A Beginner's Look at Swapping an LS-Series Engine into a Classic Truck

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Gen III For Dummies

A Beginner's Look at Swapping an LS-Series Engine into a Classic Truck

By Jeremy Cook
So you're tired of tuning your carb and think you're ready to move into 21st-century technology? And you think that the new GM Gen III engines might be just the ticket. It's pretty tempting to run out and grab one and jump right in, but did you know that the mounts on the side of the block are different? Or that there may not be a lever on the throttle body to attach your accelerator cable to? Or that there's pretty much no way you're going to get your truck running right without purchasing a harness and reprogramming the computer? None of this is meant to scare you off It's quite the contrary, actually. Since the swapping of these engines into earlier vehicles is becoming so popular so fast, we thought we'd take a look at just what's involved, as well as what's available to make the job easier.  The LS series of engines from GM, commonly referred to as Gen III engines, began production in 1997 with the aluminum-block Corvette 5.7- liter LSI (its higher performance sister is the IB6) with similar versions in the F-bodies (Camaro and Firebirds). The cast-iron block 4.8-liter, 53-liter, and 6.0-liter entered production in the '99 truckline. The top dog of the truck engines is the 345-horse Cadillac Escalade engine, which is essentially the 6.0-liter with the LS6 heads and other components. Although the basic design is the same, we quickly learned that there are several small differences among them. We will concentrate more on what it will take to actually perform the swap and not on extracting every possible horsepower (something we will be looking into at a later date). We focused on the '63-72 GM truck chassis, but most of the principles discussed are the same for just about any vehicle with two framerails and a hood.
Obviously scouring wrecking yards is going to be the easiest way to find what you are looking for. We'll tell you up front, the aluminum LS1s are already not the easiest engines to find, and the price for a low mileage unit with the trans still attached will normally run at least $4,000. But just think of how many trucks GM have sold since late 1998. Soon the wrecking yards will literally be filling up with the cast-iron versions, and they still have all the potential in the world to make additional horsepower. Sure there's a weight difference, but we build trucks, remember? Anyway we checked with owner Dave at Goldenwes truck Wrecking, and the going rate for a complete 4.8-or 5.3-liter with low mileage (say30-40K) and a 4L60E transmission attached is in the neighborhood of $3,200. Now figure the price to build a nicely equipped early small-block and back it with a 700-R4, and you'll quickly see why these engines are starting to look good. Of course, LS1 engines are available as crates from GM Performance parts, and there are companies like Street & Performance that eliminate the running-around part of the equation by keeping a good stock of low-mileage engines that can be equipped to suit your needs. Also, wrecking yards may still be dirty, but the smart ones have kept up with the times and can be accessed online. They
may have listings for their complete engines or simply respond to inquiries by e-mail, but it's entirely possible to have a Gen III engine delivered to your door without ever leaving the garage. THE ISSUES ARE MOUNTING:
To get an idea of how to mount up one of these engines, we Called a few companies, namely Total Cost Involved and Street & Performance, visited a shop or two that regularly installs LS engines in street rods, and even checked out a couple of do-it-yourselfers. But everyone we checked with basically had the same idea, which was to fabricate some sort of adapter plate that bolts to the block. Then an early-style Chevy mount would bolt to the plate. From there, the possibilities are endless, yet the end result was always the same: to have something for the early mount to slide over and the bolt to run through it horizontally from front to back, The general consensus was to have the engine sitting as close to where the old small-block sat as possible. Also, Chevy engines run on the four-degree rule. That is, the engine usually sits on a four-degree downward angle from front to back. Even though the LS engines sit at a zero angle in the Vettes, the four degrees is recommended to help with your pinion angle.
  In some trucks, it may be feasible to set the engine back a bit further to help the accessories or even the stock mechanical fan clear. But something to consider is that switcing to elecnic fans or a push fun, or even moving the accessories around, may be easier than relocating the engine mounts or modifying the crossmember. The A/C compressor and power-steering pump on the truck engines are mounted very low on the engine and could present a problem where the frame pinches as it reaches the front There are also balancers that run closer against the block than others; the Vette is a fu1l 1- l/2 inches shorter than that of the trucks. The best source we found for these types of issues was Street & Performance. Not only do they have a vast knowledge of everything Gen III, they have a huge inventory of both OE and their own custom brackets and pulleys to help overcome any clearance issue you might have. Of course there's one factor that may dictate exactly where you will be mounting your engine: the oil pan.
Corvettes, F -bodies, and trucks are all different, yet interchangeable, which is good news. More good news is the fact that in both of the '63-72 swaps we saw performed, the truck oil pan couldn't have contured around the crossmember better. Nonetheless, while speaking with Scott Leon at GM Perfonnance and Mark Campbell of Street & Performance, we learned that there are several transplants in muscle cars that require modification to the pan.
  Finally, we keep mentioning using the 4L60E transmission that came behind nearly all of the cast-iron LS engines. One reason is the nice price break you usually get by buying the two together. Another is the fact that unless you are running the 4L60E, you will have to change the Flexplate and possibly order a different wiring harness, as the cormections for the 4L60E are usually included in the harnesses that are available. But just as everything else we have discussed, there are companies like McLeod Industries and Advance Adapters that offer components to enable mating the LS engines to a variety of earlier transmissions, both automatic and manual. The actual mounting of the transmission to the crossmember could't be easier. In some cases, it may be necessary to use a universal crossmember from somewhere like Classic Performance Products. In some trucks, you can get away with easily redrilling the mounting holes on the stock crossmember. Undoubtedly, the driveshaft will have to be shortened this is an area where you will have to rely on the professionals. And, just for the record, different shops measure for driveshafts in different ways, so call ahead any time you have to shorten or lengthen a driveshaft. Well, now that the engine is solidly mounted in place, let's take a look at what else is involved to get you back on the road.
If you've heard anything about installing a Gen III engine in any vehicle, it's that sorting out all of the electrical connections for the coil packs and multitude of sensors can be a nightmare. And if you're hoping that you may save a few bucks and figure it out yourself, it will be a nighmare. Moreover, if you don't send the computer out to a qualified shop for reprogramming, the engine simply will never run at its full potential if at all. Companies like Painless Performance, TPI Specialties, and Street & Performance pride themselves on being ahead of the curve for these types of swaps, and each offer a complete harness that will make the install worlds easier. Other than four leads and grounds, most of these kits are truly plug and play and have all of the weather-pack plugs already attached with all the relays and the diagnostic link at the correct length with detailed color-coding and labels. And speaking of grounds, it was stressed to us several times just how important proper grounding of the engine is. The recommended method is from the battery directly to the engine or transmission, and then to the engine to the frame and the frame to the body.
   Each company had different methods of reprogramrning the computer, but the general idea is to remove all of the programs that will not apply once the engine is transplanted. One of the most important of these programs is the Vehicle Anti Theft (VAT) device. Another has to do with the removal of the charcoal canisters for fuel vapors. Finally, similar to aftermarket re-programmers, the correct transmission type, gear ratio, and tire diameter is inputted to help you get the most out of the engine. On '74 and earlier vehicles, emissions programs can be removed without effecting the clean-running LS-series engines.
Running the Gen III engine requires the use of a high-pressure fuel system equipped with a return line. The most common solution is to install an in-tank fuel pump that accepts a fuel line. Once again, the manufacturers are ahead of the curve, as Street & Perfonnance works closely with Rock Valley to make available several-style fuel tanks with the in-tank fuel pump already installed. Another option that we have seen is to install a frame mounted-type fuel pump with the proper pressure and that allows for a return line.
Most of the Gen III engines have cable-operated throttle bodies. However, some of the Vettes and all the trucks beginning in '03 are "drive by-wire" or electronic throttle bodies. While the current solution is to convert the throttle body to the earlier one, Street & Pelformance informed us that they are working on a system to work with the drive-by-wire setup because it is here to stay.   Well, there you have it all the key issues to prepare for when you make the jump into Gen III. Be sure to check out the Web sites of the aforementioned manufacturers to see which of their products are for you. There is a wealth of knowledge contained on those pages that we could not even begin to tell you about here. But if we learned anything with this, it's that "winging it" simply won't work. The power and technology is waiting. Us regular guys just need to catch up.

Here is the most plentiful source of Gen III engines there is: wrecked '99-up GM trucks and SUVs. We've seen 'em with as little as 3,000 miles on them.

The '99-up truck oil pans are a great fit with the crossmember in '63-72 GM trucks. It couldn't be a better match if it was planned.

The first obstacle to overcome is getting a mount to fit the new-style bolts on the block. 

Here's a F-body pan that had to be trimmed extensively for use in an early muscle car. 

The setup that Total Cost Involved recommends is their polished aluminum adapter plate. It's super thin thanks to countersunk bolts, and it accepts the early-car-style Chevy mounts. Their frame mount is a universal piece. It can be trimmed down as far as needed to fit and then welded to the frame.


Although the stock crossmember can sometimes be moved or redrilled, this crossmember from CPP, made specifically for '63-72 GM trucks, makes the job much cleaner. It will slide wherever you need it to before bolting it in.

Here's a Total Cost Involved adapter in action. Here, the owner simply welded a piece of tubing to the frame mount for the early-style mount to fit over and bolt to. 


A LS-series wiring harness from a reputable company is something you simply cannot avoid when working with these engines. All of the hard work has been done for you; it is simply plug and play. It's also mandatory that you send your computer out for reprogramming. It's advisable that you use the same company you're getting the harness from. Shown is the Painless Performance kit for '99-up LS-series engines.

Scott Leon of GM Performance sent us his version of the same basic idea that he used for a '70 Chevelle. It's a chunk of billet with a hole drilled for the mount bolt. 

While advancements are being made every day by companies like Street & Performance, it is recommended to find a pre-'03 engine that has a cable-driven throttle body rather than a "drive-by-wire" unit, or swap the throttle body for the earlier unit. A cable is easily adaptable to the stock accelerator linkage. 



Here is a daily-driven 5.3-liter in a '72 Chevy with thousands of miles on the odometer and not a single problem to speak of. And there's more power and torque on hand than any stock small-block.


It's always best to have shop and assembly manuals on hand to make sure your installation is correct and to make the project as easy as possible. We recommend factory manuals, available at Greg's Automotive