The Porsche M96 vs M97 engine differences are actually a hotly debated topic. Which cars use the M97 vs M96 and which engines have the fixed IMS bearing are two of the more controversial subjects. We’ll start off by covering the basics on each of the engines, the differences between the two, reliability & problems, and so on. And then we’ll provide our well-researched opinion on the IMS bearing and for what years it was “fixed”.
Both the M96 and M97 are engine families rather than specific engines. The M96 is the earlier version and was produced from 1996 through model year 2007. In model year 2005 the M97 engine started to make an entrance, phasing out the M96 engine. Additionally, both of these engines are used in the 986 & 987 Boxster’s and 996 & 997 Carerra 911’s. The M97 engine was also put into the 987 Cayman starting in model year 2007.
Porsche M96 Engine
The M96 made its introduction in 1996 as a 2.5L flat-six in the Boxster 986. Throughout its heyday from 1996-2005 it powered the Boxster (986 and 987) and Carrera 911 (996 and 997) vehicles. Impressively enough, the M96 came in 5 different engine sizes. The Porsche Boxtser vehicles had three options, a 2.5L, 2.7L, and 3.2L flat-six engine. The 911’s were equipped with larger 3.2L, 3.4L, and 3.6L flat-six options.
The 2.5L engine was only used from 1997-1999. The engine block was poorly designed and Porsche had some quality control issues in the factory that were leading to cracked cylinder liners. The 2.7L entered in 1999 as a replacement for the 2.5L. The 3.2L option was offered along side these smaller engines for “S” series cars.
The M96 engine receives a lot of criticism due to IMS bearing (intermediate shaft) failures, rear main seal leaks, and cylinder cracking. We’ll discuss these in more depth below.
Porsche M97 Engine
Similar to the M96 engine, the M97 is a 24-valvve water-cooler flat-6. However, while the engine was built off of the same platform as the M96 it features a number of differences that we’ll cover below. The M97 was produced in 2.7L, 3.4L, 3.6L, 3.8L, and 4.0L engine sizes.
Starting in mid-2005 the 997 Carerra S began receiving the M97 engine. Until 2008 the base model 911 Carerra’s used the M96 engine which was eventually phased out in 2009 by the direct-injected MA1 engine. Both the 987 base Boxster and S series had the M96 engine in it until 2007 when they received the newer M97 engine.
The IMS bearing was purportedly fixed for the M97 engine. While failure can still happen and some people still have concerns with the bearing, the failure rate is lower than on the earlier M96 engines. However, M97 IMS bearing failure is a lot more costly as it requires the majority of the engine to be taken apart to get to it.
M96 vs M97 Engine Differences
Although these two engines are very similar in nature there are some important differentiations. We’ll cover the big differences here and then provide some thoughts on the IMS bearings between the two since that is a debated topic.
Increased Displacement
The first and most noticeable difference is that the M97 is a larger engine. While the Boxsters with the M97 still received 2.7L that was used in the base model, the Boxster S 3.2L was increased to a 3.4L, increasing power from 276hp to 291hp. The 2.7L received a small 5hp increase. When the 987 Cayman was released in 2007 it followed the same 2.7L base model and 3.4L S model structure.
For the 911 Carerra, the M97 was also still produced in a 3.6L size, similar to the M96. S models however did receive a larger 3.8L engine. And a 4.0L engine was produced specifically for the GT3 RS 4.0.
Displacement was increased by boring out the cylinders and fitting in larger pistons. Overall, the S models received larger engines while the base models kept the same sizes as the M96 predecessor with only minor power increases.
Adjusted Timing
Aside from the larger displacement, the timing was adjusted to create a smoother torque curve and to handle the power increases caused by the larger engine sizes. However, the intake and exhaust valves remain very similar to the M96 in terns of lift and sizing.
Jet Pump to Mechanical Pump
The brake booster vacuum pump for the M96 was a “suction jet pump”. The details of how jet pumps work are rather technical, so you can read about it here if you’re intrigued. The M97 received an upgraded pump and switched from the suction jet design to a mechanical pump. Avoiding the technical differences, the mechanical pump provides more consistent vacuum supply and therefore a more consistent braking experience, especially when at altitude or when driving aggressively such as on a track.
Electronic Oil Level Sensor
The only way to check oil levels on the M96 engine is by pulling out the dipstick. It had no electronic oil monitoring. The M97 added electronic oil level monitoring so that you could see at all time where oil levels were at, the temperature of the oil, and oil usage. While not a major change oil level monitoring is a good feature to have to prevent serious engine damage from running low on oil. It is also helpful for detecting leaks.
M96/M97 IMS Bearing Upgrade
This topic is where the debate begins. We’ve done a lot of research on IMS bearings and will provide what we believe to be an accurate assessment.
From 1997 until early 2005 the M96 engine used two different IMS bearing designs: the dual-row 5204 bearing and the single-row 6204 bearing. The 5204 bearing was used until early 2000 when it was replaced with the 6204 bearing. The bearing seals on the 5204 bearing deteriorated over time leading to failure. Failure was most commonly associated with age of the bearing and not necessarily mileage on the engine.
Porsche changed the design in early 2000 due to failures and problems with the 5204 bearing. However, the single-row 6204 design is actually considered the least reliable of them all. So, in early 2005 a larger single-row 6305 bearing was introduced. It was bigger and stronger but still not bulletproof, albeit it is considered the strongest of the three.
So, Porsche fixed the majority of the IMS bearing issues in early 2005, although 2005+ IMS bearings are still susceptible to failure. But the number of cases of IMS bearing failures with the 6305 is a lot less than the predecessors.
So, which Porsche engines have the “fixed” IMS bearing?
Since the 6305 bearing wasn’t fitted until some time in the earlier part of 2005, there are some very early M97 engines that still have the bad 6204 bearings. The bearings were also upgraded for the M96 engine at the same time.
So, there are both M96 and M97 engines with old and new bearings on them. Anything with a build date of mid-2005 or later should have the better IMS bearing whereas anything before that will have the worst of the three. It isn’t clear exactly when the switch took place so it is difficult to say whether engines with early 2005 build dates have the new or old bearings.
The downside to the M97 engine’s IMS bearing is that it requires a complete teardown to access it, whereas you only need to remove the flywheel on the M96 engine to access it. While M97 IMS bearing failure is a lot less likely, it is a lot more costly to fix if it does break.
Porsche M96 vs M97 Reliability
The most common M96 engine problems are IMS bearing failure, rear main seal oil leaks, cracked cylinders, and cylinder scoring. Unfortunately, the problems that are common with this engine are on the more expensive side to fix. IMS bearing and rear main seal issues are most common in old cars that haven’t been driven frequently and spent a long time sitting. So while a nice super low mileage M96 might sound tempting, the RMS and IMS are probably ticking time bombs. Fortunately, the IMS bearing can be preventively fixed. We’d give the M96 an average grade for reliability without the IMS fix, and slightly above average when it is fixed.
The vast majority of the M97 engines have the improved IMS bearing which gives this engine a leg up in reliability over the M96. Common M97 engine problems are cylinder scoring, cam solenoid failure, and coolant pipe failure. Most of the reliability issues with the M97 stem from the engine overheating and causing cooling system failures. When properly maintained and cared for, the M97 engine offers solid reliability.
Overall, the M97 is considered to be more reliable than the M96, predominantly since there are a lot less M97’s out there with the old IMS bearings. A 2005+ M96 will be pretty comparable to the M97 in terms of reliability since both with have the stronger and improved bearing.
Porsche’s are unfortunately very expensive to fix. And in terms of reliability costs, the M96 wins since it is a bit cheaper and easier to service compared to the M97. Overall, these are both great engines. But proper maintenance and care is vital for them to remain reliable.