The TTA is stock with the exception of a 9" K&N conical filter to replace the factory air box. It made a noticable difference but made my boost go from the factory 16.5 psi to over 20 psi thus creating lots of knock (19-22 deg.). I had to install a adjustable wastegate acctuator to turn it back down, currently its ~16.5-17 psi. The car has 45K on it and the stock valve springs have been found to be pretty much crap from the start. They are supposed to be 90# but prove to be more like 70#. This appears to be evident in the plot as my HP falls off way short of the red line. It should be making max power at ~5500-5600 rpm but maxes out at ~3600-3800 rpm and just goes flat at that point. Also at least one of my plug wires was arcing when you put anything metal near it so I know they are shot (I have a new set of MSD wires to install now). But according to a bunch of the TTA guys the valve springs are a must...1 set of new 100# springs are on order.
As for mods to the TTA there are a few guys still around that have had them from the start and also had a few GN's in there mix as well.
John Pearcy
http://www.johnsperformance.com/ and
http://www.89tta.com/ Julio Don (aka Razzor)
http://www.alkycontrol.com/ Dan McDonald (aka Grumpy)
These three guys are the experts on the TTA and GN/GNX's. I have spent many hours tlaking with them all about my car. They all will give you the same line "keep it simple, avoid the gimicks and the car will fly". The details have long been figured out for these cars so all you need to do is follow their list and you will be in the low 11's at ~124 mph.
By the way ATR is no longer in buisness.
Julio Don's 89 stock appearing TTA ran 10.550 at 132.22, 1.539 60ft 3850 race weight w/driver
Now his car has a few more mods but this is what he told me to do.
Scott,
Keep it simple...
These are must do items.
Engine & Drivetrain
1. Adj. Fuel pressure regulator..get the billet one from Johns.
2. RJC Power Plate
3. Injectors... MSD 50's
4. Chip.. Eric Marshall.. www.turbotweak.com
5. 160 thermostat
6. 100# valve springs
7. You will need a heavy duty WG actuator to go past 21 PSI.
8. 3"MAF pipe w/K&N 8" or 9"
9. Fuel pump.. walbro 340 or equivalnet and hot wire kit.
10. Shift kit. "The Real Art Carr" in California not Texas
11. Tranny cooler.. the bigger the better.
12. 3" Downpipe with cat delete/test pipe w/dump
13. Progressive alcohol injection 
14. Good tires...drag radials
Stock MAF is ok
stock boost control is ok
No trans brake
Leave the stock turbo and converter on the car..until
its time to build the tranny..then do converter and
upgrade turbo to match.
Filter for drivers VC is good thing to do. Locate a VC
in the junkyard from a 3.0 FWD motor.. and some use
the identical covers that are on the TTA.. then put a
filter on the Pass side as well. If you want a
recovery for the PCV.. the AHW machine PCV deal is the
best.
Inside the car..
1. Scanmaster
2. boost guage Autometer 30/30 boost/vac.
3. If you like guages, get an electric fuel pressure guage from autometer.
4. One more item to note, audible knock detector from
Caspers electronics.. for when your eyes are not on the scanmaster.
The above with an engine in proper tune will make the
car fly. Get away from gadjets, big turbo's,
intercoolers, etc... until there is absolutely no
other way around it. The car will go 11.50 or quicker garunteed
HTH
Julio I currently have a bunch of this stuff ready to go so maybe by the end of the Summer I'll get to dyno it again and see what it does then.
Scott
