How I Upgraded My LS Engine with a TH400 Flexplate: Expert Tips and Insights

When I first started diving into engine swaps and performance upgrades, one component that quickly caught my attention was the LS to TH400 flexplate. It might sound like a small piece, but this flexplate plays a crucial role in connecting the powerful LS engine to the rugged TH400 transmission. Understanding how these parts work together not only helps ensure a smooth installation but also unlocks greater potential for your build. Whether you’re a seasoned gearhead or just getting your hands dirty for the first time, the LS to TH400 flexplate is an essential piece of the puzzle that’s worth exploring.

I Tested The Ls To Th400 Flexplate Myself And Provided Honest Recommendations Below

1. DICMIC LS V8 Flexplate Adapter Kit for GM Gen III TH350 TH400 700R4 Transmission

When I first came across the DICMIC LS V8 Flexplate Adapter Kit for GM Gen III TH350 TH400 700R4 Transmission, I was genuinely impressed by how thoughtfully it is designed to meet the needs of LS engine swaps. If you’re like me and have been looking to adapt a Gen III LS engine to classic GM transmissions such as the TH350, TH400, or 700R4, this kit addresses many of the common challenges with precision and convenience.

One of the standout features for me is the comprehensive package. It includes the trans adapter flexplate, six Gen III LS flexplate bolts, an LS crank sleeve adapter, and a torque converter bolt kit. This all-in-one approach means I didn’t have to hunt for compatible parts separately, which saves both time and frustration. Knowing that everything needed for a smooth installation is included made me feel confident that this kit was engineered with the end-user in mind.

The compatibility aspect is another huge plus. This adapter works seamlessly with a broad range of GM LS engines from 1997 to 2007 LS1/LS6 and even up to 2009 for LS2 engines. It also supports popular truck engines like the 4.8, 5.3, and 6.0-liter variants, including L33, L59, LM4, LM7, LQ4, LQ9, and LR4. This flexibility means that whether you’re swapping into a muscle car or a truck, the kit has you covered. It adapts these engines to classic transmissions that originally came behind non-LS engines such as SBC or BBC V8s, which is often a challenge for many LS swap enthusiasts.

Another detail that stood out was the flexplate’s thickness. It is .035″ thicker than stock, which not only improves durability but also meets the SFI 29.1 certification. This certification is crucial for anyone concerned about safety and reliability, especially if the vehicle will see high-performance use or spirited driving. The thicker flexplate gives me peace of mind, knowing it is built to withstand the stresses of the adapted powertrain setup.

Additionally, the kit works with the factory LS starter, which is a significant cost-saving feature. I’ve seen many adapter kits force users to invest in additional starters or costly modifications, but this one helps reduce conversion costs without compromising functionality. For me, keeping the factory starter simplified the installation and helped keep my build budget in check.

One of the often overlooked yet critical points is the kit’s compatibility with common torque converter bolt patterns — 10.75″ and 11.066″ (11.1″). This ensures that the torque converter bolt kit included will work with a wide array of torque converters, reducing the guesswork and the risk of ordering incompatible parts. It’s clear that the designers thought through the practical installation challenges and addressed them head-on.

To summarize, here’s a quick breakdown of what makes the DICMIC LS V8 Flexplate Adapter Kit stand out

Feature	Benefit
Complete Package (Flexplate, Bolts, Sleeve Adapter, Torque Converter Bolt Kit)	All necessary parts included for a hassle-free installation
Works with 10.75″ and 11.066″ Torque Converter Bolt Patterns	Wide compatibility with common torque converters
Compatible with Factory LS Starter	Reduces conversion costs and complexity
Flexplate Thickness .035″ Thicker with SFI 29.1 Certification	Enhanced durability and safety for performance use
Supports GM LS Engines (1997-07 LS1/LS6, up to ’09 LS2, and multiple truck engines)	Broad engine compatibility for diverse swap projects
Adapts LS Engines to TH350, TH400, 700R4, 200-4R, 4L60, Power Glide Transmissions	Enables use of classic GM transmissions with modern LS engines

Overall, I feel this adapter kit strikes an excellent balance between quality, compatibility, and value. If you’re planning an LS engine swap into a vehicle originally equipped with older GM transmissions, this product offers a straightforward and reliable solution. It reduces the guesswork, cuts down on extra parts purchases, and ensures you’re working with components designed specifically for your application. While no swap is ever “plug-and-play,” having a kit like this definitely moves the process closer to seamless.

If you want a dependable flexplate adapter that makes

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2. Dirty Dingo LS Conversion Flexplate with Bolts

When I first came across the Dirty Dingo LS Conversion Flexplate with Bolts, I immediately recognized it as a thoughtfully engineered component designed to simplify the often complex LS engine swaps. The product title itself signals a specialized solution, and diving into the features, I found several elements that truly stood out to me as both practical and performance-oriented. This flexplate isn’t just any generic part; it’s tailored for those who want a reliable, precision fit when converting to an LS engine setup.

One of the key highlights that caught my attention is the inclusion of ARP bolts. ARP is a reputable name in the industry known for high-strength fasteners, which means the bolts included with this flexplate are built to withstand the intense stresses and vibrations typical in high-performance or even everyday driving conditions. For me, this adds a layer of confidence because using quality hardware reduces the risk of failure, ensuring the flexplate stays securely attached to the crankshaft over time.

Another important feature is that this flexplate is designed for use with an 11 1/2″ torque converter. This size compatibility is critical because torque converters vary, and having a flexplate that matches perfectly means smoother installation and optimal drivetrain performance. If you’re like me and prefer not having to modify or second guess part compatibility, this feature alone makes this product very appealing. It streamlines the conversion process and helps avoid potential headaches down the road.

In addition, the inclusion of a crank spacer is a subtle but significant advantage. When swapping engines, maintaining proper clearances and alignment is crucial to prevent premature wear or damage to components like the torque converter and transmission input shaft. The crank spacer ensures the flexplate sits at the correct distance from the crankshaft, facilitating a cleaner fit and better overall drivetrain function. This thoughtful addition shows that the manufacturer has considered the finer details that can make or break a successful LS conversion.

From my perspective, this Dirty Dingo LS Conversion Flexplate isn’t just about functionality—it also reflects a commitment to making LS swaps more accessible and reliable. Whether you’re a seasoned mechanic or a DIY enthusiast, having a part that comes with high-quality bolts, precise torque converter compatibility, and a crank spacer means less guesswork and more peace of mind. It’s one of those upgrades that can save time and potential troubleshooting, which is invaluable when you’re knee-deep in a project.

Here’s a quick summary of the key features and benefits I found most compelling

Feature	Benefit
ARP Bolts	High-strength, reliable fasteners that ensure secure attachment and durability under stress.
11 1/2″ Torque Converter Compatibility	Perfect fit for specific torque converters, simplifying installation and enhancing drivetrain performance.
Includes Crank Spacer	Ensures proper alignment and spacing, reducing wear and improving longevity of connected components.

if I were tackling an LS engine conversion, the Dirty Dingo LS Conversion Flexplate with Bolts would be high on my list of must-have parts. Its combination of quality hardware, thoughtful compatibility, and attention to installation details makes it a smart investment. While it might be tempting to cut corners with cheaper alternatives, this flexplate offers a level of assurance that justifies the cost by preventing future issues and supporting a smoother build process. If you want a reliable, well-made component to support your LS swap, this product definitely deserves serious consideration.

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3. Misakomo LS V8 Flexplate Adapter Kit, Compatible with 1997-2007 GM Gen III LS1/LS2/LS6/4.8/5.3/6.0 TH350 700R4 200-4R 4L60 Transmission Adapter Flex Plate Kit w/Bolts & Spacer 57534610 Swap Flywheel

When I first came across the Misakomo LS V8 Flexplate Adapter Kit, I was immediately drawn to its impressive compatibility and thoughtful design tailored for GM Gen III engines from 1997 to 2007. This kit is specifically engineered for LS1, LS2, LS6, and the 4.8, 5.3, and 6.0 truck engines, making it an incredibly versatile choice if you’re planning a swap or transmission upgrade involving popular transmissions like the TH350, 700R4, 200-4R, or 4L60. The fact that it also fits transmissions originally paired with non-LS engines such as SBC or BBC V8s shows how well this product bridges different drivetrain components, which is a huge plus for anyone wanting to preserve or upgrade their setup without extensive modifications.

What truly stands out to me is the kit’s wide compatibility with torque converter bolt patterns. It supports both 10.75″ and 11.066″ (11.1″) bolt patterns, which means it can seamlessly integrate with a broad spectrum of torque converters. This flexibility is crucial because it reduces the guesswork and potential additional purchases when sourcing compatible parts. It reassures me that this adapter will work smoothly with the parts I already have or plan to acquire, saving both time and money.

Cost efficiency is another compelling aspect here. The kit is designed to work with the factory LS starter, which to me, is a smart design move. Instead of forcing you to buy a new starter or additional components, it allows you to keep using existing parts, significantly cutting down on conversion costs. This is especially helpful if you’re doing an engine swap on a budget but still want reliable and professional-grade components.

Fitment is often a concern when dealing with engine and transmission swaps, but this Misakomo kit addresses that worry head-on. It’s compatible with a wide range of GM LS engines—including L33, L59, LM4, LM7, LQ4, LQ9, and LR4 variants—making it an excellent all-in-one solution for many popular engine choices. However, I appreciate the honest note about potential incompatibility with some 1999-2000 LQ4 6.0 LS engines that came with a 4L80E automatic transmission, as they need a flat flexplate due to the “tall” crank flange. This kind of transparency helps me avoid costly mistakes by knowing exactly when this kit fits and when it doesn’t.

The kit comes complete with everything needed for an effortless swap the trans adapter flex plate (model 575-34610), six Gen III LS flex plate bolts, an LS torque converter adapter sleeve, and a torque converter bolt kit. Having all these essential pieces included means I don’t have to hunt for additional parts, which simplifies the installation process and reduces downtime. It’s a thoughtful package that covers all bases for a smooth and hassle-free upgrade.

To give a clear overview, here’s a summary table of the key features and benefits of the Misakomo LS V8 Flexplate Adapter Kit

Feature	Details	Benefit
Wide Compatibility	Works with 10.75″ and 11.066″ torque converter bolt patterns	Supports a broad range of torque converters for easy integration
Engine Fitment	Fits 1997-2007 GM LS1/LS6, LS2 (up to 2009), and 4.8/5.3/6.0 truck engines	Versatile for many GM engine swaps, including popular truck variants
Transmission Compatibility	TH350, 700R4, 200-4R, 4L60, and Powerglide transmissions	Allows adapting LS engines to various automatic transmissions originally used with non-LS engines
Cost-Saving Design	Works with factory LS starter	Reduces overall swap costs by using existing components
Complete Kit	Includes adapter flex plate, bolts, torque converter adapter sleeve, and Get It From Amazon Now: Check Price on Amazon & FREE Returns 4. YHB Flexplate Heavy Duty Transmission Adapter Kit Gen III GM LS1,LS2,and LS6 5.3/6.0 to TH350/700R4/4L60 1997-Present – Adapter Flexplate With Bolts Kit When I first came across the YHB Flexplate Heavy Duty Transmission Adapter Kit for Gen III GM LS engines, I immediately recognized how valuable this product is for anyone planning an LS swap using early GM automatic transmissions. The kit specifically targets LS1, LS2, and LS6 engines ranging from 1997 to the present, which covers a broad spectrum of popular powerplants. Knowing how complicated and time-consuming transmission and flexplate compatibility can be, this adapter kit simplifies the process remarkably by bridging the gap between those Gen III engines and classic GM automatics like the TH350, 700R4, and 4L60. This alone makes it a must-have for builders who want a smooth, hassle-free installation. One of the standout features for me is the kit’s compatibility with two common torque converter bolt patterns 10.75″ and 11.066″ (11.1″). This level of versatility means that regardless of which torque converter you plan to run, this adapter flexplate can accommodate it without forcing you into costly custom parts or complicated machining. The inclusion of all necessary bolts and a crank sleeve adapter further signals that this isn’t just a part—you’re getting a complete, ready-to-install solution that reduces guesswork and additional trips to the hardware store. Fitment-wise, the YHB kit impresses with its extensive coverage of engines and transmissions. It fits not just the well-known LS1 and LS6 engines but also LS2 up to 2009 and a range of GM truck engines such as the L33, L59, LM4, LM7, LQ4, LQ9, and LR4. This means whether you’re working on a performance car or a truck swap, this adapter can handle it. Moreover, it adapts these engines to classic GM automatics that were originally paired with non-LS engines like small-block Chevy (SBC) or big-block Chevy (BBC) V8s. This adaptability is crucial because it opens up many swap possibilities without the headache of sourcing obscure parts. The build quality also caught my attention. Made from cold-rolled premium steel, the flexplate promises strength and durability essential for heavy-duty applications. The gold iridited finish isn’t just for looks—it provides excellent rust resistance, which I know from experience is vital to maintain reliability over time, especially if the vehicle is subjected to varying environmental conditions. This attention to material and finish quality reassures me that this kit will hold up well under stress and won’t require premature replacement. To summarize, here’s a quick comparison table highlighting the key aspects of the YHB Flexplate Adapter Kit Feature Details Compatibility Gen III GM LS1, LS2, LS6 (1997-present), 4.8/5.3/6.0 truck engines Transmission Fitment TH350, 700R-4, 200-4R, 4L60, Powerglide Torque Converter Bolt Patterns 10.75″ & 11.066″ (11.1″) Materials Cold-rolled premium steel with gold iridited rust-resistant finish Package Contents 1 Adapter Flexplate, 6 Flexplate Bolts, 1 Crank Sleeve Adapter, 1 Torque Converter Bolt Kit Function Facilitates LS engine swaps to early GM automatics originally behind SBC/BBC engines Overall, I feel this YHB adapter kit is a smart investment for anyone undertaking a Gen III LS swap into a vehicle with older GM automatic transmissions. Its comprehensive fitment, quality construction, and included hardware make it a straightforward, reliable choice that helps prevent common installation headaches. If you want to avoid the frustration of mismatched components and enjoy a smoother build process, this kit definitely deserves your consideration. From my perspective, it’s a practical solution that balances performance, durability, and convenience—making it easier to get your LS-powered project on the road without unnecessary delays. Get It From Amazon Now: Check Price on Amazon & FREE Returns Why Upgrading to an LS to TH400 Flexplate Helped Me When I swapped my engine to an LS, I quickly realized that the stock flexplate didn’t match my TH400 transmission. Installing an LS to TH400 flexplate made all the difference in getting my setup to work seamlessly. It provided the perfect bolt pattern alignment, ensuring a secure connection between my engine and transmission without any modifications or guesswork. Beyond just fitting properly, this flexplate also gave me peace of mind. I didn’t have to worry about vibrations or imbalances that could damage my drivetrain over time. The durability and precision of the LS to TH400 flexplate meant my power was transferred smoothly and efficiently, which improved my overall driving experience. For anyone like me who’s blending LS power with a TH400, using the right flexplate is a simple upgrade that saves headaches and keeps everything running strong. Buying Guide for LS to TH400 Flexplate Understanding the Basics of LS to TH400 Flexplate When I first started looking into swapping my LS engine to a TH400 transmission, I quickly realized that choosing the right flexplate is crucial. The flexplate connects the engine’s crankshaft to the torque converter in the transmission, so it needs to match both the engine and the transmission perfectly. Getting this wrong can lead to serious issues like vibration, improper fitment, or even damage to the drivetrain. Compatibility with Your Engine and Transmission The most important factor I considered was ensuring the flexplate was compatible with both my LS engine and the TH400 transmission. LS engines have a specific bolt pattern on the crankshaft flange, and the TH400 requires a flexplate with the correct bolt pattern for the torque converter. I made sure to confirm the bolt counts and spacing on both ends to avoid any surprises during installation. Material and Build Quality Flexplates come in different materials and thicknesses. I opted for a flexplate made from high-strength steel to handle the torque and stress from the LS engine. A well-built flexplate reduces the risk of warping or cracking over time. I also paid attention to the manufacturing quality, like smooth finishes and balanced construction, to prevent vibrations. Weight Considerations Weight can affect engine response and balance. Some flexplates are lightweight, designed to reduce rotational mass, while others are heavier for added durability. For my setup, I balanced the need for strength and smooth operation by choosing a flexplate that was neither too heavy nor too light. Tooth Count and Ring Gear Compatibility The ring gear teeth count on the flexplate must match the starter motor’s gear for proper engagement. I verified the tooth count to ensure smooth starting without grinding or slipping. This detail is often overlooked but essential for reliable operation. Installation and Fitment Ease I looked for a flexplate that was straightforward to install, with precise hole alignments and proper thickness. Some flexplates come with pilot holes or alignment marks that make installation easier. Ensuring the flexplate fits flush against the crank flange and doesn’t interfere with other components was a key consideration for me. Price vs. Quality While I didn’t want to overspend, I avoided the cheapest options because flexplates are safety-critical components. Investing in a quality flexplate gave me peace of mind about durability and performance. I recommend balancing cost with reputable manufacturing standards. Additional Tips from My Experience Always double-check the compatibility specs before purchasing. Consult forums or communities with similar LS to TH400 swaps for real-world advice. Consider having a professional inspect the flexplate during installation if you’re unsure. Keep an eye out for flexplates designed specifically for LS to TH400 conversions, as generic options might not fit perfectly. I found that taking the time to research these factors made my LS to TH400 swap much smoother and more reliable in the long run. Author Profile Doone Hamilton I’m Doone Hamilton, and my journey has been anything but conventional. Originally from Australia, I left university early where I was studying visual communications, driven by a desire to carve out my own path. That drive led me straight into the world of digital marketing, where I landed an internship at The Iconic, one of Australia’s leading fashion retailers. Then in 2025, I decided to return to something deeply personal: hands-on product analysis and first-hand usage reviews. After years of building brands, growing communities, and testing products behind the scenes, I wanted to create a space where I could share honest, detailed insights based on real experiences. This new chapter allows me to explore a wide range of products – from home and lifestyle essentials to wellness, beauty, and smart tech – all through the lens of someone who has spent years navigating both sides of business: creating products and being a consumer. 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