By Joe McCullough – Images by the Author
Catch Up Here:
The Speedway Motors ’68 C10 Build Part 1
Speedway Motors’ 1968 C10 Build Part 2: Chassis & Suspension
With the rolling chassis for our ’68 C10 project complete, it was time to figure out what engine and transmission we should drop into it. In keeping with our theme of “cool driver on a budget,” we hit up the local junkyard in search of some affordable horsepower. What we found was a 5.3 LS engine in a 140,000-mile GMC Sierra. There’s always a bit of risk involved with buying a used engine like this, but we’ve found these GM Gen III and IV engines to be very durable, even over 100,000 miles.
LS engines are capable of some amazing things. But as pulled from the junkyard, they sure are ugly. With our “new” engine back at the shop, we got busy pulling off all the crusty old wiring and accessories. Our plan was to do a simple cam swap and rocker trunion upgrade to see how much power we could make without breaking the bank on anything fancy. To help us achieve this goal, we called in some expert help. Zach Woods runs the Speedway Motors Racing Engines shop. He spends his days building 900hp circle track racing engines, so he knows a thing or two about building reliable power.
Once we finally had all the stock junk pulled from the block, Woods showed us a cool trick for cam swapping an LS engine. With the rockers removed, giving the cam a spin will push the lifters up in the trays. Then, a pair of dowel rods inserted into the oil galleries will keep them there while the old cam is removed and the new one is slid in place. Cool, right?
We selected a BTR “Truck Norris” cam for this engine. These cams were designed specifically for these 4.8-, 5.3-, and 6.0L truck engines and promise to deliver solid midrange and top end power without compromising torque off the bottom. As Woods installed the new bumpstick, we could just hear that lumpy idle and imagined ourselves loping around town in our hopped-up C10. But we were awoken from our daydream to find that reality had reared its head and we were in for a bit more work than we expected.
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When you’re working with a used engine, it’s always important to inspect everything carefully. At a glance, all of our valvetrain components looked OK to be reinstalled and run with the new cam. But careful inspection revealed some wear on a few of the pushrod tips and rocker arms. It’s likely that the stock lifters were starting to get a bit sloppy and the added lash was causing the wear. In the interest of doing the job right, we elected to pull the heads and replace the lifters, trays, pushrods, and the damaged rockers. Woods also took advantage of the situation by surfacing the heads while they were removed.
We buttoned everything up with a new timing set and oil pump, some cool looking Speedway Motors valve covers and matching black oil pan, Tru-Ram exhaust manifolds, and the stock truck intake with a FiTech cable-style throttle body adapted to it. What kind of power would our freshened 5.3 make? Woods was kind enough to open the dyno cell for us so we could find out for sure. With the initial setup complete in our Holley Terminator and everything up to temp, Woods made the first pull. What we saw on the screen caused our jaws to drop. Our humble little cam-swapped 326-incher made almost 430 hp! We added a couple degrees of total timing and made a few more pulls, ending up with 429 hp and 429 lb-ft of torque. Even better, this engine was making over 400 hp from 4,900-6,700, 400 lb-ft at 3,300, and still making 400 lb-ft at 5,700. That’s a nice, flat power curve that will be perfect in our C10.
While the real engine was busy being a hero in the dyno cell, we grabbed a Speedway Motors SoloSwap Mockup block to do some test-fitting and confirm that the Tru-Ram manifolds would work in conjunction with the C10 LS Swap Motor Mount Kit and the trick C10 Transmission Crossmember Kit.
Once our engine was back from the dyno, it was time to mate it to the transmission before dropping it into the chassis. In keeping with the budget theme, we decided to use a TH350 that we had left over from another project. A Speedway Motors LS Transmission Adapter Kit includes a dished flexplate and torque converter sleeve to mate the late-model engine up to the old-school transmission.
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With the engine and transmission dropped into the chassis, we were ready to move onto the fuel system. The stock fuel tank had long since disappeared from our truck, but that was no problem. We chose a C10 Direct-Fit EFI Conversion tank that not only moves the tank out of the cab, it also comes ready for a drop-in EFI fuel pump cartridge. A Speedway Motors EFI fuel pump module was cut to the proper height and bolted right up to the flange on the tank. LS engines require approximately 52 psi of fuel pressure and the Speedway Motors LS Swap Fuel Filter Regulator is preset to the proper pressure and also serves as a fuel filter with provision for the return line. We tied it all together using Earl’s Vapor Guard hoses and fittings.
With everything bolted up to our chassis, it was just too cool not to show it off a bit. Our newly LS-swapped C10 made its SEMA debut in the Speedway Motors booth serving as a rolling showcase for all the parts that we’ve applied so far to our truck’s transformation. But a chassis eventually needs to have a cab and some sheetmetal bolted up if it’s ever going to be a truck. Stay tuned next month as we get to work removing five decades of dents, rust, and mouse nests!
Click on this issue’s cover to see the enhanced digital version of Part 3: Engine & Transmission on the Speedway Motors 1968 C10 Build.
