the best differential ratio

[1 TUF AC]

just wondering what differential ratios people are running behind a t 56 six speed transmission. I have 4.11 in my Harrison and it takes off like a rocket to 80km but the only thing is that I don't like is that i have to shift three times from 0 to 100 km and if you want to achieve a really good 0 to 100km time you have to be very very quick when shifting. I've had a BA xr8 and Holden SS V ute and they are all got over 100km out of second gear. But on the other hand having 411's is good around town in traffic especially when you have a big cam engine. I just think that a cobra is so much lighter than a BA Falcon so if anything it should have even taller gears. Any suggestions?

[LJ47]

I run 3.9 behind my T56 but would have preferred 4.11 but I like shifting gears.

[1 TUF AC]

Originally Posted by LJ47

I run 3.9 behind my T56 but would have preferred 4.11 but I like shifting gears.

once your rolling 4/11 are awesome. all I'm saying is for example from 0 to 80km my Cobra we'll smash my ve ssv ute but by the time I shift to third gear my ute has caught up.

[Bernica]

3:31 with a Toploader. Plenty of legs.

[Gav]

I have been going through the same thought process recently.
I had 3.9:1 when I ran the LS1 in my car and it was great.
However, when I fitted the stroker it was all revs and wheel spin.
I have a 3.45:1 in it ATM and now it is a bit too lazy for my liking, so I am now planning on fitting 3.7's in it and hopefully this will be a good compromise.

If I still had the LS1 it would definitely have the 3.9's in it.

[deano59]

I am just going to use the diff that come with the ve I bought to start with it's a 2.92 ratio .
engine is a l98 6 litre with a 6 speed auto . I actually drove this car before I stripped it and it went like a rocket so in a cobra that's 800 kilos lighter I cant see why it wont be ok. im not building a track car just a cruiser so im hoping it will be fine if not or I want to liven it up a bit I can change diff centre out at a later date .
cheers deano

[Modena]

3.7 for me

[john chesnut]

3:42. Stock LS6 with the Tremec 6 speed. Perfect for me.

[1 TUF AC]

Originally Posted by Modena

3.7 for me

I think 3.7 is the go but the only problem is if I go 3.7 my sixth gear would be useless unless I am doing 140km on the freeway. My car doesn't like to rev under 2000 rpm with the cam it has in it. I will virtually turning into a five-speed if I put 3.7 differential ratio.

[1 TUF AC]

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[Krait]

3.9 with a T56 & LS2 2nd gear starts are fairly easy. Sits comfortably in 6th on the highway.

Wish I had it here in Dubai, no hills and 140k speed limit

[DaveW]

3.7 for me as well

[Wazza]

Just in the process of changing mine from 3.27 to 3.7.

My final drive (6th.) is (I think) 0.68, not 0.5 like yours...so the 3.7 will be spot on for me.

2090 revs in 6th. , will be 110 k.p.h......

I have been doing around 1750 r.p.m. for the 110 k.p.h. up until now, and although the engine has a ton of torque...I recon purring along on the 2,000r.p.m. mark will get it running as smooth as silk.
Cheers,
Warren.

[Modena]

We have a calculator on the CCCV site too if it will help anyone;

Cobra Car Club of Victoria - final drive calculator

[1 TUF AC]

[quote=Krait;1324503]3.9 with a T56 & LS2 2nd gear starts are fairly easy. Sits comfortably in 6th on the highway.

Wish I had it here in Dubai, no hills and 140k speed limit [/QU

mine takes off in second pretty easy too. Especially when I'm just cruising around town are normally take off in second. I've tried doing some hard launches in second and I think it gives me a better 0 to 100km time but you have to ride the clutch a fair bit more to take off cleanly. I'm pretty sure the ratios I posted are right because on my engineer certificate it says I have a t 56 out of a VX ss Commodore and a R 32 GTR differential which came out from factory with 4.11 unless someone has changed that ratio on me. But tomorrow I might go for a drive and make sure the ratios and speeds are correct. I know my speedo is not out I checked that with the GPS the other day. But according to the calculator it says I do 101km in in second gear but when I drive it to speedo is a bit slow to react so it's hard to tell if I have got 100km out of second because by the time that happens I am bouncing on the limiter and I need to change to third. if sixth gear was a 0.68 ratio 3.7 would be perfect. I am still very happy with the car performance especially when you're driving through the mountain areas it's so much fun. But always thinking of different ways to improve the car even further.

[deano59]

cheers Modena
just run my thru in 6 th
Cobra Tools
Diff/Gear/Speed Ratio Calculator


--------------------------------------------------------------------------------

Looking to change tyre size, or diff ratio?
Punch in your intended stats and get the RPM for 100km/h



Wheel size in inches (e.g. 15)
Tyre Size (e.g. 295 / 40) /
Top-Gear Ratio (e.g. 0.75) : 1
Diff Ratio (e.g. 3.45) : 1





Engine RPM @ 100km/h: 1,675
Engine RPM @ 110km/h: 1,843

Tyre diameter: 617mm
Tyre circumference: 1,938mm
Tyre revolutions per second @ 100km/h: 14.33

[CHANMADD]

Mine has a 4 speed with laycock o/d, and 2.88 rear .........I can still stumble off in third........but second will give me close to 100.....first is a little long in traffic but ok..the car is only revving at around 2400 at 80 mph. With a six speedit seems the 3.7 is the poular choice......also tire diamwtef around 26 "

[joyridin']

I have 3.7 behind my T56. My 6th is .54.

[gjkrv8]

3.45 with LS1 with stock cam. Never use 6th. I reckon 3.7 would be juuuust right :-)

3.45 cruising around town is good though.

3.7 on the track I reckon would be good too, I find on some of the slower corners you are pretty low on the revs coming out the other side in 3rd. Lucky theres plenty of torque.

cheers Gregg

[1 TUF AC]

[quote=1 TUF AC;1324507]

Originally Posted by Krait

3.9 with a T56 & LS2 2nd gear starts are fairly easy. Sits comfortably in 6th on the highway.

Wish I had it here in Dubai, no hills and 140k speed limit [/QU

mine takes off in second pretty easy too. Especially when I'm just cruising around town are normally take off in second. I've tried doing some hard launches in second and I think it gives me a better 0 to 100km time but you have to ride the clutch a fair bit more to take off cleanly. I'm pretty sure the ratios I posted are right because on my engineer certificate it says I have a t 56 out of a VX ss Commodore and a R 32 GTR differential which came out from factory with 4.11 unless someone has changed that ratio on me. But tomorrow I might go for a drive and make sure the ratios and speeds are correct. I know my speedo is not out I checked that with the GPS the other day. But according to the calculator it says I do 101km in in second gear but when I drive it to speedo is a bit slow to react so it's hard to tell if I have got 100km out of second because by the time that happens I am bouncing on the limiter and I need to change to third. if sixth gear was a 0.68 ratio 3.7 would be perfect. I am still very happy with the car performance especially when you're driving through the mountain areas it's so much fun. But always thinking of different ways to improve the car even further.

.

I went for a dirive today and I think found out why I couldn't get 100km out of second gear. It looks to me that my tacto is out buy at least 500rpm. Because the calculator say I should be reving 2000rpm @ 60kph in 4th gear but I am reving 2500rpm. normally I don't rev over 6000rpm but today i rev it to 7000rpm but the tuner sad he set the limiter to 6300rpm. And the gps says i did 100km out second so I'm pretty sure my tacto is out or my limiter is off and I have 4.3 diff gears. It definitely went a lot better when rev it That little bit more. i have a vdo tacto maybe it needs to be reclabraded or something. I might go past the tuners and get them to plug the laptop in to see if the revs Maching up with the tacto. At idle my car sits at 1100prm but it doesn't sound like it idling that fast. I am 90% sure my tacto is out but it could be something else.