I have just acquired a new 2008 XKR moving from an E46 m3.
I wished i had done it sooner.
I have installed a Quicksilver exhaust which is well manufactured. The sound is a good blend of mellowness and aggression (depending on the rpm!)
Ran a before and after dyno and confirmed the figure of 20hp flywheel gain at 5500 to 6000 rpm but also got approx 30 ftlb of torque at the same rpm range.
Tomorrow I fit a new supercharger pulley from Paramount which they claims adds 4lb boost and 30 hp at the flywheel. Has anyone used the same pulley and if so with what result
I ask because it seems the gain should be more than that.
One question:
Has anyone tried ECU modification and with what result (especially adverse)

 

That is a pretty good increase on the exhaust...I will be real interested in your gain with the pulley.
BTW just a point of interest...a M3 THOUGHT he was going to take me the other day...I would say you made a good choice in the XKR even though I was a little surprised that he wasn't even farther behind when he broke off (FYI I never got into sport mode).
The claims the performance guys make are always suspect and it will be quite interesting to see a real world installation of the pulley aka horsepower increase. I would also love to see your experience after you have driven for a while as I have heard of a few instances of people commenting about pulley slippage (although they sound like they have been drag racing...and i mean DRAG RACING on the strip). Their comment that I remember was a goodyear gator belt (don't have any idea what this is by the way) seemed to cut down on slippage if it occurs for you.
I would also love to hear about your final specs as to 0-60 and quarter mile if there is any way you can gather those for all of us interested parties here....

 

I have Miltek exhaust (from paramount), upgraded pulley, ported S/C and paramount ECU mods on my 07 XKR convertible. I didn't dyno car before mods (should have) but after it only produced 318 whp, which seemed low to me. I have not been to a drag strip, but do have a gtech and can't record much below a 4.8 sec 0-60 which again seemed low since many car mags were getting mid 4 times even though jag claimed 4.9. I think paramount exaggerates their #'s and their site shows 508 crank hp, but they never say what before mod crank hp is, or what wheel hp ends up at. Car should be producing around 500 crank hp with mods I have, but really doesn't seem that much faster than stock.

 

318whp is extremely odd. You should be producing more power than that without any modifications to your car...I would definitely have it looked at. Something may be up.

For comparison reasons, my X350 XJR was able to muster out 340rwhp on a 4th gear pull on a dynojet. This was obtained with only a supercharger pulley that increased boosted by a claimed 1.5lbs.

 

Three issues:

1. All dynos are not the same and will vary by 20 whp or more (say 25-30 crank whp). My Dyno guy said that also some cars will even vary by that much between two runs. He also said that the XKR was amazing that it consistently put in almost identical runs. Mine showed 306 whp before exhaust mods which is admittedly a bit disappointing. However it feels a lot faster than my M3 and it is certainly easier to get it out of the hole.
2. I guess the important thing is to ensure if you spend money that you are actually getting an improvement which mean you put your car back on the same dyno after the modification. My Dyno guy is very sceptical about ECU mods (but not faster pulleys!!).
3. All cars are not the same and all tracks are not the same.

Still be interested in hard evidence on ECU upgrade. My suspicion is that most people buy a pulley and ecu mod and most of the benefit comes from the pulley..

Pulley slippage can be a problem. At the dyno was a guy with a 7 liter chevy angine and a R2300 Eaton putting down 600 rwhp . He had a pulley slippage problem. I wonder why?

 

As a side note something that does not seem to have come up but appears (at least in the suspect advertisements) to be a good bang for the buck is the K&N air filter. Seems I have seen something like 8 Hp gain as a selling point.
I have had the front end off of my car and am amaazed that the thing can really breath at all. A guy on another forum removed all of the offending airbox and snorkle (his was an XK BTW without the dual airbox) and put in a conical airfilter where the airbox used to reside. No confirmed benefits though other than seat of pants. I would be really surprised after fooling with this intake system myself and seeing all of the hijinks (bends, kinks, and just overall length which I bet is at least 5 or 6 feet) that there isn't something (maybe alot) to be gained in the whole affair...especially on something like a supercharged car that is stuffing so much air into the engine...

 

FYI here are a few pics that the guys sent me....

 

New pulley fitted and seat of the pants says a substantial inprovement. (havent had the tyre chirp in 2nd before)The Dyno will tell but cant book that for a week or so.
Jag mechanic thinks there is a valve limiting the amount of boost Anyone ever heard of this? If so it makes the whole exercise potentially pointless unless that pressure limit can be raised.
I know there is valve to relieve pressure/load on the s/c when boost is not required and wonder if that is leading to the confusion.

 

If you want to consider air filters this is worth a read: http://www.bobistheoilguy.com/airfilter/airtest1.htm

 

My guess is that any sort of limiting factor in pressure would have been exposed by others that have done this process.
Having said that I would also guess (and have seen as much in reviews of increasing the pressure via the pulley) that the octane of the gas is very important with the additional boost. This makes sense as the engine control should reduce timing to account for what would may be detonation at this higher pressure.
I know it would be a pain but I might suggest two tests on you car...one with say high octane auto gas (aka 93 octane or so) and then one with 100 octane racing or aircraft gas (or maybe just throw in one of those octane boost liquids?...which may not really do anything...they are as suspect as the performance vendor claims :-). I am thinking that you will get quite a boost in horsepower with the higher octane gas and have heard that with those that have run higher boost on their Jags. Having an actual horsepower increase due just to octane would really give insight into limiting factors for the engine with these mods.
Man this is fun...glad you have taken the time to allow us to live vicariously in your travails through this performance exercise...thanks

 

Totally agree on octane rating but would not use 93 unless my life depended on it. I run 98 on a daily basis. Might try avgas at the track My friend has just bought a s/h GT3 and we are going to hire a track or an hour or so as soon as it gets here and give boh of them a burst.

 

a little late, but worthy nonetheless I suppose.
goodyear gatorback belt was referred to earlier.
it's a higher quality fan belt made by goodyear with crosshatched ribs instead of the usual straight rib belts. provides better grip I guess? I always buy them just because it's a more quality rubber. but you may also have difficulty tracking down one that will work for your car.
I had a '95 XJR and tried to get a gatorback belt for my supercharger, but no one carried it because of the odd length/number of ribs combination. had to go jaguar OEM on that one.

-pancho

 

so far no problems with belt slippage but knowing there is a grippier belt is very handy.

 

Any dyno results yet on new pulley? Waiting here with my breath held...I am betting on a 50hp increase and thinking that I might NEED this on my R....
Just an aside (if you don't mind me asking) where did you get pulley and how much are they going for? Also am interested in the diameter of the new pulley for nothing other than just a data point.
Thanks
Guy

 

Are you concerned about water intrusion thru the front (lower) grille since the filter sits so low?? It looks like rain water splashing from a car in front of you will kick up enough H2O to cause issues. Has this been an issue or are you just driving it on dry days?