A Tuner’s Guide to the E92 BMW M3

Engine

The E92 M3 introduced an all aluminum, dual overhead cam, 4.0 liter V8 dubbed the S65B40. The S65 produced an advertised 414 horsepower at 8,300 RPM and 295 lbs ft of torque at 3,900. Much like Motorsport engines before, the S65 is much more of a spinner than a torque monster and is most lively in the upper half of the RPMs. The individual throttle bodies mean throttle response from just thinking about it and the individual throttle bodies produce an intoxicating symphony bellowing under the bonnet.

The S65 engine shares a vast majority of its components with the S85B50 – or simply known as the V10 engine in the M5 and M6. This is because the S85 was more-or-less chopped like a top chef down to 8 cylinders and had a few components redesigned along the way to reduce weight and better fit the E92 M3.

The S65 engine does not offer effortless low RPM acceleration from larger displacement V8’s common in American cars. But, if high revving engines is your thing, you’ll have a hard time lifting your right foot. The S65 was loved so much in fact, that it received the International Engine of the Year award 5 years straight. Spell that with me: F-I-V-E years. That’s 80% of it’s production life cycle.

It’s that good.

Engine Specifications
Block: 90-degree, siliconized aluminum, with no liners, 98mm cylinder spacing
Displacement: 3,998cc
Bore and Stroke: 92mm bore x 75.2mm stroke
Heads: Aluminum with 35mm and 30.5mm valves
Weight: 445 lbs

Summary

Pros Cons
Exotic Sound Low Torque
8,400 RPM Redline Rod Bearing Failures
Throttle Response Troublesome Throttle Actuators
400 WHP w/Bolt-ons Turbo is the Only Safe FI Option

Problem Areas and Solutions

Unfortunately the S65 engine isn’t flawless. Few engines are. Of the handful of items to address, one is of major concern and should be considered as necessary as an oil change and performed as soon as the vehicle is purchased, if they hadn’t already been replaced and the work documented by the previous owner. What are we referring to?

Rod Bearings
In short, the factory rod bearings have extremely tight clearances, not allowing for sufficient lubrication, and are known to wear abnormally quick. If they wear too far it can result in a catastrophic engine failure. There have been reports of rod bearing failures at less than 20,000 miles while other cars have over 200,000 miles on original bearings. In late 2011, BMW updated the rod bearings from a copper/lead material to a harder aluminum-tin alloy however this seems to have done nothing other than prevent monitoring wear by oil analysis. As the BMW community is concerned, all S65 engines with original rod bearings are on borrowed time. If the rod bearings fail, you’ll be looking at a new engine and easily a 5-digit repair bill.

Rod Bearings Solutions
There are a number of BMW specialists that offer replacement rod bearings. BE Bearings and VAC Motorsports have become the most popular rod bearing replacement option as of late.

BE’s bearings have been designed in consultation with experts from NASCAR, Indy Car, and former BMW M-Division engine designers, and are manufactured by Clevite. BE recommends use of their designed ARP rod bolts, but if they are back ordered it’s okay to use OE rod bolts but do not use non-BE designed ARP rod bolts.

VAC offers “friction resistant” coated rod bearings that “is a physical layer (not just a treatment to the layer) with both a high embedability factor, and a ‘dry lubricant’ property. What makes them so good is that they can run tolerances that BMW engines like and not see the typical failures that one associates with the OEM units.”

The price of a replacement S65 engine can be well over $10k so we feel it’s a good idea to also budget a minimum of $2,500 for rod bearing replacement after purchasing one of these cars. It’s also a good time to replace motor mounts, since they’re cheap and the technician will already be there.

Throttle Actuators
These should not be considered a preventative maintenance item but they are a common failure piece with this engine and a real pain to replace when they do. It’s the throttle actuators. Throttle actuators contain a circuit board and gears that move an arm that in turn controls the opening of the engine’s individual throttle bodies. There is one throttle actuator per bank, so 2 total. If one fails, the engine goes into limp mode. Due to their placement in the engine and labor cost, it’s advised that they are replaced in pairs. New throttle actuators sell for $850 or so each. Factor a minimum of $2,500 to replace both from a repair shop.

Throttle Actuator Solutions
Exactly why the throttle actuators fail in the first place has yet to be determined. Some claim the plastic gears wear and cause too much play. Others say it’s the circuit board. There’s even the idea that the throttle rail gets gunked up and resists spinning, which puts additional load on the gears and then fries the circuit board. There are companies that sell replacement gears made of material that won’t wear and others who repair the circuit boards.

Increasing Engine Performance

The BMW S65 produces over 100 horsepower per liter from a naturally aspirated configuration right off the showroom floor. That’s pretty darn good, but there is a little more that can be extracted. Here’s are the modifications we suggestion doing and what’s best to skip.

Oil Cooling
There should be no issues with oil cooling on the street however it’s not unheard of for oil temperatures to rise to questionable levels during hot days at the track. If oil temperatures rise too high, the car could go into a limp mode. The simplest way to combat this is to install a larger oil cooler. This will provide greater surface area for oil to pass through and air to cool at speed. This should help keep the temps in check and allow for problem-free lapping on the race track in the summer months.

Intake
Replacing the plastic intake elbow that connects the front of the intake plenum to the air box with a smoother unit can net a few horsepower. By that, we mean less than 5. Dinan advertises 8 peak hp and 5 tq and that’s probably generous. The entire factory intake from the air filter to the head flows extremely well. Sure, aftermarket intakes are available, but the dollars-to-power ratio just doesn’t add up for us. Unless you’re after every last pony, just replace the factory air filter with a drop-in of your choice – like this Macht Schnell.

Pulleys
Replacing the engine’s accessory pulleys with slightly larger diameter pulleys will allow the engine to spin more freely. Gains of 9-13 horsepower on the dyno are common however some owners have reported increased coolant temperatures. Even at a price of $300 for Macht Schnell pulleys, we wouldn’t rush out to grab a set, but we do think they work well when combined with the mid-pipe modification and a tune. Just monitor the essentials.

S65 Stock Exhaust
S65 Stock Exhaust

Exhaust
The factory shorty headers flow well so don’t bother touching them. The huge bottleneck is in the connecting X-Pipe. There are 4 catalytic converters: two 400-cell up front followed by two 200-cell. Eliminate the front 400-cell cats with a set of clamp-on bypass track pipes for gains of 20+ horsepower and torque – just beware of your local emissions laws. The rear-most catalytic converters are 200-cell and eliminating those won’t net much power at all. If removing any of the catalytic converters, expect a Check Engine light. An ECU tune can eliminate the CEL and gain a few more ponies. It’s not unheard of to see 30+ horsepower from the primary cat removal and a tune.

The catback to the exhaust tips flow very good as well. Changing the muffler out for an aftermarket unit can change the exhaust note some and may get 5 horsepower or so. Modding the factory muffler box is also a popular option. Essentially, cut open the top of the muffler and replace the porous pipes with hard pipes. This prevents the material in the muffler from absorbing the sound. It makes quite a difference.

ECU Tuning
Factory engine tunes are designed to work everywhere, not just your location. A tune for your car in your region can net power gains of 10+ or more, with matching torque. Many companies offer tunes, so the choice is yours. We’d suggest looking at BPM Tuning, Technique Tuning by Frank Smith, or Evolve.

Forced Induction
While supercharging the engine can quickly increase power output considerably, there have been a string of engine failures that seem to indicate belt driven power adders increase load on the main bearing and do some nasty damage. Big power can be realized but cross your fingers for longevity. We wouldn’t do it.

On the other hand, turbo kits do not increase load on the main bearing and there have been no engine failures that tie the two together. Additionally, turbo chargers make are far more efficient at making power. The downside is they are more expensive and space in the engine bay is at a premium. Even the best turbo kit is probably less than the cost of a supercharger and a new engine. We’d go turbo if forced induction was a must.

1. Engine | 2. Transmission | 3. Chassis | 4. Suspension | 5. Brakes | 6. Wheels and Tires