Engine Pro Sportsman Series SFI 29.1 flexplate on a white background, front view, with its factory certification sticker

Engine Pro releases Sportsman Series SFI 29.1 flexplates and bolt kits, including an LS plate

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Today’s Daily Planet by Planet X Performance

Engine Pro has released Sportsman Series SFI 29.1 flexplates and matching bolt kits, Engine Labs reported Oct. 9, and the lineup includes an LS plate.

A flexplate is the thin plate that bolts to the back of the crankshaft on an automatic. The starter turns its ring gear (the toothed outer edge), and the torque converter bolts to it to carry power into the transmission. SFI 29.1 is the SFI Foundation’s safety spec for flexplates.

The problem: in a built or boosted automatic, the flexplate becomes a safety part. NHRA’s 2025 Hot Rod rules require an SFI 29.1 flexplate on automatic cars running 9.99 or quicker or faster than 135 mph.

Engine Pro says the centerplate is cold-rolled chromoly, a strong steel alloy, 25 percent thicker than stock, with a forged one-piece ring gear double-welded on. Engine Labs says each is dynamically balanced, meaning spun and checked for vibration, and lists 13 applications. LS part 32-4600 is listed for 1997-up LS engines with TH350, 700R4 or 4L60E transmissions. It has 168 teeth and is internally balanced, so no balance weight is added to the plate. For its similar LS plate, PRW notes that pairing an LS with a non-LS transmission needs a crank sleeve adapter to support the converter snout, the nose of the converter that centers in the back of the crank.

The bolts are heat-treated 8740 chromoly rated at a 190,000-psi minimum tensile strength, which is how hard they can be pulled before breaking, with rolled threads. LS kits include 06-14907 and 06-14909, the latter for flexplate adapters. Under SFI’s program, the manufacturer certifies its own product, so check the label.

Chevrolet LS3 V8 engine bolted to a transmission in a hot rod chassis (generic LS3 photo, not an Engine Pro part)
Photo: dave_7 / CC BY 2.0

Is your automatic LS build quick enough that your track asks for an SFI flexplate?

Sources

  1. Engine Labs: Engine Pro Sportsman flexplates
  2. Engine Pro: Sportsman Series flexplates
  3. Engine Pro: 32-4600 LS flexplate
  4. Engine Pro: flexplate bolt search results
  5. SFI Foundation: Spec 29.1 flexplates (PDF)
  6. NHRA: 2025 Hot Rod rulebook (PDF)
  7. PRW: 1834600 LS Sportsman flexplate

Photos: Engine Pro via Engine Labs; LS3 photo by dave_7 (CC BY 2.0)

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