AU Diff Ratio

The Mighty Red · 13-07-2005, 07:18 PM

Got quoted $440 to have a 4.11 diff ratio put in the XR (LSD)today and i also get to keep the 3.45 thats in it now,
I thought this is a fairly resonable price *( i was expecting it to be more)
Is It around the mark?

Is there any short falls with this mod that i should know about before i go ahead and do it.

The reason for this mod is purely performanced based, i am looking to get more low down acceleration,

Will i need a chip to run this mod?, meant to ask the mechanic but i forgot.
Mechanic says it wont change the speedo reading , is this correct?

Thanks in advance Gary

buickman · 13-07-2005, 08:43 PM

I will think you would have to have the T/convertor done with 4.11 gears.
You will get sick of it for street use.
I would say you will have to dig deep into your pockets for other mods to make it work right.

buickman

The Mighty Red · 13-07-2005, 09:02 PM

I am guessing that my car would be doing around 2500rpm @ 100kh

Casper · 13-07-2005, 09:04 PM

auto or manual?

The Mighty Red · 13-07-2005, 09:14 PM

its an auto

Casper · 13-07-2005, 09:19 PM

ok, $440 is cheapish so yes, good price
It will not be of optimum value without other mods but will get you going quicker
Expect at LEAST a 10% or more increase in fuel use
Your speedo will be out.. in a big way
If you change the speedo sensor your change point on the auto will be past the rev cut out so you will need to either get chiptorque to change the shift points or wire in one of those convertors to make the speedo right without changeing the shift points.

The Mighty Red · 13-07-2005, 10:04 PM

So basically i have the chip put in and then have the speedo corrected when i have it all tuned ,

I know it will use more fuel but even with the limited mods i've done ( exhaust/cai) i thought the 4.11 would give me a atleast 1/2sec over the 1/4mile with good gains to 100kmh or am I expecting a bit much

jonbays · 13-07-2005, 10:21 PM

To use a 4.11 diff you will need to mod the engine to rev WITH power hard into 5750rpm at a minimum other wise its just too low for CAI and exhaust mods.

Go 3.73 unless this is a weekend warrior only. 3.9 if you are desperate for the best 400m you can get and the engine is going to be modded to REV.

Your speedo will read FAST! at 100kmh on your speedo you will be doing 84kmh!

In a falcon Futura etc with a 3.08 diff, diff swaps will make a big difference but in an XR6 with 3.45 as standard the gains aren't as big as its not stupidly overgeared to start with.

TheSneakiness · 14-07-2005, 10:23 AM

See, I can't understand something here.

I just recently went from the 3.23 to a 3.45 LSD from an AU3 XR, actually put the speedo gear in for a 3.45 and have not had any problems. Took the ECU a little while to realise that there was different speedo gear, but I've had no probs with shift points.

jonbays · 14-07-2005, 07:45 PM

Quote:

Originally Posted by AUII_SE_Ute

See, I can't understand something here.

I just recently went from the 3.23 to a 3.45 LSD from an AU3 XR, actually put the speedo gear in for a 3.45 and have not had any problems. Took the ECU a little while to realise that there was different speedo gear, but I've had no probs with shift points.

Whats not to understand?

TheSneakiness · 15-07-2005, 09:46 AM

How everyone says "Don't change the speedo gear, it stuffs up your shift points. Go and buy this Jaycar thing that tampers with your speedo, but doesn't stuff up your shift points".

I got my damn speedo gear changed. The shift points are fine. That why I can't understand why you need to buy the converter when the speedo gear is working.

Casper · 15-07-2005, 10:08 AM

Going from 3.23 to 3.45 is not a big enough jump to affect it dramatically.
Same as if I went from 3.45 to 3.73. It does effect it but the shift point is still going to stay under the rpm cut out.
Just to test it. Put your auto in performance mode and floor it from a standstill. Watch where the auto changes... I'm betting its somewhere just after redline rather than just before. The shift points have been affected, you just havent made a big enough change to the diff gears to notice it.

TheSneakiness · 15-07-2005, 10:13 AM

Quote:

Originally Posted by Casper

Going from 3.23 to 3.45 is not a big enough jump to affect it dramatically.
Same as if I went from 3.45 to 3.73. It does effect it but the shift point is still going to stay under the rpm cut out.
Just to test it. Put your auto in performance mode and floor it from a standstill. Watch where the auto changes... I'm betting its somewhere just after redline rather than just before. The shift points have been affected, you just havent made a big enough change to the diff gears to notice it.

Uh huh. That would explain it.

20-07-2005, 04:37 PM

I enquired about 4.11s and was told that the pinion shaft is too thin and would "break like a tooth pick" with any huge clutch dump, launch etc.
The 3.9:1 is alot stronger in that department.

Now I just have to find stronger drive shafts!

au-steve · 20-07-2005, 06:07 PM

mine shifts at 5000rpm when going WOT. Thinks thats the chiptourque doing its thing though ... casper, does the chiptourque adjust the injectors pulsewidth at all? is it capable of that? and how do you get them retuned?