Page created: 3-Dec-03

Re-published: 1-Nov-09

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Technical Details

The bulk of the modifications I made to my Discovery were all made within a few months of buying it and it very quickly became apparent that they were taking their toll on performance. The biggest problem seemed to be the combination of larger tyres, which raised the gearing by about 6%, and the wind resistance of the roof rack. I looked around for ways to solve this problem and came across an article about Van Aaken and their fuel pump optimisation technique for diesel engines.

Basically, they say that all diesel engines are set up in an 'average' state of tune at the factory but that with some careful alterations to the fuel pump settings the tune can be 'optimised' for a specific engine. For the pre-electronic diesel control 300tdi engines they claim that power and torque can be increased from 111bhp and 195lb ft to  135bhp and 245lb ft respectively, which is comparable to the later TD5 engine.

The alternative seemed to be to have a larger intercooler fitted, but I liked the elegant simplicity of the Van Aaken approach and the fact that to all intents and purposes the engine is unmodified. I also have the advantage that Van Aaken are located only a couple of miles from where I live!

I decided to have the optimisation carried out and when I drove away from Van Aaken the difference was truly astounding! The engine pulled harder and more smoothly from lower revs with a significant reduction in the turbo lag that Tdi's usually suffer from. On the motorway, where the effects of the tyres and roof rack were most noticeable, in was much easier to maintain steady progress up hills and into a headwind.

Over the course of  several years since this modification was carried out, many thousands of miles were covered without any problems. The vehicle also passed several MoT tests without any concerns regarding the emissions.