BMW M20 Performance Upgrades

Austin Parsons

Meet Austin

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.

The BMW M20 engine is legendary. Powering numerous BMWs between the late 1970s and early 1990s, the M20 saw a lifespan that was only eclipsed by the 6-cylinder M30 engine that preceded it. BMW developed the M20 as a smaller 6-cylinder engine option for the E30 and E28 chassis. The M20s well-documented reputation as a tough and well-built engine has led to a massive increase in aftermarket support in the three decades since its release.

Modifying a BMW M20 engine can vary a lot in intensity. Some M20 modifications are straightforward and inexpensive, while majorly effective ones will require serious work and a good amount of cash. Luckily, with so much aftermarket support and an extremely large modding community, you can certainly start slow and build your way up.


In this guide, we’ll discuss our top four M20 performance upgrades and some additional considerations to keep in mind for each. Here’s how we’ll break it down:

BMW M20 Performance Modification Considerations

One of the most important considerations to keep in mind before modifying an M20 engine is the state of the engine before beginning. The M20 is a solid motor, but we can’t forget that the majority of them are nearly 40 years old at this point. Adding performance modifications to a neglected engine is a recipe for disaster. For that reason, it is important to make sure that you are starting with a solid foundation before going to town.

BMW M20 Engine Refresh Essentials

As with any engine of the M20s age, there are a few main areas where time has likely done damage to some of the engine’s key components. The BMW M20 is notorious for its need for fastidious timing belt service performed every 50,000 miles, or every 5 years. It is extremely important to stay up to code with an M20’s timing belt, as they are interference engines, meaning that serious damage can be done if the timing belt snaps. If you are unsure of when the last timing belt service was performed on your M20, it is always a good idea to replace it straight away.

It is also important to ensure that there hasn’t been any serious damage done to the cylinder head in the past, as hairline cracks are common on M20 heads due to overheating. These cracks are somewhat easy to identify by checking the bottom of your oil filler cap or expansion tank for a creamy, mayonnaise-like, residue. If residue is present, it is likely due to coolant seeping through hairline cracks in the cylinder head and into the engine oil. Unfortunately, the only solution to this is sourcing a new cylinder head.

Finally, it is important to sort any fluid or vacuum leaks before embarking on your M20 modification journey. Brittle rubber vacuum lines are extremely susceptible to cracking and leaking after years of use. A simple smoke test will determine if any of the many M20 vacuum lines need to be replaced. Oil leaks are also extremely common from the oil pan gasket and valve cover gasket. While these might not be the most pressing issues, it is always a good idea to future-proof your engine before doing any performance upgrades.

BMW M20 Engine Variant Considerations

While most of the modifications on our list can be universally applied to all variants of the BMW M20 engine, some performance upgrades will have a more significant effect on different M20 engine variants. Overall, the M20B25 is the variant most receptive to modification, as it has the highest flow cylinder head and highest compression as a result. 

With that being said, there are quite a few popular modifications for the other variants as well. The M20B27 is also extremely accepting of modifications, but to make significant power from one, some heavily involved modifications are required.

The early M20B23 variant is perhaps the least modifiable due to its lack of fuel injection and modern engine management system. There are some modifications available for this variant, but most are upgrades to mechanical parts rather than through tuning.

Best BMW M20 Performance Upgrades

As the M20 modding community has had the better part of three decades to develop and document upgrades, the options to choose from are extensive. Because of that, navigating the M20 aftermarket space can be overwhelming for some, with a lot of conflicting information being tossed around on E30 and E28 forums. To prevent the hassle of going through the forum cherry-picking rabbit hole, we’ve compiled the valuable information here.

Since there is a high degree of variation in terms of modification difficulty, we’ll start with the most cost-effective and least difficult M20 performance upgrade options and work our way to more involved ones. Generally, performance scales with the difficulty and cost of the modification, but there are some really good M20 upgrades that can be done on the cheap.

1) Performance Chip

This is perhaps the most touted modification for a cheap and easy performance boost for any M20 powered BMW. M20 performance chips work by making adjustments to the ECU’s fuel and spark maps, which make the engine far more responsive at all RPMs. M20 chips also raise the rev limiter by a few hundred RPM depending on your engine variant, giving you that extra bit of top-end performance.

Installing an M20 performance chip is very straightforward with proper guidance. The job mainly consists of unplugging your glove box-located ECU, pulling out the old chip, and replacing it with the upgraded one. It really is that simple. No additional tuning or fuss is required, it’ll work straight out of the box.

Unlike a lot of other performance upgrades, you don’t have to sacrifice any performance in other areas to gain the performance benefits from an upgraded chip. Most reputable chips are tuned to provide optimal performance from 91+ octane pump gas and are rigorously tested and finely tuned via a dyno to squeeze every ounce of performance from your M20. 

M20 Performance Chip Power Gain

As we mentioned previously, the performance gain that you can expect from an M20 performance chip is dependent on the variant of your engine. Interestingly, the M20B27 receives a larger boost in performance from a chip than the M20B25. Either way, the improvement is impressive. Here is what you can generally expect from an upgraded M20 performance chip: 

Engine TypeM20B25M20B27
Horsepower+15 @ 5,000RPM+23 @ 4,500RPM
Torque+15 @ 5,000RPM+28 @ 4,500RPM
Rev Limit6,900 RPM5,300 RPM

Since M20 performance chips are such a popular modification in the E30 and E28 communities, there are quite a few options to choose from. It is important to not completely cheap out when buying an M20 performance chip, as some of the chips from less reputable manufacturers aren’t likely as well developed or researched. 

While well-reviewed chips are often dyno-tested with the goal of increasing performance with no long-term cost to your engine, cheap and poorly engineered chips can do damage to your engine. Here is our pick for the most standout M20 performance chip option that has widespread support from the community. 

2) Exhaust

Another worthwhile M20 mod on the more tame side of the upgrade spectrum is a performance exhaust system. Unlike many other engines, the M20 is extremely breathable from the factory as far as the exhaust manifold is concerned. However, most M20-powered cars have restrictive elements that do throttle the engine following the downpipe. 

Upgrading to a performance exhaust has a few benefits for an M20-powered BMW. Quality M20 performance exhaust often comes with higher-flowing catalytic converters and wider diameter mid-pipes. This allows for exhaust gasses to escape the engine and get expelled easier by reducing backpressure. While the selection of performance chips above is largely dominated by a single product, M20 exhausts are far more nuanced. There are a lot of high-quality M20 exhaust manufacturers, so it is important to know what to expect from a performance and sound perspective before purchasing one.

Full versus Catback M20 Exhaust

When it comes to M20 exhaust systems, there are generally two main routes to take. A full M20 exhaust would consist of all-new aftermarket exhaust components starting after the exhaust manifold. This generally includes a larger diameter downpipe, high-flow catalytic converter, larger diameter mid-pipe, better-flowing muffler, and exhaust tip. 

Obviously, as the entire M20 exhaust is being replaced, full aftermarket performance exhausts are quite pricey. However, the performance gains and exhaust sound will be significantly more noticeable than with a lesser system. Full exhaust systems can also be made by experienced fabricators. This typically reduces cost a bit, but will still likely cost more than a cat-back system.

A cat-back exhaust is exactly as it states, an aftermarket exhaust system that begins after the catalytic converter. Typically, a cat-back system consists of a mid-pipe, high-flow muffler, and exhaust tip. While a cat-back system isn’t as involved as a full aftermarket exhaust, it will still improve the performance of your M20. 

BMW M20 Performance Exhaust Benefits

  • Decreased exhaust backpressure
  • Increased throttle response
  • 5-15% horsepower and torque bump
  • Louder / better sounding exhaust note

3) Camshaft Upgrade

One of the most common M20 upgrades, especially if the engine needs to be torn down for additional repairs/upgrades, is swapping the stock camshaft for a performance one. Over the years, it is extremely common for M20 camshaft lobes to wear considerably, reducing the overall power potential of the engine. 

Even today, many prominent camshaft manufacturers offer performance M20 cams with a high degree of customizability. Schrick, for example, provides five different cam durations for different uses. The least aggressive 272/272 grind angle cams are the best for daily driver applications with a power increase at all RPMs. For race applications, a more aggressive 308/308 grind is available for high RPM gains.

Upgraded cams change the characteristics of the M20’s valve responses, with certain cam shapes/grinds being better for different applications. If you are considering upgrading your M20 cams, it is important to do extensive research to find the right cam for your application. Generally speaking, the lower the grind angle, the better low-RPM performance you’ll have. The opposite can be said for cams with a more aggressive grind. It is important to find the middle-ground for your own individual application.

M20 Camshaft Upgrade Considerations

Depending on the level of aggression of the camshaft that you end up with, additional supporting modifications might be necessary to get maximum performance from your M20. For instance, a camshaft grind more aggressive than a 272/272 will almost certainly require a programmable ECU chip and a valve spring upgrade.

 A WAR or programmable chip is necessary to ensure that your M20 can make proper adjustments to the air/fuel mixture to compensate for the changed valve durations. Valve springs are necessary on M20s with aggressive cams, as factory springs aren’t stiff enough to handle the additional load placed on them by the more aggressive cam lobes.

M20 Performance Camshaft Benefits

  • Increased horsepower/torque at all RPMs in street applications with 272/272, 284/272 grind
  • Dramatically increased high-RPM performance in track applications with 288/288, 304/304, and 308/308 degree grinds (other supporting mods necessary)
  • Decreased chance of camshaft-related issues in the future

4) Cylinder Head Refresh


One of the most important components of the M20 engine is the cylinder head. In the M20 community, it is generally concluded that you’ll likely yield more performance from refreshing worn components than you will from any performance upgrade. Of all of the areas that an M20 engine can be refreshed, the head is of top priority. This is mainly due to the fact that the M20 cylinder head is particularly prone to wear in a few areas.

Both the M20 “885” and “200” cylinder heads are prone to developing hairline cracks or warping from hard driving at high engine temperatures. As a severe issue that can spell the end for your M20, it is extremely important to know if there are any imperfections on your cylinder head that would prevent you from achieving full power potential. 

The condition of your valves is also an extremely important consideration when it comes to the state of your cylinder head. Improperly sealing valves can cause a multitude of issues down the line, including excess oil consumption, high levels of smoke from the exhaust, and compromised engine power. Worn valve guides are also problematic and can cause a loss of power. If a timing belt on your M20 has snapped in the past, damage could have also been done to your valves, which will almost certainly cause major issues.

Perhaps the most important, yet most overlooked, aspect of cylinder head maintenance is valve spring/retainer repairs. Over time, valve springs become worn and fall out of an acceptable rate. This can ultimately lead to rocker arm failure. 

M20 Performance Cylinder Head Refresh Benefits

  • Performance will be restored to a factory level
  • A full refresh will significantly decrease engine issues for a considerable amount of time
  • Higher reliability, resulting in the ability to safely install additional performance mods

Best M20 Performance Cylinder Head Refresh Service

Believe it or not, there are still specialty shops that specialize in refreshing M20 cylinder heads. One of the most prominent shops is VAC Motorsports, who offer M20 cylinder head services with multiple tiers to choose from. 

M20 Performance Stage 1 Head Refresh

Their stage one option entails a thorough inspection and replacement of the most commonly needed components. They start by inspecting the cylinder head for cracks, warping, and mating surface imperfections. A full parts cleaning is then performed, followed by a replacement of valve guides and seals. The stage one service also includes valve reconditioning, and spring balancing. 

M20 Performance Stage 2 Head Refresh

The stage two option is a bit more involved. In addition to the inspections and upgrades performed in the stage one service, the stage two service includes an even more in-depth radius exhaust valve job, balanced performance valve springs, and M20 performance steel alloy retainers. The stage two service is a very good option for anyone considering forced induction on their M20 in the future.

M20 Performance Stage 3 Head Refresh

Their third, and most in-depth, stage three service is the whole kit and kaboodle. Naturally, the cost is quite high for an entire race-spec M20 cylinder head and is really only meant if you have racing applications in mind. In addition to all of the upgrades present with their stage two service, stage three includes new high-performance stainless steel valves, meticulous port and polish work, CCing and chamber reprofiling, and high-performance valve guides.

BMW M20 Performance Upgrades Summary

Owning a classic M20-powered BMW certainly has its perks. One of the primary benefits of owning a vehicle powered by one of BMW’s most beloved engines is the massive amount of aftermarket M20 performance parts that are still on the market today, nearly 40 years later.

While slapping on a bunch of new and shiny parts is always fun, it is important to make sure that your M20 is in a fit state to be running significant upgrades. As we stated earlier, the M20 community almost unanimously agrees that ensuring that your engine is in peak running order is perhaps the most effective performance upgrade that can be done to an M20. Refreshing your M20 will give you peace of mind from costly potential failures in the future while giving you a fantastic platform to work off of when installing additional performance mods.

M20 performance modifications don’t have to be wallet-breakingly expensive. A simple plug-and-play performance chip can significantly increase M20 performance without any sacrifices. The same can be said for an M20 performance exhaust, which simultaneously boosts performance and provides a better soundtrack for your drives.

More involved upgrades, like a new M20 performance camshaft or cylinder head refresh, have the potential to turn your M20 into a completely different beast. While those modifications are better suited for motorsport applications, a mild cam upgrade, and a refreshed head can provide the perfect OEM+ feel for a canyon-crushing road car. 

If you enjoyed the content that you read here, check out some of our other classic BMW content. For more M20 information, check out our BMW M20 Engine Guide. For E30-specific content, check out our BMW E30 Engine Swap Guide. As always, safe driving!

Similar Posts

Leave a Reply

Your email address will not be published. Required fields are marked *