If you have 16 valves you have a Zetec, no if ands of buts about it.
If you can, post a pic of your motor, or just look at it. If it says SPI on the top of the motor it only has 8 valves and you need to slap whoever told you otherwise. If its Black and has Zetec written on it then you need to slap the person who told you it was SPI.
Well since the aftermarket scene is DEAD for the SPI engine, you going to need some money and some inginuity to make it faster.
"But Dazada, the SPI only has 8 valves and ONE cam, how can it go any faster?"
Well let me answer that question with an answer. jeffescortlx has 212hp in his TURBO-ED SPI Escort.
"Well what makes my engine so special?"
A cast iron block for starters. I love being able to say I have a cast iron block rather than aluiminum. Aluminum is so...light...and...not cast iron. www.escortfocus.com will have some goodies for your SPI engine such as cams, valves, valve springs, and other head-worthy trinkets.
Sorry, I was so caught up in conversation with myself that I forgot to mention the advantage of a cast iron block. It can handle boost (nitrous, turbo) and detonation better than an aluminum block. Just modify the intake and exhaust, tweak the head and the ECU, and you got yourself one nasty little four banger.