Anyone that owns a BMW E30 325i knows that the factory M20B25 2.5L engine leaves a lot to be desired in the horsepower department. While the factory 6-cylinder is certainly enough to get a 2600 lb 325i going under its own weight, you won’t be winning any drag races.
Other than adding forced induction to the M20 equation, engine swaps are the most common method for giving a 325i E30 a bit more pep.
As engine swaps are one of the most complicated and time-consuming modifications that can be done to a vehicle, this article will only cover the basics of the most common BMW E30 325i swaps, including estimated cost, performance benefits, and common issues.
E30 325i Engine Swap Considerations
Engine swaps in any car are finicky, to say the least. Due to the complexity of internal combustion engines and their thousands of unique parts and connections, swapping an engine into a car that it wasn’t intended for is bound to be a process fraught with headaches.
The same can be said for BMW E30 325i engine swaps. While BMW has only used a few engine mount locations and familiar bell housing bolt patterns in most of their vehicles spanning the decades, other considerations like wiring harness modifications, oil pan fitment, and exhaust fabrication are among the most time and cost exhausting hurdles that need to be considered.
For these reasons, engine swapping a 325i E30 is not a weekend job unless “BMW Master Technician” is on your resume. If you lack serious technical knowledge of both the E30 platform and the engine of choice for your swap, it would probably be best left to a professional. While a professional install would significantly raise the cost, it would also minimize swap-related migraines later on.
With the added horsepower, torque, and reduced weight that the following engine swaps provide, supporting modifications are extremely important to consider. Upgraded brakes and suspension are at the forefront of the most important swap supporting mods. Factory brakes are not equipped to support an additional 30-100 hp that an engine swap would likely provide. For that, more stopping power is required.
The same can be said for suspension, as factory E30 suspension is barely stiff enough to support the meager amount of power already provided from the factory M20. Upgraded suspension is instrumental in allowing all of the additional power to be used in any condition, not just a straight line.
With those considerations in mind, onto the list!
M30 BMW E30 325i Engine Swap
Estimated Swap Cost: $1,500 with labor
M30B24/25 Donor Cars:
- 1982-1987 E23 735i
- 1982-1987 E24 635i
- 1985-1988 E28 535i
- 1988-1989 635CSi
- 1986-1992 E32 735i
- 1987-1992 E34 535i
M30 E30 Swap Guide: Garagistic.com
The M30 is not the most powerful motor on the market. It is, however, a great swap candidate for a 325i E30 for a multitude of reasons. To start, the M30 is one of BMW’s most-produced engines, in production for nearly three decades between 1971 and 1990. For that reason, they are extremely easy to source and find parts for. The sheer number of M30 engines also makes it the most cost-effective option on this list, with most M30s only costing a few hundred bucks from a junkyard or rushed seller on Craigslist.
In addition to being easy to come by, M30s are also the easiest swap option on this list, and perhaps overall. As M30 production overlapped with the production of the M20B25 that comes stock in all E30 325is, much of the stock drivetrain hardware can still be used with the new motor.
The M30 E30 325i swap is the best option for anyone looking for a healthy 30-40 bhp gain over the factory M20B25 while on a budget. The M30 engine has the reputation of being truly bulletproof, with repairs and preventative maintenance being extremely inexpensive and easy should anything go wrong.
Performance Benefits of M30 BMW E30 325i Engine Swap
Power output and exact engine performance will depend on which M30 motor you chose to swap into your 325i E30. As M30 production lasted so long, BMW made adjustments to performance and displacement over its lifespan.
For the sake of this article, we will be focused mainly on the M30B30 and M30B35 engines, as they provide the most effective performance increase and are the easiest to source.
The M30B34 engine, in factory form, was capable of producing 215 hp and 229 lb-ft of torque. That is a significant 45 hp gain over the factory M20B25 engine. This power gain has the potential to turn your 325i E30 into a completely different beast.
The M30B35 engine, once again in factory form, was capable of producing 208 hp and 225 lb-ft of torque. While a slightly less significant 40 hp gain, the 5 hp difference between the M30B34 and M30B35 engines is negligible.
An important benefit to note about an M30 325i swap is the relatively seamless integration of the M30 into an E30 chassis. As the M30 is essentially just an older and more powerful brother of the M20, the linear powerband and smooth acceleration characteristics that many E30 owners love will still remain.
Common M30 BMW E30 325i Engine Swap Problems
As the M30 motor weighs roughly 40 lbs more than the factory M20, weight distribution and handling characteristics will be altered slightly. Upgraded suspension and brakes, which should be considered for any power-boosting swap, can reduce the impact of the heavier motor.
While an M30 E30 325i swap can be done almost entirely with BMW OEM parts, some minor custom work and custom parts are needed to complete this swap.
The most significant custom parts needed for the swap are specially fabricated engine mounts. As the M30 is much larger than the M20, heavy-duty engine mounts that align the M30 perfectly in an E30 engine bay are required. They can be fabricated by hand, or ordered here by a company that produces them specifically for this swap.
Another custom consideration comes in the form of exhaust. If the sourced M30 comes from an E34, the headers should clear the steering rack with ease. If the sourced M30 comes from another chassis, modification of the M30 headers to clear the steering rack might be required.
M54B30 BMW E30 325i Engine Swap
Estimated Swap Cost: $6,000 with labor
M54B30 Donor Cars:
- 2000–2006 E46 330i, 330xi, 330Ci
- 2000–2004 E39 530i
- 2000–2002 E36/7 Z3 3.0i
- 2003–2005 E60 530i
- 2002–2005 E85 Z4 3.0i
- 2003–2006 E83 X3 3.0i
- 2000–2006 E53 X5 3.0i
- 2002–2005 E65/E66 730i, 730Li
M54B30 E30 Swap Guide: R3VLimited.com
While not the most common or powerful swap, M54 swapping a 325i E30 will result in a healthy blend of cost-effectiveness, power gains, and reliability.
Only relatively recently has the M54 become a noteworthy and beloved swap in the E30 community for a few reasons. Most of the vehicles that came from the factory with an M54, 330i E46s, and 530i E39s being the most common, have hit the bottom of their depreciation curve while also existing in large quantities. This combo has made the M54 relatively inexpensive and generally easy to find.
Much of the reason that the M54 has remained somewhat underground in the E30 swap community is the motor’s use of OBDII, opposed to earlier engines using OBDI, as wiring on OBDII engines is significantly more complicated. As time went on and people began to provide more detailed information regarding OBDII E30 swaps, the M54 grew a sizable following as a good swap option.
As there are still difficult elements to this swap, I would only recommend performing an M54 swap if you have a solid foundational understanding of the M54 engine itself and are comfortable with performing some fabrication work.
Performance Benefits of M54B30 BMW E30 325i Engine Swap
Considering the relatively low cost of the swap itself, an M54 E30 is perhaps the most bang for your buck of the three swaps listed. Despite being a common production engine when compared to older, M-based relative, the S52, the M54 provides nearly the same power figures, producing 228 hp and 221 lb-ft of torque.
In addition to rivaling the S52's power figures, the M54 weighs significantly less than both the S52 and M20B25, reducing the overall weight of the E30 chassis by 108 lbs. This weight difference would be immediately apparent in acceleration and cornering.
From the factory, the M54B30 contains notable performance advantages to many other BMW engines as far as hardware is concerned. For instance, the M54B30 has a 2.5” throttle body, a 0.5” increase over the S52, allowing for extremely quick throttle response and increased acceleration performance.
The factory 3.5” MAF installed on the M54B30 engine is also a significant player in higher airflow sensor readings, also improving acceleration characteristics.
Common M54B30 BMW E30 325i Engine Swap Problems
Compared to the other swaps on our list, an M54 swap will likely require the most fabrication work. This boils down to both clearance issues where the intake and exhaust manifolds are concerned, and issues with modernized parts such as the M54’s drive-by-wire throttle system.
As there aren’t currently any custom-made M54 E30 headers on the market, an aftermarket header set will have to be modified to fit. Most E30 owners that have performed the swap will cut the headers after the collectors and weld on 2.25” vband assemblies. Specifics can be found in the linked swap guide.
As the M54 does not use a traditional throttle cable like a standard E30 325i, modifications have to be made to the factory pedal brackets to allow for the larger electronic gas pedal from an E46 or E39 to fit. This will likely require the factory bracket’s spot welds to be removed, the bracket set in the correct position to accommodate the new pedal, and the bracket being welded back into the correct spot.
In addition to fabrication work, the M54 E30 swap will require a strong understanding of wiring diagrams, as the OBDII wiring harness will require extensive modification to be used in an E30. Most owners suggest starting with an E39 or E53 wiring harness to allow for better ECU placement later on. This harness will need to be spliced to an E30 harness with the use of wiring diagrams. This is likely the most difficult portion of the entire swap, as there is a lot of information to manage at this step. Luckily, M54 E30 swaps are becoming increasingly more common and there are a lot of solid resources and guides to help you through the process.
S52 BMW E30 325i Engine Swap
Estimated Swap Cost: $15,000 with labor
S52 Donor Cars:
- 1996-1999 E36 M3
- 1998-2000 E36/7/8 Z3M
S52 E30 Swap Guide: rmeuropean.com
Raising the stakes by a significant margin, swapping an S52 into an E30 is a recipe for a tire shredder. With an 80 horsepower jump over the stock M20 found in a 325i, this swap is best for an enthusiast who needs the additional get-up-and-go for serious track duty.
As one of the most performed E30 engine swaps, an S52 swap has the advantage of being well documented and refined. A serious issue for enthusiasts looking to swap an uncommon engine into an E30 chassis is the limited information as far as specifics are concerned. That is no such problem for S52 swapping a 325i.
Just because there is no shortage of information on S52 swapping a BMW E30 doesn’t mean that it is easy. It is quite the opposite, in fact. Similar to the M54 swap discussed above, S52 swapping an E30 requires a slew of custom parts and moderately difficult fabrication.
In addition to the added difficulty of the swap itself, the S52 engine only came in a few M models throughout its build cycle, making them more difficult to source for a reasonable price. The rarity and high demand for one of BMW's most celebrated performance engines have made the S52 a pricey E30 swap option. If you do have the money to spend, S52 swapping an E30 comes close to perfecting the performance vehicle.
Performance Benefits of S52 BMW E30 325i Engine Swap
Both on paper and in reality, the numbers associated with this swap are impressive. Not only will the already light E30 chassis be taking on an additional 80 ponies and 70 lb-ft of torque, but the overall weight of the vehicle will drop by roughly 50lbs due to the S52’s aluminum head.
That is only the beginning as far as impressive figures are concerned. The S52 platform is essentially made to be modified, with a cast-iron block that is strong enough to handle enough boost to put you into the 400 hp range. Even simple bolt-on mods can skyrocket S52 engine performance, with high-performance ECU chips and cold air intakes being the most common mods to push numbers close to 260 hp.
While excessive amounts of power are fun, sometimes the trade-off is reliability. That is not the case with the S52. The only major repair/preventative maintenance item that needs to be addressed is rod bearings, but beyond that S52s are often still seen running smoothly with 300,000 miles on the clock with regular maintenance.
Common S52 BMW E30 325i Engine Swap Problems
Good things rarely come easy, and the same can be said for S52 swapping an E30. While the final result will be unquestionably outstanding, there are many obstacles to overcome on the way.
Unlike the M30 swap, an S52 E30 swap will require a lot of hunting and gathering to collect all necessary parts. Most of the needed parts will come from early model E36 M3s, M50 powered E34s and even Porsche 944s. Most E30 owners that have performed the swap say that sourcing the parts is perhaps the most difficult part of the process.
As with most engine swaps, the task of successfully and effectively mounting the drivetrain perfectly in a foreign bay can be a serious challenge. This applies to an S52 swapped E30 as well. The engine itself can be installed fully assembled, but modifications need to be made to secure an E36 transmission properly.
E21 transmission mounts need to be used to handle the additional stress and weight of an E36 transmission. Supporting cups also need to be welded onto the transmission mounts to ensure that the drivetrain does not move from its set location.
Because the S52 is a significantly larger engine than a factory M20B25 found in a 325i, there is very little clearance between the fan and radiator. If transmission mount reinforcing is not done and the drivetrain is allowed to slide even a couple of centimeters, you'd likely be looking at a new radiator.
BMW E30 325i Engine Swap Overview
While it would be impossible to cover all of the intricacies of these E30 swaps in a single article of moderate length, this overview’s primary goal was to help you weigh the most significant pros and cons of multiple E30 swap options at different budgets.
The BMW E30 is one of the best platforms for overall driving pleasure, which is only amplified by adding more power to the equation. Whether you are looking for a moderate boost for highway driving or a track-destroying rocketship, there is an engine swap that will meet your expectations.
With the E30 modification community continuing to expand, there are countless fantastic resources that will ensure that you’ll never be stranded during the strenuous process. If you have any questions regarding any of the swaps that we have listed here, feel free to comment below.