Ok first let me give you a little background I have a 1998 XJR and friend has a 2000 XJR, when we first raced 6 months ago lets say 30mph-100mph the cars where the same nothing in it at all so performance was simular. However he later discovered his throttle body was knacked which resulted in the car stalling and creating error codes on the dash, I also found out around the same time my car had 8 holes in the exhaust.

1) Both cars where probably down on power given my 8 hole exhuast and Im not sure if a broken throttle body will effect performance?

He not long after fitted a "lower pulley" without fixing his throttle body (wrong way round to do things I know). We then re-raced the same road same speeds, I still had the old exhaust on at this point, he inched a little away from me perhaps a Jag car length roughly.
He was then dissapointed with his upgrade as he felt if didnt make much difference to warrant the money spent.

After this race I then had a custom cat back exhaust fitted and he got a new throttle body.

Of course we re-raced again same road same speeds.
This time he seemed to pull away a bit better instead of the car length last time it was a easier 1.5/2 lengths.

Now I was expecting my exhaust to gain a little bit of power back that Id lost from the holes plus gain a bit perhaps. Bit he still had the advantage.

2) So the second question is how much over standard does the power pulley upgrade give? Does 1.5/2 car lengths sound about right, or has something happened to my car since and the throttle body hasnt given him anymore performance?

I need answers people....
Thanks

 

I may have answered my own question.
I did a video of my speedo pre-exhaust a few years ago and when placed onto a video editor and slowed it down my rolling 40-110mph time took 11.98 seconds.
I just did another high quality video today and my 40-110mph time is now 11.04 seconds.

So I have gained a little accerleration in that time (probably due to my poor exhaust than gains from a custom one) and with him fixing his throttle body and lower pulley mod would explain his being quicker than mine.

At least I think theres little wrong with mine......

 

You fitted a K&N also?

The lower pulley doesn't add power, it lets you access it earlier in the rev range. So pickup from kickdown will be different with each car. Basically spinning the charger quicker at any given rev range.

I see a competition brewing here....wonder what was wrong with the throttle...

 

Yes K&N also, not that that makes much difference?
Most of his jump he gained was at the start under kick down,after a while things evened out again.

 

How far in front just out of interest over a standard XJR would one with a fitted pulley pull?

 

No-one?

 

An upper pulley upgrade gives you 12-15 HP ... Cat back exhaust.. Maybe 8-10?

A good UPPER pulley upgrade would probably give you 1/2 a car length ahead, but honestly, it's hard to tell from your situation because of a mix of pulley, exhaust, throttle body, engine issues etc etc