[dcb]

I understand the desire to stay under the radar. However I don't think people whom have actually made improvements in efficiency should live in fear.

The EPA stations around here will actually test your car for $20 on the dyno. I would think that just doing that before and after the swap would be a reasonable investment.

I would also not suggest a marginal swap, i.e. 1.8L honda for a 1.8L toyota even though you could claim it shouldn't be worse, and perhaps after much research you could demonstrate it. As much as I think everyone would benefit from learning how to build custom motor mounts, I think an "engine swap of opportunity" should be avoided, and only a clear improvement in emissions/efficiency should be attempted.