SV6 with 5 speed auto Diff Gears questions.

[torana355]

Ok ive asked this in another diff gears thread but got no response. Firstly i have fairly severe diff backlash in my SV6. I am planning on getting a Kaaz diff center but i want to change the gears to a shorter ratio. Firstly since the 5 speed auto can not be tuned yet will the gear changes be out of whack with shorter diff ratio. Also i don't do much highway driving at all and wanted to know what gears i should go for out of 3.46, 3.7 and 3.9's????

Any help would be awesome.

[torana355]

Anyone have any help?

[Benboy]

Suggest that you consult with a transmission/diff specialist who should be able to give you all the info you want.

[Calaber]

You should be able to change the diff ratio without any sort of transmission re-programming, but your speedo will be over-reading (ie reading too fast) and will need to be re-set. 3.9 is really a bit low for road use and while you will have terrific accelleration, maximum speeds in all gears will be reduced substantially from your present ratio and your fuel economy would be non-existent. 3.46 or 3.7 are more useful road ratios, it then depends on what is more important to you - much better accelleration than you have at present with substantially reduced fuel economy (ie 3.7) or slightly less improvement in accelleration, but acceptable economy (ie 3.46). The choice is yours.

[torana355]

You should be able to change the diff ratio without any sort of transmission re-programming, but your speedo will be over-reading (ie reading too fast) and will need to be re-set. 3.9 is really a bit low for road use and while you will have terrific accelleration, maximum speeds in all gears will be reduced substantially from your present ratio and your fuel economy would be non-existent. 3.46 or 3.7 are more useful road ratios, it then depends on what is more important to you - much better accelleration than you have at present with substantially reduced fuel economy (ie 3.7) or slightly less improvement in accelleration, but acceptable economy (ie 3.46). The choice is yours.

Cheers mate. My biggest concern was the transmission would not change down gears in power mode at the right time like it does with the standard ratio. All my driving is Start/Stop traffic so i would think a shorter ratio would actually improve the fuel economy?? I think i will go 3.7's. If anyone on here has actually changed their ratios i would love to know what ratio you went and how the 5 speed auto box has handled it as well as around town fuel economy. Cheers.

[Fishman88]

Hey mate i did this mod to my VZ calais Alloytec [3.46 LSD] . Its fun in Semi auto mode but when left in auto i found it hard to drive. U will hit overdrive gears at 60km/h in 5th gear, so city driving would be harder i fink. U will be reving about 2500rpm at 110km/h so economy will be go up. Freeway cruising is made easier wont need to change to 4th gear i found. This is my experience but ask others with the same engine n tranmission. I now have the standard 2.87 n found it easier to drive n better ecomny too. Its just too bad that the 5 speed cant be tuned otherwise would kept the 3.46 LSD. Hope that helps mate goodluck.

[torana355]

Hey mate i did this mod to my VZ calais Alloytec [3.46 LSD] . Its fun in Semi auto mode but when left in auto i found it hard to drive. U will hit overdrive gears at 60km/h in 5th gear, so city driving would be harder i fink. U will be reving about 2500rpm at 110km/h so economy will be go up. Freeway cruising is made easier wont need to change to 4th gear i found. This is my experience but ask others with the same engine n tranmission. I now have the standard 2.87 n found it easier to drive n better ecomny too. Its just too bad that the 5 speed cant be tuned otherwise would kept the 3.46 LSD. Hope that helps mate goodluck.

Damb that's is what i was worried about. The fact the A5 can not be tuned may keep me from changing ratios. How much power is your car putting out after getting it tuned at CHE?

[tanner892]

I thought i remember seeing somewhere that after changing diffs the auto changes too early, I dont know if theres a calibration for this or what not but yeah, i wouldnt expect better fuel economy thats for sure, even though the theory of start stop traffic and having a lower ratio diff will require less effort you should buy with the notion of having worse fuel economy, by how much i dont know, 3.46s probly wont be too bad, but yeah 3.7 onwards would start getting bad i think, if you drive around with A/S on obviously it wont be a problem, but I imagine thatd get annoying after awhile.

[torana355]

I know implusesv6 changed the ratio's in his raptor charged SV6 but i don't know what ratio he went and how the A5 handles it.

[Fishman88]

Damb that's is what i was worried about. The fact the A5 can not be tuned may keep me from changing ratios. How much power is your car putting out after getting it tuned at CHE?

I got 189rwhp with Pod CAI headers hiflow cats and manifold insulator. Was hoping higher but oh wells drives better but!! Ive changed back to the stock airbox n for some reason feels much better.

[Fishman88]

I thought i remember seeing somewhere that after changing diffs the auto changes too early, I dont know if theres a calibration for this or what not but yeah, i wouldnt expect better fuel economy thats for sure, even though the theory of start stop traffic and having a lower ratio diff will require less effort you should buy with the notion of having worse fuel economy, by how much i dont know, 3.46s probly wont be too bad, but yeah 3.7 onwards would start getting bad i think, if you drive around with A/S on obviously it wont be a problem, but I imagine thatd get annoying after awhile.

Yep does get quite annoyin afta a while......

[impulsive]

3.46:1 is prolly the best, i think anything higher will be too high

[torana355]

3.46:1 is prolly the best, i think anything higher will be too high

Yeah i sent a PM to Implusesv6 and got some useful info from him. It seems the 3.46 works well with the A5 gearbox so im going to go with that. Now to save up the cash needed for the Kazz centre Though im sure it will be worth it having a decent lsd with a decent ratio.