How to Put an LT1 in an Old Pickup

by Richard Rowe
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Old Grunge Truck image by Brenda Carson from

General Motors' LT-series engine was the first and last major evolution of its seminal small block before it was replaced by the LS-series V8 in 2002. The LT1 (as well as the LT4, L99 and, to some extent, the super-rare Corvette LT5) shared almost all its critical dimensions with the old small block, evidenced by the fact that most LT parts are interchangeable with the small block's. The automotive aftermarket makes an LT-for-small-block swap almost as simple as a stock-for-stock replacement. It's all about picking the right parts and knowing your chassis.

Step 1

Pull out the engine and transmission from your recipient chassis and donor vehicle. If your donor vehicle is a 1994 or later Camaro/Corvette/Typhoon or later than 1992 for anything else, you'll need to dump the stock 4L60-E or 4L65-E automatic overdrive transmission. The "E" series transmissions require a stand-alone transmission control computer and can add thousands to your build. Trade your electronic transmission to someone for an earlier 4L60 or identical 700R4 with automatic overdrive.

Step 2

Remove the driveshaft and rear end from your donor vehicle. Remove the fuel injection intake manifold from your LT engine and replace it with an aftermarket carbureted intake designed to work with Vortec-series heads. A number of companies sell carburetor conversion manifolds with a carburetor and distributor, which you'll also need.

Step 3

Connect the 700R4/4L60 to your LT engine and couple them with a converter designed to deliver a stall speed of about 500 RPM over stock. Install the engine and transmission into your truck with a set of LT-conversion motor mounts (you may need to modify them for your particular application) and a custom-fabricated transmission cross-member. You may be able to simply modify your existing cross-member to accept the 700R4 if your truck originally came with a TH350 or TH400 three-speed automatic. Consider purchasing an aftermarket 700R4 shifter linkage and kit as it will greatly ease the installation process.

Step 4

Install the donor vehicle's axle if it's superior to your truck's stock rear end. Many LT-equipped cars of this era came with GM's 7.5-inch or 10-bolt rear end; the 7.5-inch is a grenade waiting to go off, and the 10-bolt is marginal for any serious performance use in a heavy vehicle. An 8.875-inch 12-bolt rear end, a 9.5-inch rear end (GM trucks from 1988 to 1996) or even a massive 1.5-inch 14-bolt rear end (GM trucks from 1973 to 1996) would be far better for use with the powerful LT engine.

Step 5

Measure the driveshaft and have it cut to length at a driveshaft shop; have the 700R4 yoke and the required rear end flange installed. Install a new fuel tank or fuel cell, new fuel pump and new lines. Install a transmission cooler for your 700R4 as the overdrive bands are prone to frying when the fluid gets too hot. Connect your engine and transmission controls, cooling system (consider an aftermarket four-core radiator) and power steering system if you're using one.

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