This is information I’ve personally gathered from taking apart stock engines over a long period of time. All measurements taken with an accurate digital scale and measurements are in lb.
Note that engines of the same SERIES (year range) can use the same counterweights front and rear, depending on the drivetrain/clutch needed. For instance, an s4 nonturbo engine can run an s4 turbo flywheel with no balance issues, if you wish to install a larger turbo drivetrain behind it. In the same example, the s4 nonturbo and s4 turbo engines use the same front counterweight. You would not want to install an s5 turbo flywheel onto the s4 turbo engine, however.
Anytime you wish to swap rotors in an engine, you must balance the rotating assembly. This is done by matching the rotors to the appropriate front counterweight and one of the 3 options for the rear, which are automatic rear counterweight (used for aftermarket flywheels), small diameter nonturbo flywheel or larger diameter turbo flywheel.
Rotor weights are taken without bearings installed. ON each rotor on the gear side is a weight code stamped, A through E. When matching rotors you should stay within 2 letters of each other, for example B and D are okay but A and D are not. The closer the letters, the closer of a weigt/balance match. For example 2 D rotors are a closer match than a B and a D.
|
84-5 GSL-SE |
86-88 Nonturbo |
87-88 Turbo |
89-91 Nonturbo |
89-91 Turbo |
93-95 -rew/-re |
| Rotor Compression ratio |
9.4:1 |
9.4:1 |
8.5:1 |
9.7:1 |
9.0:1 |
9.0:1 |
 |
|
|
| Rotor apex seal width |
3mm (w/thicker side seals) |
2mm |
2mm |
2mm |
2mm |
2mm |
|
|
|
Rotor
weight |
11.5 |
10.5 |
10.5 |
9.5 |
9.5 |
9.5 |
|
|
|
Front
counterweight |
3.0 |
2.7-2.8 |
2.7-2.8 |
2.6-2.7 |
2.6-2.7 |
2.6-2.7 |
|
|
|
Rear auto
counterweight |
4.2 |
4.0 |
4.0 |
4.0 |
4.0 |
4.0 |
|
|
|
| Nonturbo small flywheel |
25.8 |
23.9 |
N/a |
20.7 |
N/a |
N/a |
|
|
|
| Turbo large flywheel |
N/a |
N/a |
27.4 |
N/a |
22.3 |
20.3 |
|
