Welcome Night Sky and thank you for your service.
The first thing I'd do, if you haven't already, is change out the oil, change out your coolant, and inspect for leaks from the differential and transmission. Having a car sit unused for 5 years can be hard on it. After you have done those things make sure your tires and any other rubber items (accessory or 'fan' belt...even though it does drive the fan...your radiator coolant lines, heater hoses, etc) for cracks from lack of use.
After that, go for a nice long but local drive. Once that is done, inspect for signs of leaks once again. While your mileage isn't there, look and see if the water pump is leaking. Do a search if you don't know what to look for...there are a lot of topics on this.
I know none of these are answers about performance but all this needs to be sound before you start modifying your car.
With all THAT out of the way now, let's talk modifications.
You say you don't want to race it but just want performance. Well, those two are one in the same. You can up your performance and not race but racers will up their performance in the same way you will.
So here are some questions to get us started:
What do you mean by performance? Are we talking more engine power? Better handling? Better braking? (Which, if you're going with more power, you could use better braking even if you just go with better pads.) What exactly is better performance to you?
Second, what is your end game? Where do you want the car to be at the end of your modifications? Are you looking to be a little faster? Are you looking for a more aggressive sound? Do you want to eat Mustang GTs for lunch from a stoplight? Do you want to carve up a mountain road quicker than you can now? The reason I ask this is because there are better modification options depending on what you want to achieve in the end. You may want more power but not have an annoying loud exhaust. You may want better handling but not to feel like your car rides on bricks. You may want to break the sound barrier but only have a $1,000 budget.
Which brings me to question 3, what is your budget? The age old saying is "How fast do you want to go? How much money do you have to spend?" We have a member here who just put in a twin turbo LS7 V8 Vette motor in his Sky and is running 9 second 1/4 mile passes at 150 mph. Believe me when I say that even though he did all the work himself, that build didn't come cheap.
Now then, let me give you the best run down I know of modifications to your LNF (that's the engine that is in the Sky Redline) powered Redline.
- Tune - The problem with doing any of the modifications listed here comes in the form of your stock computer programming. The LNF's computer uses torque based programming to control the engine's power output. In a nutshell, the Engine Control Module (ECM or engine computer or a number of different names it has) says that for a given condition the engine should be producing X amount of torque. It then calculates the actual torque the engine is putting out under those conditions. If the engine is putting out more torque than the ECM is programmed to see under those conditions, it will pull boost to bring the calculated torque values down to the expected torque value levels.
This is what is called a "learn down" feature. This means that when you add all these power goodies to your car, the ECM is going to say "Uh uh uh! You can't have that power...so I'm going to pull boost to keep you in line!"
Naturally, if you are adding things to get more power this SUCKS.
Good news is you can retune your ECM to eliminate this as well as add more power to your car by changing boost levels, timing, and correcting fueling for these changes.
Tunes vary widely and often times it is best to do your other performance modifications first and have the tune written for the modifications you've done.
Canned tunes like the Trifecta tune can compensate for things like CAIs and high flow downpipes but they are generic tunes written to be a bit on the safe side. These work for 80% of the people out there. The other 20% are either doing more advanced modifications that a canned tune won't cover or want a more custom tune specific for their car.
If you really want to get the most out of your car, you do your modifications and then have it tuned by a shop on a dyno or by a tuner scanning your car while you drive it. The difference between this and a canned tune (for the mods you would do for a canned tune) in performance is negligible. Usually this level of tuning is for those going beyond the basics that a canned tune covers. And if you really want to get brave, you can always try doing it yourself with HP Tuners...but this may be out of most people's comfort zone and ability.
What most folks will tell you though is that there is no better performance modification for the money than a tune. You'll feel the power gains even on a stock car a lot more than any other modification on this short list.
- CAI - A Cold Air Intake does almost nothing for our cars. The stock intake is not very restrictive and is able to feed the stock turbo more than adequately enough. However, CAIs (In my opinion) do change the sound of the car considerably. In my 2.4 Turbo, the bypass valve is audible when it releases and the engine tone overall has a more throaty growl to it on throttle. Power wise though, expect very little gains here. And by very little, we're talking -1 to +1 horsepower.
- Exhaust - While there are some gains to be had here in the exhaust, we're still talking low numbers. Maybe 7 hp at best. The stock exhaust is 2.5" and flows very well with only the muffler being the main restrictor...and even that's minor. Most go with a 2.5" aftermarket exhaust unless they are looking for power output at or above 400 whp. Up to that point, a 3" exhaust really gives no gains.
- High Flow Cat - Your catalytic converter is more of a restriction than the stock exhaust. You can go with a high flow version if you want to keep emissions because you happen to LIKE trees or you can destroy the world's air supply with a catless straight downpipe (yes, I'm trying to be funny here).
- Charge Pipes - The stock charge pipes are a bit of a restriction and changing them out will give you a slight improvement in throttle response. Really though, the stock charge pipes look like hell (really GM, you had to crush them like that?!?!?) and going with an aftermarket set of pipes can really clean up the look of the engine bay.
- Larger IC - Unless you've gone with a bigger turbo putting out a lot more boost, a larger intercooler (IC) isn't going to do anything for you. HOWEVER, when you increase boost levels past stock with, say, a tune...the stock IC has been known to start to leak after a while. Now, this hasn't happened a lot, but it CAN happen. Once it does, your boost level drops to nothing and you have to replace the IC. Replacing it with one of the aftermarket ICs from DDM or Hahn Turbocraft would be a wise choice. While they are bigger, the larger benefit is they are built better than the stock units and won't start leaking with the higher boost pressures. If you decide to go with a bigger turbo in the future though or live in hot areas like the Southwest where heat soak in the IC can be an issue, then the larger IC has some performance benefits as it will dissipate heat much quicker than the stock IC.
- Other Mods - There are many other engine mods beyond these such as clutches, bigger turbos, bigger injectors, additional injectors, fuel pumps, etc but these are for when you're wanting to go beyond just the basics and make big power.
- TIRES! - I put these at the top of the list because while all the other things on this list help handling, nothing makes a bigger difference than your tires. The stock tires were marginal when it comes to handling. Most folks on here like the Michelin Pilot Super Sports (PSS). These tires have good road handling, last a decent amount of time, and do not have a lot of road noise. Me, I have Bridgestone Potenza RE-71Rs. They are incredible grip but probably will not last as long as the PSS. Both tires are pretty pricey. You can shop around but do your research and pick a tire that will suit your needs the best. Sticky tires come with a price both in money and tread life. If you're not planning on racing, stay away from tires like the RE-71Rs unless you like replacing them after 20k miles. (which I hope is what I get out of mine...about 10k down and they look like they'll make 20k.)
- Backbone Brace - These next three items are really almost must haves no matter what you plan on doing with your car and we start with the backbone brace. This brace replaces the stock recycled Pepsi can of a brace that runs down the center of your car. There are three types of braces, street, performance, and race...at least I think that's what they call them. Basically, get the one in the middle. The race brace is nice if you want to race the car but the performance (or whatever the middle one is called now) version is perfect for all around driving.
- ProBeam Brace - This brace tightens up the rear end and is second to the Backbone in improving stock performance.
- Front Brace - DDM offers two front braces, a simple Venom brace and a over the top of the engine brace. I like the Venom because while it may not stiffen up the front as much as the other brace, it still gives you good access to work on the engine. If you're not a nut like me and constantly doing something to your engine, then the over the engine brace would not interfere with basic maintenance like oil changes.
- Sway Bars - Our cars handle well stock but GM did make some sway bars that reduce body roll. I had both front and rear Z0K (that's the GM upgraded suspension code) sway bars on my car for a while and people would tell me they couldn't believe how flat the car would corner. I swapped my stock bar back up front for autocross to give it a bit more bite. I liked the Z0K front and rear though for everyday driving. This can really be a personal preference.
- Coil Overs - And if sway bars are a personal preference, coil overs are even more so. Now, I say coil overs but our cars COME with coil overs from the factory so I'm talking about aftermarket replacement coil overs and replacement springs here. Replacement springs basically are just for lowering the car. They are great is that's all you want to do but you will have a bit rougher ride than stock. And aftermarket coil over kit (That's shocks and springs together) will let you lower your car, adjust rebound/compression for different ride conditions, and give you a better ride overall than just lowering springs. If you're not looking to race, then coil overs are going to be a pricey way to lower your car. Good news is that you can set how low you want to go with coil overs. Lowering springs basically lower your car to whatever the springs are designed for and that's it.
Now, if you want to autocross, adjustable coil overs are a real benefit as you can dial in traction front to rear to balance out the car.
That's the short of it. (Really, I swear.) There is so much more to consider here but this should give you a good start. Put together a plan first, how far do you want to go and how much do you want to spend, then you can figure out what mods you need to reach your goal. Once you have that, you can decide which mods are better to buy sooner, and which ones you can wait on until later.
To give you an example of this process I take my current build:
Goal: 400 WHP autocrossing Sky.
Phase 1: 3.0" Magnaflow Exhaust. The 3.0" exhaust actually hurt performance as it was too big but will be better than the 2.5" when making 400 whp.
Phase 2: Coil Overs, Sway Bars, Front, Rear, and Backbone braces. I sold my Grand Prix and used the money from that to get all these.
Phase 3: Turbo, stock intercooler, injectors, wide band, tune. This was the initial turbo build that put a turbo on the car. I started with a 2.4 base model. This phase basically included a lot of modifications but they all had to be done just to get the turbo on the car.
Phase 4: Hahn intercooler. I was able to replace the stock intercooler with a Hahn model. I'm not running high boost now but this will be better than the stock unit when I'm at 400 whp.
Phase 5: Tires. Out with the $89 Chinese specials and in with the RE-71Rs.
Phase 6: High flow Cat and fuel rail. The stock turbo cat I had been using was very restrictive and the new fuel rail fed the larger injectors better.
Phase 7 (which is where I currently am): Return Fuel system. The new fuel rail lasted 2 weeks before I decided that a boost referenced return style fuel system would result in a better idle and more room to grow with my current injectors. Had I planned better, I would not have had to buy a second fuel rail...:facepalm:
Phase 8: Valve springs? I may not need them for what I thought I needed them for but may get them to allow me to increase RPM range. Still researching.
Phase 9: Clutch and lightweight flywheel. My clutch already doesn't like me where I'm at now so this will be a nice little $1,600 upgrade because I'm not putting the thing in myself. LOL
Phase 10: New Turbo. At this point, a larger output turbo and a tune will be the last two pieces to the 400 whp puzzle.
Build time: Apx 3 years.
I know this is a super long post...even for me...but I hope this helps you with your build planning. To do it right, you have to set a goal and then plan how to get there.