K5 Blazer LS and LT Swap: Doing It on a Chassis Built for It

Dropping a modern GM V8 into a K5 Blazer is one of the most popular upgrades in the classic truck world, and it is easy to see why. An LS or LT engine brings fuel injection, reliable cold starts, real power and far better economy than the carbureted small block it replaces. What surprises people is everything else the swap touches. This guide covers what a K5 Blazer LS or LT swap really involves, and how doing it on a chassis built for the drivetrain changes the job.

What an LS or LT swap touches on a stock frame

The engine is the easy part. The work is in making a modern drivetrain live in a chassis designed around a 1970s one. A realistic K5 Blazer LS swap parts list usually includes:

• Engine mounts or adapter plates to position the engine in the original frame
• Oil pan clearance around the front axle and differential on a solid axle truck
• Headers and exhaust routed around the steering box, frame rails and transfer case
• Transmission crossmember and driveshafts to suit a modern automatic and its transfer case
• Fuel system capable of fuel injection pressure, with the right pump, regulator and lines
• Wiring harness and engine controller to run the engine as a standalone system
• Cooling, with a radiator and fans sized for the new engine
• Brakes and suspension that can handle the extra power, which a stock K5 was never designed for

None of it is impossible, but each item is a separate decision, a separate purchase and often a separate round of fabrication. That is why swaps on stock frames so often take longer and cost more than planned.

Doing the swap on a chassis built for it

The Frame-Werx chassis is designed from the start to carry a modern GM drivetrain. It is rated for 800 horsepower, capable of all-wheel drive, and built with independent front suspension and brakes based on the GMT900 platform, so the brakes and suspension are matched to the power from day one.

When you add a drivetrain package, the pieces arrive engineered to fit together:

• Engine and transmission combinations from the GM Performance catalog, including LT1 and LT4 based packages
• Transfer case in two-wheel drive, all-wheel drive or electronic shift, with a dash selector for 2WD, 4WD High and 4WD Low
• Standalone wiring harness included in the engine package
• Exhaust included in the package, so there is nothing extra to buy
• Fuel system with the tank matched to your truck year, and your choice of an internally regulated system or an external regulator
• Rear axle ratio of 3.42, 3.73 or 4.10

A proven combination

If you are unsure where to start, Frame-Werx has a favorite pairing for a K5 on 35-inch tires: an LT1 with a 6L80 six-speed automatic and a 3.42 rear axle ratio. It delivers strong acceleration, relaxed highway cruising and gearing that suits the tire size.

Common questions

What engine is best for a K5 Blazer swap?

Modern GM LS and LT engines are the most popular choices because of their power, fuel injection and reliability. Frame-Werx offers LT1 and LT4 based drivetrain packages from the GM Performance catalog.

What transmission and gearing work well behind an LT1 in a K5 Blazer?

Frame-Werx recommends an LT1 with a 6L80 six-speed automatic and a 3.42 rear axle ratio for a K5 on 35-inch tires.

Can a K5 Blazer with an LT swap be all-wheel drive?

Yes. The Frame-Werx chassis is AWD capable, and the transfer case can be ordered in two-wheel drive, all-wheel drive or electronic shift.

Do I need to buy exhaust and wiring separately?

Not with a Frame-Werx drivetrain package. The standalone wiring harness and the exhaust are included with the engine package.

Build the whole drivetrain in one place. Spec your chassis and engine package, or see what a K5 Blazer chassis costs. Available for the 1973–1991 and 1969–1972 K5 Blazer, K10 pickups and the Suburban.