If you are the GTI owner, then p!ss off... there are plenty of SS's and wagons that will snack on your little hasenpfeffer and have room in the back to throw the remains to dispose of later.
If you are the the SS owner, then there seems to be very sketchy info about what a GTI runs in the 1/4. It looks to be low 15's, which is in the SS ballpark. Beware though, because it appears that only a few simple mods will drop them at least a second. Fortunately, the same is true for the SS.
Looking at your car:
-Chip: There is no chip. If you are using that Jetchip or other crap like that, throw it away and get a custom PCM tune. This probably will cost less than that other crap and give much better results. I recommend www.pcmperformance.com , but there are many other good (and bad) tuners out there. There are many options on how to "install" the tune and they can explain those to you. A good tune can increase power and fuel economy (when your right foot is not buried into the carpet). It can also raise transmission line pressure to get firmer shifts that will actually lengthen the life of the transmission clutch packs.
- Mufflers: The mufflers are the most restrictive part of the B-body exhaust, so any decent high-perf aftermarket replacement is a huge step up. The next most restrictive parts are probably the over the axle pipes. If you are replacing these, it makes sense to do the whole catback exhaust in 2.5" mandrel bent pipe, and maybe an X-pipe. Headers are a good thing too and many can work with cats to keep you "legal".
- TB/MAF: Without other significant mods, a larger throttle body and MAF are a waste. If you already have them, there is probably no harm in leaving them on.(Here again, if you bought a "chip?" to make these components work, a custom tune will work much better.)
- Air intake: The most restrictive part of the air path before the throttle body is rectangular shaped restrictor; next would be the air filter and box. Most people remove these parts and substitute in a straighter pipe and a cone filter. This is two steps forward and one back. You got rid of the restriction but are now sucking more hot air. There are many good setups that provide some sort of separation between the new filter and the engine bay to limit the hot air. [The big triangular shaped resonator on the top does nothing bad, but most of us think its ugly, remove it, and plug it with something like a hockey puck or a horn button.]
Some things you should consider if you are serious about some street racing:
- GEARS!! Step up to 3.73's. MPG does not suffer that badly and the performance boost is HUGE. (You could 4.10's if you are really serious.) The LT1 is a much higer revving engine than its perdecessors with lots of top end (compared to earlier engines). Be aware that sometimes 3.73's (and definitely 4.10's) will a require a new driveshaft to eliminate resonance problems at higher speeds. When you are having the gears put in, you should think about upgrading the posi unit to a rebuildable unit like an Eaton. The OEM Auburns are not rebuildable, per se, and not as strong as other units. [There is a market for good used Auburns though and you can recover some of the cost by selling it.]
- Torque converter: A good 9.5" torque converter with about a 3000 rpm stall will work wonders with gears to get an awsome launch and still be very streetable. In-city mileage will take a small hit; highway mileage will be unaffected (lock up). A 9.5" torque converter over a stock size 12" torque converter will also decrease rotational inertia and allow your engine to rev quicker. While you are messing with the trans, a TransGo shift kit is a good idea. It will help the trans take more abuse. (WARNING: Make sure your tuner knows that you are installing a shift. There are PCM "settings" that should be brought closer to normal. You do not want to a really high PCM controlled line pressure and a shift kit.) [FYI... if your trans is crapping out, there are several companies that make built-up replacement 4L60E trans for about the same price as many places charge for a stock replacement.]
- Tires: Good sticky drap radials really help the launch but do not last long. There are many brands to pick from that are good and sizes to fit. Many folks change to a 275/40R-17 for a little extra meat and a little shorter tire to improve the final drive ratio. If you get really serious (and start making some bigger hp), you might want to consider going to 15" rims in the rear. This gives more sidewall to flex during the launch to take up some of the shock. Many 15" rims will still fit over stock brakes. (15" rims will not fit over larger calipers and rotors.)
-1.6 Rocker arms and springs: Some folks will argue that this should be the first mod. I have not seen a good buildup comparision to know for sure. I have not done this mod and researched that well, so you should do some digging on your own. The idea to change the rocker arms from the stock 1.5:1 ratio to 1.6:1 ratio. The makes the valves open a little farther when actuated by the pushrods. It's like installing a larger cam without the hassle of taking the engine apart. The downside is that the inertia in the valve train is also increased. [Go back to your 9th grade science and study levers.] This translates to earlier valve float [look it up for more info]. This (and the larger lift) is why you need better valvesprings. You should be some research to decide which springs are best. You can change the rocker arms and valve springs with a small compressor/air tank, spark plug adapter, and a special valve spring tool. You must remove the valve covers (and stuff in the way), but that's about it. Again, a good custom tune will get the most out of this mod.
If you're running a "chip" like Jet or Hypertech, you're already making your car slower. Also running a different MAF and TB without programming for it will damage your transmission. Don't run anything other than a stock MAF, you can use a stock one from a Camaro which is larger but you would need to program for it.
The post above mine has a lot of the basics. You could also use www.pcmforless.com for your tune, I've heard nothing bad about them.
Oh yeah, since your car is going to be running worse than stock as is and you're hurting your trans, expect your car to go 0-60 slower than a stock car which is about 7 seconds, a new GTI is about 6.7 seconds, so be prepared to get your ass whooped by a little shoebox looking car.