What a trunnion upgrade does and why you might need one

A trunnion upgrade replaces the factory engine mounts on an LS1 engine with reinforced or adjustable versions designed to reduce engine movement and vibration. The trunnion is the pivot point where the engine mount connects to the engine block — the factory design allows more flex than many builders want, especially in high-horsepower or track-focused builds.

The upgrade matters most if you have added significant power to your LS1, installed a stiffer suspension, or are using the car for road racing or autocross. Stock mounts were engineered for comfort and NVH (noise, vibration, harshness) in a street car. Once you change the power level or driving demands, those mounts can allow the engine to rock excessively under acceleration and braking, which stresses the engine bay structure and can cause driveline bind or misalignment issues.

You do not need a trunnion upgrade for a stock or mildly modified LS1. The factory mounts handle their intended duty fine. But if you are building a car that will see track time or has 450+ horsepower, the upgrade becomes a practical consideration rather than a cosmetic one.

Key Takeaways

  • A trunnion upgrade replaces the engine's pivot point connection to reduce movement, and is most useful in high-power or track-focused LS1 builds.
  • Factory LS1 mounts are rubber-isolated for street comfort and allow more engine rock than reinforced or adjustable aftermarket versions.
  • Common upgrade options include solid aluminum trunnions, adjustable trunnions, and polyurethane-bushed mounts, each with different trade-offs in stiffness and vibration.
  • Installation requires engine lift and disconnect of transmission and exhaust components, typically taking four to six hours for a competent DIY builder.
  • Cost ranges from $300 to $800 depending on the brand and whether you choose solid, adjustable, or hybrid designs.

Factory LS1 mounts versus aftermarket trunnion designs

The factory LS1 engine mount assembly uses a rubber-isolated design that allows controlled engine movement. The trunnion itself is a cast iron or aluminum piece bolted to the engine block, and the rubber bushing absorbs vibration and movement. This design prioritizes NVH isolation — the car feels smooth and quiet at idle and cruise.

Aftermarket trunnion upgrades fall into three main categories. Solid aluminum trunnions eliminate the rubber bushing entirely, creating a rigid connection that stops engine rock almost completely. This is the stiffest option and is popular in drag racing and high-horsepower street cars, but it transmits more vibration into the chassis and can make the car feel harsher at idle. Adjustable trunnions use a spherical or eccentric design that lets you dial in engine angle and movement after installation, useful if you are fine-tuning driveline geometry or need to clear headers or other components. Polyurethane-bushed mounts split the difference — they use a stiffer bushing material than factory rubber, reducing movement while keeping some vibration isolation.

The choice depends on your build goals. A street car with 500 horsepower might do fine with polyurethane bushings. A dedicated track car or drag car usually goes solid. An adjustable trunnion makes sense if you are building a car with tight engine bay clearances or need to tune driveline angle.

Measuring engine movement and deciding if you need the upgrade

Before spending money, you can check whether your current mounts are causing problems. With the engine running and the car in gear (foot on the brake), have a helper watch the engine from the side while you gently rev to 2,000 rpm. The engine should rock slightly — an inch or two of vertical movement is normal. If the engine is moving more than two inches, or if you see the radiator or fan shroud moving noticeably, the mounts are worn or undersized for your power level.

You can also feel the problem while driving. Excessive engine movement often shows up as a clunk when you shift from Drive to Reverse, or as a lurch under hard acceleration. If the car pulls to one side under acceleration or the steering wheel jerks, engine movement can be part of the cause — though suspension and driveline issues are more common culprits.

If you have added 100+ horsepower over stock and are seeing these symptoms, a trunnion upgrade will likely help. If the car feels fine and you are just building for the sake of it, the upgrade is optional.

Installation steps and what to expect

Installing a trunnion upgrade requires lifting the engine slightly to disconnect the old mounts and bolt in the new ones. You will need a engine hoist or a sturdy jack and jack stands, and the job is not practical without them. The process typically takes four to six hours for someone comfortable working on engines.

Start by removing the engine cover, air intake, and any components blocking access to the mounts — usually the exhaust manifolds or headers have to come off or be unbolted from the engine. Disconnect the transmission crossmember bolts and support the transmission with a jack. Unbolt the old trunnion from the engine block and the mount bracket from the frame. Lift the engine just enough to clear the old mount, slide it out, and bolt the new trunnion in place. Reverse the steps to reassemble.

The trickiest part is usually the exhaust — headers can be tight to remove, and you may need to drop the transmission crossmember further than expected to get clearance. Have a helper on hand if possible. Take photos before you start so you remember bolt locations and routing.

After installation, start the engine and check for leaks or loose bolts before driving. Some builders adjust engine angle slightly after installation to optimize driveline geometry, but this is optional and requires a second lift.

Cost and brand options

Trunnion upgrade kits range from $300 to $800 depending on the design and brand. Solid aluminum trunnions from companies like Lokar or Trans-Dapt typically run $400 to $600. Adjustable designs cost more — $600 to $800 — because they require precision machining. Polyurethane-bushed mounts are the least expensive option at $300 to $450.

Labor at a shop adds $400 to $800 depending on local rates and how much exhaust work is needed. If you do the work yourself, the only additional cost is gasket sealer and any bolts you need to replace.

Popular brands include Lokar, Trans-Dapt, Hedman Hedders, and Moroso. Most are designed specifically for LS1 engines and bolt directly into the factory mount locations. Read reviews on LS1 forums before buying — some designs have clearance issues with certain header or transmission combinations, and user feedback will tell you whether a particular kit fits your setup.

Potential downsides and what to watch for

Solid trunnion upgrades increase vibration at idle and low rpm. If you spend a lot of time in traffic or at stoplights, you may notice the engine shaking more than before. This is normal and not harmful, but it can be annoying. Polyurethane bushings reduce this problem but do not eliminate it.

Adjustable trunnions can shift if not locked down properly, causing the engine angle to change and creating driveline vibration. Make sure all bolts are tight and use threadlocker on critical fasteners. Some builders check the adjustment after the first 100 miles of driving.

If your engine bay is already tight — especially with headers and a power steering pump — a trunnion upgrade can create clearance problems. The new mount may sit slightly higher or lower than the factory version, and you may need to modify brackets or relocate components. Check fitment photos and forum posts for your specific engine and transmission combination before ordering.

Alternatives if a full trunnion upgrade is not practical

If you want to reduce engine movement without a full trunnion replacement, you have a couple of options. Polyurethane mount bushings can be installed in the factory trunnion — you remove the old rubber bushing and press in a polyurethane one. This costs $100 to $200 and takes an hour or two, and it reduces movement by 30 to 40 percent without the vibration increase of a solid mount.

You can also reinforce the engine bay structure with bracing or subframe connectors. This does not stop the engine from moving, but it distributes the forces more evenly and can reduce the stress on individual components. This approach is cheaper than a trunnion upgrade and works well for street cars that do not need maximum stiffness.

If your mounts are straightforward worn out, replacing them with new factory mounts is the cheapest fix and restores the original behavior. Worn mounts often feel like excessive movement, but new factory mounts may be all you need.

Frequently Asked Questions

Do I need a trunnion upgrade if I have a stock LS1?

No. Factory mounts are designed for stock power levels and street driving. A trunnion upgrade is most useful once you have added significant power — usually 450+ horsepower — or plan to use the car for track driving. For a stock or mildly modified engine, new factory mounts are sufficient.

Will a solid trunnion make my car undriveable on the street?

No, but it will be noticeably stiffer. You will feel more engine vibration at idle and low rpm, and the car may feel less refined than with factory mounts. Many street cars with solid trunnions are driven daily without problems — it is a trade-off between isolation and control, not a choice between driveable and not.

Can I install a trunnion upgrade myself if I have basic mechanical skills?

Yes, if you have access to an engine hoist and are comfortable removing exhaust components. The job is straightforward but time-consuming. If you have never lifted an engine before, having an experienced friend help or watching detailed videos first will save frustration.

What is the difference between a trunnion upgrade and a motor mount upgrade?

A trunnion is the pivot point on the engine block itself. A motor mount is the bracket and bushing that connects the engine to the frame. A trunnion upgrade replaces the pivot point; a motor mount upgrade replaces the bracket and bushing. Many kits upgrade both at once.

Will a trunnion upgrade fix driveline vibration?

It can help if the vibration is caused by excessive engine movement. But driveline vibration usually comes from worn u-joints, imbalanced driveshaft, or transmission problems. Check those first before assuming the mounts are the cause.