BMW has been considered one of the automotive’s innovative cornerstones in the modern era. It is an understatement that BMW is excellent; I might say that they are revolutionary and fearless of what they bring to the table. The formidable prestige that brought them at this stage throughout the years of its service to our vehicles.
They are regarded as one of the “Top Engines of the 20th Century”, adding yet another award to their long list of accolades.
BMW’s M30 has been an adorned and legendary engine; with its production run spanning over three decades from 1968 to 1996, though it was produced alongside the M20 engine, and before the introduction of the BMW M70 V12 engine in 1987, it still stands as the most popular and largest regular engine produced by BMW.
BMW M30 is a Single Overhead Camshaft straight-six petrol engine; it earned the ‘Big Six’ and ‘Senior Six’ monicker following the arrival of a much smaller engine in BMW M20 straight-six in the late 1970s.
Although M337s were the premiere inline-six engine that BMW designed since the post-war era, which architecture was derived from pre-war times, M30s enjoy its improvement, refinement, and upgrades significantly helped to extend its longevity throughout its tenure.
Some of the earliest vehicles to suit M30s were the BMW 2500 and 2800 sedans and eventually in E23s, E32s, E24s, E34s, E12, E28, and BMW’s new class E3s and E9s; it even powered E9 CSLs and E24 6 Series coupes to European Touring Car Championship with its high-performance version, M88.
BMW produced the first M30 engine production models in 2.5 Liters (2494cc) and 2.8 Liters (2788cc) displacements. Increased displacement versions were introduced later on, which includes the largest version dubbed as 3.5 Liters, which is 3430cc, 70-point shy for the actual count.
When BMW started producing M50 engines in 1990, M30s are quickly shadowed by the recent engines and set to be phased out.
Engine Specification and Design
- Production Run: 1968 to 1995
- Cylinder Head Material: Aluminum
- Cylinder Block Material: Cast Iron
- Configuration: Straight-six
- Bore: 86mm (Original)
- Stroke: 80mm
- Valvetrain: SOHC 2 valves per cylinder
- Displacement: 2.5 Liters – 3.5 Liters (Largest)
- Compression Ratio: 9.0 : 1
- Weight: 320 lbs.
- Max HP: 218hp at 5,500 RPM
- Max Torque: 225 lb-ft at 4,200 RPM
BMW started to build another engine in the late 1960s when they realized the power limitations of the four-cylinder M10 engine. They added two more pistons to the current design, producing their first six-cylinder engine and the birth of the ‘New Six’ M30 engine.
Resembling the six-cylinder arrangement of the smaller six M20 engines, M30 is basically the developed version of the M10 four-cylinder, which they share a fair number of design and features such as crossflow cylinder head, 30-degree slant inclination to the right profile, chain-driven camshaft with rocker arm valve actuation and forged crankshaft.
They also have the same aluminum heads, cast-iron block, and an overhead camshaft with two valves per cylinder.
BMW continually improved the lineup throughout the 1970s and 1980s, where the potential of the M30 was emphasized; further increasing the capacity by adding more, higher-performing carburetors, less restrictive exhausts, land the introduction of the fuel injection system.
BMW achieved a capacity of 3.5 liters, 218hp, and 225 lb-ft of torque by boring the block from 86mm to 92mm and lengthening the stroke from 71mm to 86mm, which they released two versions – M30B34 for the North American market, and M30B35 for the European market.
With its performance modifications, it catered to an excellent basis for naturally aspirated adjustments. It even received a turbocharger released in two versions for the E23 – M102 and M106, 3.2 Liters and 3.4 Liters, respectively.
Throughout M30’s 27-year stay, there are six iterations of the M30.
Different Versions:
M30B25 was installed with Bosch L-Jetronic fuel injection and had a displacement of 2.5 Liters, 148hp, 159 lb-ft torque available at 4,400 RPM. It has a bore of 86mm and 71.6mm stroke. It appears in E28 525i from 1981 – 1987 and in E23 725i from1981 – 1986.
They were previously known as M06 and M68 before renaming them M30B28V. This engine, in its original form, used two ‘Solex Zenith 35/40 INAT’ 2.8 carburetors. With a 9.0:1 compression ratio.
It has a displacement of 2.8 Liters, 181hp, 188 lb-ft torque available at 3,500 RPM. It has a bore of 86mm and 80mm stroke. It appears in E3 2800 in 1968 – 1977, E9 2800 CS in 1968 – 1971, and E12 528 in 1974-1978. The specification varies depending on the market, model year, and carburetor.
Next is the fuel-injected version of M30 that debuted in 1971. Initially, it used the Bosch D-Jetronic mechanical injection system and, in 1976, was upgraded to Bosch L-Jetronic electronic fuel injection.
M30B30 is the 3.0 Liter, 194hp, 203 lb-ft torque available at 4000 RPM. It has a bore of 89mm and 80mm stroke. It appears in E9 from 1971 – 1973, E12 in 1975-1976, and E32 in 1986 – 1995.
Sometimes badged as 3.3 Liters, M30B32 has a displacement of 3.2 Liters. It has an 8.8:1 compression ratio. The US version was changed to use Motronic digital fuel injection from L-Jetronic from 1978 to the mid-1980s. It has a 194hp power, 210 lb-ft torque available at 4,300 RPM. A bore of 89mm and 86mm stroke. It appears in the E24 633CSi coupe.
Sold in European markets and used 10.0:1 compression ratio. M30B34 has a displacement of 3.4 Liters, 215hp. In North America and Japan markets, 182hp were offered, 214 lb-ft torque available at 4,000 RPM.
It has a bore 92mm and 86mm stroke. It ran from 1982-1988.
M30B35 has a displacement of 3.4 Liters, 218hp, 225 lb-ft torque available at 4,000 RPM. A bore of 92mm and 86mm stroke. It ran from 1988-1993.
M30 Engine Modifications and Tuning
M30 engines were fundamental to create an avenue for the turbocharged M102 and M106 engines.
M30B35 Turbo
Since M30 engines have a low compression ratio, you can install a turbocharger without the use of forged pistons. You may opt to buy a Garrett GT35 turbo kit for BMW M30 and install it on your stock internals, increasing the boost from 11-14 psi that can give you 400 horsepower at best.
You can also make a twin-turbo M30B25 by using a supercharger, but a turbocharger would be more effective.
Exhaust Upgrades
In parallel to the turbo upgrades, it is also essential to upgrade your exhaust concerning the gains that you put in the engine because it might create a restriction and may hamper your desired performance. Sports exhausts are great options to help with a faster flowing performance.
But don’t forget to avoid wide exhausts and it can make things worse. I suggest keeping the size range of 1.5 to 2.5 inches to maximize the flow rate.
Stroker Upgrades
If you are planning to make your M30B35 powerful, you can buy a stroker kit or aggressive cams. Plus, there are various aftermarket performance parts for M30 engines and can expand your capacity up to 4 liters by buying a 98mm stroke camshaft, short rods, 93.5mm increased bore, and forged pistons.
However, the stroker kit price can be a little expensive.
You can also increase the compression ratio by shaving the cylinder head, DIY style, then buy a cold air intake, reinforced rocker arms, headers, and performance exhaust system. This can give you around 250 horsepower.
Common Problems
First is the engine’s overheating. However, this is common not only on M30s but also on many straight six-cylinder engines that might result in a deformed cylinder head if not addressed as soon as possible.
Overheating may have been caused by a dirty radiator, thermostat, water pump, and an air-bound cooling system.
Second, are the cracks in the engine block. This is caused by the oil that does not take from the threaded sets after disassembling the engine. They can form around the threads of bolts in the cylinder head.
If you notice that you consume too much coolant and emulsion appearance in the engine, there might be a crack. You can solve this by buying a new cylinder block.
The third is the valve train issue. Most problems that occur in M30’s, in consideration of their age, are in the valvetrain due to unadjustable valves. If you ever come across this problem, you need to buy a bushing set, replace worn-out valves, and rocker arm eccentrics.
There are also reports about the MAF-sensor.
Summary
BMW M30 is a powerful engine and has proved to be a top-rated engine due to its excellent characteristics. As you might expect, despite its age, the evolution of such engines carried its legacy up to the present and proves that it is indeed a magnificent work of art.
With the correct maintenance and care, M30s can serve you more than 300,00 miles without overhaul.
I hope that we helped you to understand and clear some clouds about the legendary BMW M30 engines. Even it was released decades ago, its technical and physical prowess will be cemented in the automotive industry for a long time.
can a 1974 M30 engine run on unleaded gas? Will it cause any problems?