I pulled the engine out of the burned 2007 XK Convertible. The heads and block are still usable. I like to break it all down, send out the heads, crank etc to be checked, resurfaced, ready to go on the shelf in case someone needs.

I can't help but wonder, can a non-supercharged or a supercharged engine be modified to get more horse power?
Larger pistons?
High performance cams?
Are the parts available?
Would the electronics function properly?

Bad news on my alloy body project. The title is non-repairable so I cant rebuild this vehicle. I did remove the paint from one quarter panel to see how it looks. It does polish out to an almost mirror finish. It looks amazing. Pics will be up in a day or so.

 

I will answer but I'm also going to try to keep it simple as I don't want to write a book about it....

If we just keep ourselves to the NA engine and forget the supercharger engines for now, it's possible to get more performance by modifying the engine. Basically what you want is, to get it to consume more air. Larger pistons are great way to do it, more cu. in. will always give you a stronger engine because of more displacement = more consumption of air. High performance cams are an option also, although it's not an advisable one. First of all they will shift the usable rpm band higher, which gives you lower torque at low rpm and higher torque at high rpm. An high performance cam will also cause intake charge pollution by exhaust blow back through the intake at low rpm. This will cause even lower torque and an erratic idle behaviour of the engine. Not what you really want. Modifing the cylinder heads is a good option, optimizing the valves and valve seats to allow the biggest possible diameter of the opening. Bigger valves work well either, if they are available. Ported cylinder heads with three angle valve seats could add something like 20 hp in an XK engine, without a raise in compression ratio.

A free flowing exhaust will give some extra power, because of less pumping losses to expell the exhaust gases. this should not be taken over the top because gas speed through the exhaust (pipe diameter) has to be sufficient. If this speed drops to much, it might even give you less power.

Basically, with an NA engine, the electronics will function properly in a certain range because of the principle of how they work. Measuring air. it will compensate by itself if more air is drawn in. If the mods are taken to the extreme, you might reach a limit in what the system can handle, which might make adjustment necessary like ECU mods, higher fuel pressure and/or bigger injectors.

There is some availabillity. Arden sells bigger displacement engines and cams at a very steep price, although things like porting of cylinder heads can be done at a good machine shop or a random engine tuner.

A NA 2007 XK 4.2 engine might give you around 350 hp with modified heads, free flowing exhaust and ECU tune, which still can be done all together for a reasonable price.

 

Hi,

Please let me add this, do not be offended.

It is not about air consumption alone, engine power is dictated by how much combustible air-fuel mixture can be burnt efficiently in the engine in a given lapse of time. This is the general principle.

Also, if the air can be made to contain more oxygen, the more fuel can be converted into energy, as in adding nitrous oxide or nitromethane or other compounds as long as the combustion is deflagrative and not detonative, i.e. that the flame propagation front speed in the engine is kept under the limit of causing engine "knock".

T.

 

I'm not offended. I said I was going to keep it simple.....

Feel free to make it complicated

 

Nee, is al moeilijk genoeg zo, ik zal U dan maar de diagrammatiek besparen.

Tot later,

T.

 

Can I take a whack at answering a complex question as simply as possible?

Yes, but it's financial suicide, you'll be throwing good money after bad.

Thanks.

 

Dutch07xk, What about a XKR? Can it be modded out to get say 600+ hp spending a reasonable amout of cash? I'm talking about the 5.0L engine of course. Just would like to hear your thoughts

 

Thanks for the info. You guys know your #%!!@!

 

Yes and some of us are full of it too. Many don't realize that these engines are already close to the max HP of what they can potentially produce and still maintain good reliability and durability. Getting 300HP out of 4.2L (254 cu.in) without a blower is nothing to sneeze at.

 

Sneeze, sneeze!
I think its pretty puny. Porsche get more power out of a 3.6 litre flat 6 and they are renowned for reliability.
Aston Martin take the 4.2L Jag motor, stroke it to 4.3L, fiddle with the cams and heads and ECU to get 300kW and put it in the V8 Vantage. Pretty reliable.
Ferrari make a thing called the 430 which is a 4.3L V8 and get 330 kW.
Audi's 4.2L V8 produces 250 kW - or more! - in the S4 and RS4.
I have an XK 4.2 and I wish it would produce a bit more grunt. I even went to the ECU tuners who assured me that they could modify it for a 10% - 15% increase in output, but they failed dismally and gave me my money back.
When I bought it, back in 2006, they hadn't produced the XKR and were a long way from the 5L version and I always remember Jeremy Clarkson road testing the early XK and screaming "More Power, More Power" as he flogged it round the track. But I love the looks and the performance is mostly adequate, except when some wannabe in an old Holden drags me off at the lights. (For those who don't know, the Holden is a GM product designed and built in Australia and may be available in the UK rebadged as a Vauxhall).

 

In case of the XKR I'd always go for the easy bolt-on mods like a pulley that makes the supercharger spin faster. This also makes the most advantageous power to price ratio. Then the ECU, exhaust and high flow air intake.

If this still is not enough, basically you get to the same mods that I described before. The XKR might also need bigger pipe diameter on the exhaust and headers. Increased back pressure on the exhaust will limit the development of high power levels and will make the engine thermally unhealthy, which can reduce longevity.

Out of my experience engines can take as much as twice the power of the standard engine. Mostly it's other drivetrain components that can't handle it, like gearbox and clutch. Still, most of them have no problem handling around 50% more.

An engine with modified heads can run more efficient and healthier than a standard engine, if it's a well done job, because of more efficiency in the combustion process. Around 20 years ago cars in Germany could get a tax reduction after modifying the heads because the emissions were lower.

The standard 4.2 has with 300 hp a low power output. Various other car makers produce 3.5 litre V6's with the same output. But this has one advantage. The standard engine will be a good candidate for modifications.

 

With a good tune, pulley and exhaust 600hp should be feasible; there is a lot to be had for this particular engine just in the tune itself, contrary to the 4.2 XKR, which requires more mechanical mods.

 

I have not seen anyone experiment with nitrous oxide. It is a comparatively cheap mod, which, if done correctly, can easily add 75 reliable horsepower. The best source locally for nitrous is a local race shop. The technology is well proven and reliable, so long as one does not get greedy.

Another mod is long tube exhaust headers. All the exhaust mods I have seen are pricey (pretty) cat-back systems. The 2002-04 Ford Thunderbird uses the basic Jag motor, somewhat detuned. Stainless Header Mfg. of Fargo, ND. makes a reasonably-priced long tube header for this Thunderbird. One of the reasons the OEM exhaust manifolds (all cars) are so restrictive is the requirement that the cats be placed as close to exhaust ports as possible in order to reduce warm-up times. Thank you California for this restriction, which immaterially reduces emissions. Long tube headers place the cats downstream and are illegal in CA. But, they really produce the hp.

 

Perhaps, you mean close to the max HP that can be achieved, and still fit under the hood of said Jaguar? In a hot rod, where you can change the intake and exhaust and not worry about space, this becomes a different matter.

 

A buddy put a super charged engine into a XJS and 20K later....