Change Diff from 3.27 to 3.45 or 3.7?

joshtaylor87 · #1 11-06-2008, 11:09 AM

G'day guys, I have been thinking about doing this for a while now but not sure which way to go. I'm worried that going to 3.45 won't make much of a difference but going to 3.7 will be geared too low. I mainly do city/town driving with the occasional highway trip up/down the coast. Drive 45mins each way to work and back. About half of that is 60/70km zones other half 80/90km zones.

What do you guys reckon?

Would I get much of a difference out of a 3.45?
Would 3.7 be too low?

I'm after a fair increase in acceleration from stand still. Having an alloytec as well as the 4speed auto, 20" wheels, and 3.26 diff it's a bit sluggish off the mark.

Cheers

Cousin Slow Poke · #2 11-06-2008, 01:10 PM

I wouldn't waste my money on just a 180kw Alloytec car.... Especially with just the A4 dinosaur. With the A4 if you change it you'll use a hell of a lot more fuel. One of the reasons it's 3.26 to start with is so it's still economical, especially on the highway. You need the benefit of a 5th and/or 6th gear for low rev touring when you start going for higher diff ratios.

Don't take this the wrong way, but save your money for when you upgrade to something worth changing the diff gears in.

All this is just my opinion though...

joshtaylor87 · #3 11-06-2008, 02:24 PM

Yeah no worries mate, I will be holding onto the car for a few years so I want to get it a bit more enjoyable to drive. I was going to do tune, CAI and Diff and stick with that until I sell it in a few years time. But might just do the Tune and CAI and see how I like that. From your experience with the Calais did the Tune and CAI give it a bit more kick down low? Thats all i'm really after, i'm happy with the mid to top range. Just lacks a bit down low on take off.

But just so I am more informed so I can make the right decision on whether or not to do the diff...the 4th gear ratio in the 4sp Auto is 0.70 5th gear ratio in the 5sp Auto in SV6 is 0.75 and 6th gear ratio in the 6sp auto in SS and SSV is 0.67. This to me looks like 4th is on par with 5th and 6th in the other boxes so it would rev around the same in 4th as in 5th or 6th (top gear on the other auto boxes). Is this the right thinking? Or does the gear ratio have nothing to do with the relationship between diff ratio and rpm etc?

Sorry for being so vague but don't have any experience with all these ratio's.

Cousin Slow Poke · #4 11-06-2008, 03:09 PM

Quote:

Originally Posted by joshtaylor87

Yeah no worries mate, I will be holding onto the car for a few years so I want to get it a bit more enjoyable to drive. I was going to do tune, CAI and Diff and stick with that until I sell it in a few years time. But might just do the Tune and CAI and see how I like that. From your experience with the Calais did the Tune and CAI give it a bit more kick down low? Thats all i'm really after, i'm happy with the mid to top range. Just lacks a bit down low on take off.

Yeah mate, with the CAI and a decent tune you should DEFINITELY notice a lot better responsiveness with the throttle. It won't necessarily be a whole lot quicker off the mark but it feels like a different car to drive - much more enjoyable... I had the SS Inductions Growler on the Calais. You may want to consider saving some money and doing the exhaust instead of the diff ratio change too. Just make sure you specify you want resonators, x-pipe and MUFFLERS or it will drone and fart like a mofo. Personally, I reckon you'll be happy with the performance once you've done those three. Oh and I just realised, you have the single zorst atm so going to a dual zorst and getting it tuned you'll find you end up with similar to what I had on the 195kw Calais. I.e. 150rwkw. That's because the only thing that makes yours 180kw and not 195 is the tune and exhaust AFAIK

Quote:

Originally Posted by joshtaylor87

But just so I am more informed so I can make the right decision on whether or not to do the diff...the 4th gear ratio in the 4sp Auto is 0.70 5th gear ratio in the 5sp Auto in SV6 is 0.75 and 6th gear ratio in the 6sp auto in SS and SSV is 0.67. This to me looks like 4th is on par with 5th and 6th in the other boxes so it would rev around the same in 4th as in 5th or 6th (top gear on the other auto boxes). Is this the right thinking? Or does the gear ratio have nothing to do with the relationship between diff ratio and rpm etc?

I can see exactly what you're asking but I honestly don't know the answer to this one - not mechanically minded enough when it comes to diffs I'm affraid.

joshtaylor87 · #5 11-06-2008, 03:44 PM

Ok thanks for that C.S.P. I will try and do some more research into the Diff side of things. But I will definitely get the Tune and CAI done first and see how that goes. I'll also look into the dual exhaust setup as you mentioned. I do already have Pacemaker extractors and 2.5" single exhaust and some sort of resonator but it does drone quite bad but sounds awesome past 3000rpm so I'm happy to put up with the drone just for the sound of it past 3000rpm. Probably not a good thing as it makes me drive it harder to get rid of the drone lol.

Over the last few weeks i've been thinking hard about whether I want to keep it or reduce my loan by selling it and getting a VT/VX SS. It's a hard decision to make so I have put it on car sales for $38,000 I highly doubt that anyone will buy it for that much but if someone wants to pay that much I would sell it. Thats kinda my way of making up my mind for me. It's been on there for 2 weeks now and not 1 enquiry (as I thought will be the case). I know $38,000 is a lot to ask even if I have spent over $50,000 on it! So thats why i'm looking at doing a few extra mods to it to get it a bit more enjoyable to drive as it looks like I will be holding onto it for a few years to come.

Cousin Slow Poke · #6 11-06-2008, 04:01 PM

Quote:

Originally Posted by joshtaylor87

I have spent over $50,000 on it!

HOLY CRAP!!! Why not just buy an SV6 or Calais to start with?

What would you look for to replace it?

I know a BLOODY GOOD and BLOODY QUICK (thanks to quality mods) red VT Clubsport for sale. Local ACT HSV Club member is selling it - only mentioned it cause I literally got a club email about it 30 seconds ago.

sinister6 · #7 11-06-2008, 04:06 PM

well i've heard that tha 3.7 will make it launch well off the line, while still keepin some sort of econmy for cruisin. but yes, as soon as the diff gears are increased it will tend to guzzle a bit more of the liquid gold.

joshtaylor87 · #8 11-06-2008, 05:40 PM

Quote:

Originally Posted by Cousin Slow Poke

HOLY CRAP!!! Why not just buy an SV6 or Calais to start with?

What would you look for to replace it?

I know a BLOODY GOOD and BLOODY QUICK (thanks to quality mods) red VT Clubsport for sale. Local ACT HSV Club member is selling it - only mentioned it cause I literally got a club email about it 30 seconds ago.

Yeah if I was to replace it I would be looking at VT/VX with V8 whether it be just an executive or an SS so long as it had an LS1. But I've pretty much made up my mind on keeping the Lumina seeing as though I've spent so much on it already!

Quote:

Originally Posted by sinister6

well i've heard that tha 3.7 will make it launch well off the line, while still keepin some sort of econmy for cruisin. but yes, as soon as the diff gears are increased it will tend to guzzle a bit more of the liquid gold.

Yea it's a hard one cuz of fuel prices these days. I just don't know how much extra fuel its going to use. I guess if I went with a 3.45 it would be very minimal but in saying that the acceleration increase i'm looking for would be very minimal as well. I've got a spreadsheet someone did up for me from another forum and it shows that currently at 100kms it revs at 1792rpm with a 3.45 it would rev at 1896rpm and at 3.7 it would rev at 2044rpm. Not sure how accurate these figures are. It does seem close i think at the moment it sits somewhere between 1800-1900rpm at 100km/h so the spreadsheet saying 1792rpm is fairly accurate.

So I'm not sure how much more fuel it would burn with an extra 250odd rpm's (if I go the 3.7)

Bombaman · #9 11-06-2008, 10:09 PM

Quote:

Originally Posted by Cousin Slow Poke

HOLY CRAP!!! Why not just buy an SV6 or Calais to start with?

The Sv6's come with a 2.92 diff, so he would still be looking at replacing it.

To the OP have a look around for a LSD from a Manual V8, belive their running 3.46 in the utes, not too sure about the sedans/wagons

Cousin Slow Poke · #10 12-06-2008, 02:20 AM

I like my factory M6 with 3.7 diff

Can't wait to try the new Tremec T6060 M6 box though. Coupled to an LS3 underneath a Senator... Mmmmmmmmm

burnz · #11 12-06-2008, 04:33 AM

Quote:

Originally Posted by joshtaylor87

G'day guys, I have been thinking about doing this for a while now but not sure which way to go. I'm worried that going to 3.45 won't make much of a difference but going to 3.7 will be geared too low. I mainly do city/town driving with the occasional highway trip up/down the coast. Drive 45mins each way to work and back. About half of that is 60/70km zones other half 80/90km zones.

What do you guys reckon?

Would I get much of a difference out of a 3.45?
Would 3.7 be too low?

I'm after a fair increase in acceleration from stand still. Having an alloytec as well as the 4speed auto, 20" wheels, and 3.26 diff it's a bit sluggish off the mark.

Cheers

on our last criuse syd/can/bath/syd, one of the driver's car was running 3.9 down from 3.08 . the engine rpm's were up just 500, (2500 rpm @ 110 kph)
their wasent that much extra in fuel consumpion, but a big difference launch capability.

monaro327 · #12 12-06-2008, 10:10 AM

the difference between the high output alloytec and the standard one isn't the exhaust. it's the cam phasing, the 180kw doesn't have cam phasing the 195 does phyically different motors and different ecu's aswell.