Completed Modifications

K&N Filter Induction Performance Kit (FIPK) for less restrictive air intake. Side effects included more engine noise (you can clearly hear the turbos spool up and the bypass valve actuate) and an annoying intake resonance (commonly described as a "hooting owl") that I fixed by installing an aftermarket blow-off valve (see below). This modification was probably good for a few horsepower once the boost controller was installed and the engine began inhaling more air, but I did not think to verify this on the dyno.
Greddy Type-S Bypass Valve (BPV) to keep the turbochargers spooled up between shifts. The stock bypass valve is actually sufficient for normal levels of boost (up to 1.1 bar or so), and the benefit of the Type-S is minimal. In my case, the primary reason for installing this was to eliminate the annoying intake resonance that surfaced after installation of the FIPK (see above). I previously tried the Blitz blowoff valve, but a drawback to replacing the closed-loop BPV with a BOV that vents to the atmosphere is that metered air is purged from the system, resulting in an overly rich mixture when it activates, felt as a slight stumble shorly after letting off the throttle.
Optima Red Top battery. This 1050 CA / 830 CCA sealed spiral cell battery can be mounted in any position and relocated to the trunk if desired. It is also small enough to accomodate most strut tower braces (note that modification of the stock retainer bracket was required for installation). I bought this battery when, after six years of faithful service, the original could no longer supply enough juice to prevent spark blowout at high RPMs. What I didn't know at the time was that my alternator was not only failing to charge at full capacity but draining the battery when parked. The Optima was so strong that it put up with this charging system problem for over two years before throwing in the towel on the way to Le Mans in 2003. I had to replace it with a traditional battery in France to get to the race and back home for proper repairs, but I will definitely buy another Optima when the time comes - most impressive!
A'PEXi Super AVC-R electronic boost controller to safely allow higher boost and produce more power. I like this unit because it is truly "fire and forget:" simply set the boost pressure limit and the boost actuator duty cycle (BADC) and the unit learns the boost curve automatically. Two different limits can be set and toggled between on-the-fly. The display shows current boost pressure and injector duty cycle (IDC) as digits or a bar chart. The boost pressure reading is accurate and eliminates the need for a separate gauge.
The BADC setting provides the unit with an estimate of solonoid activity necessary to achieve the desired boost limit. If it is set too low, the unit may never achieve the desired boost pressure, regardless of how long it tries to learn. If it is set too high, the desired boost pressure will be exceeded temporarily, and again the unit will have difficulty learning. This is puzzling to me, as the algorithm should be straightforward:
```
check pressure
  if below threshold then close wastegates
  if above threshold then open wastegates
repeat
```
Another annoyance is that this unit does not work at high altitudes. When driving in the Alps, the unit shuts itself off above 5-6k feet, limiting boost to about .5 bar. A'PEXi customer support has verified this behavior but offers no solution. Now that I live in the UK, this flaw is not a concern, but replacement will be necessary if I move back to higher ground.
If you're in the market for a boost controller, the latest offerings from A'PEXi and Blitz are much more flexible, but with capability comes complexity and some might find them a bit harder to set up properly. At any rate, a boost controller represents the absolute best bang for the buck investment, but if you're not careful, BANG is exactly what your engine will do!
A'PEXi turbo timer to keep the engine running until the turbochargers cool down. I would have preferred a turbo cool-down device that was temperature based, but such devices are too expensive. Blitz offers a model that computes cool-off time by monitoring boost activity before the ignition is switched off, a nifty idea. My unit is basic can be set to keep the engine running for a specified time period, which works fine. I normally leave it set for 30 seconds but bump it up to several minutes after an exceptionally hard drive.
Note that it is tricky to wire a turbo-timer without disabling convenience functions such as passive alarm activation, keyless entry, automatic headlight shutoff, power antenna retraction, etc. Eric Gross offers some good tips on his Turbo Timer Installation web page for those interested in this modification.
Redline Shockproof fluids for smoother shifting and less drivetrain loss. I have MT-90 in the transmission and transfer case and ShockProof Heavy in the rear differential. The difference from stock was subtle at best. Some have expressed concern that these GL-4 fluids may be too aggressive for the brass synchronizer blocking rings, but after discussions with Redline, the community is confident that this is not an issue. After 50k miles with these fluids, I have observed no abnormal or premature wear.
Magnecore wires for better spark. I had these installed with the first major service at 50k miles. They didn't make any difference as far as I can tell, but perhaps they would have allowed a spark plug gap wider than .034.
Spark plug cover plate made by EK2MFG and finished by Dave Best. This is just something neat that some fellow Team3S members designed and sold.

Yokohama ES100 245/45WR17 Ultra High-Performance Radials. These are widely regarded as the best match for this platform in this price range and hands-down superior to the expensive all-season radials previously on my car.
When it comes to upgrading the brakes for the street, the best bang for the buck is Porterfield cryo-treated rotors (solid, not cross-drilled!) with Porterfield R4-S pads (see above), which served me well for years of driving on the Autobahn in Germany. When I moved to the UK and began participating in track events, R4 racing pads worked very well but there was evidence of overheating. After abnormal brake failure at Donington Park and a sheared stainless steel brake line in the left-rear caliper, I decided to order a four-wheel StopTech upgrade from Supercar Engineering. The kit includes massive calipers with custom-sized pistons (to balance front-rear bias) squeezing cryoed 332x32 and 322x28 rotors on floating hats, the rear hats having integrated parking brake drums. Titanium backing plates protect the caliper piston seals, and stainless steel lines maintain pedal feel when the fluid gets hot. The pads are a standard size used by Brembo, Porsche and others, so options are plentiful and reasonably priced. This kit was built to my specifications and served as a prototype for StopTech's official off-the-shelf front kits for the Stealth / 3000GT platform and for a retail four-wheel kit from Supercar Engineering.

Here are a few pictures comparing the rotors and pads with stock 2nd gen. Here are a few installation notes. Based on my experience with this kit, here are a few issues to consider when deciding about brake upgrades.
While my stock 2nd gen 17x8.5 wheels will accommodate the brake upgrade, a second set of rims eliminates the need to remount tires for track events. Though it is easier to find 18" rims with the necessary caliper/spoke clearance, fewer track tire options, higher cost and compromised handling and durability make 17" a better choice. I decided on "hyperblack" Enkei RPM2 17X9 5-114.3 40mm 18.7 lb rims wrapped with Yokohama A-032R 275x40R-17 H-compound competition tires.

For those preparing to accept the wheel fitment challenge, avoid frustration by reviewing Greg Wurst's stock wheel fitment guide and the 3SI Wheels gallery.
Engine monitoring is critical for tuning and general diagnostics, and while various data loggers for OBD-I models (1991-1993) have been available over the years, no solution was offered for the hybrid ECU models (1994-1995) until very recently; Mirage Computers, Inc. began selling data loggers for Palm M-series PDAs in spring 2004! It works great with my m515 and provides an indispensable look at engine behavior. If you have a 1st gen car with OBD-I ECU, check out Dmitry Yurtaev's open-source (GPL license) Palm data logger. What I'd really like is a configurable dash that would allow me to decide what to monitor and how. Here's a quick image depicting what I have in mind.
Many folks feel that the stock exhaust system is too restrictive and should be replaced with an aftermarket alterative. However, dyno testing reveals that the stock exhaust actually flows quite well and that such an investment is not necessary unless boost is increased drastically. The biggest restrictions are the precats, the main cat and the downpipe, in that order, and replacing each is necessary for the others to make much of an impact. When my stock downpipe developed a leak in the flex section, I replaced it with an EK2MFG downpipe that offers two 2.5" pipes mandrel-bent into a 3" pipe for improved flow over the stock tee connection. It bolts up to all three cats for emissions or to precat eliminators and a test pipe for the track. Other options are reviewed in John Monnin's downpipe comparison; while all improve upon the stock tee connection, most eliminate the front precat (emissions risk) and lack one or both flex sections (complicates installation and could crack headers as engine mounts age). For more information, take a look at Erik Gross' page.

The stock cat-back system flows nearly as well as aftermarket systems, and the selectable exhaust valving becomes increasingly important for volume control as restrictions upstream are eliminated. Still, stainless steel exhaust systems sound good and save weight, so I may pursue it eventually. The Borla system is relatively cheap and sounds fantastic outside the car but has an unacceptably annoying resonance in the cockpit between 2k and 3k RPMs where the car is driven most often. Borla customer service provides inserts to address the irritating drone (while restricting flow!), but owners report that they are ineffective. The HKS exhaust is a similar design and has no resonance but reportedly suffers from fitment problems. The Greddy system is more expensive and higher quality, flowing just as well (some say better), great sound, no resonance, but exits on only one side of the car (aesthetically not as pleasing). Another option would be to design a custom exhaust system, which would have the added benefit of maintaining the stock appearance, with dual tips on both sides rather than the ridiculous coffee cans that come with most systems. Someone else on the INTERNET Stealth/3000GT group made a similar modification; compare my stock exhaust sound (29k) to the modified exhaust sound (27k).

Planned Modifications

The American-spec cars have injectors that max out at around 6000 rpm when running 1.00 bar of boost. The stock fuel pump also runs at a reduced voltage at low RPMs, which may explain detonation issues in that range when running higher boost. Though I observed acceptable air/fuel ratios during my dyno session (i.e.- the mixture is not leaning out and causing a dangerous situation), I will soon install a Denso Supra fuel pump with hotwire kit that provides full voltage at all times. Since the increase in volume would overrun the stock fuel pressure regulator, I will also be installing an adjustable FPR. This sets the stage for upgrading from the stock 360 injectors to the European 440 or even bigger 550, 560, or 720 injectors and fuel controller to support larger turbos.
Folks with substantial engine modifications complain that the stock clutch slips under hard acceleration. Some aftermarket clutches offer more holding power, but usually at the expense of drivability, transmission load and clutch longevity. With my more standard mods, the stock clutch (with 100k+ miles on it!) works well under all but the most aggressive launch conditions, so I plan to replace it with stock parts. Here's a page showing clutch, synchro and seal parts for the Getrag W6MG1 (which Dodge and Mitsu claim has no user-serviceable parts and must be replaced in its entirety!).
One of the biggest problems to overcome with these cars is getting cool outside air to the intake. The engine compartment is so tightly sealed that the engine struggles to draw in even the hot air available to it. It is amazing how much power increases when the car is driven with the hood popped. I have some ideas on how one might design a custom cool air intake system and I hope someone markets an effective solution.

Previous Modifications

Michelin Pilot XGT-Z4 245/45ZR17 Ultra High-Performance All Season tires. In general, these are an improvement over the Pirelli P7000 they replaced; the Pirellis were a little better on dry tarmac, but the Michelins wear longer and stick better in adverse conditions, important while living in Europe. I'm now on my second set, the first having lasted just under 50k miles. The new set have worn well through two track sessions, one dry and abrasive and one wet and slick. This model has been replaced by the more expensive ($50 more per tire) Sport A/S, though I managed to find the XGT-Z4 several months after the new ones were on the market.
Bosch winged wipers to keep the blades from bowing away from the windshield at higher speeds on the Autobahn. I actually am not too happy with these blades. The force of the wind on the blade wing makes it very difficult for the wiper motors to return the blades to rest position, and they don't seem to wipe the water from the windshield that much better than regular blades.
Custom stainless steel braided brake lines for safety and to eliminate brake sponginess. These were custom made for Mikael in Sweden, Roger in Switzerland, and I in Germany. I couldn't feel much of a difference on the street after installation but am confident they help maintain the firm pedal feel I enjoy at the track despite elevated brake fluid temperatures. Also, there is very little chance of failure with lines like this.
FIRST: Stillen Metal Matrix brake pads for better braking and less brake fade. These pads wear faster than stock and create more dust on the wheels but improve braking from high speeds on the Autobahn. The stock rotors continued to warp with these pads.
SECOND: Porterfield R4-S pads with cryo-treated discs (Brembo blanks) for better braking and less brake fade with no warping!! These pads are slightly less effective than stock until warmed up, but then they grab much harder. Moderate dust. These pads were not effective at track temperatures; I had much better luck with R4 pads up front and R4-S pads out back. I had the calipers stripped and painted when the rotors were installed. This was not cheap, but it really cleaned them up and I think they look terrific.

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