Guys - I was wrong (diff gears)

[Febs]

For months I put off fitting 3.46s to my A4 because I was sure they'd use more fuel. Maybe not around town, but on the highway where I do about 60-70% of my driving.

I finally decided I wanted to go quicker and got sick of the single-spinner, so I gave in and had a new LSD centre fitted along with some 3.46s (I scored the gears for free from a mate, so that helped the decision too :D).

I've had them in for about a month now, and I've gotta say - I was dead wrong about the fuel economy.

I do roughly 360km/week of highway driving (F6 mostly) and about 150-250km/week of city-suburban driving. I used to average about 13.1-13.5l/100km with that sort of driving, but now I'm getting under 13.0l/100km. My last tank (measured at the bowser, although my trip computer is dead accurate) returned 12.8l/100km. Seems the lower gearing around town is helping a lot more than I expected, making for much better overall economy.

Then of course there's the other benefits...

- I love my exhaust, but there was always a bit of drone in 4th at around 60-75km/h (not heaps, but enough to make me leave it in 3rd). The drone's now almost all gone...certainly enough to make me leave it in 4th all the time.

- And of course, it's helped heaps at the strip. People told me I could expect 0.2s off my 1/4 mile time, and that's exactly what I got. From 13.540 to 13.340...and that was in 100% humidity!

So all up, it's made my car a pleasure to drive, gave me better fuel economy, and was well worth the $700ish it cost me. :)

Cheers,
- Febs.

PS: Speedo has been adjusted for the new gears, so fuel economy figures are accurate.
PPS: Before anyone says "Go the 3.73s!", I've driven an A4 with them and it revved too high above 110km/h for me. Felt great around town though. :)

[MNR-0]

Good review. It really depends on your style of driving and where you drive. For those that do a lot of freeway driving 3.46 is PERFECT. For those that do 70%+ city and suburban driving 3.73 are PERFECT.

Last 2 tanks on my 3.37 gears I got 500 and 478kms. Had 5 litres left in the tank too - consumed 70L fuel. So for city driving 3.73s will yield even better mileage IMO.

[jab]

Have you found the LSD has made much difference? How has it affected driving? Was it worth getting? How does it affect traction?

[Padina]

Have you found the LSD has made much difference? How has it affected driving? Was it worth getting? How does it affect traction?

Sh!t YEAH!!! :D Speaking from experience mate, going from a VX single spinner to a VZ LSD with 3.73:1 makes a hell of a difference. LSD is definatedly a must in all my future cars.... but then again, so is a V8..... ;)


Cheers...:D

[Febs]

Have you found the LSD has made much difference?

In day-to-day, normal driving...no, because I rarely lose traction when driving around town (only when I want to).


How has it affected driving?

When you want to, it makes getting sideways easier...but it also gives more control when going sideways. The single-spinner would sometimes get sideways around a corner (when provoked), but didn't feel as controlled.


Was it worth getting?

:yup:


How does it affect traction?

Much better traction off the line at the drags (you still lose traction, but it hooks up a lot quicker). With the single spinner my 60ft times would range from 2.2 to 2.4. With the LSD they were all around 2.1-2.2.

Cheers,
- Febs.

[muzza]

What, dont you reckon leaving the car in 4th (instead of 3rd) around town is largely responsible for the improvement in fuel economy??????????????????
:D

[Febs]

What, dont you reckon leaving the car in 4th (instead of 3rd) around town is largely responsible for the improvement in fuel economy??????????????????
:D

Heh, I should've been a bit clearer.
I only started leaving it in third a few months before the diff gears went in. Before that (ie: last year) I always left it in 4th and used to get 13.1-13.5l/100km.

Leaving it in third with the 3.07s, and doing a lot of suburban driving usually got 13.5l+.

Cheers,
- Febs.

[cosmo vyss]

Thanks for the update Febs.
I think its an excellent idea that ppl post up reports of how much of a difference or performance/economy or lack of they got from a mod. This mod is one of particular interest as fuel prices are going north and the majority of threads i have read said fuel economy would be worse.
Has anyone else had an improvement with fuel economy with new diff gears?

jb

[COOKIE!]

Sh!t YEAH!!! :D Speaking from experience mate, going from a VX single spinner to a VZ LSD with 3.73:1 makes a hell of a difference. LSD is definatedly a must in all my future cars.... but then again, so is a V8..... ;)


Cheers...:D


It dosnt help the fact that you now have a extra 100+rwkw at your disposal now does it padina :lol: :lol: :lol:




3.73's are the best you know you want them feb's or at least in a month you will :stick:

[Febs]

3.73's are the best you know you want them feb's or at least in a month you will :stick:

Maybe in a year when I'm done with uni* and don't have to drive down to Wollongong 3 times a week. Until then these will do nicely. :)

*Speaking of which...I really should put the laptop away and start listening to my lecture. Damn uni wireless making it easy to access the forums anywhere on campus. :lol:

Cheers,
- Febs.

[Pickles]

Febs-How did you adjust the speedo & transmission shift points?-Via edit,or some other way? Have an A4 Monaro myself & will eventually be doing this mod myself,not particularly for drag racing,but because I feel it will make the car more driveable.I had a VL Group A(HDT) some time back,and I had the diff ratio changed from 3.08(standard) to 3.45.It was like having another 20-30 h.p,& just made the car more responsive etc.What other thoughts do you have? Cheers, Pickles.

[LS1VT]

Thanks for the update Febs.
I think its an excellent idea that ppl post up reports of how much of a difference or performance/economy or lack of they got from a mod. This mod is one of particular interest as fuel prices are going north and the majority of threads i have read said fuel economy would be worse.
Has anyone else had an improvement with fuel economy with new diff gears?

jb
When i recently changed to 3:46, i noticed the fuel economy dropped off a bit. Maybe it's the way i drive or maybe it's because it revs a little higher, but it's all worth it with the extra accelleration. Sometimes i wish i had gone with 3:73s.

[Jphdg]

When i recently changed to 3:46, i noticed the fuel economy dropped off a bit. Maybe it's the way i drive or maybe it's because it revs a little higher, but it's all worth it with the extra accelleration. Sometimes i wish i had gone with 3:73s.


Well, personally myself, I jumped in the deep end and just went the 3.73's, but like MNR-0 said, probably depends on your driving requirements and environment you drive in to help make the decision on which is best to use.

I don't do lot's of highway driving and am absolutely rapped with my choice. It is awesome all round.

I still averaged around the 10.2l per 100Km for a Melbourne - Geelong and back with a little driving around Geelong, so I am happy enough with it but could not really compare to the 3.46 as I never tried them.

I am averaging around 18.5 in the city lately, but probably the foot gets heavy at times so that would not help.

First few weeks it was nearly at 20 :lol:

Main thing though is if you are happy with what you got and it suits your driving needs, that is what counts the most. :D

[Peter B - CV8]

Febs-How did you adjust the speedo & transmission shift points?-Via edit,or some other way? Have an A4 Monaro myself & will eventually be doing this mod myself,not particularly for drag racing,but because I feel it will make the car more driveable.I had a VL Group A(HDT) some time back,and I had the diff ratio changed from 3.08(standard) to 3.45.It was like having another 20-30 h.p,& just made the car more responsive etc.What other thoughts do you have? Cheers, Pickles.

Pickles,
I had the diff ratio changed to 3.46's and have now done approx 2,000 k's since the change. The car launches much better - and just wants to take off without provoking uncontrolled wheelspin. I felt that it used to bog down a little prior to the diff change.
I am using less fuel around town (usage dropped from approx 17litres per 100 k's down to low 15's.
Freeway driving usually sees me getting 10's and occassionally low 9's and at 110kph the engine is revving at just a whisker over 2,000 rpm.
The speedo was out of calibration - but this was corrected a few days after the diff change when I had my mafless edit done. I've also got the 2nd hole mod to the airbox & GTS MAF pipe.
Next step is for a cat back exhaust system (take a look around the rear diff area & you will see all the crimping etc on the standard pipes) - and a freshen up of the edit.
If you are ever in Sydney & want a drive of the car let me know.

[Febs]

Febs-How did you adjust the speedo & transmission shift points?

Had it done by Dick's Electronics, as Dick had already done a mafless tune on it. He does it a little differently from what I can tell (editing the raw hex dump from the PCM), but it can be done via Edit/etc.. or Tech2 by changing the PPK (pulse per km) value too.

That fixed up both the speedo, and more importantly - the shift points (changing the diff ratio will throw them out of whack).


just made the car more responsive etc.What other thoughts do you have?

Definitely. Going around a corner now you can just put your foot down slightly and accelerate easily without having to drop it down a gear. For me, that's the best part - not being bogged down low in the rev range. Much nicer to drive. :)

Cheers,
- Febs.

[fatas]

now i can get the 3.46 just tell the wife it will save fuel and money thanks febs now time to go play at wsid. :lol:

[Mongy]

Has anyone else had an improvement with fuel economy with new diff gears?

jb
Yep. But that's about to go out the window with 3.9's :lol:

[BakerSS]

Can any one tell me what their engine RPM is when cruising at 110kph with 3.46/3.73/3.9 diff gears in an A4?

My standard A4 and 3.07 gears gives me around about 2000rpm or so from memory at 110.

Thanks

[Mongy]

Can any one tell me what their engine RPM is when cruising at 110kph with 3.46/3.73/3.9 diff gears in an A4?

My standard A4 and 3.07 gears gives me around about 2000rpm or so from memory at 110.

Thanks


http://www.ls1.com.au/forum/showthread.php?t=21511 Gives you the lot.

[BakerSS]

Thanks very much, just what i was after!

[Pickles]

PETER B-CV8-Thanks for your comments-I might take you up on that-Sounds like you are getting the same benfits in responsiveness,driveability etc,as I did with my GPA-which is just what I am looking for now.Cheers,Pickles.

[markone2]

Can any one tell me what their engine RPM is when cruising at 110kph with 3.46/3.73/3.9 diff gears in an A4?

My standard A4 and 3.07 gears gives me around about 2000rpm or so from memory at 110.

Thanks


2600rpm at 110kph.....A4 ...4.11 diff gears

[raff]

I put a complete 3.73 hydratrak in my A4 clubby some months ago and at the time I was mainly just puttering about. It certainly helped the economy. I have recently moved interstate and changed work direction which see's me freeway driving every other day. I think the 3.73 for freeway driving works spot on. I avg around 12-13l/100km which is a blend of freeway, spirited driving and around 11lt/100 freeway only. It sits on 110km/hr at 2250rpm and 130 at around 2400rpm which is certainly comfortably and gets you closer to that 'sweet spot' for overtaking ect. I would say 3.73 are probably a little much if you like sitting around the 150km/hr mark but unless your in the NT, when would you??

My 2c, 3.73 work for me for freeway driving doin the 100-130kmhr stuff and are bloody spot on for around the streets driving. Im happy with my gears and a recommended choice :D (at the end of the day anything beats the 3.07!!!) :bash:

[VooDoo]

I think Febs in now convinced. I took him for a drive in the lux-0-barge with 3.73's and he loved em. Driving from Brisbane to Sydney with some spirited overtaking returned 11.9L/100K's for the trip. Even after driving around sydney for 2 days the ecconomy is still 13.0/100. Hopefully the new dual 3" system doesnt affect it too much.

[Febs]

I think Febs in now convinced.

Haha, I was more impressed with the note from your cam and those dual 3"s. Not too often you hear those sort of noises coming from a luxobarge. :)

I like 3.73s in the A4 (have ever since I took forrestd's ute for a quick spin), but the revs at 120-130 shit me.

Cheers,
- Febs.