Hi,

I recently had my (2003 XKR) engine checked for a chirping sound when cold. The guys at the shop said they know exactly where the sound is coming from and it needs a new modified supercharger belt, tensioner and idler pulley. So without thinking about it too much I said go ahead and do whatever needs to be done.

All done and chirping sound gone I left the shop happy. Then at home I looked under the hood and indeed the belt etc was replaced with slightly different looking parts (the belt has now longitudinal grooves which I don't remember seeing before). Then I started wondering is the grooving only change or did the size of the pulleys maybe change too? I've read you could get up to 10% power increase by changing to either larger lower pulley or smaller top pulley. Does anyone have more info about this new modified belt kit?

Thanks,

 

you have had a double sided belt fitted..the tentioner and pully will have been changed as well ..this gives a better drive to the s/charger..double sided drive I have this mod on my car..there in no performance upgrade..you will need to change the s/charge drive to do this

 

You now got a dual sided belt, but the supercharger speed isn't changed with that. You could still go for a smaller upper pulley and use this belt, but when changing the lower pulley you need a new longer double sided belt, and I am not sure if you can get these in the lengths needed (so you would have to go back to the “normal” belts again, which should also work without chirping…).

 

avis your are 100% correct but to go back to the normal belt he will need his old tentioner and int pully wheel as the are different..ill bet the upgrade he has had will have cost a lot of cash

 

Thanks guys. Much appreciated!

I wasn't really after for more horsies anyway. Was just wondering

 

Only the pulley just above lower pulley would have to be changed back, not the tensioner.

 

I've just had a smaller upper pulley, which is supposed to add 30 bhp or so. The original belt was refitted with no problems or slippage, the car has even better mid-range acceleration and I haven't noticed any difference in fuel consumption. In real money (UK pounds!) it cost me £260 and took about 3 hours. Since the car runs on petrol/LPG (propane) I had to have the propane adjustment tweaked by the people who did the conversion - that took about 5 minutes. David

 

To know if all is well, you would actually have to do a dyno run for power measurments and verification for the a/f ratios, or did they do that within the 5 minutes?


Sorry to go of topic, but an advantage with LPG is that it has a higher octane rating (yes I know about many disadvantages also), so ideally you would have to be able to change your timing when running in LPG mode for optimum power, as that possible with your system?

 

Just for information....... As well as changing the idler and tensioner a new power steering pump bracket is also fitted, this so called upgrade use to cost £600...

I would not do it and haven't when I rebuilt my XKR engine

 

Thanks for chipping in all! I'm more educated now

I was just worried about the sound that came from the engine when cold so I thought I'd better get it fixed before anything really bad happens. And since I'm quite new to this car I thought I'd let people who actually know something about these things do it for me. Looks like a tight place to do anything in the front of the engine... Cost me £445 but it fixed the problem and I have peace of mind

 

still off topic - the lpg system wouldn't work if it is out of adjustment (it switches back to ,petrol). Gaspower UK have done a dyno test on an XKR supercharged (Frequently Asked Questions (or FAQ) Gas Power UK offers advice on filling up with Autogas or LPG and travelling abroad with LPG, including an FAQ and do's and don'ts.Gas Power UK, Devon LPG Autogas Propane Car Conversions - but the graph doesn't expand when clicked). I intend getting an engine management remap and dyno at some point, to optimise the whole system, whilst running on LPG.

 

Sorry to stay of topic.. As long as you have a piggyback lpg ECU (which prefferably also alters o2 values) you can have 2 different maps. In theory you could then run much higher boost levels and outperform normal fuel systems, then I might even be interested ;-)