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Swapping an 8.1L Big-Block in a 1973-1991 Square-Body Chevy Pickup

8.1 Get-R-Done

Fred WilliamsPhotographer, WriterStaffPhotographer

Depending on where you live, big-block Chevy 8.1L engines can be found cheap. We are not sure why, but compared to the LS-series truck engines, these torque tanks are plentiful and inexpensive. This modern GM big-block is similar to the LS engines but also unique. And they are heavy, with iron blocks and heads. Most of the hot rod guys prefer the old-style big-blocks, and most of the off-road guys prefer the LS engines, so the 8.1Ls seem to get ignored. Plus, they don’t have a ton of aftermarket support in terms of upgrades. They are also not the best for fuel economy, so you’d almost wonder why we chose one. Well, they are abundant in 3/4-ton trucks, vans, Suburbans, Avalanches, and RVs from around 2001 to 2010. Some were even dropped in boats. And did we mention they are bad on gas, heavy, and cheap?

We swapped one in our 1986 Chevy military truck and couldn’t be happier. The engine runs smooth and is grunty. Well, we could be a little happier if we hadn’t found a rear main seal leak after we had the engine all bolted in place, but that is the gamble of just stabbing a used junkyard engine in your project. Overall, we are elated with our new-to-us big-block. Here are the swap highlights if you are contemplating one for your square-body GM.

Build Me One!

The folks at Tilden Motorsports build LS engines for hot rods and 4x4s and reworked both our wiring harness and ECU for the Alaska Army Truck. The company can also build you a complete 8.1L big-block for your project with upgraded cam options, heads, and intakes. Tilden recently built this 600-plus-horsepower, 700–lb-ft 8.1L for a customer.

Tell Me More!

Want to learn even more about the 8.1L? Check out this article from Car Craft magazine on the Hot Rod Network website. It dives deeper into the nitty-gritty of these engines and ways to get bigger power out of them.
http://www.hotrod.com/articles/gm-vortec-8100-the-454s-forgotten-big-brother/

Show Me More!

You can watch the swap and the suspension upgrades and the first adventure we took our 8.1L Army truck on Dirt Every Day. Search YouTube for “Alaskan Army truck adventure.”