ACT XACT B-Series Streetlite and Prolite Flywheels

ACT XACT B-Series Flywheels: 600110 Streetlite and 600105 Prolite

You've got a clutch job planned for your B-series Integra, Civic Si or del Sol VTEC, and the flywheel choice will affect how the car feels long after the gearbox goes back in. ACT's 600110 Streetlite weighs 12.2 lb. The 600105 Prolite brings that down to 8.7 lb. Both are one-piece forged chromoly steel, with the same 112-tooth ring gear and 220 mm friction surface.

Choose for the driving you actually do

Streetlite is the starting point for a car that still does the commute. ACT recommends it for street and race use, with street or drag racing as its preference. You aren't choosing the lightest option, but you also aren't taking on Prolite's stated reduction in driveability just to save another 3.5 lb. ACT describes Streetlite's gear rattle as OE to mild.

Prolite makes more sense when you're putting together a road-race or rally car and engine response takes priority. It's ACT's lower-inertia choice, with reduced driveability and mild to moderate gear rattle in its description. That doesn't make it the automatic upgrade over Streetlite. If you're regularly creeping through traffic, weigh those compromises against the response you're looking for.

A lighter flywheel stores less rotational energy. Engine speed can change more quickly, but you've also got less stored energy available as you pull away. Your clutch disc choice changes the picture too: a street disc and a ceramic race disc won't give you the same takeoff feel. Choose the pair around the car's use rather than chasing the lowest flywheel weight by itself.

Steel construction and later servicing

These aren't aluminum flywheels with separate friction inserts. ACT starts with a heat-treated chromoly steel forging, CNC machines it and dynamically balances the finished flywheel. The induction-hardened ring gear and friction face are part of its one-piece construction. You can have the face resurfaced within ACT's limits when it needs cleanup, without buying a replacement insert.

Prolite is still a steel flywheel. Its lower weight doesn't change the material, ring-gear tooth count or listed friction-surface diameter. ACT lists SFI 1.1 for both versions.

Verified manual applications

A 1995 del Sol Si and a 1995 del Sol VTEC aren't the same application. These flywheels are listed for the B16-powered VTEC model, not the SOHC Si. The same care applies to a swapped Civic: the badge on the trunk won't identify the engine, gearbox or clutch you've installed. Check that actual combination before choosing either flywheel.

ACT lists both flywheels for the 1990-1991 Integra as well as the later B-series applications, but that doesn't make every B-series clutch disc interchangeable. Match the clutch to your transmission and verify its fit against the flywheel. These aren't K-series flywheels, and automatic cars aren't covered.

What comes with it and what to check

You get one selected flywheel. The clutch is a separate purchase. Follow ACT's installation instructions and the fastener specifications for your application; don't transfer assumptions from a different engine or flywheel. The flywheel step sets the relationship between the friction face and pressure-plate mounting face, so keep that dimension correct.

For later resurfacing, ACT calls for a flywheel grinder and no more than 0.040 in / 1.02 mm of material removal. Have the machinist remove only what's needed for cleanup while maintaining the proper step. That maximum isn't permission to take another 0.040 in off at each clutch change.

ACT provides a 12-month limited warranty under its published terms. Keep your receipt; installation labor isn't covered. Both part numbers carry a California Proposition 65 warning.