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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In our last installment, we stripped Scarlett, our '72 coupe project car, down to the firewall, inside and out. So began the LS conversion that will ultimately replace her conventional small-block with a 416-cubic-inch LS3 stroker, and change her Turbo-400 automatic out for a six-speed manual.

With the engine compartment vacant and detailed, it was time to get the motor in. We'll start here with prepping it for that job, as well as describing the modifications we (which in this case means Street Shop's Tray Walden and I) had to do in order to get it and its accoutrements bolted into place. The good news is that since the engine compartment of the shark was made large enough for a big-block, there's plenty of room for an LS-series mill; it's just a matter of arranging everything where it needs to go.

We began by dressing the engine, starting with the sensors. In addition to the throttle- position and mass-airflow sensors (available from most Chevy Performance Parts dealers), we had some specialty wiring that needed to go into place.

Since part of this project is trying to keep the visible part of the car nominally original in appearance, we've retained stock-style gauges, which were redone by Corvette Instrument Service in Florida. Unsurprisingly, some adjustments were required to fit the SBC sending units into the LS block. To keep the temperature-sending unit screwed deep enough into the head to give an accurate reading, we mounted it in an adapter sourced from CIS, who also sold us an electronic oil-pressure-sending unit. We screwed that into an elbow fitting that let us tuck the unit high and tight beside the block above the oil filter.

1972 Chevrolet Corvette Ls 2/30

We also needed to add knock sensors, and since the FAST XFI computer we'll be using for the fuel injection doesn't use the stock LS3 units, I made a trip to the local O'Reilly for the '80s-era GM sensors and control module that are required for the XFI. With these in hand, we opened up and re-threaded the knock sensor holes in the block, which are significantly smaller on the LS, then screwed in the sensors.

In order to make the LS block bolt up to the factory frame, we used a pair of Street Shop machined aluminum adapter plates. These let us mount a pair of standard motor mounts from Energy Suspension to the plates, which then bolt directly to the LS engine block. Because we built this motor knowing it wouldn't be going in a car that came with an LS, we already had Holley's LS conversion oil pan, and as it turned out, it cleared everything beautifully once we had the motor in place.

Although we had taken out the motor and transmission in two separate pieces, by removing the radiator and core support (which we were replacing anyway), we realized we could install the powertrain combo as a unit, and that's what we did. Since assembling the American Powertrain T56 Magnum six-speed transmission (and the modifications required to make it fit) is a pretty substantial piece of work, we'll detail that process in a separate installment. For now, suffice to say we did it before we shoehorned the engine back in.

For an accessory drive, we used a billet pulley system made by Street Shop, Inc., where we're doing the install. The Street Shop system uses a pair of belts: one to run all the critical parts such as the alternator and water pump, and a second one for the air-conditioning compressor, which it mounts low on the passenger side in the factory LS position. Since we'll also be installing a Vintage Air climate-control system (which we'll also cover in a separate article) to replace the non-functional factory air, we used that company's A/C compressor. While the pulley system we specified was polished and anodized, to match the polished compressor, other finishes are available.

Since the pulley system was designed around the aftermarket Street Shop chassis, we knew there would be some interference issues using it with a stock frame. The problems proved twofold: the water pump, whose already-modified outlets exited almost directly into the upper control arm of the passenger-side front suspension, and the compressor, which had a similar problem with the location of its inlet/outlet.

1972 Chevrolet Corvette Install 3/30

01 Before we put in the motor, we installed the flywheel (shown) and Quick Time bellhousing, and hung the American Powertrain T56 trans on the back. I’m sure it’s possible to do all this with the motor in the car, but it’s much easier on the stand.

1972 Chevrolet Corvette Install 4/30

02 The starter went on along with the other components on the rear of the engine. This’ll get complicated later, as there’s an electrical connection we’ll have to make that’s located on the block behind the starter.

1972 Chevrolet Corvette 5/30

03 Unfortunately, there’s not a hole in an LS block that’ll readily accept an old-style water-temp-sending unit, so we used an adapter from Corvette Instrument Service. While it’s possible to mount it remotely with a different type of fitting, doing so will result in less-accurate readings.

1972 Chevrolet Corvette Oil Pressure Sending 6/30

04 We also used an oil-pressure-sending unit from Corvette Instrument, since we did away with the manual gauge and the attendant risks of running a reedy plastic tube full of hot oil into the rear of the gauge.

1972 Chevrolet Corvette Mount Sending 7/30

05 To mount the sending unit, Tray Walden drilled and tapped a hole for a 90-degree fitting that let us tuck the unit up beside the block, just above the oil filter.

1972 Chevrolet Corvette Drill 8/30

06 While the block came ready for current-production knock sensors, the FAST XFI computer we’ll be using relies on earlier GM-style sensors that require a larger threaded hole. A little drill and tap work, and Walden had the holes ready.

1972 Chevrolet Corvette Knock 9/30

07 One of the two knock sensors mounted in place. Unlike LS sensors, which are wired directly to the computer, these earlier sensors are routed first to a control module, which then sends its signal to the computer.

1972 Chevrolet Corvette Ati 10/30

08 Unfortunately there was a bit of a miscue when the harmonic balancer was originally selected for the engine build. As a result, we had to special order an ATI balancer with a smaller inside diameter to get the proper interference fit.

1972 Chevrolet Corvette Street Shop Adapter 11/30

09 In order to make the LS block bolt up to the factory frame, we used a pair of Street Shop aluminum adapter plates. These let us mount a pair of standard motor mounts from Energy Suspension (which we modified lightly) to the plates, which then bolted directly to the block.

1972 Chevrolet Corvette Holley Ls Conversion Oil 12/30

10 Holley’s LS conversion oil pan provided excellent clearance, with plenty of room between it and all of the steering-system components.

1972 Chevrolet Corvette Street Shop Billet Pulley 13/30

11 For an accessory drive, we used a Street Shop billet pulley system. The setup uses a pair of belts—one to run the critical parts such as the alternator and water pump, and a second one for the A/C compressor.

1972 Chevrolet Corvette Pulley 14/30

12 The pulley installation began with bolting on the bracketry that will hold the pulleys. This is crucial, since it determines the spacing at which the different accessories will sit away from the block, and therefore whether or not the belt will run true.

1972 Chevrolet Corvette Power Steering 15/30

13 Once all the brackets are in place, the front of the engine may be dressed with accessories such as the alternator and power-steering pump (shown). The pulleys and tensioners (two, since there are two belts) may likewise be bolted into place.

1972 Chevrolet Corvette Install 16/30

14 All together, and ready for the belts to go on.

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