Topic: Swapping from 3.73 to 3.91 diff

[Arabas]

as said some time ago, i feel that GT/Redline/ GXP, should have either a 6speed tranny or a higher diff ratio. since changing the gearbox to a 6speed seems to be the most expensive solution and there isn t a plug and play solution out there, maybe changing the diff would be a good idea.
LV said in another thread where the NA diff with LSD can be found, and i already found some fair prices for it (as long as these are in good condition of course).
How much will a diff 3,91 would help acceleration?
maybe changing tires and using a different dimension (245/35/18) would give the same result?
maybe doing both would even help better?

which solution is worth the money and would give a better acceleration?

drawbacks for each solution?

to be honest, i don t know a lot about this whole thing and i am in the learning process. so , if anyone knows pls jump in and enlight me.

[Kuprito]

Low profile tyres have less traction.

The best way is putting 16" rims with 255 or so and 50-55 profile. I think Kelu drags that way.

Less air inside the tyres also helps traction.

Every single thing that helps to launch the car will damage the +100km/h acceleration and viceversa.

[Yogi]

Low profile tyres have less traction.

Why do you say that?  I've never heard that before. 

[Uranium-238]

Less give in the sidewall. Ever seen a picture of a car with slicks launch? The softer the sidewall, the more it acts like a spring to dampen the torque at initial launch.

[Gentleman Jack]

Every single thing that helps to launch the car will damage the +100km/h acceleration and viceversa.

with the exception of lowering the weight....  

[kennysabarese]

I don't think replacing the diff is the best solution. I think you can just replace the gears with something from Richmond. There are kits for the Camaro and Vette and their diff's are similar so I dunno if those units will fit inside.

Here is a starting point: http://www.camaro5.com/forums/showthread.php?t=87200

[Kelu]

Kuprito is right, smaller height of the tire makes less traction, think about drag slicks: huge height so they will torque (squeeze) instead of slipping.

Arabas: get this and play http://www.f-body.org/gears/

[LatinVenom]

Is a lot easier to change out the diff than changing the internals.
Not only that but you can keep your stock in good shape and let the other one take all the beating.

[Sol Asylum]

Is a lot easier to change out the diff than changing the internals.
Not only that but you can keep your stock in good shape and let the other one take all the beating.

It also most likely cost less to change the diff and takes less time to do.  If you replace the internals you will have to R&R the diff anyway but you will have to have the proper tools to disassemble the internals and reassemble things.  Then you will have to measure and set all the clearances, backlash, etcetera.  If you have ever done this you know it will take some time and skill to do, if you pay someone else to do it then its added cost.  Plus it leaves you with the question did it get done correctly?

[kennysabarese]

a) 3.91 NA diff is not much of a difference than the 3.73 he has now. Most Camaro's go from 3.43 to 3.73 or 3.9 or even 4.1  that is a big jump. 3.91 is not much of a jump at all.

b) since there are no NA Kappas where he lives, he'll probably have to get one shipped to Greece, might end up costing way more than a gear swap.

[Critterman]

There is about 250 rpm difference in 5th gear between a GXP and an NA

[Sol Asylum]

a) 3.91 NA diff is not much of a difference than the 3.73 he has now. Most Camaro's go from 3.43 to 3.73 or 3.9 or even 4.1  that is a big jump. 3.91 is not much of a jump at all.

b) since there are no NA Kappas where he lives, he'll probably have to get one shipped to Greece, might end up costing way more than a gear swap.

It doesn't have to be a Kappa, just a Getrag 265 and since they are made over there (Europe) it may not be so hard to find.

[kennysabarese]

Kelu was looking into this, but I don't think he came up with much. Maybe that same diff is used in some non-GM cars. Cuz there aren't many RWD GM vehicles in Europe.

Arabas. Let Kelu know if you find anything.

[Yamatr3]

Last time I checked, Richmond Gear does not make gears for our diffs. 

[kennysabarese]

But our diff's are the same as the Camaro/CTS/G8 I thought. And there are Richmond's available for that.

[Morfious]

I thought our diff came out of a CTS.

[Arabas]

so, changing tire dimension is out of the picture, correct?
it sounds like the easiest solution, but i was kinda looking to avoid this, since the ride height will drop and i already have the HR springs, so it would be a problem for me.
two solutions from what i have read so far
-NA diff 3,91 not a big difference, but a small difference plus plug n play which is good, very good actually. so it is around $400 plus shipping + installation
-Richmond rear end gear 4.10 $600 plus shipping +installation.

i suppose the second solution would give a batter result, but more $$$ spent and it requires to have a technician that really knows what he is doing (we DON'T have DDM around here..) 

[Kelu]

Your conclusions looks good to me Arabas, the main reason why I dropped the idea with NA diff is because the difference will be minimal and I don't know how strong is that diff, I would prefer to get a Quaiffe differential from UK and sleep tight no matter how much power I will make if it will be the case.

[Arabas]

Kelu, i believe that the NA diff is EXACTLY the same with the GXP only with different ratio, so i suppose that it could hold the tuned power of the GXP.
i suppose the Supercharged 2.4 makes around the same torque and power, so it should be OK.
now about Quaiffe, what have you found and how much would it cost?

[Kelu]

800E iirc but don't ask me for a link cause I lost it )
My previous quaiffe lsd was same price.

[Arabas]

800 euro is a very fair price!!!

[Kelu]

The guys from US have almost same price for it, ie 1000-1200$

[Arabas]

if you find some specs for it or a link, pls post it (i have found the Opel GT intheir website, but i m sure it s for the 1967 model...)

[Kelu]

http://www.quaifelsd.com/applications.aspx
Pontiac Solstice inc. GXP     QDF23B     $1,515.13
Saturn Sky inc. Redline     QDF23B     1,515.13

http://www.quaife.co.uk/catalogue/products/qdf23b

According to this link, they confirm the lsd fits on CTS V6 too (2.8, 3.0 and 3.6):
http://limitlessperformance.net/quaife/quaife_atb_differential/qdf23b/i-307320.aspx

Something from the in-house solution:
http://www.solsticeforum.com/forum/f102/quiafe-lsd-63417/

Also our stock one (including the NA one) are pretty good but I know a guy which broke 2 of them with upgraded turbo. I'm afraid to change the turbo or even run slicks in my races, It might broke on my 530Nm (390 lbs-ft) crank torque that's why I mentioned Quaife.

I know is not a cheap solution but is the strongest, Quaife has lifetime warranty, pretty sure we will never brake it, we will post the issues on other parts of the tranny after installing this 

I told you not to ask for a link 

[kennysabarese]

I thought our diff came out of a CTS.

Yes, our diff is the same as the V6 CTS. But the platform is the same between the Camaro/CTS/G8/Holden/Vauxhall  same car different body. All the differentials can swap in and out. Unfortunately, all the other cars have a shorter gear ratio than us. If we had more power stock we'd probably have a 3.4 final drive ratio.

GM has some vehicles with a taller ratio. They are trucks. Someone even has a 4.10 out there, but I don't think it's a vehicle available in Europe. They have a better chance finding it out of a different car like SA mentioned.