1972 Chevrolet Corvette Scarlett Project Car - LS3 416 Installation

Down The Rabbit Hole: Inserting an LS3 416 into our '72 project car—very carefully

Jeremy D. Clough Feb 17, 2014 0 Comment(s)
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After pulling the motor back out, we removed the accessory drive and the water pump with it. Since the outlet fittings were screwed into the pump, I backed them out and plugged the holes, being careful to seal the threads, then drilled and tapped a new pair of holes that would locate the outlets higher up, and at an angle. While the original fittings were different sizes (one large, one small) we used a single size for replacement. A little thread sealant, and we were in business.

The compressor, however, got a little more involved. Instead of moving the outlets themselves, Walden used a longer straight fitting in the rear, effectively extending it upwards, and for the front welded up a forward-facing 90-degree fitting that would clear the suspension parts. Making clearance for the body of the compressor required even more surgery, as we learned that one of the reasons we initially had trouble getting the motor bolted in was that the compressor was resting on the frame's front crossmember.

This led to the touchy business of cutting the frame, bending the flaps back enough to allow clearance for the compressor and belt, and then re-welding it back in place, making sure the frame was properly gusseted for strength. In the process, we also had to remove some material from the lower control arm, as well as from the bracket that mounts the LCA to the frame crossmember. Once again, instead of just grinding away material, it was cut, bent, and then re-welded.

Once this was done and painted black, we started the tedious crane-and-jack work of easing the powertrain combo into a spot where we could slip the bolts through the motor mounts and tighten it all up.

Other than wiring and plumbing it, the primary physical connection that still needed to be made was between the motor and gas pedal. There was no way the factory throttle cable was going to reach all the way to the FAST throttle body at the front of the motor, so we got a Lokar LS1 cable and bracket from CBI, the local speed shop. After threading the butt end of the cable through a washer and the bushing located at the top of the gas-pedal arm, the cable was threaded through its AN-style braided stainless sheath.

The rear part of the sheath mounted to the firewall from the engine-compartment side, while the oversized forward end had to be cut to length before being fitted into its hose end. Cutting the tiny braided hose (it looked to be -2 AN, roughly 1⁄8-inch inside diameter) was as much fun as you'd expect, with its sharp little pieces of wire readily drawing blood, but the real excitement was in adjusting the throttle-cable bracket.

Unfortunately I was never able to find a bracket that would bolt up readily to our FAST LSXR intake. As a result, we had to resort to the LS1 bracket, which didn't stick out far enough to line up the cable properly with the throttle body. We have machine tools, however, and aren't afraid to use them: I used the lathe to machine a spacer that would step the mounting point for the cable out the required ¼-inch to make it line up. Walden, meanwhile, made the two nuts required to mount the bracket assembly to the intake, as standard nuts wouldn't fit in the recesses provided for that purpose.

All in all, we machined six parts to make the throttle cable work, five of them from scratch, and the whole shebang took the better part of a couple of work days. The part we didn't have to make ex nihilo was the adjustable brass stud that holds the end of the cable and slips into a hole in the throttle, giving the cable something to pull against. Unfortunately it was well oversized for its hole, so to the lathe it went.

Once we had everything made, modified, and assembled, I picked up the Corbeau driver's seat that was sitting next to the car and set it back in the passenger's compartment, then sat down. Pushing my right foot down hard on the gas pedal, I watched the cable do its work and rotate the throttle all the way back.

Considering the fierce power of that 635hp LS3, it occurred to me that I'd never again be that cavalier about bringing it to wide open throttle.

1972 Chevrolet Corvette Engine 2/30

15 The LS3 with the trans already mounted, ready to be installed. While you can do this with a cherry-picker engine hoist, the crane made it much easier.

1972 Chevrolet Corvette Install 3/30

16 Installing the powertrain required a careful balance of location and angle, the trick being to slip the trans down its tunnel underneath the car without punching the front of the motor through the fiberglass front clip. We used a crane and a pair of floor jacks, and as many hands as were available.

1972 Chevrolet Corvette A C 4/30

17 In addition to the body of the A/C compressor itself, the red-capped fittings where the hoses connect to it caused major clearance problems. The water pump presented a similar issue.

1972 Chevrolet Corvette Cut 5/30

18 Since the compressor originally rested on the front crossmember, we modified that part of the frame by cutting it, bending back the flaps for clearance, and re-welding it in place. A little grinding, a little black paint, and we were back in business.

1972 Chevrolet Corvette Replace Factory 6/30

19 To make room to attach the hoses to the compressor, Walden replaced the factory fittings with an extended straight fitting at the rear, then welded up a 90-degree elbow for the front fitting.

1972 Chevrolet Corvette Water Pump 7/30

20 To make the water-pump fittings clear the suspension mounting points, I unscrewed them from the pump and plugged those holes. Next, I drilled and tapped two more holes, relocating the fittings above the originals, at an angle.

1972 Chevrolet Corvette Modified 8/30

21 The modified fittings for the Vintage Air A/C compressor, capped in blue and red. While it’s still close, the modified fittings make it possible to route the hoses around the suspension mounting points.

1972 Chevrolet Corvette Compressor 9/30

22 By the time we were done with the frame mods, there was sufficient clearance between the compressor and the frame/control arm/control-arm mount. Running clearance for the compressor belt was adequate as well.

1972 Chevrolet Corvette Install Throttle 10/30

23 Installing the throttle cable starts from the rear. After threading its butt end through a washer and the bushing located at the top of the gas-pedal arm, the cable was slipped into its AN-style braided-stainless sheath, and the pedal was bolted back to the firewall.

1972 Chevrolet Corvette Rear 11/30

24 The rear part of the cable mounted to the firewall in the factory position. We routed it in a gentle S-curve behind the rear of the intake and up beside the passenger-side fuel rail.

1972 Chevrolet Corvette Ls1 Throttle 12/30

25 We started with an LS1 throttle cable from Lokar, machining a spacer to get it to sit at the proper offset for our FAST intake and throttle body. We also had to make the nuts to bolt it to the intake.

1972 Chevrolet Corvette Braided Steel 13/30

26 Once the bracket was bolted onto the intake, we were able to measure the length of the braided steel hose that the cable passes through, and cut it to length. Word to the wise: Tape the hose, and keep it taped while you twist it into its fitting.

1972 Chevrolet Corvette Throttle Cable 14/30

27 This little fella connects the throttle cable to the throttle body itself, and locks onto the end of the cable. Unfortunately, it was too large to fit the throttle body, so I turned it down in the lathe, narrowing the hex head to make it sit deeper and reducing the diameter of the body.

1972 Chevrolet Corvette Installation 15/30

28 Success at last. With all the extra parts made and fitted, now something actually happens when you push down on the gas pedal…and it’ll happen a lot more dramatically once we get the motor wired and plumbed.


Energy Suspension
San Clemente, 92673
Vintage Air
San Antonio, TX 78266
Holley EFI
Bowling Green, KY 42101
Fuel Air Spark Technology
Memphis, TN 38118
American Powertrain
(931) 646-4836
Street Shop, Inc.
Athens, AL 35611


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