The supercharger used on all models of the 4A-GZE is an Ogura Clutch Company model TX12, designated by Toyota as "SC12," and features an electromagnetic clutch to disengage the blower assembly when not necessary in order to improve fuel economy. The discharge rate is 1160 ccs per revolution and it is rated at 15,000 rpm and 2.0:1 pressure ratio safely. Also refer to http://www.mr2.com/TEXT/SuperChargerInfo.html
The OEM supercharger used on the 4A-GZE is very similar to a traditional two-lobe Roots-type blower, with the exception of a slightly modified rotor shape. In 1985 this type of Roots blower was already outdated, and delivers compressor efficiencies in the low 50% range under increased boost. Extreme temperature from increased boost and the poor OEM intercooler lead to below-average performance compared to other small-displacement forced-induction motors.
Checking the Oil
The SC unit is pretty durable, but the oil level does have to be checked occasionally. The SC dipstick is towards the back of the engine (towards the trunk), in line with the oil-refil cap on the back side of the supercharger -- low down. It has a small yellow butterfly handle. A flashlight might help locate it. Use a plastic syringe with some plastic tubing -- an old, clean, printer cartridge filler will work.
Pics by seven_mgte and 86AW11 (MR2OC)
Lubricant is Toyota part number 08885-80108, costs around $50 for 50ml. Total gearhousing capacity is 130ml. Some have had success with GM fluid (around $7.50) or Ford (part number E9SZ-19577-A around $10, you'll need 1.5 bottles) -- you need the oil for a "roots type" supercharger.
Supercharger Belt Slippage
Belt slippage is a common problem with the supercharger (refer Supercharger Belt). The problem manifests itself with an intermittent squealing or an air leaking type of sound over a particular RPM. A noticable drop in boost and power is usually observed during the slip.
Lean Conditions on Modified Supercharged Motors
Supercharged motors suffer from a lean condition at low RPMs when boost is increased:
(refer Grunt Box)
Also see: http://mr2.org.nz/mr2/4agze.html
- Oversized crank pulley; HKS, Cusco, NST, ELP, Fensport, Nevo
- Underdrive SC pulley; Speedchaser or late model GZE 10psi SC pulley