Diff gears! 3.7's or 3.9's?

[HERONVY]

Hi guys, before i get flamed for posting up "another one of those diff gear threads" hear me out...

Im looking for a straight answer here with as much info as possible

If you dont know already i drive a manual vy 2002 S pac on a daily basis, it has just been cammed, had 1.9:1 roller rockers fitted, custom tune and upgraded valve train gear.
It goes well now, has an awesome lumpiness to the idle (sounds like an early torana ) and i can feel the extra power, however i feel that it is a bit sluggish down low and you cant feel the extra power as much until you hit mid-high revs.

Now my mechanic suggested fitting up a set of different ratio diff gears to get that low end sluggishness out of it so i can feel the power all through the rev range and take off a little bit quicker than the standard 3.08's

What im asking here is what is the difference between 3.7's, 3.9's and 4.11's? As i dont know much about gear ratio's etc.

What is the best set i can fit up to it? What is good for the street? I want to launch quicker and faster, but still maintain some sort of high end power (i dont want to sacrifice all my high end power lol)

Thanks for reading, hope to here some good responses soon!

Cheers, Al

[wraith]

For a manual I would say stick with 3.7's. 3.9's will mean you will run out of revs quicker and 4.11s are good for burnouts.

[walesy]

basically the number represents the number of rotations of the pinion gear to the ring gear, or close to tailshaft rotations to wheels (not 100%accurate depending on wheels tyre combo) so 3.7's will be the pinion gear rotation 3.7 times, to the ring gears 1 rotation (thats why you see diff gears as 3.7:1 etc)

i cant really comment on which ones you should go because mine is an auto, i use 3.9's which are really pokey off the line, but will rev higher at 100km/h 4.11's will rev higher at 100kms but take off slightly quicker than 3.7's or 3.9s.

hope this helps
Walesy

[VY Rossi]

I have 3.9s in my manual vy ss and they are great sitting on 2000rpm in 4th at 60km, 1800rpm in 6th at 110km and it launches hard

[HERONVY]

Cheers guys for the fantastic responses, its been extremely helpful :-D
Best response ive had to any post in a long time

Anyway, down to business !
Seems like 3.7s are the go, ill have a ring around the commodore shops and look online to see if I can get a set for my car

What would I be looking at price wise for a set of these gears? Just the gears not the casing and whole assembly
New or used doesnt matter

Cheers, Al

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[walesy]

3.7's are alot easier to come across than 3.9's and 4.11s so your in luck, but they are still really expensive, from memory i paid about $750 for my 3.9s, just dont go getting cheap chinese brand gears as they are known to break

[Dr HaxZaw]

dont the manuals generally come in 3.45??? or did you put a different diff in it at some point?

[walesy]

dont the manuals generally come in 3.45??? or did you put a different diff in it at some point?

yes i missed that in the OP, manauls are standard 3.46 and auto's are 3.08

[HERONVY]

dont the manuals generally come in 3.45??? or did you put a different diff in it at some point?

Mmm well thats a completely different can of worms, still has the standard diff in, hasnt been looked at since I bought the car.. Lol
So... Dont go 3.7s???

Al

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[wraith]

3.7 will still be a benefit. Holden's are pretty lazy off the line.

[HERONVY]

3.7 will still be a benefit. Holden's are pretty lazy off the line.

Yeah I agree, hear lots of good things about quick take off with the 3.7s , so looks as though ill still end up hunting a set down

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[james1988]

If your going through all the effort. I would go 4.11's everytime. Or atleast 3.9's.
There's going to be about 30% increase In revs.
And if you have done other engine work like cams etc you're not going to mind the little extra in fuel costs.
My friend went from 3.08 to 3.7 in his vt exec and it wasn't very noticeable.

[walesy]

My friend went from 3.08 to 3.7 in his vt exec and it wasn't very noticeable.

really?? i went from 3.08's to 3.46s and it was a big difference, then after my burnout comp days were over (after the respray) i went to the 3.9s for more drag friendly fun

[HERONVY]

If your going through all the effort. I would go 4.11's everytime. Or atleast 3.9's.
There's going to be about 30% increase In revs.
And if you have done other engine work like cams etc you're not going to mind the little extra in fuel costs.
My friend went from 3.08 to 3.7 in his vt exec and it wasn't very noticeable.

That being said ... If I went 3.9's or 4.11s would I lose alot of power mid-high revs?
Meaning quick take off, but gutless up high? Still liking the idea of 3.7s, seems like a good mediocre

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[wraith]

3.9 and 4.11 isn't that good on a manual you will find your self changing gears really quick.

[james1988]

Sorry. Since we were talking about 3.08 ratios I thought it was an auto.
Its a difficult decision. Cos it's such a expensive job to have to do again if you pick the wrong ratio.

[HERONVY]

3.9 and 4.11 isn't that good on a manual you will find your self changing gears really quick.

Yeah thats what im fearing, seeing it is a street car and i dont do burnouts, so 3.9's + 4.11's seem unnecessary

Sorry. Since we were talking about 3.08 ratios I thought it was an auto.
Its a difficult decision. Cos it's such a expensive job to have to do again if you pick the wrong ratio.

Yeah , i'll get under and have a look at what it has stamped on the diff and see where to go from there, pretty sure that walesy + haxzaw are right on this one about 3.45's though
Seems like 3.7's still seem like the go due to the "streetability" of them, they are a mediocre type choice, the car wont be revving its tits off and getting nowhere once it hits about 5-6k revs and will still be an improvement over the standard diff setup ..hopefully lol

Al

[Dr HaxZaw]

i reckon 3.7's are your best bet as well.... at 100kmh should only be a difference of about 200 revs by my calcs
not really going to effect fuel economy at all to me

[HERONVY]

i reckon 3.7's are your best bet as well.... at 100kmh should only be a difference of about 200 revs by my calcs
not really going to effect fuel economy at all to me

3.73's it is! chasing down a second hand set now

Al

[HERONVY]

Just got up underneath and it says ratio: 3.08:1 so yeah no wonder shes sluggish off the line lol

Managed to get onto a set of 3.73s for 300 brand new, so pretty stoked atm :-)

edit: pic here:


Sorry for the bad quality, was difficult holding the camera all stretched out and was shaking when i took the pic lol
..its hard getting under lowered cars, should of jacked it up to get a better pic.. meh

Al

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[Dr HaxZaw]

hhhmm interesting that its 3.08 for a manual... at least you have got a set now lol

[HERONVY]

hhhmm interesting that its 3.08 for a manual... at least you have got a set now lol

yeah was a bit shocked due to everyone saying that it was 3.45 but oh well. Thats true, now just gotta get em delivered and fitted up

Al

[Hothousevys]

hey mate just wondering where you managed to get your diff gears from. i am chasing a set but am having trouble tracking some down. how much are you looking at to get them installed

[M01ST]

I just go a diff out of a r8 clubby apparently 3.7s from factory?? Vy sv8 had 3.08 goes a lot better with 3.7s.

[VY Rossi]

Thats correct they are 3.7 from the factory