A few years ago, I started a topic on the M42 Club forum about making an ITB kit for my car, a 1997 BMW 318is, an E36 with an M44 engine. The M42 Club still exists, but it regularly loses uptime these days, and the sister thread over on bimmerforums was never as detailed as the M42 Club thread and with the image hosting I used at the time having gone down, the thread doesn’t make much sense anymore. Since then, YouTube, Facebook groups and Discord servers have overtaken forums as places where people go to find DIY information, and YouTube is the only useful resource out the three since it is the only one with persistent information. Facebook and Discord are extremely difficult to search for previous posts and information shared can never be as detailed as it was on forums, because of this I see the same question (or some variation of it) pop up every few days on different groups – what should I do to my M42/M44 to get the most out of it?

To answer that question and to share the information I’ve accumulated over the years, this will be the first in a series of articles focusing on tuning the E30 and E36 318is platforms, specifically focusing on the M42 and M44 engine. The goal being that whenever someone asks what they should do with their 318is you can send them here and they will get the answers they need.

The best place to start is probably to answer the question that most keyboard warriors ask; Why?

Why tune the M42/M44/318is platform?

When I say 318is, I don’t really mean the 318is specifically – I mean cars with the M42/M44 engine, but that gets a bit long-winded so we’ll use 318is to mean ‘318is plus the other cars with the M42/M44 engine’.

When I originally started the build thread on the ITB kit, I immediately started by heading off the keyboard warrior questions:

However, this isn’t a build thread where I just want to share my progress, this is an explanation on how to get the most out of your platform so I will have to address these questions at some point. Ultimately however, it all comes down to fun. If the only question is ‘what is the best car’, then the answer is ALWAYS the newest car. Technology moves forward so if you want to set the best lap times the highest performance model of the most modern car will always be the right choice. If you enjoy tinkering, enjoy the feel of a specific car or otherwise see cars as a hobby then the question changes to ‘what is the best car for me’, and that answer is entirely subjective and a 318is might be that car.

I’m not a historian so I’ll skip over the deep details, but the E30 318is was introduced as a homologation car; it was a vehicle that was always intended to perform in motorsports. When new, they had different suspension than the base model cars, and respectable power from a 4-cylinder engine (103kW) at the time. Similarly, with the E36, they were sold with different suspension than base cars, the M42 engine and later the M44 engine with the intention of being a sportier car than the base 318i. With the 318is there are two big things that work in their favour compared to all the other cars in the E30/E36 line-up:

1. Weight
2. Power

I can already hear a groan from the 6-cylinder crowd about the power, but I will get to that.

Weight

The 318is has a substantial weight advantage over all the other variants, and for the E36 cars this also includes the M3. I’ve had my car on a weigh bridge, with me in it and fluids, and it comes in at a featherweight 1240kg, more than 100kg better than the M3 LTW and more than 200kg better than the base model M3. The actual curb weight of an E36 318is is closer to 1140kg. Obviously when comparing power to weight ratios the M3 is a substantially faster car, but 200kg+ weight difference makes for a noticeably different driving experience with a far nimbler vehicle – and this isn’t just due to the weight difference, but I will have to come back to this point.

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
M3 (US)	0.124
M3	0.164

Looking at the table above, the 318is is more comparable to the performance of the 323i just by showing up to the party, and the M42/M44 engine wasn’t just in the 318is, it was also in the base Z3 and some of the E36 compacts which have better power-to-weight meaning some of these cars are more comparable to a 325. So, this brings me to the first reason for why the 318is might appeal to you:

It is a lightweight car, and it is easy to make it lighter. If you just want to get into a base level of motorsport, the 318is can be made a lot lighter by binning the creature comforts, and it has major head start in being lightweight compared to its contemporaries. The reason it was so lightweight to begin with is because the engine is two cylinders shorter, and on a steel block that makes a big difference (all the cars including the M3 had steel blocks). Being a rev happy lower torque engine compared to the 6-cylinder cars, it also meant that the driveline was considerably lighter with a smaller gearbox and differential, all heavy cast items so being smaller represented a substantial weight savings. You also get a different driving style with a rev happy engine which appeals to a lot of people as a ‘driver’s car’, but I’ll get to that soon.

I mentioned earlier the weight savings make a big difference and not just because of the weight savings. The 318is is a mid-engined car and has a different weight distribution than all the 6-cylinder cars. You’ll often come across sources talking about BMWs having a 50:50 weight distribution, when weighed that is usually correct with a tiny rear bias (say 50.5:49.5). With the 318is, the engine being shorter, sits almost entirely behind the front suspension making the weight distribution more around 52:48 and if you a competent driver that is something you can feel. As an example, compared to a contemporary NB MX-5, it is a much easier car to drive fast with a much lighter nose under braking.

When people have built big power M42/M44 engines (225kW+) for competition, the weight of the engine and the weight distribution change are factors they will consider.

Power

Power is a funny one, since by any modern standard the 318is is not a powerful car, but against its contemporaries it was respectable. Power in the context of weight however shows it to be a competent choice. What most people don’t realise though is that marketing exists. Marketing is the reason the Mazdaspeed MX-5 had such a small power bump, and it was why the M42/M44 engine was restricted by BMW – they needed to have lower performance compared to the higher trim models. The MX-5 couldn’t be allowed outperform the RX-7, and likewise the 318is couldn’t be allowed outperform the 320i and so was restricted in performance. This is the same reason why the lighter Z3M was a slower car than the M3 despite sharing the same engine; BMW restricted its performance by using a very long final drive so that it wouldn’t be a direct competitor with their halo car. So how did performance restrictions come into play with the M42/M44?

The M42/M44 was primarily restricted through its intake. The ITB kit that I put on my car all those years ago wasn’t just a simple bolt on mod, it was something that I spent hours optimizing using CFD to get the best flow characteristics. Initially I was expecting 5%, up to 10% if I was lucky, changes in power but dyno results showed up to 16% change in peak power and up to 25% change in power across the midrange. This one modification changed the power to weight ratio to be the equivalent to a 328i, with no other changes. BMW had significantly restricted the performance of the M42/M44 and it wasn’t until I started tinkering with it that I realised by how much.

In the interest of thoroughness, power and power-to-weight are not the only measure of performance. The torque delivery of all the 6-cylidner cars is much better than the M42/M44, starting earlier and delivering more. This creates a totally different sensation when driving of immediate power delivery. The 318is needs to be kept in the higher RPM to feel the power, but again that might be something you enjoy or be seeking for motorsport. It is different but the takeaway from this should be that the engine can deliver substantial improvements in power with very little attention. None of the 6-cylinder engines see as substantial a response to intake changes.

Takeaway

The M42/M44 engine is capable engine that benefits from small changes due to being restricted by BMW when released. The E30/E36 platforms both benefit from the smaller engine due to the notable difference in weight compared to the larger engines. This allows for a rev happy car that benefits from having close gear ratios or a tight final drive, and the difference in weight balance and weight change the car’s behaviour to be more dynamic and responsive compared to its heavier counterparts. Will you outperform an M3 in an absolute sense? Not without building a serious engine (and I will get to that in later articles) but if you enjoy a bit of tinkering and the specific style of driving it comes with, then this might be the car for you.

In the next article I’ll get to answering the questions of what you should do to the M42/M44 and to the cars that come with these engines. For the time being, now you understand why you might find this platform interesting. This answers the first two questions I posted all those years ago:

Q Why don’t you just by a faster car? – A This car is fun.

Q Why don’t you just do an engine swap? – A I don’t need to, and this engine is fun to drive.

I’ll get to question 3 in a later article.

Going forward I’ll be covering modifications from easily accessible bolt-ons, to what is required to build 200kW+ engines.