Topic: Swapping from 3.73 to 3.91 diff

[Kelu]

why you dropped the idea?

Kenny reply was very strong:

The only reason I am against the NA diff is because it seems like a lot of investment for a small amount of improvement.

Let me restate my opinion:
The differences are too small for 600-900$, going on a 3.9 or 4.1 differential will kill the launch in the benefit for high rpm acceleration, we will spin like crazy on 1st. We have an AWESOME launch even with stock wheels/tires, I think I proved that on my races. I would rather work on power on high rpm instead of killing the low rpm in low gears, going into 4th gear will be a very small difference because of 1:1 ratio.

I would rather work on that very long 4th gear than swift everything from the differential ratio if you want to keep the mods related to tranny.

For drag racing, I would forget about this and go for drag slicks and call it a day. Drag slicks on smaller wheels will gain a lot more than changing the diff.

SC can launch better because doesn't have so much torque down low, is just an improved NA engine, they can launch insanely better than a turbo engine (both on street tires). IF the cars would race on slicks on a prepd track than the turbo will kill the SC from the first yard to the end.

PS: Arabas, please, play with that calculator, you will understand my point, looks like Kenny got it

[DeepBlueGXP]

Kelu, it's difficult to find smaller wheels on the 5-110 lug. 

[kennysabarese]

There's been a pair of 16's for sale on the BB for a long time. Pretty sure they haven't sold yet. Brentil is the seller.

I would say anyone who is considering changing gear ratios for drag racing needs to do some research to find out what is optimal.   If you change the rear to be taller, you will have to shift out of first sooner, but you will put more power down. If you then change first, then you are back where you started.

The moral of the story is, I have no clue what I'm talking about, so you better go do your research before you listen to me

[Kelu]

They are not anymore listed, at least on my searches but:
http://www.discounttire.com/dtcs/filterWheelProductsBySize.do?rc=TDNINT&bp=5-110&wd=16&rw=&c=1&fcf=&fcpr=&fcst=&fcs=false&fcb=&pager.offset=0

Besides that, any Saturn model which was borrowed from Opel like Astra might have 5x100 and would be cheap to buy as used in US.

Around here I can find smaller wheels from other Opel models too.

My biggest problems about drag slicks:
1) I can't buy any drag slicks like Mikey Thompson, Hoosier from Europe, shipping from US costs around 100$ each and another 20-75$ customs tax.
2) Because all my strips/races are far from my city would be a PITA to ask friends to carry them for me
3) Any racing tire puts me in the Professional class among 10s-11s cars
4) I live in a small apartment and deposit space is very limited

My best solution would be street legal drag radials, but than again 1) and 4) remains. I plan to do this for next season.

[Critterman]

SC can launch better because doesn't have so much torque down low, is just an improved NA engine, they can launch insanely better than a turbo engine (both on street tires). IF the cars would race on slicks on a prepd track than the turbo will kill the SC from the first yard to the end.

Kelu you are wrong in your statement.  I come off the line at 1500 RPM, anything higher and I just spin.  The S/C's torque is all down low, at 2k I have over 200 foot pounds of torque, building in a flat line to 5800 rpm.  All my power is down low.  Part of the reason Joe's GXP closes on down on me is because of my very long 3rd gear.  I get to 60 in 4.7 seconds it takes another 8,7 to 9 seconds to 100 which is my terminal speed in the quarter mile, still in 3rd and not at the rev limiter.
 
I would get the jump on Joe, because I never told him the secret to the timing lights   I needed the .3 seconds to stay ahead at the end of the quarter.

[Kelu]

Critt:
http://www.seorom.ro/gt/dyno/new-pwr.jpg
418Nm at 3200rpm, that means 310 lbs-ft on a low number dyno, I'm pretty confident Joe is around there too, that is a lot more destructive for traction on launching than 200 lbs-ft at 2000rpm which builds up.

[MEGAS]

If i may shred some light...
let's see how shorter is the 3.91 FGR comparing to 3.73...it's abt 4.6% shorter.

For 3.73 FGR
1st 36 miles
2nd 59
3rd 89
4th 134
5th 184(theoretical)

For 3.91 FGR
1st 34 miles
2nd 57
3rd 85
4th 128
5th 175

miles are top speed in fuel cut off of 6300 rpms.

[MEGAS]

and this is a comparsion table for stock 3.73 and 4.1

ps numbers are km/h not miles in this table

[Critterman]

Megas, that is close, but with a 7400 fuel cut off, it is about 105 on the clock at that RPM.

Kelu - I have a lot more low end torque than a GXP, a GXP has more top end.  Your torque line looks like a mountain, mine looks like a slight rise. 

[Yogi]

The difference in torque multiplication will be = 100*(3.91 - 3.73)/3.73 = 4.83%!
Not worth the money and trouble, IMHO.

[normsf]

The difference in torque multiplication will be = 100*(3.91 - 3.73)/3.73 = 4.83%!
Not worth the money and trouble, IMHO.

You may be right when it comes to the street, but almost 5% edge over your competition in racing is a light year. Thanks Norm

[LatinVenom]

If you combine that 3:91 with drag radials or a set of slicks the car will jump off the line with no tire spin.

[Yamatr3]

Just to set everyone straight on the diffs and parts etc.   

The Sol, CTS, STS use the same diff, all parts and diffs are interchangeable and have the same mount points.  There are variations in the mounts and revisions that have taken place, but on the whole they are interchangeable. 

The Camaro and G8 both use different diffs and parts are not interchangeable.  You can however,  take a Camaro diff and put it in the G8 and vice versa, the mounting points are the same.  You can not take the internals out and swap them, as they have different size ring and pinions.  I would be very surprised if the ring and pinion in the Camaro and the Solstice are the same size. 

On the Quaife, I will say it is almost a must have for performance driving.  There is a HUGE difference between the stock clutch type LSD and the gear driven Quaife.  If it's a street car, you will notice way more noise than the stocker.  Now, I am making this statement with my car having about 360hp to the wheels.  You might not notice the difference with lower hp.  Only reason I say this is because I have had both in my car back to back.

Hope this helps.

[spartan]

A little birdy told me a certain vendor has indicated there is work ongoing with an LSD solution that blows away the Quaife.  I'm leaking this because there is so little buzz lately about new products.  We need something to get us going!  Come on vendors!

[Kelu]

Say what?

[spartan]

That's what I thought when I heard it!  Maybe a source will jump in and tell us more but they seem to be very disciplined and release info on their own time table.  And they are known to be folks with many enthusiasms.

[kennysabarese]

Just to set everyone straight on the diffs and parts etc.   

Hope this helps.

Thank you for the clarification!

[Yamatr3]

Thank you for the clarification!

Anytime!!  I'm so full of useless diff info...LOL

[DirtyMike]

whats the difference between gen1 cts diff and the cts-v diff?




and if/when the diff is out...would prob be good idea to put in zok crosmember

[Arabas]

A little birdy told me a certain vendor has indicated there is work ongoing with an LSD solution that blows away the Quaife.  I'm leaking this because there is so little buzz lately about new products.  We need something to get us going!  Come on vendors!

any indications of $$$. any other info??? can you leak  the initial and last letter of the vendor maybe?? 
it would be great if the venodr could leak some official info, like a sneak preview, so as to check reactions it and we can arrange our financials...

[spartan]

Cost is estimated to be slightly more than Quaife.  No reference to the actual manufacturer was made.  I suppose we may see it if it survives testing but who knows when they'll tell us more. 

I don't know where to begin to search for a possible new solution but apparently it exists.  Hopefully we'll hear more as it becomes apparent that it is viable.

[Arabas]

OK.... here goes nothing....

the labour for swapping a diff is $200.
i just contacted a very polite sir from a company with used auto parts from Ohio (LV guided me with the link he posted). the cost is $350 for a used carrier 3.91 with lsd and i m waiting for a quotation on shipping cost (as long as they use USPS)

in order to procceed with this experiment, i would appreciate if someone could tell me if the two diffs (that is 3.73 and 3.91) are interchangable.
if it requires further modifications, i m not willing to do it.
if they are interchangeable, i will give it a shot..
anyone who know, pls let me know

thx

[Critterman]

See Yama's post


The Sol, CTS, STS use the same diff, all parts and diffs are interchangeable and have the same mount points.  There are variations in the mounts and revisions that have taken place, but on the whole they are interchangeable. 

[Arabas]

Thx a lot Critterman! you confirmed what Dave said.
yesterday i e-mailed Dave form DDM who was more than kind to help me out on this.
so, Dave said
"If you are swapping the entire thing, it will be a plug and play. Just remember that your speedometer will be off. Also make sure you get a differential from an 2008 or newer 2.4L as there are 3 styles of differentials found in the 2.4L and you need to make sure that you get one with the torque arm on it."
since this tip comes from Dave who has worked on so many Kappas, it's valid 100%.
Vince said he will coreect my tune for the speedometer if i go on with this project.

the only thing i have to deal now is how to reduce the huge amount of shipping cost they asked me for and to check that this diff is has the torque arm on.

if someone has a 2.4 diff with limited slip and with the torque arm on it and wants to sell it, pls pm me
is there someone in the forum from Ohio and could help out with the company i m buying the diff from?  but i don t really want to be a pita for anyone, but i think i may need some help.

thx  for all your help

ps i renamed the title of this topic

[Yamatr3]

Here are some pics for you.  First is a NA diff and the original mount point. This is probably going to be the one your getting.  Second is a pic compliments of Moms Sol showing an NA diff and the replacement GXP Diff.  The third is a pic of the ZOK cross member.

If it was me, I would have the diff shipped to Dave, have him remove the ring, pinion and shims, and just ship those to you.  Then you can just replace your ring and pinion with the 3.91 ones.  It is a fairly simple job, but you will have to re shim the assembly.