Message text written by "Graham Stretch"
Also known as an exhaust gas recirculation valve, it is vacuum limiting and
stops the engine oil being devoured by your carbs, as used to happen on
Stromberg equipped cars before they fitted these, and engines don't like
having oil in them, yes it took the lot once it got going!
Oops, Graham, close but no cigar. There are three valves that have been
bandied about on this thread.
1) PCV valve - Positive Crancase Ventilation purges blowby gases from the
2) EGR - Exhaust Gas Recirculation introduces controlled amounts of exhaust
gas (mostly CO2) into the intake mixture during part throttle conditions to
3) Gulp Valve - A valve to eliminate the backfire that occurs in a
catylitic converter during over run due to unburned petrol and the
introduction of extra oxygen (air) from the air injection system.
You are probably unfamiliar with the third system as only the US were
subjected to these demonic systems (which do, BTW, reduce emmissions)
because by the time you folks had to face up to auto emmissions we had
figured out how to meet the requirements without resorting to such things.
Most american cars in the late 70's and early 80's had an air injection
pump (euphemistically called a smog pump) that pumps excess fresh air into
the exhaust manifold very close to the exhaust valve to encourage further
oxidation on the exhaust mixture thereby reducing hydrocarbon emmissions.
I have played with the odd MG and late model Spit and found that tuning a
carb to 5% CO with the air injection disconnected one will see a marked
drop once the air injection is reconnected. The system works. But it also
clutters the engine bay and the pump has an annoying, wimpy sucking sound.
Electronic Fuel Injection can control mixtures well enough to avoid these
systems and the resulting engines are less cluttered and devoid of any
wimpy sucking sound.
US of A
Fully smogged TR8 (wimpy sucking sound and all but still fast)