You've got a lot of options when it comes time to repower your project truck. Certainly, rebuilding the original engine is a cost-effective choice, but is it the best use of your time and will it yield the results you're ultimately after? Depending on who is doing the wrenching, your engine build might not turn out the way you'd like it to. The easier solution is to simply call up your local GM Performance Parts-certified dealer and choose one of the company's many crate engine options. After that, you're just an engine swap away from monster horsepower and, quite possibly, a better driving experience.
We just picked up a '73 Chevy C10 pickup with the intent of turning it into a respectable cruiser. Our first goal after taking delivery of the dilapidated truck was to swap out the worn-out Gen 1 small-block 350-cid engine and put something a bit more modern in its place. After weighing our options, we decided that transplanting a carbureted version of GM's LS1 powerplant would be painless and run hard while yielding respectable fuel economy with an overdrive transmission.
Keeping our wallet in check was as simple as choosing the smallest LS-based engine GM offers, the LS327/327. This 5.3L powerhouse is similar to the one offered in late-model GM pickups but with a few notable exceptions. Your garden-variety 5.3 puts out 295 hp and 325 lb-ft of torque; GMPP advertises the LS327 to crank out 327 hp and 347 lb-ft of torque by way of a more aggressive camshaft and a friction-reducing piston coating. According to GM, not only is this engine an excellent candidate for an engine swap in an older project truck, but also for late-model Silverados or Sierras that are ready for a heart transplant.
We took our engine to Westech Performance Group for a dyno session to validate GM's numbers and took advantage of the tuning session to test some new parts from MSD, Holley, and Edelbrock. Baseline testing showed our engine cranking out 361.8 hp and 378.1 lb-ft of torque with an Edelbrock Performer RPM intake manifold, MSD ignition system, and a Holley Street HP Series 650-cfm carburetor. The power peaked at 5,600 rpm before the valve springs let us know they were not going to allow the engine to rev any higher without floating the valves. So we swapped out the stock springs for a new set of Comp Cams Beehive valve springs and a new Comp Thumper camshaft that would give the engine more power upstairs.
The cam swap completely changed the attitude of the exhaust note. The engine was breathing through a set of Kooks long tube headers with 18-inch collector extensions. After the cam change, the engine growled at idle with one of the lumpiest idles we've heard in a long while. It sounded like every great V-8 should. The cam and spring upgrades were worth 23.2 lb-ft of torque at 4,300 rpm and 49.6 hp at 6,400 rpm. More importantly, the motor was safe to rev into mid-6,000-rpm territory now, without any hint of valve float. Once we were satisfied the rings were seated during our initial dyno pulls and all was well, we drained the conventional motor oil from the pan and refilled it with Lucas Oil's 5W30 full synthetic motor oil. The change was worth another 3 hp and 4 lb-ft of torque throughout the entire powerband. In the end, our 5.3 cranked out 414.5 hp at 6,400 rpm and 405 lb-ft of torque at 4,300 rpm.
The LS327/327 long-block (part number 19165542) can be purchased through GMPP retailers like Scoggin-Dickey Parts Center for $3,149.95. The Holley Street HP carb (part number 0-82651) from Summit Racing adds another $501.95, the Edelbrock Performer RPM intake manifold (part number 71187) adds $285.95, the MSD 6LS controller (part number 6010) adds $312.70, the 8.5mm MSD plug wires (part number 32819) add $61.00, and the MSD coils (part number 8245) add $631.00 to the price tag of the motor. The running motor ends up costing $4,941.55 except for a few carb studs and base gaskets and didn't require any trips to the machine shop or an engine builder, and it rips off power numbers that'll make our Chevy run hard. Follow along with the photos and check out this economical alternative for repowering your daily driver or classic project truck.
The Build
This is what the LS 327/327 looks like once its out of the crate. Except for the Kooks headers, this is what you get. Its up to you to provide the accessories, either from aftermarket companies or from the GMPP catalog.
1.The 327 relies on the popular...
1.The 327 relies on the popular LS1 "cathedral port" aluminum cylinder head design to make power. Note the factory-installed steam lines that connect the four corners of the cooling system. These lines aid in preventing steam pockets from forming in the engine. Steam pockets are a no-no when you're trying to keep an engine cool.
2a.There are slight clearance...
2a.There are slight clearance issues with the Edelbrock Performer RPM intake and the steam lines, which can be remedied by modifying the shape and routing of the lines. Westech had a set that eliminated the front-to-rear connections, which was fine for our test session. We'll be adding the missing link before the truck sees the engine bay of our '73 though.
2b.
3a.The new single-plane intake...
3a.The new single-plane intake manifold uses the factory-style O-rings (not provided with the manifold) to seal to the cylinder heads, which plays right into the no-hassle nature of this engine. GM made it very easy to work on the LS thanks to O-rings like these. There's a small amount of casting flash throughout the plenum and intake ports in the manifold that could stand to be smoothed out. We wanted to test the manifold as it came out of the box though, so we left it alone.
3b.
4.Automotive Racing Products...
4.Automotive Racing Products provided the carburetor mounting studs. The intake manifold was attached with 6x50mm hex-head bolts and AN washers that were torqued to 11 lb-ft.
5.The MSD 6LS ignition controller...
5.The MSD 6LS ignition controller is more than just a spark box. It offers several programmable features to control timing and rpm adjustments. Using the supplied Pro Data software, you can program a custom timing advance map, two different rev limiters for starting line holeshots and peak rpm, and a step-retard to remove up to 15 degrees of timing at a specific time. This is an ideal feature when running nitrous oxide. The 6LS also has the capability to constantly alter the ignition timing at idle to help smooth out a rough idle if you so desire. And if you're not into playing with computers, MSD supplies six preprogrammed timing advance curves that are stored in plug-in modules. The Edelbrock intake has mounting lugs for the 6LS at the front of the intake.
6a.Using the intake manifold...
6a.Using the intake manifold mounting location, the controller was too close to the carburetor for our liking, so we stacked two extra base gaskets beneath the carb to solve the clearance issue.
6b.
7a.We went with a Holley Street...
7a.We went with a Holley Street HP Series 650-cfm carburetor to meter the air and fuel for our LS. The Street HP carbs offer many of the features of the high-end Ultra HP carbs except for the billet metering blocks and base plates-for about half the cost. Our favorite features of the 4150-style Street HP carb include screw-in air bleeds for fine-tuning the fuel curve, contoured venturis for increased airflow, and idle mixture screws that won't vibrate loose from the metering blocks. You also can't go wrong with the new shiny finish of the Street HP, and the Dominator-style float bowls add the capability to plumb your fuel lines from either side of the carburetor.
7b.
8.The LS327 does not come...
8.The LS327 does not come with ignition coil mounts. The mounts are available through your local Chevy parts dealer. We found ours at the local junkyard. The MSD system plugs right into the coils and then only needs a 12-volt constant and switched power leads and a battery ground hookup. After that, it's just a matter of programming the controller or plugging in one of the providing timing curve modules (inset).
9.When the motor was ready...
9.When the motor was ready to fire, we filled the crankcase with Lucas SAE30Plus motor oil for the break-in period.
10.The carb only needed minor...
10.The carb only needed minor main jet changes to bring the air/fuel ratio in line for maximum power.
11.Westech's manager, Steve...
11.Westech's manager, Steve Brule, then flogged the motor at cruising rpm to simulate real-world driving conditions and tuned the high- and low-speed air bleeds to find a balance between power and driveability.
12.By now, we had found the...
12.By now, we had found the rpm limitations of the stock valve springs. We decided to change the camshaft and springs, so off came the ignition coils and valve covers. Once again, we found O-rings beneath the covers, which made the parts swap clean and easy.
13.After removing the rocker...
13.After removing the rocker arms and pushrods from the engine, Steve busted out this unique tool that compressed the valve springs enough to remove the retainers and locks. We'd love to tell you where to get the tool, but the company is now out of business. Sorry.
14.Next, we removed the balancer...
14.Next, we removed the balancer from the crankshaft and then the front timing cover and timing chain. This gave us access to the cam retainer, which was also removed.
15.We can tell you where to...
15.We can tell you where to get these trick cam installation tools. They are made by JPR and we found them at thunderracing.com. The rods slide into the tunnels below the lifters and support the lifters so that you can slide the camshaft out without removing the intake manifold or lifters. We were able to do a complete cam and spring swap in under an hour using these tools.
16a.Our Thumper camshaft specs...
16a.Our Thumper camshaft specs out as follows: Gross valve lift for both intake and exhaust lobes is 0.554 inch. Duration at 0.050 inch is 219 degrees on the intake side and 233 on the exhaust side, and the lobe separation is ground at 109 degrees. Once the cam was slid in place, the retainer and timing gear were reinstalled. The retainer bolts were torqued to 17.7 lb-ft and the timing chain bolts torqued to 25.8 lb-ft.
16b.
17a.Finally, we installed...
17a.Finally, we installed our new Comp Cams Beehive valve springs , and since the LS comes with hydraulic lifters we simply torqued to 22 lb-ft without needing to check the valve lash. The Beehive springs are good for up to 0.625 inch valve lift and 125 pounds of seat pressure at 1.800 inches installed height, which is plenty of control for an even more aggressive cam design. The durability of these springs comes from the use of very high-end wire that is "micro peened" to stress-relieve the part. Put simply, these springs work and will last.
17b.
18.Our final test with the...
18.Our final test with the LS327 was to drain the SAE30 conventional motor oil and refill the crankcase with Lucas Oils new 10W30 Racing synthetic motor oil. The switch was a good one because we found even more power in our combo.
The Final Word
Whether you add the Thumper camshaft and Beehive springs or not, this motor rips and makes an excellent replacement mill for GM pickups. With over 325 lb-ft of torque at 2,500 rpm on tap, the LS327 has plenty of grunt for work and play. We are currently gathering motor swap parts for our '73 Chevy project truck and will report back in a couple of months how the swap went and whether we were able to score some decent fuel economy from our square-body truck.