Ill cut straight to to the point ....13.9 (101.5mph) e.t 1/4 mile on a very very hot night in Sydney (34c / 93f ) would a quaife differential with shorter ratio liven up my n/a 4.2 and improve my e.t on the strip and if so would it be significant improvement to actually notice it.

 

You'll see more of an improvement in ET's with the ratio change. More consistency and control with the Quaife. Adding the Quaife to mine was the biggest improvement I've done to the car. Night and day.

 

flyc2c do we know if there are ratios available for the 4.2 v8 diff

 

I'm not sure a ratio change would improve it, 1st gear is short enough you're already dealing with wheel spin. The engine power curve is quite flat, so there is also less benefit from a quick ratio gear box than if it was a very peaky motor.

How close to red line are you at exit trap? Ideally, if you do want to play with gear ratios, you'd be just at the next shift point as you crossed the trap. What will benefit, will come down to shift points, as you're already probably traction limited in 1st.

 

Tervuren so your saying a TCU (transmission software tune) will benefit the ZF
Unfortunately there is no one out there that has cracked the ZF we even tried to upload the transmisson tune from GT3 xkr (with cambo's help) but it wouldnt stick

 

The XK (and XKR) already has 3.31 gears in it, there was only one shorter ratio available to suit the Ford/Visteon 8" and that's 3.58, I do have one of those gear sets in my stash but I'm not sure how much of a gain you'll get over the 3.31's, not so much i'd say, maybe a 10th of a second over the 1/4 mile.

I also have a complete Gen2 8" diff in pieces stashed away as well, it needs a rebuild though...

An LSD (Quaife or whatever) will make a huge difference to the launch though (60ft times), as well as generally improving the driveability of the car on the street (especially in the wet) it totally transformed my XJR.

 

Cambo

Ive got this listed on the spec sheet you sent me

Transmission 6 SPD AUTO TRANS ZF 6HP26
Colour MIDNIGHT
Trim INTERIOR METALLIC PACK
3.07 FINAL DRIVE RATIO
255/35 FRT/285/30 RR ZR20

If I do in fact have the 3.07 ratio im sure the 3.58 would liven my xk right up

 

Parts catalogue says 3.31 for all 3.5L and 4.2L X150's, no difference mentioned for supercharged or naturally aspirated, likewise the Specs Book from JLR also says 3.31 for all versions.



Yeah I remember seeing 3.07 mentioned in the build summary from Topix, but that either makes your car a very special custom-build (unlikely) or there was a mistake in the recorded build sheet (very likely, and happens often).

 

Yes I highly doubt the customer purchasing the vehicle would have requested 3.07 final drive so 3.31 it most likely is then

 

Just saw the fact that the aston vantage is fitted with a 3.91 final ratio and offered in limited slip are these parts interchangeable with jaguar

 

No the V8 Vantage has an entirely different gearbox and diff to the XK.

Actually the Aston has a transaxle...

 

Ok it's a little different. LOL!

 

Well you learn something new everyday, I knew the boxes were different but had no idea it was a transaxel set-up

 

They are freakin complicated things too...



The automatic is basically a manual gearbox with a an automated shift system, uses a traditional type clutch and all... just lots of solenoids and actuators to operate everything...

What an engineering feat...

 

it Sounds similar to the 360 f1 gearbox

 

cambo whats the weight distribution on the vantage and xkr

 

I have nfi...

 

just did a quick google search

Aston v8 -49/51
Aston v12 -52/48

XKR - 53/47

DB9 - 50/50

Damn wish we had this transaxel set-up !!