AE86 Light Tuning Guide
The first Toyota to feature the 4A-GE, the AE86 Corolla/Sprinter retains great popularity around the globe for it's balance and pure fun of rear-wheel drive configuration. The following are guides to making the best of AE86.
The AE86 is now over fifteen years old. Before starting on any suspension modification, the most important step is to refresh and renew all suspension bushings and weak joints and welds. Without this, none of the expensive modifications will come to any fruition. Be sure after any modification or installation, check the wheel alignment ...important!
Basics in Suspension - Streetable Performance
Strut tower brace are almost a necessity in making the inherently weak body structure of the AE86 to respond to the sporting inputs of weight distribution. The front bar makes the turn-in smoother and more predictable. Any of the two-point braces available commonly are fine.
Shocks and Springs should be set to whatever you choose your AE86 to do. For general purpose of fun for the street, use springs no stiffer than 6kg for front and 4.8kg/mm for the rear.
The spring rates are generally a matter of personal taste. The general rule of thumb is softer spring for less sticky tires... and stiffer for more aggressive grip tires. Set the spring and shocks to use about 80-90% of stoke at maximum g-force the tires generate. Reserving the last bit to compensate for road irregularities and severe weight inputs.
Shock absorbers should be chosen to dampen the movements of the suspension. It should work to stabilize the car's movements and not to inhibit it. Shocks that are too stiff will prevent proper suspension stoke speed and will create more understeer with lack of speed in weight transfer to the front. The 5way adjustable Tokico Illumina shocks work fine for street use. TRD 8 way is nice too with smaller increment settings for track use. Oil shocks tend to be more predictable than gas charged shocks for sports driving. The gas shocks tend to rebound quickly and cause loss of traction easily during faint motion and switch back from one side load to another.
Anti-roll bars or sway bars are used in conjunction with the springs to offset the cornering load and prevent excessive lateral body roll without affecting fore-aft pitch.
Engine - Before getting crazy...
To fully utilize the AE86's balance, the engine need not be heavily modified. As a matter of fact, many experienced drivers prefer the 4AG at mildly tuned 140hp or so. The most important part of this is to remember that the AE86 was not designed to handle much more than 140hp. The chassis is flexible compared to the current batch of new cars and the more power you feed it, the more the deficiencies in the chassis becomes apparent.
The first step in tuning the 4AG for light duty is to inspect the motor itself, the 4A-GE if built and maintained should last a fairly long time, holding much of it's original output for many seasons. The crucial and the most important element of the 4A-GE is it's esthetics. The sound, the response, and willingness to be revved. Yes, this sounds like a all-show, no-go talk...but when any of this is missing from a 4A-GE, it seems lifeless..
Check, inspect, and rebuild if necessary...When all is well, it's time to move on and add flavor to it.
A popular conversion for many import seem to be air cleaner and exhaust. Yes, go ahead, it helps to do this, unlike many newer engines, this does add response and top end power. (Honda B16 engines actually lose power when the air box is replaced by some free-flow filters!) A free-flow filter system should be added when using free-flow exhaust. (makes sense huh?) For near stock applications, do not go more than 10mm oversize on muffler systems. The exhaust should breathe out enough gasses to not restrict engine's breathing, not more. Its should act to maximize flow speed at any given speed. The filter should be chosen to match your exhaust's character. Always locate the intake so it gets cold air from outside.
A lightened flywheel greatly improves response of the 4A-GE and should be used for any engine that will see road racing and autocross. However, using excessively light units will be a de-merit, as you will lose inertial torque which is necessary to maintain engine speeds when shifting to a higher gear or dealing with loads of drivetrains. Choose the flywheel wisely, lighter for more response, and heavier for more stable power transfer.
ECU (Electronic Engine Management Processor ) is what determines the functions and parameters of all the peripherals and devices for operation of the motor. A factory OEM ECU contrary to popular belief, is actually a very efficient unit. It is essential to work initially from this OEM spec. There's always a question from people asking which "chip" gives the most horsepower... This is actually a silly question because the chip, or the ROM software is written for a certain application and in many cases do not fit your requirements. For example, the HKS "chip" should be used with the HKS's menu of components to give close to the specs they advertise. Otherwise, the specs can differ greatly. Mapping your own fuel/timing curve and various sensor inputs can be tricky and dangerous. You should always consult professional tuners, not backyard mechanics or salespeople. Overall, the OEM works quite good for many light tune applications and if need be, can be adjusted with piggy back systems which work in conjunction with your OEM ECU. Always use a fuel map professionally created for your engine. Your friend's 4A-GE... set up exactly the same, will still have slightly different requirements than yours.
Unlike suspension upgrades, modifications to the engine should be applied very cautiously, often a small mistake in a vacuum line hookup or ignition timing will send the ECU into malfunction mode and results can be very costly and disastrous. Watch exhaust gas temperatures, A/F ratios, injector pulse, timing maps and most of all, listen for detonation. If you are not familiar with any of these terms, don't attempt anything.