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Discussion Starter · #1 ·
I have seen several people on this board asking about swapping gear ratios on their XLR's. I recently completed a switch on my 2005 base and thought I would share some of my "lessons learned".

First thing you need to know is that it is not easy or cheap. I had assumed that I could use a Corvette Getrag pumpkin (c6 only) and it would be a simple "bolt on" - wrong. Even though they look the same on the outside, the interface to the transmission is different - you have to use your old pumpkin and just swap out the gears. Can't figure out how to insert pictures from my computer to show visual.

I bought a nice C6 3.42 pumpkin with ~41K miles for the job, not realizing the issues with the bolt up. Ended up taking both pumpkins to Unitrax (company in So Cal) to swap the gears and get it all squared away this was about $600. Luckly, my car came with a 2.93 ratio and the 3.42 gears barely fit. If you have the 2.73 or 2.53 ratio, it will require machining of the internal casting to allow the extra large gears to fit (bearings will be OK). The Z06 gears have larger bearings and will not swap easily.

Then, I had D3 do the install. This went pretty smooth, mechanically. The problem was that they could not program my ECU or TCU (they both need to be programed for the new gear ratio). If you have a 2006 or newer, supposedly they are easier to program. I ended up sending my ECU and TCU to PCM Performance ($600) - they had the software to get the speedo changed, as well as do a "hot tune" and modify the shift point and shift firmness settings - BIG DIFFERENCE!

While the 17% ratio difference does not seem like a lot, it is directly proportional to the torque at the wheels. Add the performance tune and I feel like I can keep up with the Corvettes.

I did lose a mile or two per gallon, and probably my top end speed (only been there once anyway), but it made a world of difference.

All said and done, it was about $2300 and a few weeks to complete.

So, for all you guys out there that have been asking - yes, it can be done.

Send me a PM if you want more details.

Hope this was helpful...

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