89 crx hf exhaust
 

Presently I'm getting 42 to 44 MPG city driving. I need to replace the old exhaust system . I am thinking about aftermarket headers and a stainless steel exhaust the rest of the way back. Will this improve or hurt my economy? Also what size tube for the exhaust. Or do I need to keep everything stock including the HF exhaust manifold/catalytic converter?

Keep everything stock unless it is broken and needs replaced. Exhaust systems need to be tuned to be efficient. Simply buying aftermarket headers, piping, and mufflers is hit or miss, mostly miss. I can't see any reason to replace an exhaust system that isn't broken, for fuel economy reasons.

On my 97 hx my cat was pretty clogged so I got some 4-2-1 headers from my friend for 20 bucks and replaced the manifold and cat. I left the super tiny stock exhaust. The thing runs alot better. Usually when you put a huge cat-back on it takes away gas milage on our little engines because it moves the power band higher. It takes power away below 3k rpm where we need it for milage and puts a little power at the top end. But I think headers would be ok for you. I know the exhaust on the hf is microscopic so im not sure if it will help or not to get slightly bigger. Such as throwing a stock exhaust from a crx si or something. You could maybe try putting the exhaust manifold from a stock civic ex 92-2000. It would flow a little better and probably be cheep.

In the CRX I used to own going back to stock exhaust improved mileage by almost 5mpg and it had a life time warranty from Honda for as long as I owned it, it was amazing and light weight.

On the Civic VX over sized exhaust will burn out o2 sensors very quickly and reduce mileage.

Needing to have the CRX's engine up to 3,000RPM is supper rare, I hardly ever saw my engine speed get much over 2,500RPM

About what does honda charge for a stock setup? Will they warranty it if you install, or just them?

At Majestic Honda - The Internet's #1 Honda Automotive Parts Store (one of the great honda parts sites) I found this for your car: Honda 1989 CRX HF exhause manifold parts.

-james

They told me that the warranty is good if I install it and the cost was about 10% higher then the auto part stores for a decent exhaust system, the quality is twice as good, the civic vx that I sold 4 years ago has a small exhaust leak on the exhaust system that is over 8 years old and I've never had a auto part store exhaust system last that long.

Clean and paint in "grill paint" or any other high heat paint. Will last 5x as long. Even if you just go to napa and get oem replacement parts...