The Ideal Solo 2 AE92 GT-S

I've had the pleasure of regularly autox'ing my GT-S for almost 2 years now. In that time, I've noticed certain major areas of the AE92 chassis that need special attention in order to become competitive. Most of these items are common in other SCCA Street Prepared (SP) classes/cars, but since no one that I know of has plans of seriously prepping the AE92 GT-S to the full extent of SP class rules, I guess the task of sharing the info to prospective competitors driving the AE92 falls on me.

You'll find that a vast majority of the following components aren't that flashy, are fairly basic, and most of all, actually make a positive improvement in vehicle performance specific to the Solo 2 time trial environment.

• Completely Built 4A-GE Small Port
  If you've been reading up on the different 4A-GE motors, you should know by now that the '90+ small port motors have a broader torque band (starts a lot lower than the large port motors), higher compression pistons, the same bulletproof bottom end, and the infamous piston oil squirters. What we're really interested in is the faster response from the high comp pistons and the improved intake charge velocity which makes for a nicer torque curve. Since Solo 2 courses usually have a variety of corners speed-wise, having the ability to power out at will is a must. The large port motors have fair bottom-end torque, but they tend to pull harder than the small ports at the top end. If you have courses that are designed just right such that you're always past 5000 rpm in any given gear, it isn't such a penalty to have the large port motors. That said, I'd take the small port any day because you just don't know what kind of course layout you'll see. Obviously, building the motor to include a rotating and reciprocating mass balance job, port matching the intake and exhaust ports to their respective manifolds (one inch max from the interface per SCCA SP rules), and setting the valve clearances uniformly/correctly. Going with a nice set of individual throttle bodies (e.g. TWM Induction or the 20v 4A-GE throttle body kit) on the high comp motor will yield more benefits than on a low comp motor.
• Fully Programmable ECU
  Since you're already using the individual throttle bodies, you'll need a nice, aftermarket programmable engine management system. I've been checking out the specs of the big brands out there (MoTec, Electromotive, Haltech, DEI, and an oft-unheard of FJO), and I would pick the FJO 341B for its value and performance capabilities. MoTec is obviously a nice system, but its price is a bit high for what you get, in my humble opinion. DEI seems fairly basic after looking at its specs and doesn't allow too much flexibility for future mods/upgrades. The Electromotive TEC-II and TEC-III systems are pretty much the industry standard for grassroots motorsports and there are lots of highly capable tuners out there. The FJO costs about the same as the TEC-III, is more powerful, and has lots of room to grow with your needs. High-revving, high comp, naturally aspirated motor? Twincharged (supercharged and turbocharged) motor? Either of the former plus variable intake systems? It's got it all covered.
• Lightweight Flywheel
  Less mass for the engine to accelerate is always a good thing. The stock flywheel on the AE92 GT-S weighs in at 18 lbs. You have a decent choice of manufacturers to choose from; Fidanza (the most popular for anyone with a 4AGE-powered vehicle in the U.S.), Toda, Mueller Fabrications, and HKS.
• KBD Exhaust Header
  It's been dynoed to give anywhere from 3-6 extra horsepower. Plus, it's lightweight; maybe a third of the stock manifold. Increases bottom-end torque, yet it lets the engine breathe better at the top end.
• Shortened and Mandrel-Bent 2" Exhaust System
  Since this is an autox-only car, you should have ditched the catalytic converter a long time ago. The SCCA General Competition Rules (GCR) book specifically states that all exhaust systems must terminate behind the driver and not be too loud. Easily done... Take the KBD header's outlet pipe, mate a custom-made, mandrel-bent 2" system with an inline muffler (you can find some that will fit in the "tunnel"), then make it exit directly in front of either of the rear wheels. I'll probably make mine exit on the right side, just so I don't get deaf from the exhaust tone. Imagine the weight savings and increased exhaust flow since you don't have to pipe it over the rear suspension subframe.
• Completely Rebuilt C52 Transaxle
  The C52 has a reputation for chewing up its mainshaft bearings and 2nd and 3rd gear synchros. And that's on the street! You can imagine how much worse things can get in an autox environment with the lightning-fast shifts, severe dynamic loading, and wide range of speeds. Get a surplus C52 tranny, tear it down completely, replace the mainshaft bearings and 2nd and 3rd gear synchros, and shim everything on the tight side of spec. That should make for a bulletproof tranny that'll take any abuse you can dish out. Notice that I didn't mention buying a new C52 transaxle assembly from your local dealer--unless you shim the clearances yourself, you don't really know how well the "new" C52 will hold up.
• Quaife ATB LSD
  Since the AE92 GT-S has a FF drivetrain, it inherently asks a lot of the front tires--acceleration/deceleration while trying to maintain the lateral acceleration. While taking a corner, the outside front corner will experience a much higher load than the inside front corner. With an open differential (which all stock U.S. C52s have), the power will be applied to the inside wheel and just waste it. What it should be doing is applying it to the outside wheel since it's already loaded and hooked up to the track surface. The Quaife automatic torque biasing (ATB) limited slip differential (LSD) does just that. Now, instead of feathering the throttle from the apex to the exit, you can judiciously romp on the throttle much earlier and carry more speed at the exit. Quaife's application for the C52 is also the same as the unit in the earlier Mk 1 (AW11) non-supercharged MR2's C50 tranny, so you shouldn't have too hard a time locating one.

• Advance Design Double Adjustable Coilovers
  I've had a chance to try out different suspension systems on the AE92 GT-S in an autox environment. While I had very high hopes to get the Tein HA coilovers for my car, I was surprisingly (and sadly) disappointed that they weren't as nice as I had thought them to be. Don't get me wrong--they're fantastically great coilovers. But, I felt that the valving could've been better, particularly on the compression side. My friend's GT-S felt a bit too soft for me. As usual, your ride preference will differ. The Koni Sport adjustable struts feel like they have slightly stiffer compression valving than the Teins. The problem is that using too high of a spring rate (we're talking 350+ lbs/in) up front will blow out the compression valving on the Konis. The solution? An expensive one, I'm almost sorry to say. Head up to the Sacramento area in California, and have the suspension gurus at Advance Design/Ground Control build you a custom set of coilovers. You'll need to shorten the Advance Design strut bodies for the front end. Unmodified, the front strut bodies are only 0.75" (~20 mm) shorter than the front Koni struts. You'll need to shorten the Advance Design struts at least 1" (25.4 mm) to re-gain the compression travel that's lost when you drop the ride height. These struts are also double adjustable which means you can adjust both the rebound and compression valving individually. Just supply your suspension engineer with some basic info about your car (weight distribution, spring rate, type of racing, etc.) and you'll be able to ideally custom-match the compression and rebound valving to your car. The best thing is that you can rebuild the struts yourself--no need for extended downtime and costly rebuilds at the shop. Just buy the rebuild kit and do it yourself in the comfort of your own garage! Neat, huh?
• Whiteline Bushings
  Chances are your stock bushings have crapped out a long time ago. Let's not forget that the 1988 model year is already 14 years old! Anyway, new bushings will do a better job of preventing unwanted dynamic suspension geometry due to deflection.
• Front Camber Plates
  Like most FF econoboxes being autox'ed, the AE92 lacks the front camber to fully utilize R-compound tires. I've found that -2.5° to 2.75° of camber up front is ideal. You won't get those numbers without modifying the suspension somehow. Camber bolts are a simple, inelegant, cheap solution. Beware though, because they can easily loosen up the slightest amount and mess up the camber settings. The ideal solution is to get a hold of some camber plates.
• Upgraded Anti-Swaybars
  Since your chances of finding a set of TRD bars are pretty low (they were discontinued as of early 2002), you'll have to resort to the Whiteline/Selby bars. You even have the choice of a fixed or adjustable rate rear bar! Definitely always a good advantage if you drive on surfaces with differing levels of grip (high grip concrete or low grip asphalt).
• Upgraded Brake System
  This is an easy one... Porterfield R-4S or Hawk HP-Plus pads, a quality set of rotors, stainless steel braided lines, and high quality brake fluid (Motul or Castrol). If your car's like mine and has 239,000+ miles on the clock, you should rebuild the brake calipers and make sure everything's in tip-top shape. If you get a chance, remove the front brake shields as the rotors will need more exposed surface area to the ambient air.
• Wheels & Tires
  Get the lightest set of 13"x7.5"-8.5" wheels that you can afford. Why a 13" diameter wheel/tire? It effectively shortens the tranny's gearing and helps the engine rev faster. Some choices are Volk (custom order from Japan), Keizer, Duralight, Lenso, and Panasport. Slap some Hoosier A3S03 225/45/13 tires on 'em and you'll have one of the lightest possible wheel-tire combos. Less mass to accelerate, remember? For rain tires, get the Kumho 235/45/13 ECSTA V700 tires. These tires weigh about twice that of the Hoosiers, but their increased tread depth is a must on a wet course.

• 4-, 6-, or 7-Point Roll Cage
  Unless you've completely stripped the car down to its unibody frame and re-welded the seams, your car is prob'ly on the flexible side of things. This can make the handling slightly unpredictable; you may have a hard time setting up the suspension because of this. Although a roll cage really isn't necessary for closed cockpit cars competing in Solo 2 events, it is a quick solution to stiffening up the chassis. The problem is that high quality, complete bolt-in roll cages for the AE92 chassis aren't readily available in the U.S. You have to pay upwards of $800 in Japan, then spend another $300-$400 to ship it here. You might be better off taking your car to a race fabrication shop. But, if you're looking for a nice cage, I'd recommend the Safety 21 7-point cage. I'm gonna get one of the local race shops to add a removeable crossbar on the main hoop for the harnesses, seatback brace, and in-car video camera mount. The entire cage weighs in at approximately 65 lbs.
• Lightweight Race Seats
  I've had my eye on the Sparco Evo seats for a while now. I'm a skinny guy and these seats are the only ones out there that comfortably support me. Even more importantly, they weigh in at ~15 lbs. each.
• 4- or 5-point Harnesses
  Keeps you safely restrained in the seat. Period.