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Jaguar XK8

Published: 10th Dec 2014 - 0 Comments - Be the first, contribute now!

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Here’s how to give yours some sharper claws

Right now, the XK8 is one of the best value modern classics that you can buy. Broadly similar to the Aston Martin DB7 but at least half the price on today’s used car forecourts, it’s all you’d expect from a Jaguar and unlike the XJ-S – which donated its chassis – looks great in all shapes and forms!

Given their outstanding value, there’s real scope to make an average XK8 into both a fast road car or also an unlikely yet competitive competition tool. Here’s how to do it right!

BEFORE YOU START

Decide how much a scalded cat you want. As XK8s are inexpensive for what they offer, if you are looking for XKR-level performance then it’s probably best to buy one of these in the first place because you’ll end up with a better car with all the right bits as well as numerous improvements from the outset.

For example, if you don’t already own an XK8, typical price differences between a standard model and an XK8R are, on average, £1000 – that’s a sum which won’t get you a lot of aftermarket goodies let alone turn an ordinary XK8 into an R alternative! And unless your XK8 is very good or special to you, then it might also be worth selling and trading up for the same reason. Just give it some thought! The XK8 is fast approaching its 20th birthday and while there are many scruffy ones around, in general they age pretty well. Rust will be a problem on early cars but shouldn’t be terminal. The bumper region is particularly susceptible especially at the rear where bumpers have been known to fall off.

Mechanically now that the Nikasil engine bore wear has been eradicated along with timing gear tensioner failings (when replacing, use the tougher 4.2-litre parts) the engine is tough and longlasting, including the superchargers on XKRs.

When new, the automatic box was filled and sealed for life but according to Jag experts Racing Green Cars of Hants (http://www.racinggreencars.com), experience has proven that many gearboxes have failed due to oil degradation. So change the lube.

The suspension features a lot of bushes and these wear – although you were probably going to replace them anyway. Wheel bearings have always been an issue with the XJ-S and the XK8 plus wear will be compounded by fitting larger wheels and grippier tyres plus the harder cornering forces exerted on a track. Make sure yours are A1.

It’s worth pointing out that while the tuning and improving principles are across the board, they mainly relate to the 4.2 versions as interest in the original 4-litre mainly petered out as their values slumped.

HOTTING ONE UP

Remember what we said about buying an XKR from the outset? Well, the limited number of specialists who tune XK8s broadly agree and as a result, there’s not a lot you can do with a stock V8 engine other than fit better induction filters (K&N) and a sports exhausts but happily this does give a useful performance increase as both systems are quite restrictive, the latter in particular. David Manners for example (http://www.davidmanners.co.uk) sells a sports stainless system for under £1250 while XK8 experts Paramount Performance (http://www.paramount-performance.com) quotes around a 10bhp increase for its set up with a sports air filter box from K&N adding another six horses. Other easy tweaks include a rechip and remap or an upgraded ECU. Paramount markets such a set up for a little over £700.

But that’s pretty much it for the standard engine; you could have the cylinder heads reworked but Jaguar did a good job to them at the factory so the gains won’t justify the cost.

Alas, according to Elite and Performance Jags (01332 265826), fitting the brawnier later 4.2-litre engine (which gives 300bhp) is not as simple as it sounds because, although the inferior 4-litre set up suffices, it ideally requires the 4.2’s ECU plus needs the later six-speed auto.

So you need an XKR – and it is here that significant gains can be wrought over its standard and sufficient 370bhp. After a similar induction and exhaust uplift, you can then start to tweak the supercharger. Paramount Performance offers a special induction kit for £300 that is said to up the ante by more than 10bhp for starters. Spend ten times that and the company promises in excess of 400bhp care of better supercharger cooling and a superior exhaust. This beats the 4.2 XKR which kicks out 400bhp and 408lbft of torque. Racing Green Cars quotes 428bhp from a 4.2XKR engine with a remapped ECU upgrade, costing around £650, but with significant gains in vital mid-range torque, all 450lbft of it.

Making a supercharger spin faster for added power is an old tuning trick and works exceptionally well on the Jaguar engine. Racing Green Cars says that, along with better breathing and its sports exhaust, between 50bhp and 60bhp is unearthed, with another 20bhp on offer if the ECU is modified to suit.

The company achieves this by using a larger crankshaft pulley rather than a smaller supercharger pulley to reduce the chance of belt slippage at high speed.

At £425 plus £200 fitted, the company warns that while you may see performance pulleys advertised for well under £100 on the web, these are often badly made and don’t fit properly in the compact confines of the V8 and has even seen the block modified with a grinder to make space!

Paramount Performance agrees but uses a smaller supercharger pulley as it’s a quicker, easier fit saving the end user money, but stresses it’s to a Jaguar design and quality; around £350.

The ultimate lies in the United States where a Kenny Dell supercharger upgrade can see as much as 650bhp from the V8, which has been known to have been stretched to as much as 4.8-litres.

Remember that Aston, using the same basic block, albeit dry-sumped, achieves 4.3 and 4.7-litres.

HOTTING YOUR CAR UP

BUDGET

* Road tuned sports exhaust

* Superior induction kit

* ECU or chip upgrade

* Modified supercharger pulley on XKR engine.

Various types available

FULL THROTTLE

* Free flowing exhaust

* Remapped ECU in conjunction with better breathing

* Kenny Dell supercharger

* Increase engine capacity

HANDLING THE POWER

BUDGET

* Geometry reset

* Uprated, lowered springs

* XKR brakes

FULL THROTTLE

* Fully uprated braking system

* ‘Poly’ suspension bushes (but only if you intend track work)

* ATB limited slip diff

* Mods to automatic gearbox

Handling The Power...

Considering it’s more a GT, the XK8 handles really well but it does ride surprisingly high for a sports car, a result of the requirement for snow chains in Germany.

Thus the quick fix has to be a set of sportier, stiffer springs, say 25-30mm lower at around £300 from sources such as Racing Green Cars (http://www.racinggreencars. com), then better, adjustable damping and the inevitable poly bushing, although the Surrey-based specialist warns that unless you’re exclusively doing track work, the stock Jag spec dampers and bushes are difficult to improve upon without spoiling refinement unduly.

A standard XK8 benefits from XKR anchors if you can find them second-hand, otherwise it can get expensive, although you may feel worth it. Paramount provides a full kit comprising Alcon callipers and discs at £4500 all in, while David Manners is marketing Brembo types for the front at under £1000 per side.

Racing Green Cars markets kits from Brembo and Arden, the latter company which also makes uprated steelflex brake hoses for a better feel. RGC has developed a specific upgrade for XK8s already fitted with Brembo hardware.

The XK8 has always run on fat tyres – up to 20inch on the special editions – so no problems there. But you’re wasting all your time and money on other mods if the basics aren’t right, namely proper top quality tyres recommended for the car and a thorough geometry check and reset from a Jaguar expert.

A choice of 30mm or 50mm wheel spacers are popular fits (Racing Green Cars) albeit for looks and not for the track, while the company markets a nifty kit, at £245 fitted, which converts the standard power steering into a switchable two-tier system, adding lightness for town work but a heavier feel at high speeds.

At the other end, with all this new found power you’ll probably welcome a limited slip diff to complement the standard traction control. Produced by Quaife to Racing Green Cars specification, the ATB (Automatic Torque Biasing) differential is one answer at £895 (£500 fitting).
Finally, let’s talk about the elephant in the room – that automatic transmission! No XK8 ever came with a manual gearbox and unless you really want to splash the cash you’re likely to be stuck with it.

Elite and Performance Jags is known for fitting a modified gearbox taken from the Aston Martin Vanquish, and when we spoke to the company it had two such converted cars in its workshop. However, it freely admits that interest in this swap has virtually vanished due to the sheer cost involved – now at over £10,000.

What you can have instead, from Racing Green Cars, is a sequential ‘Speedshift’ fitted, which operates the J-gate selector manual override via steering wheel paddles, albeit only for XKR models. At £1554 fitted it’s a much more viable proposition.



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