I have a 4.0l Xj40 and am looking to complete some modest upgrades to boost HP.

I have looked at the AJ6 Engineering site, and have read good reviews - though wanted to educate myself a bit more upon possible set ups before contacting the company.

I believe the stock set up is 240 HP - I would like to get a 15% gain if possible.

Thank you,

 

I would like to boost my XJ40's performance too . However, I was told that that would hurt the tranny in long run due to increasing torque . The reason behind was that maximum HP that tranny could handle was 240 HP .I presumed XJ40 AJ6 and XJ12 using same tranny box

 

hmmm...

Perhaps it is best this way - I just got another speeding ticket in the S-type on the drive home from work...

Thanks for the quick response Cadillac.

 

The 4 litre XJ40 uses a ZF4HP24 gearbox, while the V12 uses a GM unit. I don't know the official torque limits for the ZF, but they are a very robust transmission and the standard 4 litre engine's power out must be well within its capabilites.

In the 1980s and 1990s, several tuning companies offered vastly expensive twin turbocharged versions of the XJ40, at least in Europe.

Janspeed's TwinTurbo 3.6 produced 290-odd bhp and an unaltered ZF4HP22 (non-electronically controlled forerunner of the ZF4HP24 used in the 4 litre). Quite a few of these were sold and many of them are still on the road and have not suffered reliability problems even at big mileages. Germany's well known 'Arden' Biturbo 3.6 was more powerful still, with 330bhp and 322lb ft, also used the standard gearbox without issues.

Later 4 litre cars were modified by Chasseur, and called "Stealth" Jaguars. These used a Turbo Technics installation, generally of 340 bhp / 405lb ft and used an unaltered ZF4HP24 transmission without any adverse reliability problems. Again, these are less rare than you'd think and I know of a couple which have done big mileages without problems. Chasseur offered up to 460bhp in the XJ40, but I don't know which transmission they used for this.

A 15% increase in power will be well within the capabilites of the transmission.

David

 

That twin turbo kit sounds like a winner to me Anyone got one lying around they don't want?

 

Thanks David for your valuable post

 

David,

Thank you for the post.

Any idea of where to source these products?

I check ebay.co.uk though if you have any suggestions, much appreciated.

 

Anyone fork out the $$$ to fill up on 100 octane unleaded just to see how much it improves performance? 100 is $8.99 a gallon here in San Diego these days.

 

Flling up with 100 octane wont do any more good than say 91 octane in these cars. All the octane does is allow higher compresson before preignition occurs. It also makes for a less explosive combustion IIRC.

I had a half tank of 91 octane and dumped a quart of Xylene into it and it ran no different.

 

Thanks for the info.

 

I saw a chip on Ebay that will give you 100hp gain, for 19.99 and free shipping!!