car uses the milder specification which idles nearly as well as standard and maintains the low end drivability which is lost with more aggressive specification cams, yet still can deliver awesome amounts of power. Considering this car puts out 480bhp with a mere 24psi, it shows going OTT with cams isn’t always required.


Cooling, one of the biggest problems for the Astra is detonation caused by high intake temperatures, many normal coolers on the market struggle to handle large power but the Airtec continues to amaze me compared to other coolers of a similar form factor. It’s much more about whats inside an intercooler than the size.

Even pushing 480hp it still maintains amazingly low intake temperatures within 15-20c of air filter temperatures meaning denser air charges and less induced detonation. Only this afternoon I had higher intake temps of a low boost Garrett at only 15 psi running another similar sized cooler pulling intakes easily over 30 degrees above air filter temperature and only producing around the 340bhp mark.

Fuel Injection Systems:

Finally electronics, to make this all work. To get the car to work right you need to be able to know whats going on. To properly run over 400hp you need a MAF that can read all the air coming into the engine. The stock Astra VXR 80mm MAF becomes over welmed at around 380hp and starts to lose resolution and clips.

The MAP sensor on the VXR is primarily used for boost regulation so the car can double check the boost levels it is running, this allows the car to adjust the boost and turbo in real time. However there is a problem, the stock ECU can only measure just shy of 22psi. So you need to switch to an openloop locked method to control boost and take the adjustment away from the ECU. Even running a 3 or 4 bar map sensor on an Astra H or Corsa D doesn’t help you as the internal memory and maths used in the ECU only understands numbers up to 22psi.

Injectors, you need suitable injectors for the job, Astra 630cc are suitable until around 420bhp and 875cc will take you right up until about 530bhp. Corsas being more efficient can run about 450-470bhp from 630cc’s with larger injectors such as 750cc or 870cc available to push even higher.

If mapped properly you should have no issues with emissions testing and very very minimal loses in economy. We use the stock regulator, it has proved perfectly fine and as we have no need to change fuel pressure it is fine as it is. The Aeromotive internal fuel pump has proven perfectly fine for these applications without the need to install external tanks.