just another note on the gm deisel,these things use a LOT of air thus the reason for two turbos feeding one blower as the 892 v8 did.first of all it is a two stroke so it fires and produces power on every downward stroke and exhausts on every upward stroke,so you can see the need for lots of air,there are four vaves per cyl and they are all exhaust vaves,air enters thru ports in the cylinder walls thru the crankcase.the intake charge is pulled in to the cyl underneath the exhaust gases so extra air pressure is needed to make the eng more efficient as it is the intake charge that pushes out the exhaust gasses.there would be no need to have both on a four sroke eng as one or the other would be enough.the 2 strokes had no bottom end power at all,were made to be run at high rpm under load,incredible power at high rpm but not fuel efficient,they were putting out five and six hundred horsepower back when cat and cummins were still struggling to get four hundred out of their motors. :p
