petrol (better known as dirty fuel) produces a hell of a lot of carbon , lead was used to reduce the explosion in the chamber and coat the exhaust valve , if you stick unleaded petrol into a old car , it will strip the old engine exhaust valve of its seat and send it upwards into the cyl head . the way to stop this was placing a special hardend seat into the exhaust seat of the head , when a plane is up thousands of feet into the air the last thing you would want is the engine fouling up carbon , this is why av fuel burns clean and produces no carbon , otherwise planes would drop out of the sky like flys being sprayed with toxin . as for strait through exhaust system is fine if you like to take off the cyl heads and get the hard exhaust seats done , unleaded fuel make them run HOT as there is NO lead in the fuel , if you want them to run hotter and redo them every 500 odd kays like a tourist racing car , that's ok too , not my money .
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