Tuning the BMW M42 and M44 Engines – Part 2
In the previous article, I discussed some technical reasons that make the M42 and M44 engines cars a great jumping off point for building a car around. I focused mostly on the E36 (the platform I’m most familiar with) and to a lesser extent, the E30. These engines are also used in the Z3 and are a popular choice for Lotus 7 style track cars, and in no small part because they are cheap. Their under appreciated nature means that they’re typically around $500AUD for a whole engine and I regularly see people struggling to give them away. An easy way to find them is from people who are doing a 6-cylinder swap and are unaware that a few pokes with the effort stick can get some good results. So, what are those results? I won’t make you wait until the end of the article to find out, but you will need to read the whole article to understand how this is achieved.
Setting Expectations
I’ve seen as much as 222 wheel horsepower (whp) from a naturally aspirated stroker (which for perspective is about the same as the euro spec S50B32 used in the E36 M3) and up to 800whp from turbo cars. The focus of this article will be on naturally aspirated cars, though I may on occasion mention something beneficial to turbo builds when it comes up.
What Should I do to my Car?
Typically, the most common question on various Facebook groups is ‘what can be done to this engine?’ followed up with a few comments about something they have heard or seen, which is almost invariably wrong. Unfortunately, there are more than a few charlatans when it comes to performance car parts, and when it comes to BMW there is more than one person out there who misrepresent the results they get or are very opaque with how they achieved their results to drive up sales of unnecessary parts. For this reason, this article will be written based on real results from my own testing, as well as results courtesy of Rama Diaz and John Phoenix.
To keep the articles in a presentable size, I’ll just be presenting some results at a high level and lightly discussing how they were achieved. Later articles will go into the specifics about how different additions do (or more importantly, don’t) affect performance so that you can better distinguish between performance parts and wasting your money.
Please note, when presenting dyno results there can be large amounts of variability between different dynos, locations and details as seemingly insignificant as tyre pressure can affect the results. For this reason, usually the best way to interpret a dyno is the percentage of change between two results on the same dyno rather than discussing measured power, but for the sake of convenience I’ll still use power for its ease in conversation.
Real World Results
Below are the results from a factory power run, and the implementation of the prototype RHD ITB kit, this was before I optimised it for my car. This was the car as featured in my old YouTube video. You can get the ITB kit here.
Most interesting to me is this chart which shows the performance change as a percentage across RPM, which should conclusively put to rest that ITBs cost low and midrange power as you can clearly see midrange power was higher by as much as 22% over factory.
Here are some results all jammed together (in wheel kilowatts). (2.9L) refers to the volume of the airbox as I did some testing with variations of the volume. What it shows for most people though is that simple exhaust modifications, such as a high flow muffler, do in fact improve the power seen at the wheels. For this test I had a flange installed on my muffler and swapped between the two mufflers on the day.
What is great about the RHD ITB kit is that it can be run using the stock ECU, which I did for many years and all the above results show that you can achieve significant results just from modification of the induction and extraction systems of the M42 and M44 engines. If you want to start playing around with it a bit more, you can get a lot more out of it very quickly.
In NSW there is a single make (E36 318is) race series where cars are capped to 100wkW (133whp) and the only change between those cars and the charts above is ECU tuning.
Below is an unopened engine with an RHD ITB kit and a straight exhaust plus a standalone ECU that has been tuned by Rama at RHD. This engine was a bit exceptional, typically they cap out at 100wkW, but who knows, you might get lucky!
Below is a more typical result:
To really drive my point home, here is a standard engine against a tuned engine with an intake and exhaust.
On my own car I was able to hit 100wKw with the standard ECU by using the right cams. A later addition of a tuned standalone ECU saw me peak at 112wkW with an M44 engine.
Built Engines
Now we’re getting into the meaty end, and these results are courtesy of John Phoenix. John spent many years perfecting his stroked and bored super tourer replica to get the most out of it naturally aspirated. He was limited by displacement for his racing class, keeping the car at 2.0L. And to keep some realism on these results, John ran his builds using Ethanol so these results are 15-20% better than what you could expect from conventional fuel combined with his target driving envelope being track work meant that he wasn’t limited by pesky issues like parking lot driveability. You can see (and hear) John’s car below:
John’s most powerful build was an 87×88 bored and stroked M42, with a factory head with some of the hottest cams you’ve ever seen running S54 ITBs.
In the video below you can see him cranking out 226 whp, substantially exceeding the power output of an E36 M3.
Stroker Kit
John’s experience in building engines has been essential in informing my decision to proceed with building a complete stroker kit, particularly the dyno below. This graph shows two power curves for the exact same engine with a single change; one is running an 88mm stroker, the other is not. And your eyes don’t deceive you, there is a 40hp difference from this modification on its own.
The kit that I’m putting together will not have the same output that John was able to achieve. The cams I’m targeting are far milder that what John ran (but they’re hot enough I promise) and my target market isn’t for ethanol but for regular fun road and mixed track use. I’m anticipating between 125-142wkw (166-190whp), but once everything is put together and tested I’ll share the results.
Head Work
One of the things that is conspicuously missing in this article is headwork and there is a reason for that. Unfortunately, headwork is quite complex, and so it is rarely tested on its own and is usually part of larger builds so it can be difficult to test back-to-back with no other changes. The article above also shows that excellent results can be achieved without headwork as the heads in these cars are done well, despite what unscrupulous tuners may tell you. That said, I will be installing my own shiny CNC ported head with oversized valves because it will support the build with a larger swept volume and bigger cams. Below you can see the results from the flow bench, with the top two lines being the intake before and after and the bottom two lines being the exhaust before and after. There is about 20% better airflow through the head, and though that won’t translate to 20% more power it will help me get everything out of the last bit of RPM.
Bringing it all Together
Using all that information I thought I would update the power to weight ratio chart. From my testing, about 30kW is lost in the drive train from the rated power, so I’ve added that back into the measured values used from above.
| E36 Model | Power to Weight Ratio (kW/kg) |
| 318i | 0.066 |
| 318is | 0.090 |
| 320i | 0.076 |
| 323i | 0.087 |
| 325i | 0.098 |
| 328i | 0.099 |
| 318is (Intake, Exhaust and ECU | 0.121 |
| M3 (US) | 0.124 |
| 318is (Stroker Kit) | 0.144 |
| M3 | 0.164 |
| John’s Race Spec Monster | 0.172 |
And yes, John’s car was about 3s a lap faster than his previous M3.
The next articles will start to drill down into specific components needed to achieve specific results, how they work and what to expect. Everything detailed in these articles can be purchased through the website, but if you can’t find it or have questions, please send me an email!
If you want to follow on about the parts on YouTube, you can see it all here!