also, remember if you put in a high flow exhaust system it can change your midrange torque. so you may actually lose a little zip but gain more on the elsewhere.
example: engine now flows to say a 2inch header tube creating the proper back pressure then to a 2 1/4 cat/muffler etc. with the new exhaust it could go engine to 2 inch headers and them 3 inch cats/exhaust.
it depends just research it throughlyand i certainly don't know enough about it to be anymore help. sorry.
these cars unfortunately are not like my ol' '65 vw where a dual 40mm carb setup and some high rpm pushrods tweeks would put power to the pavement allowing for wheelies.....oh to be 21 again