So last weekend I installed a Manual transmission differential in my AT 2013 G37S rear wheel drive. Going from a 3.3 ratio to a 3.69 should have been a performance upgrade as many of you have experienced but my car don’t like it for some reason. The engine isn’t nearly as responsive as it was before the install. The engine would build RPMs faster with the 3.3 vs the 3.69 so that tells me I’m not making as much power as before. Has anyone experienced this problem from a simple differential swap?
I have confirmed it is a 3.69 LSD. Something I did before installing the exhaust was start the car and run through the gears to check for noise and vibration. The cats were open or exposed but I can’t imagine that would effect anything. No check engine lights or anything.
Is a tune to calibrate the ecu to the new ratio necessary?

 

Solved the problem! For some reason I thought to try the ECU relearn or whatever it’s called. Problem solved! So if you start your G with open cats and it has now power after, try the throttle or ECU relearn.

 

So.... how's the car with the LSD and shorter gearing?

 

absolutely love it!!! Fuel hasn’t really changed and no other quirks to mention either. It’s like adding 35hp or more! A friend has a tuned f150 ecoboost that would gap me by about 2 cars in the 1/8 and now I’m just a lil faster than him. Tires wear a bit faster because it’s pretty easy to drift on dry pavement now!😉.

 

How's your cruising speeds at 80mph?
Have you had any problems with cruise control engagement?

 

To be honest I haven’t tried the cruise control. I can’t imagine it would change since the sensors are on the wheel side of the diff.
if speed was measured on the drive shaft side then likely there would be a problem due to the gear change. I’ll try it though just to be certain. It’s a noticeable difference in rpm at highway speeds. A chart showing the difference can be found somewhere on here but it seems like 200-300 rpm difference at 70. It’s worth it for me since we don’t use this car for travel. It’s almost hard to shift quick enough to second before hitting rev limit. It’s definitely fun! Especially on rainy days for some wet roads drift...

 

I'm interested in doing this one day as they're not so difficult to find. You should check cruise and rpm @80mph.
Additional data is helpful around here.