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RON'S HINTS & TIPS FOR OPTIMUM PERFORMANCE AND ECONOMY

Some suggestions for maximising performance and economy on any engine, but especially important on a tuned one.

1) EGR VALVE.

The egr or exhaust gas recirculation valve feeds a controlled amount of exhaust gas into the inlet manifold. The amount of gas is most commonly measured by the change in maf sensor signal when exhaust gas replaces fresh air, the signal dropping when less air enters the engine. Up to 40% of the air can be replaced with exhaust gas, the aim being to reduce combustion temperature and therefore reduce NOx production.

It is NOT a system for reducing temperatures to prevent damage to the pistons or other parts. In fact exhaust gas is only fed in on part throttle - ie light load such as when driving in urban areas. As soon as the load increases above about 60% no exhaust gas is fed in. So anyone who claims disabling the egr valve will damage the engine should explain why the engine is not damaged on loads from 60-100% when the egr system is inactive. So at speeds above about 80mph or much lower when towing there is no egr system working yet the engine survives, thus proving that these clowns are talking rubbish.

The egr valve can either be in line with the inlet manifold air inlet (eg BMW (see photo left , Ford, Vag, ) or fitted on a separate connection between inlet & exhaust manifold (eg Peugoet/Citroen/ Rover L series). The inline type are prone to becoming clogged with carbonised oil. The oil is from the crankcase ventilation system and the hot exhaust gas carbonises it in the valve. Here's a photo (below right) of a Rover 75 egr valve after 90k miles.

You can see that the airway is significantly obstructed by the gunge, never mind the egr valve mechanism. Fitting a bypass removes the obstructing mechanism and the prevents further build up. (Cars to euro 4 emissions spec can't always be bypassed without the engine warning light (MIL) coming on and in some cases limp home mode occurring. One owner devised a means of preventing the light coming on on a Euro 4 BMW - more here. This method may work for other vehicles.

2) CRANKCASE VENTILATION VALVES Photo of a BMW (+ Rover 75/MGZT/Freelander TD4) unit here

As we've learned from the previous section, oil fumes from the crankcase end up in the intake system, having entered it between the air filter and turbo inlet. There will be a regulating valve of some sort and often a filter or separator to reduce (usually not very effectively) the amount of oil passing through. This is why the intercooler, hoses and inlet manifold is coated in oil: the more worn the engine the worse this will be due to increased piston blow by. BMW have now added this to the service schedule for replacment every 100Km/60k miles and the latest version doesn't have a filter.

3) INTERCOOLER HOSE SEALS

As mentioned above, there is always some oil in the intake system and often this will lead to the joints of hose with metal intercooler inlet & outlet deteriorating. If there is an oily deposit where hose meets intercooler (or inlet manifold and /or turbo outlet) then there is a leak, which will allow air as well as the oil to escape. even a small leak can have a significant effect on the performance at low rpm when the turbo isn't producing any boost to swamp the leak. A known problem on the BMW M47 r engine in the 75/ZT/TD4

4) DRIVING TECHNIQUE

Hands up if you drive your diesel as if it has a petrol motor? I counted 50% of you.. - you know who you are. Maximum torque is around 2000rpm on a diesel and the turbo starts to work from around 1500rpm then the torque tails off above 3500-4000rpm. If you rev the engine to 4000rpm before changing up, the revs will only drop to about 3000, so you have missed out on the maximum torque region of 2000-3000.

Since it is torque that accelerates the vehicle (and determines its top speed*) doesn't it make sense to keep the rpm in the region of maximum torque? By keeping the rpm in this 1500 - 3000rpm area you minimise noise, maximise fuel economy and minimise engine wear. To prove the point, I compared the 30-70 time through the gears on my X-Type and found that it was quicker changing up at about 3200rpm than it was at 4000rpm.

There are some drivers who do the opposite, grinding along at 1000-1500rpm. Using this range is fine if it can be done on very light throttle and I often let the revs drop to around 1000 in top gear on a whiff of throttle. BUT as soon as any acceleration is required or more than a whiff of throttle is needed to maintain speed I change down. Below 1500rpm the turbo produces little if any boost so you are in fact driving a non-turbo diesel and we know how 'dirty' & gutless these were.

* You may here claims that torque accelerates the vehicle whilst bhp determines its top speed. Not so, the bhp figure is derived from torque - this is the fundamental force originating from the expanding combustion gases pushing the piston down. The vehicle will keep accelerating until there is no reserve of torque left (its all been used overcoming the air drag, friction and tyre losses). If you knew the torque and engine rpm at this point you could determine the bhp from the formula bhp = torque x rpm/5250. If you can prevent the torque tailing off too much with rising rpm, you can achieve high bhp figures, hence a 1L motorcycle engine can produce 140bhp, not because it produces much torque, but simply because what torque there is can be maintained to 12-15k rpm ditto for a F1 engine. Or put it in a diesel context, if it was possible to make a turbo diesel rev to 6000rpm and produce the same torque as it did at 4000, then a standard 140bhp Mondeo would produce about 200bhp.