450 SL Exhaust Question
 

having a 450SL exhaust manifold replaced, it is the type with
the "built-in" catalytics. The mechanic wants to use 380 exhaust
manifolds and "increase" the size of the 3rd catalytic.
Is this doable? downside? He says this will reduce the noise level
and heat buildup in the engine, but otherwise have no effect.

Thanks

akas

The three way cats of the 380 will never take the fuel mixtures of the 450. They will overheat and destroy themselves very quickly.

The 380 cats need an O2 sensor Lambda control system to keep the mixtures much leaner than a 450 can run.

The best combination would be to get an exhaust from a 77 to 79 450. This would have the cat under the car. It also would fit. The 4.5 is a wider motor than the 380 so I doubt that the crossover cat will be long enough.