Slant Six 170 vs. 225

Unless you upgrade the exhaust, as in headers, or at least opening up the exhaust manifold outlet to 2.25" or 2.5", you'll not see much of a difference at all. If you put more in, you need to be able to get more out and the stock 1 7/8 exhaust pipe ain't gonna get it done.

Also, while a decent article, that article up there ^^^^ is way biased towards its sponsors. Even doing everything they did, you ain't gonna see a 77hp increase still naturally aspirated. 50-55, I could see.