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Yes, this is yet another story on swapping LS engines into a 1960s GM muscle car. But most of those stories don’t offer all – or at least most – of the major parts that you’ll need to complete your swap. If nothing else, this can be a great introduction to what’s available to solve many of those common issues involved with LS engine swaps. Holley offers a ton of parts that are designed to make this swap as easy as possible.
This could be a story a little like “The History of the World in 30 Seconds” if we decided to take on all the different GM cars that you would want to wrangle an LS in into. Instead, we’ve chosen to highlight one particular body style, the 1964-1967 A-body...in this case, a 1967 Chevrolet Chevelle. Of course, this also covers the Buick Skylark, Oldsmobile F-85 and Cutlass, and the Pontiac Tempest.
Here’s our completed LS swap in the ’67 Chevelle using a cable throttle kit from Lokar and inlet air tubing pieced together from multiple sources using a factory MAF.
If you have the right perspective, many of the scenarios we’ll discuss will also carry over into other vehicles that use similar parts, like the 1978-1988 G-body, early Camaro, rear-drive X-car or perhaps even a C-10 pickup. This story will offer guidance concerning the pieces you’ll need, along with a few tech tips that might make the swap less stressful.
What we can’t do is offer all the parts you’ll need nor dodge all the pitfalls, but we can steer you in the right direction based on the multiple LS swaps we’ve attempted. The driving force behind this story came about because we were totally immersed in this exact swap while helping our friend Eric Rosendahl as he wrestled with his ’67 Chevelle 300 Custom sedan. The car was originally powered by a 383 small-block Chevy that was backed by a Tremec TKO five-speed, and a 12-botl with 3.55:1 rear gears.
Eric wanted a more sedate powertrain so he replaced that nervous 383 with a 5.3L LS engine bored to 5.7L specifications with stock 5.3 heads for more compression, a mild camshaft, and a stock LS2 intake backed by a 4L60E four speed automatic overdrive trans. All we had to do was connect the dots. Eric’s plan called for a factory ECU and wiring harness. This presented some challenges in terms of both locating the ECU and routing the huge anaconda-like snake of a wiring harness.
Assuming the engine will be controlled by EFI and you don’t want to wrestle with a factory ECU and its monster wiring harness, Holley has a simple and affordable conversion in the Terminator-X. The harness is minimal and extremely easy to connect and use. That blue hose extending from the ECU is the connection for manifold vacuum to the built-in MAP sensor.
While he eventually accomplished this task, it would have saved perhaps 6-8 hours of planning and pre-fitting work if we’d had instead used a Holley Terminator-X ECU or even perhaps a Holley HP ECU and harness. The advantage of either of these ECU’s is that they are significantly smaller than the GM computer and also employ a drastically more compact wiring harness that is dramatically smaller than the GM version. One reason Eric wanted the GM ECU was to be able to integrate control of the 4L60E transmission but the Terminator-X MAX version also offers the ability to not only control a 4L60E/4L80E transmission but also electronic throttle as well.
Mechanically, one of the first decisions involved the combination of Holley motor mounts and the Holley rear crossmember. Eric selected the clamshell style mounts, which required replacing the factory frame mounts. The next issue to address included the oil pan. Chevelles and early Camaros position the LS very tight to the front crossmember and Holley’s shallow front 302-2 pan fit very well while not extending below the crossmember. Other so-called muscle car pans deserve careful consideration as many are significantly deeper, extending below the crossmember, making potential pan damage an almost certainty.
The Holley pan also integrates the oil filter exactly like the OE pans. Other aftermarket pans require either a remote mounted oil filter or must use a separate billet aluminum adapter that increases the cost. The Holley pan is self contained and includes a matching oil pump pickup.
This cast aluminum Holley pan (PN 302-2) works exceptionally well in Chevelles that are generally very tight to the engine crossmember. Note how it is shallower at the front of the pan – this is what the Chevelle and early Camaros need to fit properly. This pan also integrates the oil filter in the stock location.
While we were under the car, Eric decided on a maintenance-free exhaust, deciding on a set of Hooker cast iron 2 ½-inch outlet manifolds along with a pair of Blackheart exhaust pipes. This improved ground clearance over a set of full-length headers. A great compromise for those looking for both power and ground clearance would be a set of intermediate length headers. We’ve included the part number for those headers in the accompanying parts list. There are also complete exhaust systems available from Hooker or Flowmaster for these early Chevelles that can also be found in the parts list.
A great advantage to the Frostbite LS swap radiators is they come with threaded bungs to allow a fitting for the specific application. So for an LS swap, the upper hose from the engine is 1 3/8-inch with the closest being a 1¼-inch diameter barb while the lower hose that connects to the thermostat would be a 1½ inch barb on the radiator.
The cooling system is another area that requires some decisions to be made. Eric had previously acquired a replacement aluminum radiator for the small-block’s leaking copper brass unit. This radiator choice necessitated hours of searching and trial-and-error fitting of hoses and adapters to account for the difference in hose sizes. The nipples on a stock replacement Chevelle radiator are 1¾-inch for the lower and 1½ for the upper. LS engines use smaller hose bibs with the lower at 1½ and the upper measuring 1 3/8-inch.
An easier approach might have been to opt for a Holley Frostbite radiator. These engine swap radiators come with a large, -10 threaded connection that use a hose nipple that can be matched to the engine’s hose sizes. These nipples must be purchased separately and we’ve included the correct sizes in the parts list. SPAL is another Holley brand, one that specializes in electric fans, and their catalog offers a multitude of single and dual-fan options for these radiators. We like to run a dual fan assembly mainly because they can be staged, and they also offer clearance right at the water pump centerline which is often where additional clearance is needed.
In Eric’s case, he was using a Vintage Air accessory drive purchased from a friend. Holley also offers a variety of accessory drives divided into three categories of Low-, Mid-, and High-Mount versions. While the Low-Mount version is cool, it interferes with the Chevelle’s steering box so the option would then be for the Mid-Mount orientation. These accessory drive systems are modular so you can combine them with whichever stock balancer came on your engine. Balancer height determines the pulley placement for these systems. This is an advantage over the Vintage Air system that requires a custom aftermarket balancer that is somewhat pricey. If clearance to the radiator or electric fans is tight, you can opt for the shallowest Corvette drive.
Here we’re adding the Sniper fuel pump to the tank along with the fuel level float assembly. The kit comes with a 255 LPH pump that will support well over 500 normally aspirated horsepower. With the Sniper tank installed in the car, we used Earl’s Ultra-Pro PTFE hose and fittings to connect the tank to the fuel delivery system. The tank is 1 inch deeper in the front to accommodate the in-tank pump assembly with capacity at 20 gallons.
With the engine and transmission in place, Eric turned to the fuel delivery system. It’s worth noting that the best way to ensure a smooth running EFI engine is to start with a well designed fuel delivery system. Sniper offers a retro-fit in-tank fuel pump module, should you intend to retain your stock tank. Eric decided to replace the original tank in favor of a new Sniper assembly. This powder-coated tank came complete with a 400 liter-per-hour (LPH) in-tank pump and mount, as well as a fuel level sender. This required some minor assembly which Eric completed in short order. He decided on a GM Corvette style filter regulator mounted up near the front of the chassis, using the Chevelle’s original 3/8-inch fuel line as the return. Another option would have been to use a Holley filter regulator mounted near the fuel line with a large capacity filter. Holley also offers a combination filter-regulator that has become quite popular.
The engine came with a composite intake manifold without a fuel rail and a set of unknown injectors. When we attempted to start the engine, it would not fire. After hours of diagnostics, we discovered a set of fully plugged injectors. We could have had them cleaned and flow tested but that would have set us back over two weeks, providing a minor savings over a brand new set of injectors. For this engine, we chose to use a set of new Holley 42 lb-hr injectors that allows Eric to step up the power at some point in the future. We also included a Holley Sniper fuel rail kit to complete the fuel delivery portion.
With the engine in place and properly wired, it refused to fire. We discovered our take-out injectors were all plugged up. So we ordered a set of Holley 42 lb-hr injectors to replace the factory Flex-Fuel injectors that were slightly smaller. The engine then fired immediately.
Because Eric was looking for ultimate reliability with this conversion, he elected to use Earl’s Ultra-Pro PTFE fuel hose and fittings. The Ultra-Pro hose uses a high quality, non-conductive polytetrafluoroethylene liner. This material is non-reactive, which makes it ideal for long-term use with gasoline, ethanol, methanol, and even nitromethane! However, the hose does require its own specific Ultra-Pro fittings, which are more expensive than standard AN fittings and hose. The projected lifespan of this hose makes it a wise choice.
In this install, Eric chose to use a 4L60E automatic, but we thought we’d offer suggestions for a manual transmission conversion. The most common selections will either be a four-speed like a Muncie or Super T-10 or, more likely, either a Tremec TKO /TKX five-speed or perhaps one of the T-56 six-speed variants. Regardless, you’ll need a bellhousing. Our experience with OE bellhousings is that after years of heat cycling, they are often off-center when checked for concentricity.
One of the small things that can screw up your LS swap is to make sure the alternator is wired properly. Holley offers a plug terminal with a wire connecting the “L” terminal on the alternator to the charge indicator light in the dash. If a charge light is not used, you must a small, 50-watt resistor in line to prevent alternator damage.
We wrote an accompanying story (which you can read by clicking here) on the Lakewood aluminum bellhousing and found this part is very close to perfect right out of the box. It’s still advisable to check concentricity, especially if using a Tremec TKO/TKX transmission as these gearboxes demand proper alignment. If you’re going for a T-56 style six speed, Quick Time offers a steel scattershield that will mate to the six-speed’s unique bellhousing arrangement. You might also investigate a Hays LS style flywheel, clutch, and pressure plate assembly. Another option is making the leap to a hydraulic clutch release system. Holley offers a couple of options aimed at use with the T-56 six speeds as well as the Tremec TKO/TKX and older four-speeds.
After replacing the plugged injectors, the engine came to life, but after 10 minutes of run time it still felt soft and clearly needed tuning. Because this is an OE computer, it will require custom tuning that generally costs between $500 and $1,000. This is on top of the cost of the original ECU from an outside source as well as the new harness. Added all up, this would exceed the cost of a Holley Terminator-X unit and nearly equal the cost of a 24x Holley HP ECU and harness kit. Plus, this does not address the additional time spent taking the car to the tuner, perhaps more than once. We bring this up not to necessarily condemn the factory ECU choice, but rather to offer additional options.
This overview of options for an LS swap is aimed at helping you make informed decisions on major equipment components that will be necessary to complete the swap. There are a ton of little details like switched 12-volt availability, the need for multiple good grounds for the electronics, and a dozen other pieces to the puzzle like driveline alignment that you will still have to face. But with a solid plan and good execution, an LS swap can deliver 21st Century power and convenience to your classic street machine.