Gaining power?

If I removed the air silencer and installed a K&N panel filter on my stock 1990 SC 5-speed, how much power would I get. This is still my daily driver so I can't sacrifice gas mileage. (24 mpg is bad enough on highway).

I also need a specific exhaust system recommended to me. I've been looking at the flowmaster kit for this car, off of their website www.flowmastermufflers.com. Should I go with this kit or something different? Again, mileage cannot be sacrificed. I also plan to remove the cat converters and replace with straight through down pipes. Is this safe for my application, or should I run different cats. There are no emission laws in Saskatchewan where I live. What is a good pipe diameter to run, double 2.25" into resonator with 2.5" single out, double 2.5" in with 2.5" single out, or double 2.5" in with 3" single out? For my downpipes, what size of pipe should I run off the stock manifolds? What about the HEGO sensor, what do I do about that?

I still have stock manifolds, which I do not intend on changing soon. Basically needing the ideal exhaust system for these things without loosing the mileage. Also, I plan for a 5% overdrive pulley on the blower at a later time. Please help.

Thanks,

Brett

Some ideas

Hello Brett.
Removing the silencer and adding a K&N MAY gain you 1-2 horses. Not much.
I did notice a very small difference when I removed my silencer.
As for the exhaust the stock manifolds will hook up to 2.25 down tubes nicely.
Downtubes 2.5 or larger don't fit around the manifolds well (so I have read).
Wynn and Texas Thunderbirds sell 2.25 down tubes with the O2 bung.
He also offers exhaust manifold porting. Stock ported manifolds are fine for stock to mildly modified engines (I think that 300HP with no problem).
For your intentions a 2.50 center section should be fine.
Both Flowmaster and Dynomax make cat back systems.
The biggest restriction is the resonator and the center section of the exhaust system.
Just replacing the center section will ease up on the back pressure.
The bottom line is, what are you willing to spend and what is the end result that you would like.
Hope this helps.
Bill

You will get better gas mileage from opening up the intake and exhaust and letting the engine breath easier.