The figure that most performance parts manufacturers quote is brake horsepower (BHP) increase. This is probably the most widely used term for describing how well (or not) that an engine is performing. While the BHP figure is a good basis to determine how well an engine is performing, it is not the best to indicate how strong the engine is. BHP indicates the rate at which an engine will produce power, i.e. the more BHP the quicker you can move through the rev range while on the road. The other (and ultimately more important) figure to know is the torque output. Torque is a measure of energy transmitted at an angle perpendicular to a point of origin, or turning force generated at the crank.
So, what is the difference? Well, the more torquey an engine, the easier it will be to tow heavy loads, overtake at motorway speeds and drive uphill, etc.. The more BHP, the quicker you will be able to accelerate or change speed. One of the lesser know facts amongst the automotive world is the difference between petrol and diesel engine cars. What you will normally find with petrol cars is that the power (BHP) and torque (lb/ft) figures follow each other quite closely. For example, an Mk2 GTI 8V Golf has a stock power output of 112BHP and torque of about 120lb/ft. Diesel engines however, follow a different trend. The process of burning diesel produces more energy than petrol, but has been deemed somewhat less desireable because of higher emission levels (until recently) and higher noise levels. Diesel cars can usually produce torque figures that are around double their power figures. For example, the new Passat 2.0 TDI produces 130BHP and over 200lb/ft torque. What you tend to find is that a petrol engine will have more power than a diesel engine of similar displacement and aspiration, but the torque delivery is totally the other way round. This is why the Mk4 TDI kit car caused so much of a stir in the WRC, where its 300lb/ft engine was a cause for concern amongst its predominantly petrol based competition. Uphill, there was no stopping it.
Diesel technology has progressed over the last couple of years, meaning emissions are now at an all time low and in some cases lower than some petrol engines. But they are still quite noisy. Manufacturers seem to be stuffing their diesel cars full of sound proofing, which only reduces the power to weight ratio of their cars. Modern cars are getting heavier, not lighter, but a lot of this is due to ever changing laws meaning more and more safety features. Safety is a big seller of cars. Fortunately, car manufacturers are making their engines more powerful to cope with the extra loads, and this seems to be an even bigger seller!
So, when the time comes for you to buy a new car (you won?t be selling the GTI though, right?) would you consider a diesel? Just think of the bags of torque at your disposal. Improved fuel economy. ARE YOU MAD? IT?S A DIESEL! Get back in your GTI and go for a long drive.
