performance upgrades

Guys i own a 2/14 petrol 90 It has a turners engine done 30.000 miles head has been sorted to run on unleaded fitted with a webber carb.
im not expecting the rtuck to be a racing car ! but are there any mods i can do to improve ferformance? Do they make a k&n type filter for these? would an electric fan help? iv noticed the air box intake pipe uis facing the back of the car towards the bulk head is this right?
I did fill up with super unleaded today and noticed a bit of difference.. any advice appreciated.

best thing to do is fit a 200 TDi ex Disco.

That was in my plans for next year but until then id like to make this engine a little more livable

for what you'd spend on effective mods to the 2 1/4 you could get a good 200TDi and the job would be done.
You'd start saving on fuel big-time too - you should get 30+ mpg easily.

ahh a 90. is that a series II or III?

50mph to 60mph with a standard drive chain.
The problem is not going the problem is stopping and turning.

Ps
Between 12MPG and 22MPG

Its neither mate but its does have a 21/4 petrol engine in common.