It’s no secret that BMW has a special relationship with inline-6 engines. The straight-6 is to BMW what reliable econoboxes are to Honda or headache-inducing supercars are to Ferrari, nobody does them better. A case can be made that the BMW M30 is the engine that truly sealed in BMW’s unparalleled reputation for creating reliable, powerful, and efficient straight 6s that have true staying power.
In this guide, we’ll take a look at BMW’s longest-running production inline-6 engine, the M30. We’ll cover its specs, the multiple variants that came over its 27-year production run, some of its most common problems, and some of the most popular modifications for it.
If you like this guide, check out our similar guide on the “Baby Six” BMW M20 engine as well.
BMW M30 Engine Specs
|BMW M30 Engine
|2.5L (2,494 cc)
2.8L (2,788 cc)
3.0L (2,986 cc)
3.2L (3,210 cc)
3.3L (3,295 cc)
3.4L/3.5L (3,430 cc)
|Bore x Stroke
|86.0 mm x 71.6 mm
86.0 mm x 80.0 mm
89.0 mm x 86.0 mm
92.0 mm x 86.0 mm
|8.0:1 – 10.0:1
|Long Block ≈ 427 lbs
|158-215 hp @ 5,500-6,600 RPM
|156-225 lb-ft @ 3,500-4,300 RPM
BMW M30 Engine Variants
The M30 had a production run of 27 years between 1968 to 1995, making it BMW’s longest produced engine. That’s a crazy long time to have an engine in service. As a result, it was used in over a dozen distinct chassis and received quite a few tweaks along the way. That’s putting it lightly.
In total, the M30 was reworked 10 times, producing that many base variants. As engine technology became more advanced over the nearly three decades the engine was in service, the M30 received upgrades like fuel injection (as opposed to earlier carburated versions), compression ratio changes, and increased displacement. In addition to the regular production variants, there were also a number of specialized variants used by Alpina and the BMW M-Division.
The earliest variant arrived on the scene in 1968 under the hood of the new-for-the-time BMW New Six, also known as the E3. The M30B25V remained in circulation until 1981, powering larger BMW coupes and sedans including the E9, E12, and E23.
The ‘V’ in the engine code represents the word carburetor in German, as the first M30 variant used two Solex Zenith carburetors. The ‘25’ in the engine code represents the 2.5L displacement of the engine. While the M30B25V was the lowest output variant of the “Big-Six,” producing 148 horsepower and 156 lb-ft of torque, it was more than enough to get the following vehicles going under their own weight:
- 1968–1977 E3 2500
- 1974–1975 E9 2.5 CS
- 1973–1976 E12 525
- 1976–1981 E12 525
- 1977–1979 E23 725
Following the first iteration of the straight-6 came the M30B25. That sounds awfully familiar, doesn’t it? Well, that is because the first and second variants of the M30 are pretty similar but with one significant difference, the fuel system. The M30B25 drops the ‘V’ designation present in the earlier variant because it got upgraded to a Bosch L-Jetronic electronic fuel injection system.
The switch to a more modern fuel system meant better performance, improved fuel economy, better emissions, and less fiddling around overall. While electronic fuel injection wasn’t added to the 2.5L M30B25 until 1981, other variants like the 2.8L and 3.0L M30s received electronic fuel injection a few years earlier. Being a more modern variant, the B25 was used in more modern chassis like the E28 and E23.
- 1981-1987 E28 525i
- 1981-1986 E23 725i
The M30B28V was released concurrently with the M30B25V and they were used in mostly the same chassis. The main difference between the engines is displacement. Compared to the B25V, the B28V had a significantly longer stroke at 80mm compared to 71.6mm. That resulted in 0.3L of displacement, making it a 2.8L variant. The additional displacement led to a healthy bump in power too, with the M30B28V putting out 168 horsepower and 174 lb-ft of torque. The B28V was mainly used in mid-trim coupes and sedans including the following:
- 1968-1977 E3 2800 / 2.8L
- 1968-1971 E9 2800 CS
- 1971-1971 E3 Bavaria
- 1974-1976 E12 528
- 1976-1978 E12 528
- 1977-1979 E23 728
Well, if you’re good at recognizing patterns, you probably see where this one’s going. Like the B25, the M30B28 (without the ‘V’) is simply the fuel injected version of the 2.8L variant. The B28 shares the same bore and stroke as the B28V, but the modern fuel injection system increased power and torque to 181 horsepower and 177 lb-ft of torque. Released in 1977, the M30B28 was used in more modern chassis than the carbureted 2.8L variant including the following models:
- 1977-1978 E12 528i
- 1978-1981 E12 528i
- 1979-1986 E23 728i
- 1979-1987 E24 628CSi
- 1981-1987 E28 528i
Other than the one-off M30B33V, the M30B30V was the largest displacement carbureted version of the BMW “Big-Six.” It was essentially just a bored M30B28V, with a 3mm larger bore than the former engine. At the time of its release in 1971, it was one of the most powerful engines BMW offered in their production cars, producing a peak of 182 horsepower and 188 lb-ft of torque. As a result, it was put in some true BMW gems including the following vehicles:
- 1971-1975 E9 3.0 CS
- 1971-1972 E9 3.0 CSL
- 1971-1974 E3 3.0 S / 3.0 L / Bavaria
- 1976-1979 E24 630 CS
- 1977-1979 E23 730
The only variant that was more powerful than the B30V in 1971 was the M30B30. Surprisingly, the carbureted and fuel injected versions of the 3.0L variant ran concurrently with each other until 1979 when the B30 took over completely. It ran from 1971 until 1995, making it the longest-running M30 variant by far. It produced up to 197 horsepower and 200 lb-ft of torque in its prime, but was hampered a bit with the introduction of catalytic converters. Nonetheless, it is a very important engine in the BMW catalog.
- 1971-1975 E9 3.0 CSi
- 1972-1973 E9 3.0 CSL
- 1972-1975 E3 3.0 Si
- 1975-1978 E12 530i
- 1976-1976 E12 530 MLE
- 1977-1978 E24 630CSi
- 1986-1995 E32 730i
- 1988-1990 E34 530i
At this point, we’ve covered all except for one carbureted variant of the M30, as the rest feature either L-Jetronic fuel injection or Motronic digital fuel injection. The M30B32 featured both kinds of FI depending on the year. It also had a lower compression ratio compared to other variants at 8.8:1. The B32’s displacement was upped to 3.2L, despite being used in many models with a ‘33’ or ‘33i’ designation.
- 1973-1975 E9 3.0 CSL
- 1976-1984 E24 633CSi
- 1976-1979 E3 3.3 Li
- 1977-1984 E23 733i
- 1979-1981 E12 533i
- 1979-1986 E23 732i
- 1982-1984 E28 533i
- 1984-1986 E30 333i
Honestly, the M30B33V is a strange engine that doesn’t even really need to be talked about honestly. It had a very short production run between 1973 and 1975 and only powered a single car during that time. It was essentially just a stroked M30B30V, yielding 0.3L of additional displacement.
- 1973-1975 E3 3.3 L
As with a ton of other BMW engines, the US got the crappier version of the M30B34 with a lower 8.0:1 compression ratio compared to the 10.0:1 compression Euro version. Power differed as well, with the US version pumping out 182 horsepower compared to 215 horsepower. That’s a pretty big difference when we’re talking about low displacement naturally aspirated engines. Regardless, it powered some pretty cool mid-upper range models in both the US and abroad.
- 1982-1987 E23 735i / L7
- 1982-1987 E24 635CSi / L6
- 1985-1988 E28 535i / 535is / M535i
Well, it took a while to get here but the highest displacement variant is the M30B25. Like a couple of other BMW engines, the ‘B25’ designation doesn’t quite match the engine’s actual displacement. In actuality, it is closer to 3.4L. Regardless, it is the top M30 variant that features the newest technology out of them all, including Bosch Motronic 1.3 digital fuel injection. The B35’s production run was short-lived, only around from 1986 to 1992. It has the best reputation out of all of the variants too, due to its high output of up to 217 horsepower and 232 lb-ft of torque. It was also used in some pretty cool BMWs including the following models:
- 1988-1989 E24 635CSi
- 1986-1992 E32 735i
- 1987-1992 E34 535i
Special / One-Off Variants
In addition to the standard production M30 variants, there were also a couple that saw dedicated use in special models or for special purposes. The E34 Alpina B10 Bi-Turbo is a good example, which featured a specially modified M30B25 equipped with forged pistons and two turbos, bumping its output to a record-breaking 355 horsepower. At the time, the B10 Biturbo was the fastest sedan in the world.
The M30 was also the basis for a number of other unique turbocharged BMW engines including the M102 and M106. Both engines served as a bit of an experiment, with the M102 being BMW’s first turbocharged inline-6 engine. It’s pretty cool that the M30 essentially started the turbo-6 revolution for BMW, as look where we are now.
Common Problems and Reliability
The fact that the M30 was in production for nearly 30 years and barely received any fundamental updates over that time period (outside of fueling improvements) should tell you a bit about its overall tenacity. It truly was a winning formula out of the gate and suffered very few common problems related to the engine’s design itself. Some (including me) say that the M30 is one of the most reliable BMW engines ever made. It was truly one of the main engines that gave BMW such a good legacy as far as inline-6 engines go.
The M30’s biggest strength from a reliability standpoint is its simplicity. After all, they are pretty barebones SOHC, 2-valve-per-cylinder engines that lack any kind of modern tech like VANOS variable valve timing or Valvetronic. That also makes M30s very easy to work on and simple to diagnose should something go wrong.
While M30s are pretty bulletproof mechanically, even the last produced ones are nearly 30 years old at this point. At that age, any engine is going to have some problem areas and that’s certainly true for the M30 too. In general, all of the M30’s common problems are related to age in some way, including failing cooling system components, cylinder head cracking, and various oil leaks.
Cooling System Issues
Cooling system issues are common on almost every BMW up until recently. They were especially bad on early BMW inline-6 engines like the M30, M30, and even M50. Items like the factory radiator, expansion tank, coolant hoses, radiator fans, thermostats, and water pumps are all common failure points on the M30 if they haven’t been replaced.
Most of those items fail as a result of age. I dealt with the same thing on my M20-powered E30, as all of the cooling system components started failing one by one until I decided to just overhaul everything. Water pumps and thermostats are truly the components to watch out for. M30s use plastic impeller water pumps, which are known to fail prematurely. If you are looking into buying an M30-powered BMW, a new water pump should be high on the list of priorities if you don’t have records of when it was last replaced.
Cylinder Head Cracking
One of the more damaging issues that can happen to an M30 is a cracked cylinder head. Like almost every other BMW engine from the era, the Big Six utilized a cast iron block and an aluminum cylinder head. As we just talked about, the M30’s cooling system is – to put it lightly – junk, especially 30 years down the line. That doesn’t mix well with relatively fragile aluminum cylinder heads that are very susceptible to damage from overheating. And, unfortunately, that is the fate of many M30 cylinder heads.
If the engine does overheat, it can cause the cylinder head to warp, bend, or (most commonly) crack, resulting in other issues. In most cases, the head will crack, allowing coolant to leak into the engine oil and cause other related issues like additional overheating and head gasket failure. Unfortunately, M30 heads themselves are just weak due to their overall construction, so the only way to ensure that you don’t run into the issue is to make sure that your cooling system is up to par.
It’s important to check for cylinder head cracks if you are trying to source a cylinder head or are looking at an M30-powered BMW. The easiest way to tell is to check the dipstick to see if the oil has a ‘chocolate milk-like’ consistency. You can also check the oil filler cap for a white milky buildup. Alternatively, while the vehicle is cold, you can remove the radiator cap, start the car, and look to see if there are any bubbles in the coolant. All of those symptoms indicate that the head might be cracked.
Popular Upgrades and Modifications
Beyond being one of the most reliable engines that BMW has built in recent decades, it is also one of the most popular engine swaps into an array of different cars and a popular engine to modify. Many enthusiasts are pretty happy with the M30’s factory performance, especially the higher displacement variants. My 1994 535i had great low-end torque and felt peppy in every gear throughout the entire rev range. For that reason, it is swapped into a ton of other lighter chassis including E30s, E21s, and 2002s.
When it comes to modifications, the M30 is known for one thing, forced induction. They take boost like an absolute champ and some people have milked over 1,000 horsepower out of them. It is a lot harder to get much power out of a purely N/A setup and is far more costly. To break the 300-horsepower barrier N/A, you’d be looking at a standalone EMS, B35 cylinder head, bored block, high compression pistons, an upgraded cam, and more.
Forced induction is truly the only way to make big horsepower on an M30 and that is a pretty hefty commitment. Obviously, BMW and Alpina agree that turbocharging is a viable option on the M30 as they did it themselves. It is just such a good candidate for FI due to the fact that the bottom end is so strong and can realistically hold close to 400 horsepower before opening the engine becomes a consideration.
As with any forced induction conversion, there is a ton to consider. There are a few dedicated M30 turbo kits available on the market with specially made manifolds, intercooler piping, and downpipes, which makes installation a lot easier.
In reality, most people who go the FI route end up custom fabricating and piecemealing a kit out of other turbo components. That is obviously the more time-consuming and expensive route, but you’ll likely end up with a nicer final product that suits your wants to a tee. Since turbo M30s are so popular, there are luckily quite a few individual components, like manifolds, downpipes, and exhausts, available from reputable manufacturers which makes things a bit easier.
If you are dead-set on an N/A M30 build, or simply want the best bang for the buck without dropping a fortune on the build, a cam upgrade is the way to go. Just like with a turbo setup, there is a ton of nuisance to making the right camshaft choice, as it truly does hinge on what characteristics you want from the engine. It is important to mention that some variants, like the B34, won’t gain as much power from a cam as other variants due to a lower compression ratio.
A while back, factory S38 camshafts weren’t as hard to come by, making them a really good option as a performance cam swap for regular M30s. Now S38 cams are nearly impossible to find and if you can, you’ll have to refinance your house for one. Luckily, there are some other good options out there that won’t bankrupt you.
Almost every M30 owner that does a cam swap goes with the Schrick 284/280 cam. It is a tried and true camshaft that will tack on a decent amount of mid-range and top-end power without sacrificing too much low-end torque. You can’t expect a cam to transform the performance of your engine, but it is a good option if you are looking for moderate gains.
I know I just said that a cam was the best bang for the buck N/A M30 mod, but I might have to take it back, cause a performance chip is up there too. In fact, a performance chip is what most enthusiasts would recommend for a naturally aspirated build first, mainly because they are relatively cheap, require no additional parts, and actually produce some notable gains.
Once again, it is very hard to scrape any additional power and torque together with an N/A M30 without doing some pretty extensive and expensive engine work. That’s because BMW truly did optimize it pretty well out of the box. The point of a performance chip is to adjust the factory fuel and ignition maps to take full advantage of the hardware that BMW provided. Installation of the chip is relatively easy and takes most people around an hour to remove and replace the factory chip in the ECU.
The Turner Motorsport Conforti chip is unquestionably the most popular performance chip for not only the M30, but most vintage BMW straight-6s in general. They have an extremely solid reputation in the community and have been shown to produce impressive and proven results. For 200 bucks, you can potentially see gains of up to 24 horsepower and 29 lb-ft of torque, which is the best you’re going to do in terms of performance for money.