hey guys just want to know if someone can tell me the difference between hfc and test pipes

 

One is a catalytic converter, one is an open pipe.

 

hfc still has a cat so still mostly legal and cleans the air somewhat.
test pipe is just a straight pipe with no resriction on exhaust flow more hp but illegal and not environment friendly.

 

At least in CA, there is no such thing as "mostly legal." There is 'legal,' and there is 'illegal.' You'll get the same ticket for each, but test pipes will be caught easier by your standard cop, due to extra noise and the smell of unburnt gasoline. A state ref will have no issues giving you the same ticket for either one.

And while we're giving tuning tips, unless you're running turbos, SOME restriction is good (increases torque). Don't buy into the whole peak HP argument, but rather, look at power increases in the everyday powerband ranges.