Building BMW Engines for Club Racing Competition and Power to Weight Ratio Classes
Selecting the right engine platform for a club racing car is one of the biggest decisions a racer will have to make. In the last few years most of the competitive classes have shifted towards the power to weight ratio method of classification. For some engines and chassis this has been great, but for others it has made them uncompetitive. Power to weight ratio classes have a way of making high revving naturally aspirated engines uncompetitive. Some engines have natural advantages in power to weight classes. High displacement engines with low rev limits do well due to their broad torque curve and relatively low horsepower numbers. This means they can operate in a wide rev range and still put out a good amount of power.
Below is an example of two dyno graphs from the most popular BMW six cylinder race engines with 3.2 liters of displacement. You can see that the S52 engine has a broad torque curve and a relatively low horsepower curve. Many complain that this engine “runs out of steam” towards the top of its RPM range. However, when we consider it for a power to weight ratio class it has the distinct advantage of having a peak horsepower number that is very close to its peak torque number. The S54 has a better torque curve than the S52, broader and flatter. However the horsepower curve pulls very high all the way to 7800 rpm. This means that a car with an S54 in it will have to have much more weight in it than one with an S52. That is of course unless the engine is detuned in the top of the powerband.
We’ve outlined what the majority of the competition is using and why they’re doing well with those engines. Our primary focus was to take the engine we’ve been racing for several years and have developed into a very reliable and simple endurance racing engine. The BMW S14 engine has its strengths but those strengths have never been said to be low end torque and a flat broad power curve. Traditionally these little 4 cylinders had to be driven at very high rev ranges in order to make horsepower and be competitive. Unfortunately what used to make this engine successful years ago simply won’t work for power to weight ratio racing.
We decided to start from the drawing board with our engine platform and see if we could take a new perspective on the S14 and make it competitive with the six cylinders. The reason we wanted to do this was because swapping the 6 cylinder into our incredibly light E30 chassis would bump us up too many classes and we’d no longer be able to race in the class we were in. Even our current S14 was already on the verge of being in the next racing class due to its high horsepower numbers.
We had several goals:
- Lower peak horsepower numbers
- Increase peak torque and broaden the torque curve
- Increase reliability of the motor if possible