Tweet
Part 2. We continue...
| Staying true to the brand by using VAG group parts throughout, the first step was collecting AXG spec'd bits from eBay.de. The AXG model is the most powerful diesel T4 VW produced, with factory fitted variable vane turbo it rolled of the production line with 151bhp. It was only sold as LHD in mainland Europe. We got hold of the AXG intake parts, including the all intake pipework and exhaust manifold. The design of the AXG manifold is as good as it gets, with a plenum chamber designed to match the extra intake pipe work factory fitted to the AXG |
 ACV(left) vs AXG(right) |
 Stock vs VNT20 |
The decision was made to go bigger, but not too big. I picked up a VNT20 turbo from an Audi A6 that also had the 2.5 block. As this turbo is vacuum regulated, as opposed to the pressure controlled ACV, we also had to source an AXG ECU, so that the N75 valve could have much more control. As everything is custom on this build, the lads at M V Engineering had to fire up the angle grinder and TIG welder to modify the turbo compressor outlet, in order for it to miss the brake master cylinder. Factory AXGs were all LHD so the servo location was not an issue. The turbo was then coupled up to an AXG downpipe, to get rid of all the new and improved explosions; this was coupled to the straight through 2.5" exhaust system. The noise the engine makes is music to my ears, that 5 pot is like the Pavarotti of engine noises when the pedal is pressed to the metal. Most people who hear it ask the same question "Is that a diesel?" |
| After the GT2052V turbo, there is an oversized custom made Top Mounted Inter Cooler (TMIC). Mario and I had discussions about moving to a Front Mounted Inter Cooler (FMIC) but the cons, long pipe work causing lag and issues with routing space due to the air con radiator, far outweighed the pros of direct airflow. In order to be sure that the TMIC has cool air pulled over it, we 'popped' the back of the bonnet, emulating the stand-off setup that Beetles with oversized Porsche engines use and also enlarged the sculpted stock air feed in the bonnet. The TMIC is huge, but it allows for the shortest possible distance from the turbo to the AXG intake manifold, meaning lag is non-existent. Its size also helps with airflow, being a plenum reserve for instant, continuous pressure, when required. The difference to power delivery over the previously used charge cooler is very noticeable. Initial testing proved it does a fantastic job, as even when pushed on a hot day, the temperature stays in the mid 70's, averaging well under 50 degrees under normal driving conditions. In order to match the huge amounts of forced cool air, Keith at United Diesel stepped up to provide the required fuel levels, not only converting the fuel pump to above AXG stock specification, but also building the injectors from scratch. Making sure they were all perfectly balanced, with an ability to provide a much higher flow long term, if a bigger turbo is ever added. The extra power caused a few issues, if you didn’t watch the rev counter like a hawk, it would result in a temporary loss of compression. Another trip to see Mario and the addition of Rosten valve springs with titanium retainers soon cured this, the engine now revs cleanly to 5300 without issue. We now actually have the scope for much more power, as fuel is plentiful, the camshaft is stock. |
 |
Move on to Part III...
Over sized oil cooler:
Move on to Part III...