Diff gears....

[mickkcim]

At 100km/h I'm doing 1850rpm
At 110km/h I'm doing 1950rpm

With 3.27s

 

[PIR4TE]

Yeah every time I keep forgetting Calais comes in auto only!

Overall you are better off with stock gears for economy and 0-100 performance driving (within the speed limit) in our car with auto, seriously. I think the most common mistake owners make in an effort to improve performance in this car is to swap the gears for more changes / high RPM and wringing its neck chasing the HP, whereas maximising traction and torque will get you off the line quicker and more efficiently. Mods should be for optimising torque, not HP. Especially if you only need to change gears once to highway speed:

[video=youtube_share;u1nFONqwWhU]http://youtu.be/u1nFONqwWhU[/video]


Stock diff gear comparison:

[video=youtube_share;V4P-_bAxAtU]http://youtu.be/V4P-_bAxAtU[/video]

 

[PIR4TE]

Going 3.27 or 3.45 will get more top speed and in-gear acceleration, see this third gear roll-on from ~20kph:

[video=youtube_share;-YGQnjNyl2Y]http://youtu.be/-YGQnjNyl2Y[/video]


and past the legal limit, like 115-160:

[video=youtube_share;qHY0p-sLmuE]http://youtu.be/qHY0p-sLmuE[/video]

 

[Foggsy]

Hi Calvv8,

Long time no speaky mate! Funny you ask about diff gears as I have just done them twice in my manual and driven an auto last week with 3.91's and a manual the week before with 4.11's not that that helps you buddy.

I can tell you from first hand experience behind the wheel to forget 3.91's in an auto. First is so short I think it makes the car slower as its useless. If it was me, I think the sweet spot for diff gears in an auto VE v8 is 3.46, noting that your stockers are 2.92, you will get much better acceleration off the line but still have a great top end and low RPM cruising on a freeway. 2.92 to 3.46 is a solid jump. I went from 3.46 to 3.7 in my manual and could probably get away with 3.91's but am happy with the 3.70's. I wouldn't waste your time with the HSV ratio for auto being 3.27.........A good point to note for you is that you will be able to pick up a very low kay 3.46 out of a manual pretty cheap when guys like me upgrade to a shorter ratio. I got $750 for mine and it had 29,000kms on it. 3.46 would be my recommendation but if you really wanted too you could get away with 3.70.

Also if you want to work out what your revs would be at 100kmph there is a formula you can apply. If you know that say currently at 100 you are doing 1600rpm with a 2.92 diff ratio and you are going to put in a 3.46 then do this.....1600 / 2.92 = 547.9452 x the new ratio of 3.46 = 1895rpm.....which is your new revs at 100 if you fitted that 3.46.

I hope this in some way helps.

Arvo all, Looking seriously at replacing diff gears in my 6 speed V8, Now im thinking 3.7 ratio Thoughts please....


Cheers in Advance

 

[AD07]

Listen to what Foggsy said.
I changed my Calais from the 2.92 to a 3.46lsd. Definitely one of the BEST mods you can do to an Auto.

 

[arronm]

I did the same as above and totally agree 3.45 works great in an auto

 

[calvv8]

Thanks Foggsy and everyone else for your valued input...3.45 seems to be the sweet spot here..think its time to start getting quotes on all this...

I may need to increase tyre width too, 245/45 R18 are on there at the moment.would 265 or 255 fit in there?....

 

[christov]

This is the data I get when comparing the two. For my car at least, I'm quicker on 2.92s possibly due to shift time. The red 2014 commie is using 2.92 gears, the blue 2014 commie is using 3.46 gears.

 

[torana355]

Imo changing diff gears in a car that already has a short first gear is counter productive on a street driven car. Your 0-100 time will be slower due to three gear changes to reach 100kph, you wont see the benefit till you are well over the speed limit. You really need gearbox ratios that complement the diff gears.

 

[christov]

Imo changing diff gears in a car that already has a short first gear is counter productive on a street driven car. Your 0-100 time will be slower due to three gear changes to reach 100kph, you wont see the benefit till you are well over the speed limit.

Correct, no tangible benefit until you reach 200km/h+ acceleration as per the above.