LS1/LS2/LS6/5.3/6.0 to TH350/700R4/4L60 Adapter Flexplate

• Works on all standard 6-bolt crankshaft 1997-2007 Gen III LS engines
• Allows direct bolt-on fitment of previous generation automatic transmissions
• Supports Non-LS 4L60 as well as popular older 3- and 4-speed automatics
• No modifications required to LS engine block or crankshaft
• New LS flexplate features dual GM torque converter patterns of 10.75” and 11.10”
• Flexplate is gold zinc plated, 4mm thick, and carries a SFI 29.1 certification
• Not compatible with 8-bolt crankshaft Gen IV LS engines
• Not for use with early Gen III LS 6.0L (1999-2000) due to extended crankshaft flange

A Flexplate That Allows Direct Fitment of Older GM Automatics to Your Gen III LS Engine

Unlike some engine swaps that require modifications to the transmission bellhousing, or even requiring the bellhousing to be cut off and a different one added, GM wisely retained the Gen 1 small block bellhousing bolt pattern for the Gen III (and Gen IV) LS V8. So, most any non-LS GM automatic, including the TH350, 700-R4, or even the venerable Powerglide will bolt directly to the engine block with no modifications, though it does so with one less bellhousing bolt. The swap issue lies inside the bellhousing with the flexplate and torque converter relationship and how they attach.

To address this spacing issue in the most cost effective way possible we offer a custom LS flexplate with the LS 6-bolt crankshaft pattern and 168 tooth count. The center section is 4mm thick, which is .035-inch thicker than a stock LS flexplate and features a forged 1-piece ring gear to meet SFI 29.1 specifications. The LS flexplate is drilled for both early SBC torque converter bolt patterns (10.75" which fits Powerglide, TH350, 200-4R, 700-R4, 4L60) and later LS converter pattern (11.06” 4L60E with LS engine). We even made sure our LS flexplate allows the use of the stock LS starter, which is one less swap part to worry about/buy. There are other flexplate solutions depending on the LS engine and transmission you are planning to use. Be sure to read our LS flexplate guide in The Toolbox to explore all options.

To properly support the SBC-style torque converter found in these earlier transmissions, a machined adapter sleeve will be needed. This sleeve engages the torque converter hub and the LS crankshaft, maintaining concentric support of the torque converter as it is mounted to the flexplate. If you’re in need of the LS flexplate bolts and the torque converter bolts to mount your new LS flexplate and attach your torque converter, you may wish to order our LS flexplate kit, which includes this flexplate, adapter sleeve, and installation hardware. Then you will have everything you need (except bellhousing bolts if needed) to easily adapt an early GM automatic to your LS engine. We used this very kit on our C10 pickup project with a Gen III 5.3 LS and TH350 transmission. You can see how smoothly everything went together in our Toolbox installation overview.

A Part That Will Save You Time And Frustration Fitting Your Classic GM Automatic Transmission

In this day and age of “bolt-on” parts the term often leaves a lot to be desired. However, as long as you’re fitting a small block or big block Chevy “classic” transmission to a 6-bolt Gen III LS V8 (which includes 1997-2007 LS1, LS3, LS6, and LS7; 2005-2009 LS2; and Vortec truck engines including the 4.8/5.3/6.0 under RPO codes L33, L59, LM4, LM7, LQ4, LQ9, and LR4) this flexplate is the perfect solution. Besides the popular TH350 3-speed automatic and classic Powerglide 2-speed, this flexplate will also work with GM’s non-LS 4-speed overdrive transmissions like the 200-4R, 700-R4, and 4L60.

Note that this is not a direct LS to TH400 adapter kit. While the popular Turbo 400 isn’t supported natively due to its larger 11.50” converter bolt pattern, if you wish to use a TH400 behind your LS you can simply swap your TH400 converter for a TH350 converter and everything will bolt right up then. The modern 4L80E uses the same 11.50” bolt pattern, but is not compatible with this flexplate, nor will this flexplate fit extended length crankshafts, such as early 6.0L applications, or 8-bolt crank Gen IV LS engines such as the LSA. If you’re looking to save money and reuse a classic GM small block or big block automatic transmission behind your Gen III LS swap, this flexplate is what your build needs.