BMW E30 Track car
This is a classic tale that proves the old adage of measure twice and cut once. When Ross approached us to build a replacement engine for his E30 track car the first step was to discuss the required performance profile to match the intended use. Ross is a realist as far as driving ability is concerned and like most of us who take cars to the racetrack a few weekends a year drivability is key, so a narrow power-band screamer was quickly ruled out.

The classic pros and cons of turbocharging were talked through, potential for high power gain, that the straight six, two valve M20 engine is a good candidate for forced induction etc. This was also a well trodden path in that it has been carried out many times before. However the effects of turbo lag on a track car when recovering from a missed apex was considered not ideal. Also Ross is not one for following the crowd (neither are we!), after all if you do the same as everyone else, you end up with what everyone else has.

So having defined the criteria, the solution presented itself. Build a low compression, bomb-proof engine as stage one, use it and have fun. To be closely followed by a stage two development of adding a supercharger. Stage one consisted of the usual mods when building a proper performance engine…

- Balance and lighten bottom end
- Worked cylinder head
- Mild cam (wild race cams are a waste with forced induction)
- Programmable EFI

With the intentional low compression build power records were not going to be broken and the E30 was not going to be a rolling road king. However a couple of outings, including a thrashing by drift merchant James ‘Doricar’ and a certain Rob Willson (driving ‘instructor’ to F1 drivers) produced smiles all round. Proving that reliable power in a free revving motor counts for a lot.

As ever you get used to whatever level of performance you have and it was not long before the supercharger design was underway. You can buy all sorts of electric ‘superchargers’ on ebay – forget them. You can also find small supercharges, mainly from the new style mini. Again forget them as they just won’t pump enough air for the 2.7Ltr straight six that ended up in the E30. When you do the sums what you need is an Eaton M90. The 90 means that it moves 90 cubic inches of air per revolution (approximately 1.5Ltrs) and is the same capacity as fitted to the Aston Martin DB7. In fact the one we obtained was off a DB7…!

The key to a successful supercharger installation is to make sure it is mounted rigidly and that the pulleys are in line. A significant amount of time went into the design of the mounting bracket as the BMW designers had not envisaged that anyone would want to mount an Eaton M90 on the side of one of their cylinder blocks! It was also important that the installation looked factory and not scrapheap challenge. At DJC Racing we know that if it looks right, it usually is. If it looks wrong, then it is wrong…!

The result – as you can see, or rather hear, from the video clips is just a bit different from a standard BMW. A supercharger forcing in air throughout the rev range makes for a very rapid point-to-point A and B road machine that Mad Max would have full use of.

Click here for a gallery of the car in various stages of build. (Will open in a new window)

<back