PRW LS Swap Flexplate 168-Tooth SFI, TH400 4L80E 700R4

This is the PRW SFI 29.1-certified flexplate, part number 551356X, for bolting a GM Gen III/IV LS engine (4.8L, 5.3L, 6.0L, LS1, LS2, LS3, LS6, LQ4, LQ9 and the rest of the family) to a GM automatic transmission on an LS swap. It carries every common GM torque converter bolt pattern, so one plate covers a Powerglide, TH350, TH400, 700R4, 4L60E, 4L80E or 2004R behind the same LS crank.

It is a 168-tooth plate cut from 0.210-inch steel and rated to SFI spec 29.1, which is the certification tech inspectors look for on a car that runs quick enough to need it. The starter ring engages a standard 168-tooth mini or full-size GM starter, and the six converter bolt holes are drilled on the three common circles: 10.75", 11.06" and 11.5". Six grade converter bolts are in the box; you supply the flexplate-to-crank bolts.

On the bench, torque the plate to the LS crank flange first, then set converter-to-plate clearance before you slide the trans up. One thing worth knowing going in: this is a dished plate, not flat. Behind a TH400 or 4L80E you will usually need to check converter pilot engagement and add a thin mid-plate or spacer washers to get the 1/16 to 1/8 inch of converter float you want, rather than bottoming the converter against the plate. If you are running a non-LS transmission converter behind the LS crank you also need the ICT Billet 551165 hub spacer to space the converter correctly.