K&N

Just a few thoughts
An air filter is designed to remove the harmful particles which can cause engine wear, before the get mixed with oil. (The oil filter of course helps).
Very very small particles cause little damage, large particles will be trapped by most filters (Even K&N ) FIAT and the automotive industry in general spend their multi-million pound budget to develop an AIR FILTER specifically designed to remove the most damaging particle size and still have the correct amount of air required for efficient combustion.
I would suggest that the original Air Filter will do what it says on the tin.
It is a trade off.
Air density also plays it part related to the temperature of the air entering the filter.
The air filter housing is designed to allow cooler air flow maximised by the flared inlet creating a venturi effect.

The original airbox works the best on a standard road going X19.like, I agree. However K&N, pipercross, etc. are just as efficient at removing particles over particle size range but have the advantage that they can maintain a higher flow rate over time as paper filter performance drops quite quickly. The automotive industry uses paper as it's much cheaper.

I was going to ask about the manifold heat-shield as mine is currently off the car. I've got it, it was removed by me when the manifold to downpipe flange started to leak exhaust.

I'll refit it this weekend, promise.

I need some air filter trunking as well, mine came with a length of that aluminium cooker ducting in it's place!

Thanks Martin the K & N came this morning. I am going to lag the exhaust manifold and pipes. Fit the K & N and apply self adhesive aluminium foil to the underside of the bakelite shield. Then have some 5" aluminium pipe leading from the carb intake down to the side intake.
In the boot I am going to replace the rockwool with aluminium backed polystyrene sheet or that windscreen shiny bubble wrap to cut down the heat there without holding moisture.

If you are fitting a filter that allows a greater volume of air to enter the carb, then it's worth rejecting the carb to up the amount of fuel. Then you'll have a tad more power. Otherwise, you'll be running a bit on the lean side.

Eurosport have the jets in stock.

Regards,

Mickey

Thanks, I have done that, it made the car more easy to drive in slow traffic as well.

Good idea putting alu on the bottom of the drip tray David.