If you’re looking to drop some modern LS power into your ride but want to keep that bulletproof, old-school Turbo 350 (TH350), you’re in luck. It’s a classic combo that saves money and weight, but it isn’t a direct “bolt-and-go” situation. At Dream Factory, we’re all about making the complex simple. Here is the breakdown of how to make this marriage work.
The Pro/Con List
| Pros | Cons |
| Budget Friendly: No need to buy an expensive 4L60E or 4L80E and a standalone controller. | No Overdrive: Your highway cruising RPMs will stay high (3rd gear is 1:1). |
| Weight & Size: Lighter and smaller than modern electronic transmissions; fits in tight tunnels. | One Missing Bolt: The LS block is missing the hole for the top-passenger side bellhousing bolt (not a structural issue). |
| Durability: The TH350 is a proven, mechanical beast that’s easy to build for high HP. | Manual Passing: Without a properly setup kickdown, you’ll have to downshift manually. |
| Simplicity: No wiring harnesses or computers required for the transmission to shift. | Fuel Economy: You’ll lose about 30% efficiency compared to an overdrive setup. |
What You’ll Need (Parts Checklist)
To mate an LS (Gen III/IV) to a TH350, you have to address two main things: the crankshaft spacing and the torque converter bolt pattern.
- Flexplate Adapter Spacer: The LS crankshaft is about .400″ shorter than the old Small Block Chevy (SBC). You need a spacer to support the nose of your TH350 torque converter.+1
- Conversion Flexplate: A standard LS flexplate usually won’t line up with a TH350 converter. You can either elongated the holes on a stock 6.0L flat flexplate or buy a dedicated conversion plate.
- Engine Mount Adapters: To keep your TH350 in its original factory location, use “setback” style adapter plates.
- Kickdown Cable (Optional): If you want the trans to downshift automatically when you floor it, you’ll need a specialized cable for LS throttle bodies.
Amazon Parts List
As an AI, I can’t provide live “clickable” affiliate links, but you can copy/paste these specific search terms or part numbers into Amazon for exactly what you need:
- The “Budget” Fix (Spacer Only):
- Search: “ICT Billet 551165“ (This is the adapter hub that lets you use a stock LS flexplate with an old converter).
- The Complete Kit (SFI Rated):
- Search: “LS to TH350 Adapter Kit with Flexplate“ (Look for brands like Michigan Motorsports or Speedway Motors for the plate and spacer combo).
- The Transmission Mount:
- Search: “Energy Suspension 3.1108G“ (The standard poly mount that fits almost every GM trans).
- The Kickdown Solution:
- Search: “Lokar KD-2350HT“ (The gold standard for connecting a TH350 kickdown to a modern engine).
Expert Tip from the Garage
If you’re using a 1999–2000 6.0L iron head engine, you actually have a “long crank” and don’t need the spacer! For everyone else, don’t skip the spacer—if the torque converter nose isn’t supported in the crank, you’ll wipe out your front pump and thrust bearings in no time.