Undertray?

[JonnyFive]

Does anyone know if the air that passes under the undertray (Between ground and tray) is low or high pressure?

If you cut your undertray underneath the air filter side, and fitted one of these;

http://www.demon-tweeks.co.uk/Performance/Air_Filt...

And some piping would it work quite well as a cold air feed? On the NB theres not really anywhere for air to come through as the lamp is in the way..

(I'm just trying to come up with ideas that might work quite well that might not have been done so much over here)

[mad4amanda]

IIRC the air under the car is moving faster as it goes through the gap so its higher pressure , but then I got confused as if its high pressure how about downforce vs lift?
Bigger concern for me though would be driving through a puddle , Id go for a headlight vent instead!

[JonnyFive]

mad4amanda said:

IIRC the air under the car is moving faster as it goes through the gap so its higher pressure , but then I got confused as if its high pressure how about downforce vs lift?
Bigger concern for me though would be driving through a puddle , Id go for a headlight vent instead!

We can't get those on the MK2.. And the air through the bumper just goes through the rad so no air from there either really.

[MX-5 Lazza]

Pretty sure it's low pressure under the car on a Mk2. Don't you have a vent in the wing into the wheel arch on yours?

[JonnyFive]

MX-5 Lazza said:

Pretty sure it's low pressure under the car on a Mk2. Don't you have a vent in the wing into the wheel arch on yours?

The slatted bit on the front of the arch? Does that make any difference?

I have been reading about the "Randall" ones which cut into the bulkhead and feed from there and wonderered if something else would work

[GravelBen]

mad4amanda said:

IIRC the air under the car is moving faster as it goes through the gap so its higher pressure , but then I got confused as if its high pressure how about downforce vs lift?

Faster airflow = lower pressure

[Mr MXT]

GravelBen said:

mad4amanda said:

IIRC the air under the car is moving faster as it goes through the gap so its higher pressure , but then I got confused as if its high pressure how about downforce vs lift?

Faster airflow = lower pressure

Good old Bernoulli!

[MX-5 Lazza]

JonnyFive said:

The slatted bit on the front of the arch? Does that make any difference?

I have been reading about the "Randall" ones which cut into the bulkhead and feed from there and wonderered if something else would work

The wheel arch is supposed to be a high pressure area. My air-filter is located right over that hole and is covered in dirt that's come up through there so the air is definitely going the right direction.
The hole in the bulkhead is a nice idea but not practical on a Mk2 as there are brake lines that would have to be relocated where the hole would need to be.

[mad4amanda]

GravelBen said:

mad4amanda said:

IIRC the air under the car is moving faster as it goes through the gap so its higher pressure , but then I got confused as if its high pressure how about downforce vs lift?

Faster airflow = lower pressure

Ah got it round the wrong way thats why I was confused many thanks!
Still wouldnt put a vent there though.