Can anyone give me insight on upgrading the exhaust on my 2.5?

I am looking at the choices...

Heat Coated Exhaust Manifold
Free Flow Cat Conv
2" 4 cyl Perf Exhaust OR 6 cyl stock Exhaust

Are these mods worth the money?
How much improvement will I see for each/all?
What is the difference between adding the Perf 4cyl or stock 6 cyl exhaust?
What are the other options out there?
Any other suggestions?

Upgrading the exhaust on a 2.5L (96hp) 4cylinder enging, even at a 10% gain, will hardly be noticable.

The car may run better with some inprovements in gas milage, however it has been my experience, that those people who are trying for improved performance don't give a rats ars about mpg. Most want a 12 second quarter mile performer which ain't gonna happen with the stock 4 cylinder coupe. Something like a Borla exhaust will make the car sound a lot better with some modest performance improvements.

I agree, you are not going to get great performance from the 4s unless you pay 7K for the SD4.

I am looking for mods that will improve the gas mileage and longevity of the car. If they also increase performance a little, Yeehaw! Otherwise, I am just happy to have a fun car to drive and keep miles off of my new car.

I am thinking about picking up a 6 cyl, strictly for performance reasons...

In my 1986 coupe, I replaced the catalytic converter with a free-flow unit, replaced the muffler with a free-flow unit, replaced the air filter with a K&N filter, replaced the spark plugs with Bosch Platinums, and advanced the timing a few degrees.

The EPA rating for the 1986 2.5 liter with 5-speed Isuzu is 24 MPG city / 36 MPG highway.

Plotting fuel economy in city driving (going to work, school, grocery store, etc) for 1000 miles, the car averaged 27 MPG. On the trip to Run For The Hills 4 (about 1200 mile round trip, most of it cruising at 80-85MPH), the car averaged about 40 MPG.

The mods, along with the advanced timing, did increase the performance slightly. Nothing to write home about, but it was enough that I could tell the difference (just barely).

The advanced timing might have hurt the fuel economy a little (not sure), so you could possibly do better. I was also using wide tires (215/60-R14 front, 245/60-R14 rear), which would increase rolling resistance and hurt fuel economy. And I don't drive like grandma, either.

Your results may vary.

[This message has been edited by Blacktree (edited 07-22-2002).]

Both my GT, one all stock and one with a 3.4L, have the Borla exhaust and K&N filters. That is the extent of the engine mods. The 3.4 has a t440 auto, the stock 87 has the 5 speed. Both get 30+ mpg.. I don't know much about their performance. Each can peg the speedometer, with the 3.4 can be done in 3rd. Mostly I use the cars for highway cruising. Driving around town, I sometimes get carried away.

I really want to replace the stock exhaust, but I think I will replace the stock suspension and the stock wheels/tires first. These have 100K miles on them.

I picked up and installed a K&N Air filter tonight. I hope this will help keep the engine from choking.

After the suspension and wheels/tires, I will probably replace the stock exhaust with the following: perf 4 cyl exhaust w/ dual twin tips, free flow cat conv, and heat coated exhaust manifold. Spring time should be good for this mod...or maybe a Christmas gift to myself! Hehe