10 Facts about LS swapping a Tri-Five Chevy
The 1955, 1956, and 1957 "Tri-Five" Chevrolet Bel-Air, Nomad, 210, etc, are the most popular and desirable cars to ever come out of a GM factory. Their iconic styling is instantly recognizable, and their popularity is as great as ever, but these cars are showing their age in the performance department. For more reliable cruising, and more power, combine classic cruisers with modern LS power. What's not to like?
Engine & Transmission
LS swapping a Tri-Five Chevrolet was once considered quite a chore, but with companies such as Classic Performance Products and BRP Hot Rods offering LS conversion kits, the job can be completed in the comfort of your own garage. With all LS and LS-based engines having almost identical external dimensions no matter the displacement, one can opt for any of these motors without fitment issues. Similarly, the 55-57 Chevy cars can accept your choice of an old or new manual transmission or any of the General Motors automatics (TH400, 4L60E, 6L80E, etc.). Basically, in layman's terms, the Tri-Five Chevy can accommodate just about any LS engine/transmission combo one can concoct.
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Motor Mounts
In order to properly nestle the LS engine into the engine bay, the original motor mounts will need to be removed from the frame rails by grinding the heads off of the rivets. The LS mount plates will typically include the necessary measurements or a jig to properly align the mounts onto the frame where new holes can be drilled to secure the mount in place. It is worth noting that the frame will need to be notched approximately 2" if running a low mount A/C compressor, but the kits include a pre-shaped filler panel that is easily welded in place to enclose the modified frame.
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Oil Pan
When swapping in an LS engine, it is important to have the correct oil pan to avoid crossmember interference issues. The oil pan of choice for most swaps is the LH8/GM Musclecar low clearance oil pan kit that includes a quality cast-aluminum pan, windage tray, pickup tube, dipstick, and gaskets. This pan is much more robust than the old stamped steel SBC units and does a better job of dissipating heat. When used in a Tri-Five application, a very small portion of the front right of the pan will need slight trimming to clear the passenger side frame rail.
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Accessory Drive
Accessory drives for the LS can be a bit of a headache in many cars, but the Tri-Five Chevrolets are able to accommodate most drive setups without any issues. As previously mentioned, any accessory drive with a low mount A/C compressor will require a small modification to the passenger side frame rail if air-conditioning is being used. Many have had great success with the truck-style accessory drive setup, but these tend to place the alternator higher up on the engine. In general, the alternator is the most likely culprit to have interference issues, but the motor mounts being used play a large role in the placement of the engine and its accessories, so be sure to test fit everything during the mock-up stage to make sure no accessory clearance issues are present.
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Transmission Mount
While a number of transmissions will work in the Tri-Five cars, a body seam in the transmission tunnel will need to be flattened down to allow for sufficient clearance. This can accomplished by simply making a few relief cuts around the radius of the body seam and flattening the seam down with a hammer. From this point the transmission can be lifted into place using a jack and the transmission crossmember brackets can be marked, drilled, and mounted to the frame rails.
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Driveline
Depending on the transmission used, the total driveline length will vary. The driveshaft will typically need to be shortened several inches, which can be accomplished by simply sending off your original driveshaft to be cut down to length, or by ordering a custom unit from any driveline specialist. Some folks have had good success using donor driveshafts from various GM vehicles produced over the years, but in any case, be sure to have the yoke for whatever transmission you are using, and the correct universal joint at the back for the differential.
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Radiator
To keep a higher output LS engine cool, the old radiator should be scrapped and replaced with a new LS swap radiator from manufacturers such as Be Cool or DeWitts. Some radiators will be made to the factory radiator dimensions whereas others will be a wider cross-flow design. In either case, minor modifications will be needed to get you up and running. For a traditional style radiator as sold by DeWitts, no mods are required to fit into the core support, but creative routing of the coolant hoses will be required since the radiator outlets are more centered than on a crossflow. The outlets on a LS crossflow radiator are retained in the stock locations (passenger side end tank) for easy hose routing, but holes will have to be cut into the core support for the outlets and new holes drilled to accept the radiator mounting brackets. That said, Be Cool does offer a Tri-Five kit that includes a new aluminum core support if you are looking for a no expenses spared, no custom fabrication option.
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Exhaust
Stock LS exhaust manifolds are a viable option, however, many prefer to go with long-tube headers for increased performance and sound. Whichever route you go, be sure your choice of headers match the exhaust assembly you will be using. Exhaust system options for LS-swapped Tri-Five Chevys seems to be vast and plentiful with offerings from Flowmaster, Pypes, Borla, and Magnaflow, to name a few. Exhaust setups come with various hangers, exhaust clamps, and other accessories to complete the install. That said, experimenting with a custom made exhaust setup can be good fun in itself.
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EFI Fuel Tank
Fuel-injected LS engines need approximately 60 psi to run, so a revamp of the fuel system will need to be in order. Perhaps the easiest solution is to purchase an EFI-ready replacement fuel tank for a Tri-Five Chevy that will have nearly identical dimensions as the stock unit and mount in the original location, but with an in-tank fuel pump and all necessary provisions for the LS's fueling needs. Another option would be to install an external fuel pump and fuel filter somewhere along the frame rail as well as a return line to route unused fuel back into the tank.
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Wiring & ECM
Many folks cringe at the thought of wiring a modern engine, with all of its electronic gadgetry, into an older car, but with various companies offering complete plug-n-play wiring harnesses and ECMs specific to the intended application, the hardest part is likely deciding where to mount the computer and how to route the wiring. For those who are performing a swap on a budget, many individuals have successfully used a donor GM harness and ECM to match their engine model, but this will require that the computer be flashed by a tuning company to eliminate the vehicle anti-theft software.
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For help with mods or service on your car, check out the how to section of LS1Tech.com