Air intake tract.

[Petrus]

Following the TRD inlet elbow sale thread I think it may be useful to show that end in it´s entirety:




The plastic OEM elbow to the filter housing is obvious, as is the design with a restricting entry tapering out.

The alumium TRD elbow is same diameter all the length and has a bell shaped entry. For that to work optimally, the duct inside the wheel well needs be removed.



The steel ´replica´ Markiii replaces the OEM elbow between filter housing and wheel well duct. It is same diameter and has no bell shaped entry.

[Petrus]

Found another realy neat illustrative photo:





It shows both the >twice as large surface of the ´straight´ pipe ánd the bell shaped entry of the OEM elbow.
The nothing short of classical shape OEM intake horn* is designed to reduce turbulence and have a high speed laminar flow from lower revs.
Yes, it is clearly restrictive at the top end.

The duct in the wheel well will have sóme kinetic push at the high rev range but serves foremostly in reducing inlet noise.

The inlet of the duct behind the fuse box is not restricting the standard flow.
It máy be restricting the flow with the Markiii stub; probably about on par, but when removed there will be turbulence at the straight entry, reducing effective flow.
It is easy to understand that the flat entry behind the fuse box will certainly be restrictive in comparison with the TRD bell shaped intake opening of the same diameter.

So the wheel well duct:
- TRD inlet: Take it out.
- Markiii inlet: Leave it in.
- OEM: Take it or leave it 



* classic shape intake horn

[Petrus]

By Jove, that gives me nostalgic memories.
No doubt several more here can remember when the family car had a pan shaped air cleaner on top of the carb/engine with such an intake stub. Some had a 90 dec¡gree bend that in summer was to be aimed towards the headlamp and winter down towards the exhaust manufold.
Diffrent times; pre nois/emission worries times, same stub shape. Quite amazing. Logical but still amazing. I lóve it!

[Petrus]

https://www.mr2roc.org/forum/index.php?topic=66586.msg801949#msg801949

[m1tch]

Just use some flexible brake duct hosing between the 2 parts, or just fit a cone filter behind the battery.

[Petrus]

Just use some flexible brake duct hosing between the 2 parts, or just fit a cone filter behind the battery.

The duct option is functionally the same as the Markiii.

The cone filter behind the battery is a wáy different road.

[m1tch]

Just use some flexible brake duct hosing between the 2 parts, or just fit a cone filter behind the battery.

The duct option is functionally the same as the Markiii.

The cone filter behind the battery is a wáy different road.

Indeed, probably about £10 maybe less for the brake duct, not much more for the filter behind the battery, not sure how much mkIII pipe costs, can't be too much for a bent bit of pipe considering you can pick up the same from an exhaust place.