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How To Replicate LS Engine Dimensions with a Steel LS Mock Up Block

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LS engines are being swapped into just about everything these days. We’ve seen them in Subarus, Porsches, Toyotas, and the list goes on. They offer cheap, reliable horsepower right out of the junkyard. Problem is, if you’re working to cram one of these engines into a chassis that wasn’t made for it, you’ll have lots of measuring and fitting to do. A mock up block will greatly simplify this process.

If you're looking to do something crazy, like this LS-swapped Subie, then you'll find a mock up block to be very helpful.
What is a Mock Up Block?

If you’ve ever worked with one of these mock up blocks before, you know what a game-changer they can be. Every part of the swap process is made easier by having a lightweight facsimile of your engine that can easily be lifted in and out of the chassis while you’re working. These work great for building mounts, checking header clearance, mocking up accessories on the front, or making sure the intake will fit under the hood. Not only that, but when you’re welding, grinding, or otherwise throwing sparks, your actual engine can stay safe and clean across the shop instead of sitting in the chassis and in harms way.

The steel LS Mock Up Block is a valuable tool to have in the shop. We recommend keeping a coat of oil on it to keep it from rusting when not in use.
Why Use a Steel Mock Up Block?

Most of these blocks on the market are made from cast plastic or foam with threaded inserts where critical accessories like headers and water pumps will go. In theory, these work just fine and will accurately simulate the engine as designed. But in practice, they tend to be a bit too fragile. We don’t need to tell you that intake manifolds, transmissions, headers, and the like are heavy. With too many of them hanging on that plastic block, they tend to crack and the threaded inserts have been known to pull out.

Here's where the Speedway Motors Steel Dummy Block comes in. These are made from 12 gauge steel, offering a great balance between light weight and the necessary strength to actually put them to work. We’ve already used them in the shop and had intakes, cast exhaust manifolds, accessories, and a transmission bolted on with no trouble. The bottom line is that these are tough enough to become a tool that you’ll use again and again.

What LS Engines Does this Mock Up Block Replicate?

In short, all of them. We know there’s a ton of variation across Gen III and IV LS engines. Cathedral port, rectangle port, iron block and aluminum, 4.8 to 6.2. But thankfully, their external dimensions are largely the same. The short block version of this dummy engine accurately replicates the block, allowing the use of your cylinder heads, while the long block adds simulated cylinder heads that adjust to replicate standard and LS7 heads.

Whether you’re upgrading from the old school small or big block in your muscle car or doing something completely outside the box, a mock up block is a handy tool to have in the shop. In fact, once you’ve used one, you’ll never want to attempt a swap without it again!

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