amp for small car with powerful speakers

I'd bet money that the so called Engineer quoted you "PEAK" power and not the actual "RMS" rating as cavyman alluded to. Your absolutely best bet would be to purchase a 4 channel amplifier with atleast an rms rating of no less than 35 wrms per channel. There are several models to choose from and I would recommend US Acoustics for the price and sound quality, but you can hardly go wrong with Alpine, Fosgate, Kenwood, Sony or Pioneer which make up the majority of the mainstream lines. You can find good deals on E-bay, but beware of  people pushing junk. Remember, just because someone advertises High Power for a cheap price doesn't mean that it is a bargain. One thing to remember when you fnally get your system up and running is that those infinity's as nice as they are are not meant to put out a lot of bass. If you want that then you'll need to buy a subwoofer and another amp or buy yourself a 5 Channel amp now.

Good Luck!