Performance Car Engines That Suck- The Porsche M96

by Mike Kojima


A few months ago we did an article on 5 performance car engines that suck. This story was highly popular, and we have had many requests for more engines that suck. So here we go, in more detail, the next performance car engine that sucks, the infamous Porsche M96 engine.

In 1998, Porsche did a major change to their flat engine line up. Mostly due to tightening emissions standards, they boldly diverted their path from the traditional air cooling to water cooling. Thus was born the M96, Porsche's first flat-6 water-cooled engine.

We didn't really know too much about the M96 until a friend bought a 996 911 for what he thought would be a relatively cheap and reliable track car. Boy was he wrong! During the cars first brisk canyon run days after its purchase, it promptly blew up! Thinking we could help him out, we tore into the engine to find that the M96 is a pretty diabolical nightmare of an engine with many faults, especially the early examples. 

Let us show you just how diabolical these engines can be!

Check out our last article on the subject!


The evilest part of the M96 engine is the IMS shaft or more, so the IMS shaft bearing system. The IMS shaft is an intermediate shaft that is driven by a sprocket and chain off of the crank at the rear of the engine that passes through the entire engine and drives one the cams at the front of the engine.

The fact that the engine was designed with such a dumb method of driving the cams is dumbfounding to begin with. Why not drive them just by taking the drive from the front of the crank like any other company would?  We think this was done so the same head casting could be used for both cylinder banks. This would save some money but would also add parts and unneeded complexity to the motor, a bad idea.


So we got a sprocket and drive chain for the shaft at the rear of the engine that goes through the entire engine right at the sump level to drive two chains that drive the cams at the front of the engine. WTF!  Why is all of that necessary.... 

Our personal theory is that Porsche previously used intermediate shafts to drive large cooling fans on the top of their engines and with the switch to water cooling, they had to do something with a shaft. That is a joke, well maybe not...


What makes the IMS shaft really dumb is that Porsche didn't use a durable bearing with forced lubrication from the engines oiling system for the shaft. They used a sealed bearing, sort of like a regular industrial bearing, or a skateboard.

The bearing proved to be very underrated for the job. In some cases, the bearing would fail outright. In others, engine oil would penetrate the seals and wash away the grease. With no grease, the bearing would fail. Strangely, failures seem to be more common with cars that are garage queens and sit a lot and cars that are driven gingerly. Cars that are track driven and are driven hard seem to have this problem less frequently. 

It seems like about 8-10% of the M96 engines fail like this.  In early M96 engines, the failure rate is much higher. These failures have driven down the resale price of old Boxsters and 996 911's and they can be had for bargain prices.

The early engines had bearings that would fail right away. When the IMS shaft bearings failed, the IMS shaft would whip around, damaging expensive stuff. Bearing debris would get circulated around the engine, wrecking havoc and finally the cam drives would fail to let the valves hit pistons. An IMS shaft failure would normally claim everything south of the intake manifold. 


Page 1 of 5 Next Page
Bookmark and Share
Monday, March 20, 2017 7:38 AM
The solution? Bolt on a Subaru engine that makes similar power and torque and is miraculously more reliable. Purists will hate you from the back of their tow trucks.
Monday, March 20, 2017 7:47 AM
Or do what everyone else in the world is doing and stuff a small block Chevy V8 into it. Then the purists will hate you while crying from the back of the tow truck. :D
Monday, March 20, 2017 7:55 AM
You should do an article on the Audi BBK 4.2 in the B6/B7 S4. Timing chain guide failures, cylinder wall scoring, valve guide issues, underpowered compared to Audi HP rating... it does sound amazing though
Mike Kojima
Mike Kojimalink
Monday, March 20, 2017 8:07 AM
The Subaru EJ257 is also a dog of a performance engine that we covered in our engines that suck series.
Monday, March 20, 2017 8:42 AM
BMW N62. Valve guides. Coolant pipe. Oil thermostat gasket. Anything made of rubber.
Monday, March 20, 2017 9:37 AM
Late-model Rover V8? Slipped sleeves, head gaskets, messed up coolant flow path on 1999-2004 Land Rover Discovery II, out-dated engine design from 1960 used 40 years later...
Dan DeRosia
Dan DeRosialink
Monday, March 20, 2017 11:52 AM
I'd almost bet the IMS thing is because they were doing some stupid attempt to reuse tooling or not have to change the design of some part or other; "hey, if we do this we can use up this stockpile of air cooled crankshafts" maybe?

The wristpin thing reminds me of the Subaru so it might be one of those things you're going to have to just deal with having a flat 6... the crank girdle is just confusing though. An engine case within an engine case? Why?
Monday, March 20, 2017 12:19 PM
Great article.

I will have nightmares for weeks.

Have you done engines that don't suck?
Monday, March 20, 2017 12:32 PM
they've done a few K20 builds :D
Monday, March 20, 2017 3:19 PM
As a Porsche technician, I can tell you that the engineers at Porsche don't really learn from their mistakes, and everyday I have some good "WTF Porsche!" moment!
Mike Kojima
Mike Kojimalink
Monday, March 20, 2017 5:51 PM
The crankshaft is way different between the aircooled engines and the M96-97
Monday, March 20, 2017 6:45 PM
Another issue that really is a problem for folks like us that like to visit the track is oil cooling. From what I understand the oil pump is not really strong enough to pump oil through long lines to a proper oil cooler. This particularly an issue because there is no where to mount an oil cooler in the back in proper air flow. So long lines to the front of the car or needed.

What most people do is run some joe gibbs racing oil that can handle crazy oil temps but costs $20 a quart...

I think LN makes a more powerful oil pump that can push cold oil through long oil lines?

ugh a depressing article

Add to it that the economy was so bad in 2009 -2012 that they sold few 911s with the redesigned motor - so the prices are unnaturally high.....means I may be dead before I can afford a modern water cooled 911 that has a decent motor like my old aircooled 911...
Mike Kojima
Mike Kojimalink
Monday, March 20, 2017 7:41 PM
This is one of the few cars where tuners and engine builders of the make roll their eyes and say sell it if it runs and buy a new car!
Monday, March 20, 2017 8:03 PM
To be fair, the earliest examples with the dual row bearing suffered a less than 1% failure rate. The later engines with the single row bearing failed at a rate of 8-10%.

This per the documents in the class action lawsuit.
Tuesday, March 21, 2017 12:24 AM

Have a long "must do" list till it runs again as new but more reliable. But then again with little mods and very few main components changed its ok till 1000hp.
Mike Kojima
Mike Kojimalink
Tuesday, March 21, 2017 12:34 AM
Not this engine the Mezger or the A91 sure.
Dan DeRosia
Dan DeRosialink
Tuesday, March 21, 2017 6:49 AM
Mike: Yeah, reusing a stockpile of crankshafts would be really weird but... I mean, there almost has to be *some* reason why they did it, right? I can't for the life of me figure it out though. Some executive saying they needed an intermediate shaft and damn the consequences?

I find it interesting how different the Mezger engine is in detail - from what I'm seeing poking at people's rebuilds, the crankcase looks more or less identical to the 962 and also the earlier air cooled engines.
Dan DeRosia
Dan DeRosialink
Tuesday, March 21, 2017 7:01 AM
Oh. Apparently they did it that way so they didn't have to have a mirror image head - one head has the chain drive from the front of the engine, one from the back.
Mike Kojima
Mike Kojimalink
Tuesday, March 21, 2017 8:11 AM
Spend a bunch of money adding parts count to save a little by having one less casting.
Cory M
Cory Mlink
Tuesday, March 21, 2017 10:30 AM
Ugh. Lots of room for improvement on this engine and I've seen a few let go. The older Porsche mechanics who were raised on air cooled engines think they are junk. But I also know many people that have tracked and raced them for years with no major issues. They swear the 996/Boxster is more reliable and cheaper to run than the aircooled cars they used to have. I guess it's a roll of the dice, just do all the durability mods and hope you're not in that 10% group with the IMS failure. I've failed 2 aircooled engines in the last 3 years so they aren't always bulletproof either.
Tuesday, March 21, 2017 1:19 PM
Next what about the VG30DETT or the different VQ35 iterations? I bleed Nissan thus why I bring those up
Mike Kojima
Mike Kojimalink
Tuesday, March 21, 2017 11:23 PM
we covered the VQ in the older article, follow the link on page 1
Tuesday, March 28, 2017 4:52 PM
I'm loving this article series Mike. It's fun to see all of these engines broken down to the small things, or in this case the big things, that make them suck.

I'm a bit of an 80/90s Mercedes fanboy so I'm hoping my favorites will stay off the list, haha!
Post Comment Login or register to post a comment.

MotoIQ Proudly Presents Our Partners:

© 2018 MotoIQ.com