Base 91 hatch 4 speed questions, please help

What is the difference between a 91 civic hatch base (70hp) and a 91 civic dx hatch (90hp). I think they have the same motor, what is the 20hp difference? a cpu? header? If i can't get the extra 20hp out of the motor easily, what would be the best way to get a little more horsepower out of the motor so it isn't such a dog?(besides a intake)

I would figure the 4 spd tranny is what robs those extra 20hp.Becouse that tranny is for high fuel economy.The best way tp squeze the most Hp out of the standard hatch would be to swap the 4spd for an si tranny and do the MPFI swap.

If you do all that u should be hanging with stock civic si's

It has to do with the ECU and there are restrictor plates on the intake manifold that don't open as far as on the dx. The tranny has nothing to do with horsepower. Also the dx and si tranny are exactly the same except for the final drive.

so if it has to do with the ecu, it probably wouldn't be worth changing it? would a manifold from a civic si hatch or crx si help give me a few extra horses, or would i just have to get a aftermarket header for it?

i heard something about the converter on the header slowing it down also.