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How To Install a Holley Mid-Mount Accessory Drive on an LS Engine

Author: Tommy Lee Byrd | 12/04/2020 < Back to Motor Life Home

When installing an LS engine into a muscle car, or any non-original application, you’re going to run into a few hurdles. Finding and buying the engine itself is the easy part, but it takes time and money to nail down the right combination of parts to properly swap the engine into your vehicle. Holley has stepped in to create a wide range of LS Swap products, including oil pans, headers and motor mounts to simplify the process. As a part of the ongoing product development at Holley, the team of engineers developed a series of accessory drive systems to fit a wide variety of cars and trucks.


The Holley accessory systems are available in several configurations to fit street cars and race cars. The most common is the Mid-Mount Complete Accessory System, as it brings the accessories in close to the engine for a clean fit with plenty of clearance on most applications. As the name suggests, this is a complete system that can take your crate engine or junkyard engine from bare bones to fully equipped.


If you’re working with a crate engine, they are often shipped with no accessories. That means you can either find a donor vehicle, or piecemeal the accessory components to find the right combination. If you’re starting with a junkyard engine from a truck, then you already know the challenges of the bulky truck accessory brackets that may have come with your engine. Even if the accessory drive works for your engine swap application, you’re dealing with older components that may or may not work properly. A new accessory drive system greatly streamlines the engine swap process and gives you the reliability of brand-new components.


The Mid-Mount Complete Accessory system is available in three finishes (natural, polished and black). We chose polished (PN 20-185P) for our LS swapped Chevy Nova. Holley also offers Premium systems, which include upgraded components, such as an SFI-approved damper, but we opted for the standard kit.


Inside the box, you’ll find every component you need to assemble the front of your engine. Holley’s kit includes a water pump, alternator, power steering pump, air conditioning compressor, thermostat, thermostat housing, a belt and all necessary fitting, pipe plugs and bolts to install the system on your engine.


Holley’s kit uses a proprietary water pump design, which features built in mounting brackets. This makes installation super simple—no need for spacers, bolt-on brackets or anything complicated. The system can be installed with the engine on a stand or installed in the vehicle, and you can perform most of the install with simple hand tools. The only specialty tools you’ll need is a damper installer and a power steering pump pulley installer. This kit can be installed in just a couple hours in your home shop, and it can save a tremendous amount of time, compared to using a combination of original and aftermarket equipment. Follow along as we install the Holley Mid-Mount Complete Accessory System on our dressed up 5.3-liter LS engine.


Bare GM LS block, front view

For this installation, we’re starting with a blank canvas. It’s a junkyard fresh 5.3-liter engine from a truck, and we have already dressed it up with Holley components and given it a nice clean-up with some Chevrolet Orange paint on the block.

Holley accessory drive layouts

Holley offers several accessory drive configurations to fit LS and LT based engines. Mid-Mount is the most common for muscle car applications, as it allows you to position the alternator and A/C compressor up top for easy service. We’ll be using the Holley 20-185P model, a Mid-Mount Complete Accessory System with a polished finish.

Holley Mid-Mount Water Pump Housing

The installation begins with the center point of the accessory drive system—the water pump. This specially designed water pump features integrated brackets for the accessories, which makes for easy installation. It has an optional steam vent port on the backside, if you plan to use a Holley 26-552 steam tube plumbing kit. If you plan to use the original steam vents, you can plug the port with the supplied 1/8-inch NPT plug.

Holley Mid-Mount water pump assembly

The polished aluminum water pump (PN 97-165) attaches to the block with six bolts. Five of the M8 bolts are 115mm long, while the furthest right attachment point requires a shorter, 50mm bolt. Don’t forget the supplied gaskets.

Holley Mid-Mount water pump impeller assembly

The water pump is shipped disassembled. We indexed the supplied gasket so it fits properly on the dowel pin and bolt holes.

Holley Mid-Mount water pump pulley attachment

Using the supplied M6x20 bolts, we installed the water pump drive assembly (PN 97-200). The pulley can be indexed so that all six bolt holes can be accessed. After all six bolts are snug, we torque them to 85 in/lbs.

Holley mid-mount damper installation

The supplied damper (PN 97-205) is installed using a special tool, and then we torque the original bolt to 240 ft/lbs to fully seat the damper. The original bolt can be removed and discarded.

Torquing damper bolt

Now we can install the new supplied damper bolt and torque it to 59 ft/lbs. Then, we rotate the wrench 125 degrees to achieve proper torque specifications.

Included thermostat

One of the key advantages of Holley’s accessory drive systems is the completeness of the kit. A good example of this is the supplied thermostat, complete with a new housing, o-ring and bolts (PN 97-169).

Thermostat housing

The two thermostat housing bolts use a standard 3mm hex tool, and we torque the two bolts to 85 in/lbs.

Heater hose port configuration

A cool feature on the Holley Mid-Mount Accessory System is the heater hose port configuration. This gives you the option to run them straight down if you want to tuck them down low. Or, in our case, we’re going to plug the lower ports with the supplied 3/4-inch NPT plugs, and use the side ports for our heater hoses. Holley includes a 5/8-inch and 3/4-inch barb fitting (PN 97-177), but you can also use Earl’s 90-degree fittings if necessary.

Alternator Installation

Moving onto the charging system, the Holley system features a polished LT1 style 150-amp alternator (PN 197-304) complete with the proper pigtail (PN 197-400).

Alternator Installation

The alternator attaches the water pump assembly with an M10 x 75 socket heat bolt (upper) and an M10 x 80 button head bolt (lower). These bolts torque to 36 ft/lbs.

Power Steering Pump Pre-Assembly

Next, we pre-assemble the Type II power steering pump (PN 198-101) by installing the hardline with the supplied banjo fitting assembly. A sealing crush washer is placed on the pump, then the hard line, then another crush washer, followed by the banjo bolt. An M8 bolt secures the hardline to the pump. The hardline kit is Holley PN 198-203.

Power Steering Pump Installation

We installed the three supplied M8 x 30 bolts that hold the power steering pump in place. The holes in the water pump assembly are slotted to allow for different pump types. You’ll want around an 1/8-inch between the alternator and reservoir for proper fitment. The bolts torque to 18 ft/lbs.

Power Steering Pump Pulley Installation

Finally, the power steering pump pulley (PN 97-152) can be installed with a special pulley installer tool. These tools are available for rent at most auto parts stores, but it’s always handy to have one of your own.

Air conditioning compressor preparation

The compact SD7 A/C compressor (PN 199-106) also features a polished case. We threaded one of the supplied M8 x 95 socket head bolts into the compressor, and then slid it into the slotted hole in the water pump housing.

Air conditioner compressor installation

Then, the A/C compressor rotates around to line up with the other bolt hole. Just a quick note that you may run into a clearance issue if you’re using aftermarket valve covers, like the Holley two-piece valve covers on our 5.3-liter engine. We had to remove the valve cover momentarily to get enough clearance to insert the A/C compressor bolt.

Air Conditioner Compressor Manifold

Many custom A/C compressor manifolds are available. This billet version looks clean and attaches with socket head fasteners.

Installing The Serpentine Belt

Using the 1/2-inch square ratchet drive, we rotate the tensioner to easily slip the serpentine belt (PN 6PK1715) into place. We like to install the grooved portions of the belt first and then slide the belt over the smooth water pump pulley as a final step.

Belt tensioner polished cover bracket

To dress up the tensioner assembly, Holley provides a polished aluminum cover. It attaches to the tensioner with a special bracket the fits behind the assembly, as shown.

Polished aluminum tensioner cover

The polished aluminum tensioner cover (PN 97-157) attaches with two small bolts. Now would be a good time to give those polished components a quick cleaning to remove finger prints and any haziness.

Holley 20-185P kit installation

The finished product adds immense functionality and great style for our junkyard 5.3-liter LS engine. The Holley Mid-Mount Complete Accessory System was a simple install that had everything we needed in one convenient package.


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