All About LS Engine Swap Oil Pans and Motor Mounts for Early Chevelles

While the idea of swapping LS engines into older muscle cars is certainly not new, things can  become a bit fuzzy when it comes to the specifics. For example, the idea of stuffing an iron or aluminum block LS engine into an early Chevelle might seem simple, but with all the options out there you can find yourself in a quagmire of conflicting information.

This article will focus on the 1964 through 1967 Chevelles. Other GM A-body cars like the Pontiac Tempest, Buick Special, and Olds F-85 will have variations that we’ve not encountered so we’ll skip those for now. The 1968-72 Chevelles are different enough from the first-gens that they get their own set of LS engine mount kits.

We will also focus on just the Gen III and IV LS engines. The Gen V LT series engines use a different engine block mounting pattern so none of the Gen III/IV mounts will work. The Gen V oil pan pattern is also different compared to the previous generations. Since we have not yet attempted a Gen V engine swap, we will avoid conjecture.

Our research has proven to us that certain oil pans will fit if matched with the proper motor mount adapters. We will first go through the motor mounts and then bring in the oil pans. We’ll also include some information on transmission crossmembers.

This would be a good place to mention that fitting the oil pan and motor mounts in a car is also affected by the angle of the engine as it sits in the vehicle. Transmission crossmember and the rear transmission mount height will dramatically affect the clearance between the vertical part of the oil pan sump and the trailing portion of the crossmember. Raising the rear of the transmission will improve the clearance between the oil pan and the crossmember.

Motor Mounts

There are basically two different motor mount adapters used to place the LS engine in early muscle cars like the Chevelle. The first version is a simple flat steel or aluminum plate that bolts to the LS block. The plates are drilled with the stock, three-bolt small- or big-block Chevy motor mount bolt pattern. This allows the use of stock or aftermarket motor mounts with the long through-bolt.

These flat plate adapters are easy to use since the stock frame mounts remain in the car. There is plenty of conjecture and misinformation about the placement of big-block versus small-block frame mounts. They do look different, but our experience is that both frame mounts place the motor mount in the same location. From that standpoint they are interchangeable.

While stock rubber motor mounts may be used with flat plate adapters, we prefer to use polyurethane mounts because they have an internal limiter plate that does not allow the mount to completely separate should it tear apart due to engine torque.

The second type of motor mount adapter uses a U-shaped steel piece that replaces the stock Chevelle frame mount. Stock or modified fourth generation Camaro clamshell-style motor mounts bolt to the LS engine.

This arrangement requires more work since you must remove and replace the existing frame mounts. These mounts also raise the engine slightly. That’s an advantage when using a cast aluminum oil pan since they tend to be slightly deeper in the shallow portion where fitment is tight to the engine crossmember.

Cast Oil Pans

This leads us to the oil pan portion of this story. There are two major variations of aftermarket LS oil pans. The earliest conversion pans were made from sheet steel or aluminum because they were easier to make. The more expensive but more durable cast aluminum pans came later. We’ll take the cast aluminum pans first since they are more confusing.

The cast aluminum pans tend to be slightly deeper in the forward portion compared to sheetmetal oil pans and work better with clamshell-style motor mounts. All of the cast pans mentioned in this story integrate the oil filter as part of the pan just like the factory pans do.

Another advantage of the cast pans is that the LS engine was designed to use a full bellhousing pattern. The two lower bolt holes are cast into the bottom of the pans. This makes the oil pan a structural member that adds rigidity. We’ve also seen 75 years of small block Chevys used with a half-bellhousing pattern with no apparent problems, but this feature is still worth mentioning.

This is a good place to discuss which cast aluminum pans do not work in an early Chevelle. Most swappers will likely be using 5.3L or 6.0L iron Gen III or IV LS truck engines. The stock oil pans have a deep sump that will extend beneath the crossmember and can be easily damaged by speed bumps or pot holes.

The earliest LS engine swappers also used the F-body/Camaro cast aluminum pan, but it requires major fabrication work to fit in a Chevelle chassis. The oil pan used on LS-powered Humvee SUVs has been renamed by Chevrolet Performance as the Musclecar Oil Pan. While it will fit in an early Chevelle, it is roughly an inch or so deeper than the crossmember. This also places it in danger of road rash.

We’ve noticed that Chevelle crossmembers between 1964 and 1967 do have slight variations. Add in possible crash damage and sagging from 50-plus years of use and there are plenty of variables that affect oil pan fitment.

Sheetmetal Oil Pans

There are literally dozens of sheetmetal (fabricated) oil pans out there, and we don’t have the space nor the inclination to detail each one. When searching for a sheetmetal oil pan, make sure it comes with an oil filter adapter. In many cases, sheetmetal pans have a separate part number for the oil filter adapter that adds significantly to the cost. The same is true of oil pickups, which are often not included with the pan unless specified.

Some sheetmetal pans can be fitted with a -8 or -10 AN fittings instead of an oil filter adapter. These allow you to remote-mount the oil filter in cases where you want to run an oil cooler. Keep in mind that adding all the external lines and oil filter mount can easily cost more than just an oil filter adapter. In most cases the stock-location oil filter adapter is the way to go.

A big concern is making sure the oil pan does not leak. The cast pans might have a slight advantage here over the sheetmetal versions, but we’ve used both and both have leaked. Most often this is because we forgot (or were in too big of a hurry) to place a small amount of RTV sealant on all four corners of the pan on both sides of the gasket. Do this and you have an excellent chance of having a leak-free pan.

Transmission Mounts and Crossmembers

Placement of the transmission mount can directly affect the clearance around the oil pan. This is most often due to interference between the transmission and the car’s floor pan. This is a common problem with large, later model transmissions that hit the stock transmission tunnel.

It’s not unusual for LS swaps to create a downward engine angle. We often see swaps where the engine sits at a rather severe angle with the transmission tailshaft down four or five degrees or more.

For example, we dropped a 5.3L truck LS engine and a 4L60E transmission in a 1967 Chevelle and noticed a somewhat steep five-degree engine angle that we traced to the transmission crossmember mount. We changed the angle to a more-gentle 2.5 degrees by adding a Hooker Fabricated Transmission Crossmember and a one-inch spacer between the crossmember and the stock transmission mount.

Here’s another example. A friend putting a 4L80E in his 1966 Chevelle had to cut out much of the transmission hump in order to place the transmission and engine at a proper operating angle. We used a Hooker transmission mount and a few spacers and managed to fit the transmission without completely cutting out the transmission tunnel. There is serious sheetmetal work that accompanies a 4L80E swap.

Hopefully this outline will help you navigate the somewhat muddy waters of adding an LS engine to your early Chevelle. Enjoy all of that new horsepower!

LS Oil Pan Spec Chart

Oil pan depths are measured from the engine pan rail. The sump length is measured from the rear vertical wall forward to where the sump transitions to vertical. That specific point is often a radius and is not consistent on all cast pans. The front pan depth is also measured from the engine pan rail.