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XJR Supercharger Upgrades

11195 Views 8 Replies 5 Participants Last post by  djdex
Hi all,

Have any of the XJR owners on here had either the upper or lower pulleys upgraded to boost 'charger rev. speed (and therefore psi)?

Part prices seem pretty reasonable and, particularly in the case of the lower pulley, fitting doesn't seem too difficult.

Is the upgrade reliable? Any issues with extra heat/maintenance?

Is the difference noticeable?


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If yr gonna do it upgrade yr intercooler as heat is most definately an issue ,one pulley upgrade can start hoses popping left right and centre, ,i think a set of sports cats and a free flowing exhaust is a good place to start .
Yep, Upper pulley gives very noticeable mid range power boost, the experts say the standard cooling should be able to cope with one pulley upgrade, but BB has certainly got a point, cos 4-5 months later my valley pipe let go and dumped my coolant on the motorway, so while it may be able to cope it will seek (and destroy) any weakness in the cooling system. All OK now, and I'm still glad I had it done!
As with DJ on the upper pulley. You will certainly feel the difference. :)
Pulleys (either s/c or crank) move the 'on boost' lower in the rev range. Added to a good cold air filter (not a cone stuck under the bonnet) and free flow exhaust adds a decent power gain, but as others have said, the cooling system needs to be in good shape, along with the s/c.

The crank pulley is easier to install. To add a smaller s/c pulley requires some material to be removed from the snout for clearance. A new slightly smaller belt and renewing the bearings in the tensioner and idler pulleys is always a good tip.

I rebuild superchargers and to be honest Jaguar have pretty much got all they can out of the system already - if adding both crank and s/c pulleys, then serious mods are to be done to the cooling, i.e. bigger surface area intercooler and separating the coolant loop from the engine coolant, along with a water/meth kit. This is just to keep the gain (around 30bhp)
Reason being heat kills the power gain almost immediately by ignition retardation to limit knock. This is why performance guys refer to the Eaton as a Heaton, it gets hot quick.
If monitoring intake temp on boost compared to ambient you'll see what I mean. Heat soak kills the gains, period. To test, just do a few wide open runs, engine cold is noticeable, then as the system heats up, the power goes down.
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Thank you all. I will do it at some point but after buying the car, taxing it, full service and just getting it back from the bodyshop with all the cosmetics sorted I need to reign in the wallet a little!

On another note, I quite like the idea of adding the bonnet vents from the newer shape XKR's to my XJR (You know the ones with "Supercharged" written down them? Yes, I am a loser); are there any practical reasons against doing this? I can't think of any right now...

Opinions on whether it will look good (and make it as unique as they ever can be), or will I look like an idiotic boy-racer who people expect to have a migraine-inducing exhaust system?
Mmmmm, bonnet vents? Not my cup of tea, but if they're properly engineered to ensure you're not dumping a bonnets worth of rainwater all over the engine I can't see a reason against them, equally I don't see any advantage in them either. I'd prefer to spend money making it go faster rather than just looking like it goes faster, if I had that money I'd be upgrading the charge cooling myself.
Only practical advantage I can see is in a reduction (however much it may be) in supercharger heat soak.

Generally speaking I'm not a fan of bonnet vents but I don't mind the XKR style. Fairly subdued, I suppose.

Have always been curious about the issue of water ingress with them. For example, what about when you wash the car? You're probably throwing the equivalent of 6 months of rain water over it in a short space of time. Wouldn't the water run through the bonnet vents directly onto the engine? Would perhaps need to look at some kind of drainage system.
I don't think they'll have much effect, the cooling rads are at the front, as is the air intake, so once in motion it's all about the air hitting the front grill, I suppose they may provide an exit for under bonnet air so might improve airflow through those radiators, but I can't see the ambient under bonnet temperature having much effect. When stationary the air intake temperature does rise amazingly high, but that's because the intake is above the radiator drawing in rising hot air don't see vents doing much there.
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