Changing internals are unfortunately pretty expensive, as you would probably only do this with even more performance in mind.

It can easily add up to $10.000 or more, as it is not just the crank/piston/rods, but maybe also strengthening the block and last but not least stronger valves.

It might be an idea to look for a used 4.2 block instead of rebuilding the 4.0, as these are relatively cheap to get, and are somewhat stronger than the 4.0 blocks (ie forged steel crank, oil jets directed to the pistons). Then we need to find out what the weakest link is, which could be for instance the valves (especially exhaust), and that shouldn't be too expensive, you can have these custom made (forgot the prices).

You could also see if you can strengthen the crankshaft (nitrating or so), though I have no experience with this.

I have no idea about polishing the heads, though it probably isn't worth the money as you can more easily boost up the twin-screw for more power.

Another way would be changing the camshafts via regrinding for instance; though that would be experimenting as thus far I have not heard anyone doing this for our cars.

Andre.

Is a 4.2 a bolt in? Or are there mods that would have to be done to get it to work?

Chris

imho not I think, as it is easier/cheaper to rebuild a used 4.2 engine (so strengthen it further than a stock 4.2 SC which was part of the question) and switch it when you want.

So far my 4.0 block is still holding whilst having more then 560 HP on the engine (assuming a  20% drive train loss).

All depends on how you are going to use the car/engine, racing or continues usage will definitely destroy the engine, no doubt there. However street use (so an occasional usage of the power) and taking good care of the engine seems to work for me so far (125KMiles).

Andre.

Some months ago I purchased an Insurance write off (body damage only) 4.2 Lt XKR for the Recaro seats, HID lights and Brembo brakes.

I have been selling off many other parts of the car as all machanics were fine.

I am also keeping the engine so if my 4.0Lt engine does go bang as Andre says I can use most of the parts to go into my car

avos wrote:

Hi Chris,

You need to change (reuse from the 4.0) some parts like the front cover, lower bed plate, and some other stuff. The block itself can be interchanged. Best would be to use the heads of the 4.2 also as then you keep the same CR. Some light machining may be required to get the 4.0 intake manifold to fit (the piece with the fuel injectors), which is needed.

However there is a benefit when using the 4.0 heads as you lower the compression (I guess to 8.5 or something) which allows for higher boost pressure after the supercharger, though I have not found a limit there yet, and think for the modest 200 BHP+ twin-screw conversion the stock compression is best, only if you like to go beyond...

All in all I think it is very doable, and some have already done it.

Andre.

Hi Rich,

The good thing is that the 4.2 block fits regardless if it is a Rang Rover or Stype 4.2 block, though you need to reuse some of the 4.0 parts. The lower part of the engine is what not will fit (with the oil filter), but that is what you can change with the 4.0 engine. Also the timing chain cover (and front pulley) needs to be reused from the 4.0 block (and some more depending on the 4.0 engine you have, ie AJ27 or AJ26).

Now I haven't done it myself (yet) though I have investigated this thoroughly (have a Stype 4.2 engine block) and I know that 1 person from the UK has already done this, I think his handle was chargerman who provided a lot of good info.

As you are using all the 4.0 electronics, there is no need for new cable looms, and also no need for doing anything with the ECU. Same goes for the gearbox; there is no need to swap (which would be way too expensive anyhow) to the 6 speed one.

Can remember also someone saying the camshaft snapped, however that is not performance related. Even though Jaguar mentioned in the 4.2 improvements list that the new camshafts are hollow to safe weight/lower inertia, these have also been used on the AJ27 engine.

Andre.

PS I am not saying it is needed to move to a 4.2 block, though if you want to strengthen it, it is probably cheaper buy a secondhand 4.2 engine (strengthen it even more, or leave it as it is), and only swap in case the 4.0 engine fails. If it never fails, you can always sell the 4.2 block again, and with my experience so far the 4.0 block is still holding very well.

Andre,

I can't tell you how helpful you've been. I think this is the route I will plan on taking when the 4.0 eventually goes. I don't suspect this will be for quite some time, though, since the car is running quite well notwithstanding the ABS/ESC and low-coolant lights that have been recently coming on for no apparent reason.

As for the ECU/EMS, are you sure that the system from the 4.2 will work?

I've read that the 4.2 incorporates a drive-by-wire throttle system and variable valve phasing, which I don't think are available on the 4.0 engine or ECU/EMS. I imagine there would be additional wiring necessary for these features and I'm not quite sure how they would integrate into the existing engine ECU/EMS harness.

I'm not so worried about the actual engine/dyno tuning, as I have a phenominal tuner in the tri-state area who would be able to flash this system accordingly.

I just did a little more homework.

The '03-07 S/C 4.2L (AJ34S) featured in the XKR and S-Type R does NOT feature variable valve timing. The naturally aspirated (AJ34) version does. Looks like I would be able to run the 4.2L heads with my EMS/ECU after all.

It will have direct fuel injection via the head, so that means already the head design is fully different.

There might be a very small chance some components could be interchanged (so cylinder block), but to be honest I think the chances are small.

Best bet to get similar or even more performance is still a TS conversion.

Andre.

Even the 5.0 will be able to be screwed for sure, and that would be interesting ;-).

The electronics would make it difficult to exchange, which is why you can't put a 4.2 engine (with all the parts) into a 4.0 car without changing the ECU and some more electronics, and that would be a tough/price job on its own.

Putting a 4.2 block into a 4.0 car whilst retaining the 4.0 electrical parts (fuel injectors to name just one) is possible. That is why I mentioned that there could be a small chance that a 5.0 block could fit other heads. Small chance though but who knows.

Probably the time (if at all) for the 5.0 will be short lived, Tata has already announced a major investment into reducing emissions, and larger engines might not be the way to go ;-). Considering the options it might be better for Jaguar to opt for a smaller engine size and turbo every bit out of it, or twin screw some.

Andre.

richyp wrote:

Guys,

Does a 4.2 block actually fit in a 4.0 hole? I know, for example, that an S-Type motor will not fit in an XK. Are the ECUs, harnesses etc compatible? Just thinking out load here. As Sid said earlier, the internals seem fairly bomb proof (tensioners beside) I have heard of a snapped camshaft although the guy claimed that the engine still ran.

It may be easier to strip the current engine and check all the specs then go for an SDM/Andre TS update. If you are interested in reprogramming the ECU there is a WDS machine for sale on ebay.co.uk at the moment (search Jaguar tools)

I suspect that a 4.2 may also require a ZF 6 as well....

Have fun!

Rich