Quote:
Originally Posted by BlaqWhole
If anything the DOHC engines might actually have poorer MPGs for what it's worth. A lot of those numbers you're talking about that gives them this or that certification are easily manipulated. And it might not really be about the engine. It could be the gear and trans ratios etc. It could be the tune. The cats...I remember Ford used to put 6 cats on the New Edge GTs. So is it a low emissions "vehicle" or a low emissions "engine"? If it is the vehicle then GM could simply slap an extra cat on it and clean the tune up and there you go.
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So here is the thing as simple as I understand it.
For some reason smaller displacement OHC engines, can pass cold start emissions easier than larger displacement OHV engines. Why I don't know, I just remember reading the tea leaves that for the C7 Z06 they wanted to go with a modern 7.0 engine. It made the power they wanted, but it wasn't going to pass cold start emissions. So they went with boost and 6.2L
So despite the fact a OHC engine may be physically larger, something about the design allows it to be more emission friendly. why I don't know that is just what I have read.