World’s First BMW DCT Transmission Build

How-To | April 4th, 2010 by 8
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The fellas over at BimmerBoost have an interesting story to share with us: a journal containing a series of episodes on World’s First BMW DCT …

The fellas over at BimmerBoost have an interesting story to share with us: a journal containing a series of episodes on World’s First BMW DCT Transmission Build. Let’s have a look at the first one and we’ll continue to pick up their saga as they move forward.

The time has come to announce the details of my transmission build. No one has attempted this before and there unfortunately are no off the shelf parts. Everything will have to be custom made for this application which means the build time will be around 10 weeks from this point. This thread will be updated periodically with pictures and details every step of the way. I will be providing complete documented details through the process.

Why is the transmission being built?

For one, to handle more power and for longevity. It is no secret I have abused my transmission from the moment I got the car. I have done more launches at the drag strip using launch control than… anyone really. These launches are abusive, generate tremendous heat, and shorten the lifespan. Once supercharged, the issue was expounded. At a single event in ’09 I used launch control 19 times with a burnout each time which generates considerable heat. I have attended 5 such events. Additionally, I have done launches on the street. I would estimate a conservative 70-80 uses of launch control up to this point.

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So the transmission is weak?

No, not at all. Actually, it took far more than anyone would have thought. At these drag events, I would also run back to back at times. Keep in mind, I bumped the launch control RPM up as high as it would go, 6200 RPM. These are 6200 RPM launches after a burnout again and again. I estimate 70-80 uses and a properly used manual clutch in comparison should be good for about 50 passes before needing to be replaced. Just to give an idea of the abuse I put it through, I needed new motor mounts a year in as the abuse in the launches took its toll. Oops

Heat also contributed to shortening the lifespan. The moment I got the supercharger completed the car was on its way to the strip, literally. No exaggeration here, supercharger was completed and the car was on its way to the Famoso drag strip. It arrived with 15 minutes to spare and no cool-down whatsoever. I’m the kind of person that didn’t want to save it for another day and decided to go for it. A mistake in retrospect as after the burnout I attempted to use launch control and it overheated. There are two levels of overheats, one that shows a yellow cog on the iDrive screen and one that shows a red cog. I got the red cog which means limp mode and no power until the transmission drops back down to temp. Instead of cooling it down, I decided to try again since now only 10 minutes were left. Launch control would not engage so I just mashed the gas and this worked. No overheat, full pass, no problem, however some timer light malfunction prevented a readout. I had a chance for one last pass back to back after this and I went for it. Tried launch control, it engaged, and on the first to second shift it overheated, red cog again, event over, no clean pass and a transmission lifespan shortened.

The best bet for launching the DCT at the strip or on the street for that matter with longevity in mind is to not use launch control. I learned this the hard way. However, the best bet for best times IS to use launch control.

How much power can the DCT take?

The unit BMW uses for the M3 is the Getrag 7DCI600. They rate it up to 440 pound-feet and 9000 RPM which is actually even a bit conservative. My transmission took about this torque level without incident driving around. It is the launches and overheats which made it so the clutch packs started slipping. It never fully gave out just the clutch packs were starting to slip and it was not going to get any better especially as I strove to add more power. If launches and drag strip visits are removed from the equation, on the street with a supercharger, absolutely no issues, just like stock. One can even exceed the recommended 440 pound-foot limit if just using it on the street like a normal person. Here is an up close shot of my transmission:

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Ferrari’s unit for the California, the Getrag 7DCL750, is rated for up to 553 pound-feet. It is also a much larger transmission and weighs 264 pounds compared to the M3’s 7DCI600’s 173 pounds. The Nissan GTR’s GR6 by Borg Warner in comparison is rated for up to 650 pound-feet. It also has 6 speeds vs. the Getrag units 7.

So, you abused your transmission, the clutch packs started to slip, what were you going to do?

Well, I decided to build it. I knew I was not about to stop adding power any time soon so this would have to be done sooner or later. I also knew I wanted to use launch control on the strip. I started contacting companies building transmissions for the Nissan GTR seeing if any would be capable of tackling the M3 DCT. If you can name a company, I contacted them. I tried anyone and everyone and only one company said they could do it and were excited about the challenge of doing it. That company is South Side Performance:

SSP is currently the premier Aftermarket Dual Clutch Transmission Specialist in the world. They have been doing work on the GR6 in the GTR as well as the EVO SST’s. They were the only company with the capability to tackle this project. Everyone else said it was not worth it, too small of a market, or that they did not have the capability to do it. Kris @ SSP told me to bring it on and that he would do what twas necessary to get this thing to perform the way I wanted on the drag strip where performance proven. I like that attitude

So what has SSP done? Well, SSP builds dual clutch transmissions that can do this:

Additionally, they are pushing the boundaries of what a DCT can take such as with their 1000 pound-foot GR6 clutch:


They are not limited to the GTR world but also build EVO SST’s that handle over 500 whp:


Seems SSP and I are proving you wrong as replacement is not your only option and not only can the DCT be repaired outside of Germany, it can be strengthened.

Here are the pictures of my transmission upon arrival today at SSP.

This is the flywheel, and the interesting thing is, the transmission counts the teeth on the back of the flywheel. No other DCT SSP has seen does this and it seems the purpose would be to detect wheelspin:


The bellhousing:


This is the beginning of what should a very interesting process. SSP will be going into the internals this weekend and we will see exactly what is going on inside and what I have done to it We will also learn how much room there is for improvement and how much potential torque we can make this thing take!

To be continued…..