Gentlemen;
The AIR "air injection reactor" aka 'SMOG pump' was just another government 'con job' from the 60s and forced upon us in 1968.
All it does is blow air into the exhaust manifolds creating a lower HC reading at idle while robbing 2-3 Hp. from the engine @ 'run' speed. Most were all 'trashed' when they came out.
Like Larry says, this was LONG before the the Cat. came on the scene, which isn't required on 1970 vehicles today and NEVER was.
When an engine is abused by operating it for long periods with one or more valves burned through or cracked, the seat for that valve (usually exhaust) is destroyed beyond 'normal' repair procedures.
There; a steel seat is used to "save the head" for the customer and NONE of this has anything to do with the fuel being used.
The Cat. being forced upon the American (motoring) public is just another form of engine abuse because of the extra/unecessary heat it creates in the combustion chamber/process.
It's this unusual operation/abuse that require these seats (sometimes) NOT the fuel.
Commercial 'fleet' vehicles use them for "preventive maintaince" is all (to save down time) on some of their vehicles only (not all) when they ALL use the same fuel.
Machine Shop personnel can often get these facts confused in their selling dialouge.
This; Coupled with decades of government propaganda on the subject is how the isssue(s) got swiched.
The Cat came first causing the engine damage, then 'unleaded' fuel which prevents damage to the Cat. Not the "other way" around!!
This is HISTORY not opinion.
"No brag son, just fact", Walter Brennen.
