Diff Ratio Change
If you want to get a bit more go off the line a lower diff ratio will help with getting the tyres turning that much more quickly and easily.
Factory ratios for the VT-VZ range are 3.07 and 3.46 for the Auto and Manual respectively - while i really wanted to go to 3.73 in my auto the opportunity arose to buy a mates manual diff (3.46) at a good price as he was upgrading to a 3.91 (which is a common ratio upgrade for the manual).
So i headed up in my car (along with the 3.46 gear set) to see the lads at Steelie Gears (Auckland). Being an Executive my car was only a single spinner (ie no limited slip diff) so this was remedied at the same time. The guys also beefed up the diff and put in some high quality Redline diff oil for longevity.
I was advised to not go ripping up the streets until a good 1000km was on the newly fitted diff so you can imagine how i felt driving home just dying to try out the new mod!! What was instantly noticable however was the cornering - turn in was markedly better as a result of the new LSD at the rear.
This mod is a hands down must for the serious streeter or weekend race car - it gives improved acceleration and actually eases some of the load going on the drive train as lowering the gearing naturally reduces stresses. The only real negative is you will be revving higher when cruising - while i used to sit on 1800rpm at 100km, i now sit on at 2100rpm at 100km. Not a huge difference to be fair but it will use slightly more gas (my car is not a daily driver so not a big concern for me but i can imagine some people might be more concerned given the latest fuel prices!)
You will also need to have your speedo recalibrated (via the PCM) as the computer still thinks you have the old diff in place and it will get all confused! This can be done by your tuner using LS1 Edit or EFI Live (Holden could do it too but they might charge an arm and a leg for the service!)