Jaguar XKR 4.0 – to 4.2 Engine Conversion

Jaguar XKR 4.2 Engine with 4.0 Ancilliaries about to be fitted

Jaguar XKR 4.2 Engine with 4.0 Ancilliaries about to be fitted

As many of us with 4.0 AJ-26 / 27 engined cars will know that once the Nikasil bore linings and timing chains and tensioners have been sorted out the 4.0 is a fantastic, smooth, powerful and refined engine which will be capable of a high mileage.

As with many products the design is improved over it’s lifetime and the same has been achieved by Jaguar with the Jaguar XK8 / XKR (X100) engine from 4.0 to 4.2 and in the new XK from 4.2 to 5.0.

The design and production of the new 4.2 AJ V8 4.2 engine in 2001 / 2002 (coded AJ-34) was based on Jaguar’s need to revitalise interest in the XK8 XKR (X100) model and therefore develop increased sales.  The primary objective was to improve performance and economy. Many internal changes took place and the whole engine was claimed to be stiffer and more robust than the earlier 4.0 version.

READ MORE below about the key features of the 4.2 over the 4.0 engine, an outline of how to do the conversion and the modifications required:

The key features of the 4.2 engine over the 4.0 are:

* Increase in bhp 300 over 290 bhp for the XK8 4.2 and 400 over 370 bhp for the XKR 4.2

* Maximum torque 310 over 290 lbs for the XK8 4.2 and 408 over 387 lbs for the XKR 4.2

* 4.2 engine is 6kgs lighter than the 4.0 engine

* Improved Eaton supercharger giving spins 5% faster than the one used in the 4.0 XKR

* Overall improved performance of 3.5% in the XK8 and 8 % in the XKR

* Improved fuel economy

* Has the upgraded 4th generation tensioners, guides, and chains

* Designed to work well with the excellent ZF 6 speed autobox and revised rear axle ratio.

With this in mind some enthusiasts have changed from the 4.0 to 4.2 Jaguar V8 XKR engine.

Here is a brief outline of how this is done by one of our specialist expert contacts. Please note that we have no further information other than that below and you will need to do further research before embarking on such an engine upgrade project.

4.0 to 4.2 Engine Swap: Base AJ27 / 4.0 XKR car:

Any 4.2 SC engine can be used, XKR, XJR, S-Type, XF and Range Rover

Use only the base engine block, so lower end / base block, heads, timing gear, camshafts, oil pump and maybe blower

Re-use from your 4.0 block:

* Front cover
* Front lower pulley
* All electronics (Ignition coils/Fuel injectors etc)
* Fuel rail/intake manifold
* AJ26 cam positioning indicator (located on the Bank A, Intake camshaft), and flywheel
* Lower sump
* Cam covers
* Camshafts (but only if the 4.2 block had VVT).

Modifications needed:

Bolt holes from intake manifold do not line up, when counting from the front, numbers 2 and 4 fit, and new M8 tapped holes need to be made in the heads for 1 3 and 5 (easy). Then port the intake manifold to ensure good alignment with the intake ports of the head.

The oil pickup is different with the 4.2 oil pump; you need to modify the original sump to allow space for the new pickup. This is important as the 4.2 engine uses piston oil jets to cool down the system (This is also why the 4.2 blocks do not have the issue with short running that washes away the oil film¦).

Camshafts, you can use the 4.2 camshafts without issues if it was a non-VVT one, but you need then to exchange the camshaft indicator (AJ26 only). The AJ26 has 1 vane, whereas the AJ27/33/34 has 4. This saves in changing the valve clearance and everything will fit as it should have been.

If using the 4.2 supercharger, you also need to use the 4.2 SC to intake elbow gasket, and modify your intake elbow a bit where the bearings form the SC stick out, 1/2mm should be milled away.

For the pioneers:

The 4.2 injectors are better; they have 12 fine openings giving a much better fuel atomization. But the impedance is different from the 4.0 ones and you need to retune the ECU. On top of that, the 4.0 fuel system is with return line, so that also has to be plumbed. Not sure if it is worth the effort.

Use the AJ26/27 camshafts, the AJ33/34 (4.2 engines) use a camshaft profile that is more focused on a wide power range, whereas the AJ26/27 is more focused on high end power. Never tested this, this is my guess on what I have learned so far from camshafts. This saves the trouble to exchange the camshaft indicator.

As it is easier to take the heads off to make the new holes, better to buy new head gaskets and head bolts. The latter are stretch type and can be used only once!

The 4.2 block has some strong advantages (especially for those that are looking for some more power), besides the bigger stroke, it has stronger internals (forged crankshaft), piston cooling via oil jets and a better combustion chamber with a good squish area.

For many people including myself this will seem too daunting buit for some auto tech guys I hope this will be of some use.

Thanks for Visiting

DCR Jaguar XK8 XKR Parts and Accessories

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