Audi Coupe GT
I purchased my 1986 Coupe GT in 1993, after having owned a same year Honda CRX Si.  While the CRX was a nice car, it did not instill passion. I also wanted to move a bit 'upscale', since most of my automotive endeavors had so far been inexpensive cars. I narrowed the choices to either the Audi Coupe GT (a car I had always liked, thanks to a neighbor who bought one new) and Alfa-Romeo GTV6 (I was working for an Alfa dealer at the time). After careful consideration, I had to admit that the Audi would be more practical for living in PA, thanks to our snowfall and subsequent road salt that would have quickly eaten the body of any Alfa. I was fortunate to find this car which I believe to be a one owner example from Maryland.
Originally this car was my daily driver, and also was pressed into duty running TSD rallies.  As with most of my cars, I replaced the dull stock wheels with aftermarkets, this time 14x6 Revolutions.  I chose this application as the Revolutions are very strong, have powder coated finish (except the rim lip) and are quite affordable.  I didn't go different from stock on the size as I wanted to maintain odometer accuracy and a high sidewall for the mostly gravel rallies I was competing in.  While a good idea at the time, I've since changed to 16" Team Dynamics for a better appearance and track duty.  The 60 series tires simply couldn't handle the nose-heavy car on the track no matter what pressures I ran. 
Due to getting a company car and some other vehicles, the Audi has sort of semi-retired from regular duty.  I only planned on keeping the car about four years when it was purchased, but the longer I've owned it the more enjoyable it has become.  I just haven't found anything yet that seems to fit me and handle with the feel I like.  Other 'CGT' owners will tell you the same thing.  So, since it appeared to be a permanent resident, I decided to blow unredeemable quantities of money on it to try to make it just a little bit better.
The first thing I did was toss the stock exhaust. I nearly danced with glee when the middle muffler rusted out and I had an excuse to replace it. I priced a few aftermarket systems (what few there are) and was appalled at the cost--$550+.  Considering the likely hp gains (minimal, and nobody could prove anything) I just couldn't see the money for stainless steel you can't even see.  So, I shopped around locally, and found a shop that was doing a lot of custom exhausts for VWs.  I showed him what I had, and told him what I wanted in sound, flow and quality.  Quite honestly I didn't expect much, as the bottleneck in the system is the catalytic converter, and not much else will fit where it is. He recommended a Magnaflow muffler and 2.25" piping from the converter back, ditching the factory resonator completely. It took a half day for him to create, uses all the stock hangers, is completely aluminized and cost me $200 installed. The Magnaflow gives the deep growl I wanted and isn't ricey at all. While I am reluctant to say it with no proof, my butt-dyno indicates the car has more power, and it's a real treat to drive with the windows down. It makes nice counds without being intrusive.
The next upgrade I was told wouldn't make much difference, but it was something I wanted to do just to say I did, and wasn't really expensive.  The 1987.5 CGT's came with rear disc brakes, replacing the rear drums as on all previous Coupes.  They also got a better engine, which I'll get to in a minute.  Those 87.5 CGT's are like hen's teeth, especially in the wrecking yards.  However, there is another solution.  The Audi 80/90 which replaced the 4000 (on which the Coupe is based) uses the same rear axle.  I found an axle assembly off an Audi 90 (the 80 I believe still uses drums).  It helped that I was friendly with this yard through my work as I was able to get the axle complete with calipers for $125.  These cars are starting to turn up in the U-Pull-Its though so you can probably duplicate this effort for about the same figure.  The only new parts I had to buy were the parking brake cables, which are unique to the disc brake CGT.  I was able to re-use the CGT brake hoses after making new steel lines, and I only had to do this because the axle was from an ABS equipped car. There are also some sleeves and brackets that need to be removed from the ABS axle for everything to fit, but it's surprisingly easy.  While the website I link to below says you need a proportioning valve and e-brake parts, that only applies to the older single cable e-brake cars. The proportioning valve I got from the 90 model is identical to the CGT one, and I didn't even alter the spring tension after installing.  Everything works fine, and you can definately tell a difference in the braking.
As seen above, I performed an engine transplant. This was a big job as I replaced the trans at the same time due to a worn 2nd gear syncro that was just annoying and I found a low mileage replacement for cheap.  The engine is a 2.3 from a 1987 Audi 5000 which is the same as a 87.5 CGT.  It has higher compression and larger valves than my previous 2.2 and puts out 135hp stock vs my 110.  This may not sound like a lot, but for someone willing to just swap engines with a used one it's a good value.  I'm dumber than that...
I actually blew a huge wad of money rebuilding this one as the mileage was unknown, and I preferred a fresh engine anyway.  Parts, even at a deep discount, were still expensive, and I don't recommend it to anyone unless you want to spend as much as your car is worth.  In addition to the rebuild, the flywheel was lightened, head ported and flowed, completely balanced throughout, coated piston skirts and stuff I don't even remember. Pretty much everything one can do and still be SCCA legal.  I'm hoping to get 165 or so hp out of it...I may be dreaming, but I'll dyno it to find out.

Why not a turbo?  I also considered doing the popular turbo conversion. This is pretty common on 4000 quattros, especially rally cars.  The Ur-Q is too rare to scavenge for parts, but the 5000 turbos are fairly plentiful as donor cars. I chose not to do a turbo conversion for a few reasons:
1)  turbo lag and little bottom end power from the big KKK turbo
2)  heat dissipation
3)  intercooler location is a problem
4)  retaining my a/c system would have required some engineering I wasn't sure I could do
5)  too much power for fwd?  (not really a concern, but something to factor in)
6)  several key components for the normally aspirated engine upgrade were already in my
    posession, and I wasn't looking to build a monster car anyway

I wouldn't discount the turbo swap for the CGT at all for those looking for real power, though there is some engineering and special parts needed to do the swap.  There are a few good sites on the web detailing how it was done on the quattro sedan, and this information would carry over to the CGT as the front of the car is identical. Due to the lack of speed parts for the 5 cylinder, coupled with the high cost of building an engine, the turbo is definately the faster/cheaper way to get the most power.

Page two click here.  The engine swap is completed + more interesting stuff.
Pages for Coupes are few and far between.  Most sites are geared towards quattros, and a lot of the information carries over.  I used to have a good 8 or so links listed here but they have all vanished save for one.
The Coupe with Revolution wheels
Trivia:  The Coupe GT is not a quattro, it is front wheel drive.  There was a model with the same body sold in europe as the Coupe Quattro. Here in the USA you could buy the Turbo Quattro Coupe (or Ur-Q) for a few years, which looks similiar but has bulged fenders and 5 lug wheels.
Quick Tip:  The fast and inexpensive way to fix excessive body roll on the CGT is to replace the stock front sway bar with one from a 4000 quattro sedan.  It is much larger diameter and bolts up perfectly.  I paid $10 for mine from a salvage yard.
Links    
Huw Powell's excellent Audi upgrades & repairs
7/17/00   Perfectly good engine removed, stunned I could do it myself!
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