Manifold Swap Project E36 M3: Part 2 - Technical

In et 9/06 we introduced our '97 E36 M3 Sedan project car and looked at the impact on horsepower and acceleration caused by fitting lightweight wheels. This month, we start to seek more power from its 3.2 liter S52 motor with a popular intake manifold swap.

To give you some background on what we're doing, you should know that in 1996, BMW sought to increase the responsiveness of the E36 M3 by increasing displacement from 3.0 to 3.2 liters. They also changed the final drive ratio from 3.15 to 3.23:1 and added a smaller, choked-down intake manifold.

The first two mods were nice upgrades with little compromise. However, the intake manifold changes increased the air velocity into the motor but only up to 4500rpm, and did so at the cost of reduced airflow. The result was a weaker top end on the later 3.2 engines. That's why, even though the OBD2 3.2 liter S52 motor in the '96-99 M3 made more torque than the '95 OBD1 3.0 S50 it replaced, peak power remained unchanged.

The same applies to the 328i that replaced the 325i in '96. Those engines are dubbed M52 and M50, respectively, and both use the same intake manifold as the M3 of the same year. Confusingly, the names of the manifolds on the S50/S52 M3 engines retained their respective M50/M52 codenames inside BMW.

The M50 manifold from the 325i or the '95 M3 is often used to upgrade the 328i or M3 3.2 engine. For a while, owners of the M3 3.2 retrofittted an OBD1 ECU along with the M50 manifold in order to run the larger 3.5" HFM (Hot Film Mass, or air mass sensor), as found in the Euro-spec M3. However, this was a costly and illegal procedure. As a result, the OBD1 '95 M3 3.0 became a more popular car for tuning.

Fortunately, things are now different for owners of the OBD2 M3 3.2, thanks to companies like Eurosport High Performance (EHP). Like many BMW specialists, it has various normally-aspirated upgrades. Its stage 1 kit, for example, includes an injection-molded carbon-fiber Evo2 intake kit plus software that removes the speed governor and sets the redline to 7000rpm. Its retails for about $738 and a peak gain of 15whp is possible, with gains of around 10whp in the upper reaches of the rev range.

With the software's new rev limit, you can hold the car in lower gears for longer. However, you get a significant drop of about 25whp between 6500-7000rpm when using the stock M52 manifold. This proves BMW was wise to set the rev limiter at 6500rpm, as shown in our baseline run (see graph).

So the EHP stage 2 kit adds an M50 intake manifold conversion kit to stage 1. It includes an adapter that allows the idle air control valve and all vacuum lines that go into the bottom of the M52 manifold to be fitted to the M50 manifold. It retails for $349 (plus the price of a used manifold - about $100 on ebay - and an optional $30 modified fuel rail cover).

We previously tested a stage 2 kit on a different car and it lost a significant amount of torque (about 8-15 lb/ft over stock) from 3200-4200rpm. However, there were gains over 5000rpm, showing a peak of 30whp at 7000rpm over the stage 1 kit. So now it would definitely pay to hold the car in-gear for longer.

The EHP stage 3 further ramps up the power (and cost) with everything in stages 1 and 2, in addition to a set of Schrick cams, a re-calibrated 3.5" HFM with an adapter to fit EHP's intake kit, as well as 24 lb/hr Bosch injectors, a fan delete nut, the relevant software and an optional traction control delete elbow.

The entire kit retails at $3396, including the first two stages. A peak gain of 35whp at 6400rpm over stock can be realized. And if you compare stage 3 to stage 1 at 7000rpm, the gains are over 45whp because stage 1 retains the stock M52 manifold that loses power over 6500rpm.

For our project car, we wanted a significant increase throughout the rev range without the cost of the full stage 3 kit. We also wanted more power than stage 1 could provide. So stage 2 appeared to be the best option, but only if we could somehow overcome the loss of low-end torque.