BMW E30 Turbo Guide
Austin graduated from the University of Colorado Denver in 2021 with a degree in technical writing and remains in the Denver area. Austin brings tons of automotive knowledge and experience to the table. Austin worked as a Technical Product Specialist at BMW for over 5 years and drives a heavily modified E30 325i with a stroker kit, all of which he built from the ground up.
Anyone that owns a BMW E30 knows that the factory M20B25 2.5L, M20B27 2.7L, and M42 4-cylinder engines leave a lot to be desired in the horsepower department. While the factory engine options are certainly enough to get a 2600 lb BMW E30 going under its own weight, you won’t be winning any drag races.
That is where forced induction comes into play. Like many other BMWs from the 80s, 90s, and early 2000s, turbocharging is a go-to solution to get some more ponies under the hood. Playing into that further are the bulletproof engines offered in US-Spec E30s which can all withstand a fair amount more horsepower than their factory output. A well-sorted BMW E30 turbo is capable of producing up to 300 horsepower without any serious internal upgrades or modifications.
In this guide, we’ll cover the basics of throwing together a complete E30 turbo setup. Additionally, we’ll recommend a couple of premade E30 turbo kits as well. While we do cover the main components required for an E30 turbo build, this guide is meant to serve as a rough starting point for your research.
E30 Turbo Engine Considerations
When it comes to E30 turbo builds, the engine in your respective model is the most important factor. While all of the engines offered in US-Spec BMW E30s are respectable in their own right, some E30 engines are better than others to turbocharge. To keep things a bit simpler, we’ll only be covering the primary three engines that came in US-Spec E30s including the BMW M20B25, BMW M20B27, and BMW M42 4-Cylinder. The M20B25 came in E30 325i and 325is models, the M20B27 came in E30 325e and 325es models, and the M42 came in E30 318i and 318is models. Early model E30 318is used the older M10B18 engine, but in this guide, we’ll be focused on late-model 318is.
Out of the three engines and models to choose from, the M20B25-powered 325i/is and the M42-powered 318i/is are the best candidates for forced induction. While it is possible to turbocharge an M20B27, additional modifications and complex engine management solutions are required.
As we stated above, the BMW M20B25 is one of, if not the best E30 engines to turbocharge. As with many other BMW 6-cylinders, the M20 is extremely reliable, strong, and resilient as long as it is maintained and tuned properly. One of the reasons that the M20B25 is such a good candidate for forced induction is its relatively low compression ratio. The BMW M20B25’s 9.7:1 compression ratio is notably lower than both the M20B27 – with a CR of 10.3:1 – and M42 – with a CR of 10.0:1. This is good for forced induction, as there is less strain put on the internal components of the engine with a lower ratio.
It is often said that the M20 bottom end can withstand power figures close to the 400 horsepower mark with stock internals. Obviously, the viability of reliably running a 400-horsepower M20B25 for an extended period of time ultimately boils down to the engine’s condition and the quality of your tune.
Despite being another engine in the M20 6-cylinder family, the M20B27 engine is not a good option to turbocharge out of the gate. There are a few reasons for this. Ultimately, the M20B27 was built as an economy-focused engine designed for improved gas mileage over performance. As a result, many of the internal components aren’t as optimized as the M20B25. The M20B27 features a restrictive “200” cylinder head with smaller ports, a tamer camshaft, and softer valve springs. As a result, the M20B27 can only rev to 4,500 RPM, which is the main limiting factor for turbocharging a B27. With such a low redline, boost can’t be built fast enough for it to be worth it in the long run.
With that being said, there is a common and relatively simple remedy to this issue. Since the M20B27 cylinder head is the main limitation, some enthusiasts swap heads with an M20B25. The bottom end of both engines is nearly identical, making a head swap easy and effective. An “885” cylinder head swap onto an M20B27 will increase displacement to 2.8L while raising the redline and decreasing the compression ratio dramatically. Some E30 enthusiasts say that this setup is actually the most ideal engine arrangement for a turbo E30.
In 1987, M20B27 engines came from the factory with an upgraded Motronic 1.3 fuel injection system and an 885-cylinder head from the M20B25. These rare engines, often called “Super-ETA” engines, are very well equipped for forced induction, as BMW did all of the hard work at the factory.
BMW M42 4-Cylinder
As the only 4-cylinder on this list, the BMW M42 engine stands out for a few reasons. The main reason is that the M42 is actually a fantastic candidate for boost. It is also the lightest engine offered in late-model US-Spec E30s, making it a good option for those looking to maximize weight savings for a track environment. Additionally, the M42 comes from the factory with a forged crankshaft and rods, making it exceptionally strong.
One of the M42’s main drawbacks from a turbo perspective is its high compression ratio. With a 10.0:1 compression ratio, the M42 is pushing the limits of what is generally deemed safe for forced induction. As a result, many E30 318i owners opt to run low-compression pistons or a low-compression head gasket. The ultimate goal should be to have 8.6:1 or lower compression which will make boost much safer and more reliable. Other E30 turbo owners also advocate for the use of E85 on turbo M42 builds, as it limits the risk of detonation.
How Much Power Can A Turbo E30 Handle?
Ultimately, the amount of power that a turbo E30 can handle boils down to the engine that you chose for your build, the amount of supporting modifications done to the E30, and the tune. If we are talking about stock turbo E30 performance, peak horsepower figures between M20-powered models and M42 E30s are remarkably similar. Both the M20 and M42 engines are extremely capable and strong out of the gate.
It is often said that the M20B25 can hold around 400 horsepower before any internal upgrades are needed. Since the M20B27 shares the same bottom end as the B25, its limit is the same. With that being said, you won’t be able to make that amount of power from an M20B27 unless you swap on an “885” cylinder head.
Like the M20, the 4-cylinder BMW M42 is also an extremely strong engine from the factory. Due to the fact that the M42 has a forged crankshaft and forged rods, it can withstand a fair amount of abuse. Most turbo E30 enthusiasts claim that the upper limits of the M42 are similar to the limits of a factory M20, somewhere around the 400 horsepower mark.
Obviously, these horsepower figures are only attainable and sustainable with a quality tune and other supporting modifications. We’ll cover that in more detail in the sections to come.
E30 Turbo Parts and Components
There are essentially two routes when it comes to turbocharging an E30; you can either purchase a premade kit or collect all of the necessary components individually. While there isn’t a right or wrong answer in terms of how you go about it, piecing together your own kit will give you more flexibility in terms of the parts that you use which can ultimately result in better quality. While there are some decent E30 turbo kits out there, you’ll always have more control and say in how your build turns out with a custom build.
In the following sections, we’ll outline the majority of major components that you’ll need to piece together your own E30 turbo kit. While we’ll hit on the big items that you’ll need, it is possible that you’ll need additional components not listed here. This is meant as a good starting checklist for a 300-horsepower turbo E30 build.
Turbo E30 Engine Management / Wideband O2 Sensor
One of the most crucial components for any turbo build, including a turbo E30 build, is engine management. Luckily, there are a ton of standalone options out there as far as E30 engine management is concerned. Undoubtedly the most popular E30 turbo engine management system is the MegaSquirt PNP engine management system which not only comes with everything that you need to properly tune your turbo E30, but it is also the EMS with the most support on E30 turbo forums. The MegaSquirt can be installed in around an hour and replaces the factory DME entirely.
The E30 MegaSquirt is designed specifically for turbo applications, with features such as 12×12 Air fuel ratio target tables for use with a wideband O2 sensor, 4-bar MAP sensor, overboost protection, and a closed loop boost controller all ready to go right out of the box.
In order to tune your turbo E30 properly, you’ll also need a wideband O2 sensor to not only measure and tune air/fuel ratios, but also to check for potential issues once a tune is installed. AEM sells a wideband for the E30 which is very popular in the E30 community and reads air/fuel mixtures with utmost accuracy.
BMW E30 Turbo Manifold and Exhaust
There’s quite a bit of hardware to keep track of when it comes to a BMW E30 turbo build. One of the most important parts of the entire E30 turbo system is the E30 turbo manifold and exhaust components that follow. The E30 turbo manifold is one of the most crucial components of the entire build, as it can determine important characteristics about how your turbo will spool and react.
E30 turbo manifolds come in many different shapes and sizes, from aftermarket log manifolds to tubular turbo manifolds with varying runner lengths. Ultimately, you’ll need to consider your E30’s engine, the amount of space in your engine bay, and the size of turbo that you intend on using. This CXRacing 304 stainless steel E30 turbo manifold is a solid option for those looking to use a T3/T4 turbo for their E30 turbo build.
In addition to the E30 turbo manifold, you’ll also need a quality downpipe and custom exhaust to dispense of exhaust gas effectively. You’ll have to find an E30 turbo downpipe that works with the E30 turbo manifold of your choice. If there isn’t a premade downpipe option that works with your turbo manifold, you’ll have to order a custom downpipe. The same can be said for the rest of your turbo E30’s exhaust system. Most people end up fabricating an exhaust for their turbo E30, as turbo setups can vary significantly from one person to another. While the fewer restrictions the better, you’ll need to weld in a catalytic converter if you are planning to pass emissions in your turbo BMW E30.
E30 External Wastegate and Blow-Off Valve
Regulating pressure within your E30’s turbo system is one of the most crucial aspects of a build in regard to reliability. With too much pressure within the system, you can do serious damage to your turbo and engine. To manage boost pressure, you’ll need a couple of devices.
The first of which is an external E30 wastegate. The purpose of an E30 wastegate is to regulate the exhaust gasses that flow through the turbocharger. This ensures that the turbocharger doesn’t produce a detrimental amount of boost. E30 wastegates are set to a specific spring rate which limits boost to that amount. 8 PSI wastegates are common with E30 turbo builds, meaning that without the presence of a boost controller, the turbo will have a maximum output of 8 PSI.
You’ll also need an E30 turbo blow-off valve to regulate the pressure on either side of the throttle body. If you let off the throttle under boost, a rush of compressed air travels through the turbo system and is immediately stopped at the closed throttle plate. At that point, the pressurized air has nowhere to go besides back to where it came from. The air is forced back into the turbo, which then interferes with the compressor wheel. This is called ‘compressor surge’ and can damage your turbo’s wheel shaft and bearings. Ultimately, if compressor surge is severe and frequent, it can kill turbo response and overall drivability.
Both an external E30 wastegate and a blow-off valve are essential in building a reliable turbo E30.
E30 Electronic Boost Controller & Boost Gauge
Building off of the components that we have already discussed, an electronic boost controller and boost gauge are critical if you intend on producing more boost than your wastegate allows. If you choose to use a MegaSquirt engine management system, it is possible to modify it to be used as a boost controller. While a wastegate is limited to the boost pressure required to open the wastegate spring, an E30 boost controller allows additional pressure to cycle through the turbo. That allows you to set boost pressure to whatever you choose.
To monitor that the correct amount of boost is being output by the turbo, you’ll need an E30 boost gauge. While it is a simple analog dial, a boost gauge is essential if you are planning on running more boost than what your wastegate is set for. If you aren’t monitoring your E30’s boost, it could be producing a damaging amount of boost without you knowing.
E30 Intercooler and Piping
A quality intercooler is one of the most important parts of any turbo build. Without a proper intercooler, you’ll be leaving power, longevity, and reliability on the table. Turbochargers inherently produce a ton of heat. An FMIC’s job is to cool the air after it leaves the turbocharger before it enters the combustion chamber. Ultimately, heat is the enemy of an efficient engine. Heat reduces combustibility or power, but also decreases engine longevity and reliability as high temperatures over sustained periods of time can warp internals.
A proper E30 intercooler can come in many shapes and sizes. While most turbo E30 builds tend to be very custom, E30 intercoolers are a pretty universal part regardless of your turbo application. Some companies, like CXRacing sell E30 intercooler kits that come with intercooler piping and the intercooler itself. If your E30 turbo setup is in an unorthodox location, it is unlikely that pre-cut intercooler piping will meet your needs. In that case, you’ll have to cut your own piping.
E30 Fueling and Spark
Adding a turbo to your E30 requires some substantial fueling mods. This is due to the fact that the engine needs to compensate for the compressed air coming into the combustion chamber from the turbo. The two most important fueling modifications that you’ll need for your turbo E30 include an upgraded fuel pump, and upgraded injectors.
There’s a wide range of injectors that will work for a turbocharged E30, it truly just depends on your power goals. 450cc, or 42 lb, injectors are a common choice for turbo M20s. Injectors in the 450cc range will get you into the mid-300 horsepower range. You can also use 650cc injectors if you intend on doing more power modifications in the future.
The other part of the fueling equation is the fuel pump. The E30 fuel pump is the lifeblood of the fuel system, as it supplies the injectors with fuel. For that reason, you don’t want to skimp on your fuel pump. The factory fuel pump is rated for around 250 horsepower before it becomes a bottleneck in your turbo build. There are some very common E30 fuel pump options that can sustain big power. One of the most popular options is the Walbro 255lph, which is good for around 500 horsepower at the crank.
Unless you are running a massive amount of boost (like 25-30PSI) chances are that you’ll be fine with Ngk BPR7ES spark plugs. If you are worried that those plugs might be too warm, you can always go a step colder which would also work just fine.
Other Turbo E30 Supporting Mods
Once you have your E30’s turbo setup compiled, assembled, and tuned, the hard part is complete. However, there are still some other considerations that you’ll need to take into account. In the grand scheme of things, a mild turbo setup will add anywhere between 30-150 horsepower to a BMW E30. At this point, E30s are nearing 40 years old. The age of the car in addition to the fact that the E30 chassis was never designed for 300+ horsepower means that other aspects of your E30 will need to be refreshed and improved.
For one, standard E30 disc brakes aren’t equipped with enough stopping power for the addition of a turbo. While stock E30 calipers and rotors are actually pretty capable, it is a good idea to purchase some performance E30 brake pads and brake fluid. Swapping brakes from an E36 M6 is another common option for those looking for a bit more braking performance.
We briefly mentioned other fueling mods, but they are an extremely important addition to an E30 turbo build if you are shooting for massive horsepower figures. Water/Methanol injection is crucial for over 500 horsepower builds as it protects against detonation and keeps internal temperatures at a safe level. An E85 fuel blend functions in a similar way and is a good pump gas alternative that will also yield a bit more power.
Suspension is another important consideration, as factory E30 suspension is likely tired and worn out by now. Components like E30 control arms, bushings, shocks/springs, and ball joints should all be checked and replaced.
BMW E30 Turbo Kits
If you don’t want to spend the time and money hunting around for all of the individual parts that make up a full E30 turbo setup, there are a few decent E30 turbo kits on the market. As the name suggests, E30 turbo kits come with all of the main components that you’ll need to get going with your E30 turbo setup. While the kits usually come nearly complete, some are missing important components, like an engine management system or intercooler, which you’ll still have to source yourself.
At the end of the day, you are always going to find higher quality parts and likely receive better performance from an E30 turbo setup that you build yourself. Since kits are made to be a budget option, many of the components included, especially the turbos themselves, aren’t the highest quality. Not everyone needs a big-dollar E30 turbo setup. If you fall into that camp, a BMW E30 turbo kit might be the option for you. Here are a couple of our suggestions for the best E30 turbo kits on the market currently.
1) Kamotors BMW E30 Turbo Kit
Buy Here: 7speedshop.com
First up is the Kamotors turbo system for the BMW E30. This kit is the best option for those looking for a solidly built kit on a budget. Compared to many other turbo kits, the Kamotors kit comes with quality components like a stainless steel manifold and TRE PNP 60lb injectors. Despite its comparably low price, this is a very complete and high-quality kit with tons of add-on options.
Included in the Kamotors kit is a no-name T3 8PSI internal wastegate turbocharger with a 2.5” V-band, oil feed and oil drain fittings and supply lines, a stainless steel manifold, charge pipes, M20 clamps and couplers, 60lb injectors, IAT sensor, behind the grille intercooler, and oil filter relocation kit. The kit can also be ordered with or without a standalone DME which changes the price by $900.
Ultimately, Kamotors has a very solid reputation in the BMW community for their turbo kits and other related parts. This E30 turbo kit is rated for 300 horsepower and is a solid option for those looking for a sizable power gain. Of all of the components in the kit, the turbo might be the only piece that you’d want to replace. While no-name kit turbos might work well temporarily, you aren’t likely to get stellar reliability from one.
2) CXRacing BMW E30 Turbo Kit
Buy Here: cxracing.com
Next on our list of E30 turbo kits is the CXRacing Catback BMW E30 turbo kit. While CXRacing is widely known for their budget products, there have been good reports about their turbo kits as well. The CXRacing E30 turbo kit is rated for 300-500 horsepower but that figure is seriously inflated if you are hoping for any kind of reliability. A power goal of around 250-300 horsepower is far more achievable. The CXRacing kit was recently revised to feature a better E30 turbo manifold design with equal-length runners.
Included in the CXRacing kit is everything that you need to get going from a hardware perspective including a manifold downpipe kit, T4 GT35 turbocharger, 44mm 8PSI wastegate, air filter, oil filter sandwich and oil line kit, intercooler, intercooler piping kit, blow off valve, catback, and a set of Vband clamps. The inclusion of a catback exhaust is perhaps the most shocking item on that list. While it is likely a decent option, the low price of the kit makes the true quality of the exhaust somewhat suspicious.
As far as E30 turbo kits go, the CXRacing kit is about as cheap as it gets. While price isn’t always an indicator of how well a kit will perform, it must be said that the CX kit isn’t the king of the hill as far as turbo builds go. It seems that user reports are somewhat varied as well, with some owners saying that their kit failed after a month and others saying that their kit has served them well for years. Ultimately, it boils down to your own individual build and the amount of performance that you push out of it.