One of the most popular ways to fit an LS motor in place of a first generation small block or big block is to make a set of adapter plates that bolt to the side of the block that accept regular small block Chevy motor mounts. These plates are easy to make out of steel plate – all you need is a chop saw and a drill. There’s a couple different designs floating around out there that locate the motor in different places. What we’ve done here is create downloadable PDF files based on the measurements for the LS and traditional small block mounting holes, to make it easy to get your measurements right. Here’s how to use them:
- Select the template that best fits your installation needs.
- Download the PDF file.
- Print it on letter size paper. Make sure to set the size option to actual size.
- Cut out the template and tape it to a piece of 1/4″ steel plate. (They’re designed for 4″ wide material.)
- Use a center punch to mark the hole centers.
- Cut the plate to length with a chop saw or Sawzall.
- Drill out the holes to the diameter marked. (0.5625″ = 9/16″.) Some may need to be countersunk or tapped; this is noted on the drawing.
- Paint the adapter plate powder coat as desired.
One thing to keep in mind with LS swaps is that the LS motor has the bellhousing flange lined up flush with the driver’s side cylinder head. The original small block Chevy has the bellhousing flange roughly an inch behind the cylinder heads. So, if your vehicle has tight clearance from the firewall to the engine, and you go with a mount that is said to put the engine in the stock location, you may have the engine hit the firewall. Keeping the bellhousing flange in the stock location when going from a Gen 1 small block Chevy to an LS motor is, effectively, putting 1″ of engine setback in your car.
We’ll be adding new templates as our LS swapped truck project comes along.
First up is our short adapter. This one would move the bellhousing flange forward by approximately 3″ when swapping from a small block Chevy, unless you use a second adapter plate at the bottom of the mount, or modify the engine stands on the crossmember. On some applications with tall engine stands, such as ’63-’72 trucks using stock small block engine stands, the stands may need modification to clear the exhaust manifolds, as this puts the stands back much further than a normal small block Chevy. The advantage this has is that the motor mount more or less in the same position relative to the block as factory LS mounts, allowing you to keep the low mounted A/C compressor found on the truck LS motors, assuming it will clear your frame rails or front subframe. You’ll need two identical copies of this one, one for each side. These are designed so the right side of the template goes to the front of the block.
Download short LS adapter plate PDF
We plan to put up more downloadable templates as time allows, including a solutions for mounting the engine with the bellhousing in the stock location.