who here has changed there rear end gear ratio?

i would like my jag to have a little more punch out of the hole. and being that the highest speed limits i ever drive on is 75mph i think a change in rear end ratio's might be the ticket. I'm pretty happy with the punch from a rolling start. its just the first 0-25/30 mph id really like to see some improvement in.

i have yet to determine my factory ratio, but its a 93 xjs 4.0L automatic.

what is available possibly for a junk yard swap of the 3rd member or aftermarket gear sets for the rear chunk?

fuel millage isn't a huge concern to me. my jag is kinda a play toy to me, not a daily driver.

 

I've done it. Since your car is a 93 convert it should have the 3.54 rear end ratio with low bias power-lok. You dont have any oem options as far as I know. If you want to upgrade to 3.73 or 4:10 you will have to adapt Dana 44 stuff. It's easier to do than it sounds if you have the experience workign with diffs. In your case since the transmission is computer controlled I would consider the 3.73 as the only practical option, going 4.10 or higher would certainly confuse the engine and transmission management programs. Additionaly 3.73 or even 4.10 from 3.54 wont make a significant difference because the issue is weight vs power and gearing can only help so much. The XJS convert is a heavy car but Its worth have a root around under the hood to make sure the AJ16 is running properly.

 

Stall it instead and save a huge headache and driveability. at least 2500 or higher

 

Agreed. 3.54 is already a healthy amount of gear. A higher stall torque converter will definitely give you a lot more out of the hole. A good converter in the 2500-3000 range will launch you hard when you want it but still drive similar to stock.

 

i had not thought of that. defiantly something to consider.

my jag seems to run good. runs smooth as silk im getting about 23mpg on the interstate plug color looked very good a nice caramel color when i did a tune up about 1k miles ago.

 

just to give you an example of how well stall speeds effect your cars performance
my Pontiac Bonneville has a 290bhp modded V8 with a 1500 stall and 3.71 gears and it is a complete DOG from a stand still.
whereas my Pontiac grand prix has a 290bhp modded V6 with a 3000 stall and 2.93 gears and it will absolutely blitz the tires at anything under 50mph.

 

Who makes a higher stall converter for the 4hp24E? Probalby no one becasue the TCU monitors engine speed and compares it to transmission input shaft speed and can detect excessive slip out side a pre-programmed range in the TCU and would set the MIL. In any case the AJ16 torque curve is quite flat from 2000 to 2500 rpm and really starts to progress upwards at 3000 RPM. I'm guessing the stock stall is about 1800RPM so upgrading to a 2500 stall if it existed wouldn't help much. You'd have to get right up to 3000 RPM stall which would totally alter the feel driveability for the worse and would certainly set the MIL.

 

yes it would totally alter the feel and driveability but most certainly not for the worse.

 

i changed rear ratio from 3.07 to a 3.73, along with a hi-bias dana LSD, also i went to a 700R4 auto(with kit) and a smaller diameter convertor(10"),lighter weight, and stall is around 2200-2400 rpm.)

700s have a 3.06 1st gear ratio,where as the original GM 400 had (like 2.70ish) 1st gear,so my total launch ratio is quite steep(in the 13s when in 1st gear).

been driving it for 20+ yrs, 4th gear is overdrive(30%), so my final ratio is when cruising,is 2.60. good for MPG and great for low speed street work.
pic enclosed!