Gen 3 LS to TH350/700R4/Powerglide Transmission Adapter Kit

• 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
• Torque converter adapter ring supports converter hub, no custom converter required
• Includes ARP fasteners for torque converter to flexplate and flexplate to crankshaft
• 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

Used LS Engines Are Cheap, But LS Swap Costs Can Add Up Quickly

We’ve seen the venerable LS swap in so many different platforms over the years. It is truly amazing as to what enthusiasts have installed these engines in. Ever since its debut in the 1997 Corvette, hot rodders have dropped the LS into other GM models, Fords, Mopars, imports, and exotics. Why? There are several reasons, including a huge factory installed base, making the LS engine easy to find in a salvage yard and cheap to buy. It certainly doesn’t hurt the argument that they are much more compact than Ford’s modular V8 or Mopar’s V8 offerings of the time and make considerably more horsepower. The 5.3 LS and 6.0 LS are real performers, and even the little 4.8 LS is an option for a real budget oriented project. There are certainly some hurdles to LS swap installation, including conversion mounts, deciding to go carbureted or stick with EFI, and so on, but one of the biggest issues is how to get that power to the ground.

If you grab an LS from the salvage yard and opt to pick up the factory transmission with it, you’ll have to consider how to control that modern electronic transmission (especially if you go carbureted induction on your LS). Not to mention the 4L60E and 4L80E transmissions are big, often causing fitment issues in a smaller vehicle chassis. We also realize that hot rodders are hoarders too, and that’s a good thing. Having a spare transmission or a couple of sets of cylinder heads on the shelf means money saved when it comes to a budget build project or can be used for bartering fodder for parts needed. So, we’re often asked how to fit an older Turbo 350 or other such “classic” GM automatic up to these LS engines. You’ve got the transmission sitting on the shop floor, so why not use it, right? It’s easier than you think!

Everything Needed for A Painless Installation of Non-LS GM Transmissions to Gen III LS Engines

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 ring is employed that engages the torque converter hub and the LS crankshaft, maintaining concentric support of the torque converter as it is mounted to the flexplate. Add in the correct high quality ARP fasteners, including LS flexplate bolts and a torque converter bolt kit to mount your new LS flexplate and attach your torque converter, and you 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.

No Installation Hassles Since Everything in The Kit Is a Direct Bolt-On Part

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 is truly a bolt-on LS to TH350 adapter conversion solution. Besides the popular TH350 3-speed automatic and classic Powerglide 2-speed, this conversion kit will also work with GM’s non-LS 4-speed overdrive transmissions like the 200-4R, 700-R4, and 4L60. If you're swapping your Gen III LS into a factory small block or big block Chevy application we offer this kit with SBC to LS adapters, which makes the engine a bolt in.

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 kit, nor will this kit 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 easy to use flexplate adapter kit is what you need.

Kit Includes:

(1) Trans Adapter Flexplate

• GM LS Gen III to early GM 3/4 speed automatic
• Works with 10.75" & 11.066" (11.1") bolt-pattern torque converters
• SFI 29.1 certified
• Forged 1-piece steel ring gear
• 168 tooth
• Works with stock LS starter motor

(1) LS Crank Sleeve Adapter

• Overall Height: 1.04"
• Inside Diameter: 1.47"
• Diameter Small End: 1.70"
• Diameter Big End: 2.00"
• Material Type: Steel

(6) Gen III LS Flexplate Bolts

• Fits Chevrolet Gen III/LS Series V8
• Exclusive, flat, 12-point head design
• Has a 200,000 psi rating
• M11 x 1.5

(1) Torque Converter Bolt Kit

• Under Head Length: 1.25"
• Thread Pitch: 7/16"-20
• Wrench Type: 12 Point