I have a zetec but I don't assume the spi is junk. Yes the valve seat is a issue but as seen posted here it can be remedied cheaply, plus there is no denying the mpgs compared to a zetec. Even when mine was stock I got 28 to 29 I achieved 32 once but I still think it was a math error haha. I know buddies with spi that are around 35 or 36mpg.
Did you know that dolphins are so intelligent that within only a few weeks of captivity, they can train Americans to stand at the very edge of the pool and throw them fish.