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How to Swap in a Carb-Equipped LS Engine

Carb-Equipped LS Swap 101 - Want modern LS power but without the hassles of retrofitting fuel injection? We show you how.

Patrick Hill Jan 28, 2014
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Since it came out in 1997, the LS engine family has altered the landscape of Chevrolet performance almost as much as Gen I series small-block. It’s a great performer in modern vehicles, but its compact dimensions and huge power make it a prime choice for being swapped into earlier Chevrolets. While the Gen I family still reigns supreme for overall cost effectiveness, its offspring (Gen III and IV) are quickly closing that gap.

One thing that still gives some trepidations about performing an LS swap into an older vehicle is fuel injection. All the wiring, fuel line plumbing, mounting a computer, etc., is still a daunting task for many when compared to bolting on a simple carburetor that you only need a screwdriver and vacuum gauge to tune. Many enthusiasts tend to stick with what they know, and a lot of guys know carbs better than they know their own cell number.

But what about putting a carb on an LS engine? Many on both sides would decry it as sheer lunacy. The fuel injection side would scream “Why are you putting archaic technology on a modern engine?”, while the carb side would yell “That’s too complicated!”

So, why convert an LS engine to a carb for an engine swap? Greg Lovell, owner of Antivenom High Performance in Seffner, Florida, is one of the country’s leading tech’s for swapping LS engines into cars. We asked him why would you do this.

“A swap like this can be done to save on the expense of wiring, elaborate fuel systems, computer tuning availability, and simply as a starting point. The swap can be driven this way for a long time,” says Greg. “Later, a fuel system and computer controls can be added for the full swap. A carb equipped LS engine is a very easy way for an old-school Chevy guy to get familiar with the Gen III and IV engine family, and not have to learn the computer tuning. He can now simply get his feet wet as opposed to diving right in.”

As it happened, Greg had an ’87 Caprice at his shop that was undergoing a salvage yard 5.3L truck engine swap and the owner wanted carburetion. Thanks to a new array of parts from Holley and its subsidiary companies, swapping in a carb-equipped LS is easier than ever. We decided to follow along, and see exactly what goes into doing this swap. It was pretty eye opening, and once you read through, it might make you reconsider your next build.


1. Here’s where we started. The 305 in our subject ’87 Caprice had over 200k miles on it, was never much in the power department, and had begun consuming oil, smoking, and was just ready for retirement.


2. Since LS engines use a different motor mount location, adapter plates have to be used when installing in a pre-LS factory chassis. Hooker’s adapter plate (part no. 12611HKR) bolts right to any LS block, and allows for the use of earlier factory motor mounts and mounting locations.


3. This salvage 5.3L engine came from an ’04 Chevy Trailblazer. For $600 on eBay, the car’s owner got a running, all-aluminum 5.3L, a real catch. Unfortunately, the factory oil pan on the 5.3L won’t work when retrofitting this engine into an earlier vehicle. Because LS engines use a gerotor-design oil pump that’s driven off the crankshaft, the oil sump pickup is located at the front of the engine.


4. The solution is Holley’s retrofit oil pan, part no. 302-1. It comes complete with oil pickup tube and baffle, and allows for a wet sump LS engine to clear earlier factory crossmembers and steering linkages.


5. The oil pan kit comes with a new pickup that shifts the sump to the rear of the oil pan.


6. This baffle plate is included to prevent oil sloth and frothing, keeping the pickup immersed in oil.


7. The Holley oil pan uses a rear sump design like Gen I small-blocks and Mark IV big-blocks, so it’ll clear factory steering systems without problems (except ’62-’67 Novas). It’s a solid cast aluminum piece, so durability and strength are no question here.


8. Out comes the 305. For less than the cost of rebuilding this engine or buying an already rebuilt 305, the owner picked up a 290 horsepower 5.3 out of wrecked Trailblazer via eBay. Yes, there is the cost of the conversion parts, but in the end, this engine will last another 200k miles (with regular maintenance, provide almost twice the horsepower and better fuel economy. Because it’s all aluminum, it takes 150 lbs off the nose of the car.


9. The upper mount bracket from the 305 is bolted onto the Hooker adapter brackets.


10. When bolting an earlier transmission to an LS engine, there’s a problem—the torque converter. The flange on an LS is a different thickness than on a Gen I motor, and it doesn’t align the Gen I torque converter properly.


11. The solution is this GM flywheel spacer (part no. 12563532- $54.69) and flywheel bolts (part no. 11569956 - quantity 6, $3.47 each). This plate makes up for the thickness difference between the LS flange and the old Gen I small-block flange. It also keeps the torque converted centered on the crankshaft.


12. With everything ready, the 5.3 is dropped into the Caprice. It was amazing how easily the LS-based motor fit into the space where the 305 used to be, and even gave us some extra room in the engine compartment.


13. The factory exhaust manifolds on the 5.3 won’t work in this setup because the outlet is in the wrong place. The easy solution were these Hooker conversion headers for a second-gen Camaro, part no. 2471-1HKR. The car already had a dual exhaust system in place, so all we had to do is trim the pipes back to mate with the headers, and viola!


14. We did run into one problem, though. The driver’s side header hit on this ear on the transmission bellhousing.


15. Another easy solution: We just cut the offending ear off. After that, the headers cleared with no problem.


16. With the engine in place, we could start bolting on the accessory drive using Holley’s accessory drive brackets. First up was part no. 21-3 for the alternator. The bracket is a two-piece design that bolts to the front of the block on the driver’s side. The alternator is a standard late model unit, part no. 01-1748X, from O’Reilley’s Auto Parts.


17. Next is the bracket (part no. 20-131) for the AC compressor. The Holley bracket uses the same R4 radial compressor the Caprice came with stock, except it relocates to the passenger side. Because we’re converting from V-belts to a single serpentine belt, the compressor for an ’88-’95 V-8 full-size Silverado is used.


18. The intake we’re using is a dual plane Edelbrock Performer RPM LS1 (part no. 71187) that comes with a dual bolt pattern to fit either Edelbrock or Holley flanged carbs. For ignition, we’re using MSD’s stand alone LS1/LS6 ignition controller, part no. 6010. It’s designed to just run the factory LS coil-on-plug ignition, using the stock crank and cam sensor.


19. Because we’re using a carb, the Caprice’s factory throttle, TV, and cruise control cables can still be used. This new cable bracket came with our intake, and installs like so.


20. The MSD ignition controller is an almost entirely plug-and-play unit. The simple harness it comes with has one master plug that bolts into the control box, then eight plugs that run to the ignition coils, plus one to a MAP (Manifold Absolute Pressure) sensor in the intake.


21. The Edelbrock intake already has provisions to mount the MSD MAP sensor here. A MAP sensor measures the vacuum pressure inside the intake manifold, and along with the RPM reading of the engine, tells the ignition to either advance or retard the timing.


22. To power the ignition, this main pink wire from the new ignition harness is run to the pink wire on the factory coil plug. This supplies the ignition with key-on power.


23. For the cooling system, you can use the stock radiator. First up is a new upper radiator hose, Gates part no. 22436, which is spec for an ’99-05 4.8/5.3 Silverado.


24. Turning to the power steering system, we installed this 135-degree hose first, which connects the fluid reservoir to the pump. Don’t try to install it on the reservoir first. You’ll never be able to secure the clamp on the pump end of the hose.


25. And the reservoir slips onto its bracket. From there, we connected the return line from the steering box to the reservoir. We reused the factory 305 high-pressure power steering line from the pump to the box, but had to change the shape of its hard line a bit for fitment. The return line was just a simple matter of reusing the factory hard line end and clamping on a new piece of hose.


26. To make things easy, we converted to an electric fan. But on an ’87 Caprice, the factory fan shroud also functions to hold the radiator in place. To clear our new fan unit, but still secure the radiator, we modified the top and bottom portions of the factory shroud as you see pictured.


27. For our lower radiator hose, we reused the factory 305 hose, and only needed to trim it back some to fit the 5.3’s return outlet. Once we had the trim and fitment just right on the old hose, we went and got a new one, cut it to match, then clamped it on.


28. Another coolant fitting we had to add was this line from the factory steam tube from the heads to the radiator. We installed a nipple fitting here, then ran a piece of high temp hose from it to the outlet on the steam tube.


29. The Holley accessory drive kit comes with a belt tensioner that installs on the passenger side to keep the new serpentine belt nice and tight.


30. The Holley accessory drive uses a Gates K060944 serpentine belt. If your parts store doesn’t carry the Gates brand, they can use a cross reference guide to find the equivalent in the brand they carry.


31. For fuel delivery we went with this Holley 670 CFM Ultra Street Avenger vacuum secondary carb. It has a lightweight aluminum main body, with billet metering blocks and base plates.


32. We mounted the relays for the ignition system here on the passenger side front fender.


33. To feed our carb, we installed a Holley electric Blue pump back by the gas tank. We just cut the factory feed line, spliced in our pump, then secured it to this crossmember.


34. To hook the alternator into the car’s electrical system, Holley includes a new alternator plug with its accessory drive kit. It’s a four-wire plug, but in our application we only needed one. With the unnecessary wires cut away, we spliced our remaining wire into the factory wiring harness per the instructions.


35. To keep the 5.3 cool, we hit the local boneyard and snagged the dual cooling fan assembly from a ’97 V-6 Camaro. After a little modifying, it fit like a glove. Then we wired into the factory harness using a factory coolant sensor, with a turn on temp of 180 degrees.


36. And here’s the finished installation. It runs and drives perfectly. The only thing left to do is visit a qualified A/C shop and have them make up some new hoses for the compressor, then charge the system.


Hooker Headers
Aberdeen, MS 39730
Seffner, FL 33584
Holley Performance Products
Bowling Green, KY 42101
Torrance, CA 90503
MSD Ignition



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