Me neither. I saw an engine simulation model recently that was built like this, which got me wondering. Maybe the model had a simplified intake system for some reason, but needed the full exhaust?
It might have been a not-fully-developed model as you suggest, but alternately I can absolutely visualize a boosted engine, probably a diesel, where the exhaust valves are independently actuated. That is exhaust valves with individual ports, one plumbed to the turbo, and the other to the EGR circuit. Then with control over valve actuation you can select whether you utilize the pulse energy for the turbine or to increase the EGR flow. ~50% EGR flow is by no means out of the question for modern diesels.
There was a 3 valve version of the Saturn 4cyl but it was two intake one exhaust. Two exhaust valves can run at a higher compression/expansion ratio for a given fuel octane rating because the exhaust valve temp. will be lower. You could achieve a single intake dual exhaust vavle configuration by simply eliminating the lobe needed to provide lift to one of the intake valves in a four valve head.-------Phil
I believe that Borg-Warner are developing something along these lines with a concentric camshaft within a camshaft which allows one exhaust valve to be advanced or retarded relative to the other. I think they call it VEMS(?).
There was a generation of Honda CB400/450 engines that had three-valve heads, but they were the conventional arrangement with two intake and one exhaust. The generation in question started in 1977 and continued through the mid-eighties.
