Less Compression = Mass. Emissons pass

[MiracleMax]

Well, high compression tends to promote the formation of Nox (oxides of nitrogen) as well as spark knock which tends to increase emmisions also. As far as running richer, that would also increase emmissions even though it might help to reduce Nox production (by simply cooling down the compbustion process).

Now if your emmissions tech guy isn't all that savy and thinks your hopped up 393 is a 302 it would probably fail by virtue of the fact that a 393 will produce a greater volume of pollution simply by being larger than the 302.

A better choice might be to run an oxygenated fuel or fuel supplement and bump the timing down so that the apparent compression ratio is lower delaying the onset of Nox production (if they do a high speed steady state load test under part throttle conditions where the combustion chamber is prone to high combustion temperatures and lean air fuel ratios)