I made a typo, F22a, Hes not swapping in a sohc, H22a (dohc, vtec). Why am i compairing Geo metro and f22? Because the common defense that the f22a's low compression ratio makes the engine good for boosting is not neccesarily true.

Longer gearing would take away a big part of your advantage for boost or anything. Long gearing = fuel economy, not performence. In no way is longer gearing an advantage for boost.

Here's what hes looking at is the price difference in his two options i believe is the best choices. The cost of doing a reliable turbo set-up on the f22 will yield you the same gains as swaping in the h22a. It will cost more money in the maintence, become less reliable do to the FI and be more hassle.

Bottom line, save for the h22a for a better platform to mod. You'll see, no one has gotten an h22a engine and switch back to f22a but there are stories of boosted f22a motors failing or people have swaped to h22 after turboing the f22a.

Of course there are well built f22 motors but is it worth the cost of putting money into the f22 motor where you can spend less money and mildly build the h22 and get the same performence?