I just bought a 88 civic to play with. It currently needs a new clutch and master cyl. Right now the muffler has rusted off and has no muffler on it. I don‘t have emissions here so that is not a problem, but what I am wondering is would it have noticeably more power wasting the money on a whole exhaust kit or would it really not make enough of a difference, if any difference at all if I just keep it the way it currently is. The noise doesn‘t bother me but since its only got a full 92 horsepower getting a few more would be useful.
No exhaust system, exhaust fumes in car, fumes can and do kill, possibily your death (and it has and does happen). so your choice.
You won't get more power by putting a system on unless you start at the engine and put a full header and exhaust system. However it's not a great idea to drive without a muffler since the noise could bother other people.
Get a muffler, even with no emissions laws there are noise laws! Also it is not safe to drive, because the fumes will make you sleepy and are toxic. You do not have to replace any more then you have to and parts can be bought that are universal fit that can be used.
