Okay l have a 97 eclipse GS. Yes GS not gst or gsx because it was a great price for $1000. GOOD CONDITION. 5 speed. Now the question... l know it has 140 hp. Now l dont wanna put a turbo...l just wanna increase horsepower, is there any way l can ? l already have an cold air intake and how much horsepower you think l can get up to?

it depends on how much u want to spend buddy. lol l have a short air intake & l rammed it (long hose that sticks out the front bumper), & l have a megan racing header. l preffer a 4-1 not a 4-2-1 if u do get a racing header. key word racing not street. & of course a exhaust system & u will probably have..35-40 horse power when done. to gain more speed l suggest, a performance chip that will cancel the speed limitor, & taking out parts from ur car a.k.a. back seats. also carbon fiber hood will make ur car lighter.

Your eclipse with just a CA l is not going to give much but around 5-8 hp. With headers, pulley, and exhaust its going to bring you up about 20 more hp. Replacing the ECU is another way but yet expensive around $500. But gives you probably around 15-20 hp with right tuning. Thats basically the basic upgrade parts.

waste of money. ha gs.. you will only get to like 200 hp at most

Ah, increasing the horsepower of an N/A. Something that is hard to do & costs quite a bit of money. But, if u want ur goal to be 200 horsepower or 250, you're looking at quite a bit of money.
For starters, there is the intake, header, & exhaust.
The intake not only includes a hard intake, but a filter, intake manifold, & lots of porting & polishing to the head.
For ur exhaust manifold, look into a 4 to 1. Do not just go with the cheapest brand, or the most expensive brand. Look for a manifold that suites ur car best. l suggest reading DOHC 2.0 Neon owner is since you're running the same engine as them, the 420A.
For ur exhaust, & since you're not putting a lot of power to the ground right now, u should be fine with a 2.5''-2.75'' exhaust system. A high-flowing catalytic converter (check with local emissions laws), resonator, & muffler would help out quite a bit as well.
You can also replace the injectors to a more high-flowing kind. Around the 400-500 cc mark. Of course, with bigger injectors comes the much needed tuning device.
For the tuning device, I've heard good & bad about every single one. But the brand that has come up mostly as good is MegaSquirt. You can find quite a few different ones here, DIYAutoTune.com.
And here is some information on wideband O2 sensors in case u would rather buy a wideband & an SAFC 1/2/Neo or equivalent. http://paceperformance.com/paceperformance/pdf/widebandshootout.pdf
For internal modifications, u can purchase high lift cams, better valvetrain (valves, valves springs, valve spring retainers etc.), high compression pistons (around 10-11:1 for an N/A motor).
Lighten up the car as much as possible. Carbon fiber hood, hatch, lightweight glass, remove rear seats, everything in the trunk, lighter wheels, etc.
There is quite a bit that u can do to increase the performance of the 420A. And, if u do decide to turbo ur 420A check this write-up out: http://dsmtuners.com/forums/articles-turbo-system-intercooler/181134-how-build-420a-stage-2-turbo-kit-under-1000-a.html

first to Gabriel, no intake header, exhaust gives u 30-50 HP. PERIOD. the most u will see is about 10-12 TOTAL from these 3 mods, it has been proven time & again in EVERY tuner magazine possible. Also the car has 140 CRANK hp, the HP at the wheel is an average of 117 on these cars, so with the simple bolt ons u MAY see 130 at the wheels, & that is on a motor that has been well maintained. If u do not want turbo then u will get about 175-220 at the wheels, & this will be after a minimum of $10,000 of all motor work & after that it will be close to undrivable because of the cams u will need it will sound more like a old muscle car than a tuner withe the big lobes for the power. look at it like this a bolt on turbo kit is designed for stock motors, like hahn racecrafts kit, it will give u 215-225 at the wheels from a simple bolt on kit & it has EVERYTHING u need even fuel management. Now to put this in perspective a stock GS-T only puts down about 175 at the wheels, so right off the bat u will have a 50 hp advantage. The kit runs about $3500 & so u would have $4500 in a car that beats the GST & most GSX cars which cost more than ur car even with the turbo.