Mock Up Engine and Transmission Fitment Like a Pro
Swap Blocks—The Right Tool for the Job
Find Featured Swap Blocks Here—
Engine Swap Block™ Mock Up Blocks
Transmission Swap Block™ Mock Up Blocks
If you’ve ever done a serious swap, you already know one thing: mocking it up first is the move of an experienced builder. Real car guys don't leave clearances and mounting geometry to chance. That’s why our engine and transmission mock up blocks are game changers for your next LS swap, Small Block Chevy, Big Block, Cummins, or Gen V LT swap project. Plus, the 6.6 Duramax, Ford 5.0 Coyote, and Honda K24Z3 are our newest additions to the Swap Block line, and more are added all the time.
So, whether you’re shoehorning a Gen III LS into a classic Chevelle or setting up a Big Block for your dragster, mock up blocks save time, money, and headaches. G Force offers lightweight, precision-cut swap blocks that let you mock up engine and transmission positioning without having to manhandle the full-weight drivetrain.
Why Use a Mock Up Block?
Let’s be real—pulling a fully dressed LS, BBC, or any engine in and out of a tight bay multiple times is a great way to trash your firewall, knuckles, and sanity. G Force’s mock up blocks are a smarter way to go. Made from durable steel, they replicate the external dimensions and mounting points of your actual engine or transmission, without the unwieldy weight.
That means you can:
- Dial in the Crossmember and motor mount placement with surgical precision
- Check the header and oil pan clearance
- Test fit transmission tunnel mods
- Align driveline angle before committing to welds or cuts, if needed.
For example, G Force’s LS Mock Up Engine Block weighs only a few pounds, but replicates all critical mounting points and external geometry—perfect for that LS engine swap you’ve been planning all winter.
Engine Mock Up Blocks Available
G Force Performance Products offers Mock Up Blocks for the most common and popular engine swap platforms
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- LS Engine Mock Up Block – For Gen III/IV LS swaps (4.8L, 5.3L, 6.0L, 6.2L
- Small Block Chevy (SBC) Mock Up Block
- Big Block Chevy (BBC) Mock Up Block
- Gen V LT Mock Up Block – For LT1/LT4/LT5 applications
- Cummins 4BT and 6BT
- Ford Godzilla and Coyote
- 6.6 Duramax
- Honda K24Z3
- Hemi
These blocks are ideal for chassis mockups, custom engine fabrication, or if you’re building a hot rod from scratch and want to test different engine setups.
Transmission Mock Up Tools Too
Don’t forget the other half of the equation—G Force transmission mock up tools. Matching your engine block to the right trans mock up ensures you get your driveshaft angle, trans mount, and floor clearance spot-on. G Force offers transmission dummies for popular swaps like:
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- 6R80
- 4L80
- 8HP70
- TR6060
- 6L80E / 6L90E
Just like the engine blocks, these transmission mock ups are lightweight and dimensionally accurate. They’re the smart move when you're dialing in a transmission Crossmember, shifter location, or measuring for tunnel clearance.
Built for Builders
These aren’t bargain-basement, off-the-shelf plastic chunks. They’re fabricated from precision-cut, rigid sheet steel. This durable steel construction with a patent-pending tab-and-slot design not only accurately replicates all critical mounting points and external geometry, but also stands up to welding heat. Meaning you can tack or weld your motor mounts and Crossmembers using the Swap Block for fitment without distortion. Additionally, as an added bonus, G-Force Swap Blocks are made in the USA.
They’re ideal for:
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- Muscle car restorations
- Custom hot rods
- Pro-touring builds
- Drag cars
- LS or LT swap vehicles
- Custom Crossmember and mount fabrication
And because G Force also manufactures some of the best Transmission Crossmembers, adapter plates, and engine mounts on the market, you know everything fits together like it should.
What are the benefits of the tab-and-slot design?
The tab-and-slot construction that G Force engineered for their mock-up blocks is much more than just a clever way to hold parts together—it delivers a suite of real-world benefits for anyone doing precision drivetrain work:
1. Perfect Alignment Every Time
a. Self-locating geometry: Each mating face features matching tabs and slots, allowing the plates (or an engine block face and a mounting plate) to come together with the tabs automatically dropping into the slots, thereby pulling the parts into the exact intended position.
2. Increased Rigidity During Fabrication
a. Built-in bracing: Unlike a stack of flat plates held together with bolts that can flex, tab-and-slot assemblies lock into a triangulated, interlocked structure.
b. Reduced distortion: With the parts held snugly together, the heat from welds has less opportunity to warp, ensuring your final installation remains true.
3. Speed of Assembly and Adjustment
a. No measuring dozens of times: Once your swap block is in place, the tabs do the work of positioning. You simply tack your motor mounts in place, check your clearances, and go.
b. Easy re-use: Need to shift your mock-up a few millimeters for an alternate oil pan or header package? Easily maneuver your lightweight mock up block, and you’re ready to go.
4. Weld-Ready Interfaces
a. Heavy-duty steel design: G Force’s tab-and-slot plates are CNC-cut from steel so they do not twist or melt when mocking up motor mounts. You can determine exactly where your mounts will live, tack them in place, then pull everything apart for final welding, knowing you’ll reproduce that perfect alignment on the “real” engine and chassis pieces.
b. Eliminates “second-guess” welds: Because you’re welding on a full-scale mock-up, you can verify fitment and function before committing to your powder-coated or painted final parts.
In short, tab-and-slot mock-up blocks are akin to a high-end Lego™ for drivetrain builders: they snap together precisely, stay rock-solid under heat and load, and let you dial in every mounting interface before you ever pick up a torch on your real parts.
How do tab-and-slot blocks compare with foam dummies?
When you’re lining up engine mounts or fabricating Crossmembers, choosing the right mock-up “dummy” can make-or-break your build. Here’s how steel tab-and-slot swap blocks stack up against the old-school foam or clay dummies:
Precision & Alignment
Tab-and-Slot Blocks
- Self-locating fit: Tabs lock into slots with exact repeatability, so your engine/trans center-line hits the same coordinates every time.
- Zero guesswork: No shims, no scribes, no eyeballing—once it drops in, it’s right.
Foam Dummies
- Variable Fit: Foam can melt or tear, causing the block’s datum plane to shift under load or during tacking.
Rigidity & Weld-Readiness
Tab-and-Slot Blocks
- Rock-solid jig: Interlocked plates resist flex while you tack or fully weld—keeps mounts plumb and square.
- Tough steel: You can legitimately tack-up and torch-weld mounts to lock in positioning.
Foam Dummies
- Zero weld tolerance: Foam will burn or melt if exposed to heat—so you can’t true-up mounts on them.
- Support fixtures needed: To hold your foam pattern steady, you often still need metal plates or temporary brackets.
Durability
Tab-and-Slot Blocks
- Built to last: Steel panels withstand repeated assembly, bumps in the shop, and occasional dropped wrenches.
Foam Dummies
- One-and-done: Foam erodes cutting tools, gets gouged during trial-fits, and rarely survives a mock-up.
- Limited shelf-life: Exposure to shop solvents, oils, and shop air will degrade foam over time.
Final Thoughts
Swapping an engine isn't just about brute force—it’s about precision. G Force Performance Products' engine and transmission mock up blocks let you plan, measure, and fabricate with confidence. They're an essential tool in any serious car builder's garage.
You can grab yours now. Check out the G Force Swap Block Collection. If you're investing time and cash into your swap, do it right the first time—mock it up like a pro.
Watch how easy it is to assemble the Engine and Transmission Swap Blocks from G Force.
Engine and Transmission Swap Block Assembly Made Easy