Air Intake Types

[Mike Wattam <MikeWattam@domain.elided>]

Dear All

The USA Stag was always supplied with the air cleaner drawing cold air from
in front of the radiator through the black steel pressing and the rubber
concertina into the air cleaner box.  The air cleaner box has a flap valve
using inlet manifold depression to operate and triggered by a bi-metallic
thermostat in the air stream.

Thus with a cold engine, air is drawn from the exhaust manifold, and as it
heats up the bi-metal strip closes off manifold suction and cold air is
drawn from in front of the radiator to improve the amount of air drawn in
and thus thermal efficiency.

The reason for this complicated arrangement was to both allow the car to
have a 'clean' exhaust to satisfy mainly California regulations of the
time, and also to give improved driveability of the engine when cold.

UK cars were initially fitted with the 'twin-trumpet' air cleaner box
(cheaper to make!) but this was changed over to the USA configuration by
1972 models.  However, note that some pre-72 UK cars were converted within
warranty when owners complained of poor cold drive-ability.

Before anybody tries to contradict this, I too have seen twin-trumpet air
cleaners on post-72 cars, and vice versa.  As these cars were made 22-29
years ago, I think DPO may have played a hand!

Mike Wattam
Chairman, Triumph Stag Register