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.
Putting our 635-horse LS between the framerails took a little bit more than just bolting o
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.
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.