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How Much Torque Do I Need In An Impact Wrench?

An impact wrench is one of the handiest tools you can own. I got by with a breaker bar and a good socket set for years, but the day finally came when I needed to upgrade. Frankly, some repair tasks cannot be done without an air impact wrench.

And an air impact wrench speeds up how quickly you can work. Impact pneumatic wrenches produce from 22 to 2,200 ft-lbs of torque.

As you shop for an impact wrench, you are undoubtedly wondering, “How Much Torque Do I Need For An Impact Wrench”? We answer that question here:

How Much Torque Do I Need For An Impact Wrench?

You need over 1,100 ft-pounds of torque in an impact wrench for most automotive repair tasks.

For example, an Impact wrench will need around 500 ft-pounds of torque to remove lug nuts, which is the most common automotive task they are used for. However, if they were overtightened by the last shop to install them, you will need an even larger impact wrench to remove those lug nuts.

If you purchase an impact wrench with 1,100 ft-lbs or more torque, you will be able to handle nearly all automotive work.

Of course, when working on semi-trucks or in the rail industry, you may need an impact wrench capable of 1,600 foot-pounds or more of torque.

Ultimately, the amount of torque you need is dependent on the task you are doing. There is not a one-size-fits-all standard impact wrench torque. Instead, their torque ranges from 300-foot-pounds to 2,200-foot-pounds of maximum torque, depending on the model.

With the wrong choice, you’ll have a heavier tool than you need or an impact wrench that is too small.


Powering a Car With An Impact Wrench

YouTube video

I love watching these guys powering a car with a cordless impact wrench. It just goes to show how much power is in one of these. Imagine if they had done this experiment with a pneumatic wrench. That car would have flown!


What Is Torque?

Torque is a physics term used to describe the measure of a force that can cause an object to rotate around an axis.

Just as force can be measured in linear movement, it can also be measured in a circle, such as the torque produced by an impact wrench or engine.

An impact wrench uses torque to tighten or loosen bolts and lug nuts when rotating. However, the distinguishing factor of an impact wrench is that it has small internal hammers that drive an internal anvil.

This hammering creates micro shocks of intense torque that makes it possible to deliver seized and overtighten bolts.

How Much Toque Does A Pneumatic Impact Wrench Have?

You will quickly identify that larger impact wrenches produce more torque as you shop impact wrenches. The maximum tool torque produced by the drive size of your pneumatic impact wrench will generally fit into one of these ranges of torque outputs:

  • 1-inch Drive: 1,475 to 2,145 foot-pounds
  • 3/4-inch Drive: 1,200 to 1,600 foot-pounds
  • 1/2-inch Drive: 650 to 1,295 foot-pounds
  • 3/8-inch Drive: 200 to 600 foot-pounds

1-Inch and 3/4-inch drive wrenches are generally used for heavier equipment, while 1/2-inch and 3/8-inch drive impact wrenches are for automotive use.

Cordless impact wrenches are the least powerful and will only produce about 600 foot-pounds of torque. A cordless impact wrench is more flexible and makes it easier to move around and work outside, but a pneumatic impact wrench is needed for more difficult tasks.

Is An Impact Wrench’s Torque Adjustable?

As with any tool, you won’t want to run your impact wrench at the max torque all of the time. Instead, you will want to choose a suitable working torque for the task at hand.

Some impact wrenches customizable torque that is controlled by a lever on the handle. However, you won’t have as much control over cheaper air impact wrenches. Instead, there are two other options:

  • Regulating Tool Pressure:  By purchasing an aftermarket tool regulator that plugs into the air hose between the compressor and the impact wrench. This gives you fine-tooth control of the airflow for your projects.
  • Regulating Line Pressure: Every air compressor has an air regulator. With some models, you can adjust the air regulator to produce more air in some cases. More air can then produce more torque output. The downside is that you may risk damaging the air compressor or the hand tool. However, you can turn the air pressure down with no risk.

Even if your impact wrench produces 1,000 or more foot-pounds of torque, you can use it for small tasks like tightening lug nuts. The key is to not sit on the nuts too long.

What Happens If You Apply Excess Torque On An Impact Wrench?

We’ve worked on some pretty stubborn projects. There is nothing more maddening than loosening a harmonic balancer on a failing engine and not having enough nut-busting torque to get the job done.

There is no harm done to your impact wrench by trying to loosen a nut that is too tight. Work on it in short 5-10 second bursts with plenty of wait time between events to keep the tool from overheating.

Conversely, If you apply too much torque to your project, you will likely damage nuts and break the bolt. Overtightening a lug nut, for example, will warp the brake rotors and damage the hub of your car.

How To Modify Your Impact Wrench To Increase Torque?

Manufacturers will have maximum torque settings on all of their wrenches. Adjusting the torque settings in this manner will void your warranty.

A better decision is to rent or buy a more powerful tool.

The only way to increase torque output on your wrench is to disassemble the impact wrench and enlarge the cylinder and exhaust ports with a grinder. You’ll also need to cut the gaskets to match the new port sizes.

This will increase the amount of airflow through these parts.

Of course, it also weakens them and introduces many irregularities.

It is more likely that you’ll destroy your impact wrench to increase the torque with a Dremel.


Frequently Asked Questions

How Much Torque Does An Impact Wrench Need To Remove Lug Nuts?

An impact wrench will need as little as 73 foot-pounds to loosen a lug nut. However, most automotive shops will choose a wrench capable of at least 300 ft-lbs of torque to remove wheel lugs.

How Much Torque Does An Electric Impact Wrench Have?

A cordless impact wrench will produce about 300 ft-lbs of torque, while a corded impact wrench can produce up to 500 ft-lbs of torque. Generally, they produce the required torque to work on lug nuts but are not good for larger fasteners.

What Size Air Impact Wrench Should I Get?

I was doing a head gasket replacement for (with?) my brother-in-law on his 1990’s car Ford Fiesta.

We hit a massive stalemate on the project when we needed to remove the crankshaft nut to loosen the timing chain (on this model the harmonic balancer required removing). I bought an electric cordless impact “wrench”, but it didn’t stand a chance — no dice.  It was way too weak.

So, I drove the car around the corner to a small mechanic shop. They used their air impact wrench on it for 15 minutes and were unable to loosen the nut, either. 

Finally, I drove to a shop that sells semi-truck tires. They had a 1-inch air impact wrench and were able to release the crankshaft bolt. I then – believe it or not – drove the car home with a mostly loose crankshaft nut. 

The key here, is to match the correct air impact wrench to your shop’s needs. As it turns out, you need 1100 foot-pounds to remove a harmonic balancer. However, for lug nuts and most other mechanic tasks, 90 foot-pounds are more than enough. 

 If you are unsure how large of a wrench you need, you can read my buyer’s guide to air tools. 

Torque/Power

Torque is pictured as a one-foot-long wrench attached to a bolt. If you were to hang a weight on that, you would be applying 1 foot-pound of turning pressure to that bolt. 

Now, you could increase that pressure by either making your wrench longer or by adding more weight. A 2-foot-long wrench with a 1-pound weight would be 2 foot-pounds of turning pressure, or “torque”. 

Power is often used interchangeably, but it has more to do with the “horsepower” of a motor and how quickly work can be accomplished. We don’t discuss that much in our reviews, but a bigger motor with the same torque could make shorter work of a task. 

Practically speaking, torque is the limiting factor around the shop. And more torque isn’t better. If you are using a wrench with maximum torque of 1100 foot-pounds to change your car tires, then you will likely want to use the regulator switch to regulate that down the lowest setting so you don’t twist a lug nut off. 

Hence, the reason I highlight the adjustable setting is to help you control the torque more easily. 

What Is an Air Impact Wrench?

To be precise, an air impact wrench is a powerful tool that delivers a high torque by using compressed air. It is used to fasten or loosen tight bolts and nuts. The main purpose of using an impact wrench is to minimize user exertion or effort. An air impact wrench is used in many applications including maintenance, tire changes, engine repairs and automotive bodywork as well as in various DIY projects.

How Does the Hammering Mechanism Work?

When working with Air Impact Wrenches, a term you might often hear is a ‘hammer.’ An impact wrench operates when an air compressor provides airpower to a motor. The motor further transfers the energy to a rotating mass called a hammer. This hammer carries a lot of momentum, with which it hits a part called the anvil.

It is this hammering impact on the anvil which results in the high impact torque. You’ll note that the only force you can feel is the motor when it accelerates the hammer, so you feel little to no torque.

What Size Air Compressor Do You Need for an Air Impact Wrench?

mechanic with impact wrench

It’s not the size you should worry about; rather, the PSI and CFM on the compressor that is the most deciding factor. Each air impact wrench has different requirements. Check with the manufacturers on what CFM and what pressure requirements the air impact wrench has. I also wrote an air compressor sizing guide that lists general airflow requirements. 

We highly recommend that you choose an air compressor that delivers at least 1.5 times more CFM than your air impact wrench requires. This will ensure that you are never underpowered.

For example, if an air impact wrench requires about 5 CFM at 90 PSI, then your compressor should be able to deliver about 6.25–7.5 CFM at the same pressure. And let’s not forget that you might need to use multiple tools with the compressor. We suggest you check the ratings of all tools and then decide which one you need.

Once you’ve carefully narrowed down your options to the appropriate CFM and PSI, we recommend you check out the size. A larger-sized tank will be able to maintain a higher CFM for a longer time. However, if you only plan to use the tool intermittently, then you can save money and go for a smaller size.

The Benefit of Twin Hammer Design

Next, I recommend you go for a twin hammer mechanism. With this mechanism, two hammers hit the anvil from both sides at the same time. This delivers a larger impact torque output. The main benefit is the longevity of the tool, as it will deliver more torque in less time and with less air power.

Driver Size

The most common drive sizes tend to be 1/2 inch. However, there are some air impact wrenches in the 3/8 or ¾ size as well. Choose one that fits your needs better. 

Bigger anvil diameters give you more leverage if you work with many large diameter nuts.

Weight

Since you might be using this air impact wrench for a long time, you must ensure that the device is lightweight. 

Generally, a composite (or partially composite) construction or high-tech alloys or titanium tend to be lighter. This will ensure that you can work more quickly with less fatigue.

Noise Level

Air impact wrenches tend to be quite noisy, which can be harmful when exposed to the noise for long periods. The quietest ones are still 86 decibels.

You should wear ear protection when operating air impact wrenches.

Longevity

If you’re investing hundreds of dollars into a tool, you must ensure that it will last you a long time.

Usually, tools with durable materials tend to last longer. If nothing else, at least make sure the air impact wrench has a long warranty. A one-year limited warranty is common on these.

Maintaining Your Pneumatic Wrench

Most air impact wrenches do not require much maintenance.

 Oiling your impact wrench every 20 days or so is often more than enough to keep them running well. Many shops oil their pneumatic tools daily, and the more frequent oiling should only help to extend their life.

Author:

Zachary Drumm

Hey! My name is Zachary Drumm! This site allows me to test new tools, piddle around in the garage, and share the insights I get from flipping cars and houses. When it comes to tools, home improvement, and being a “shade tree mechanic,” you’ve come to the right spot. If I’m not in the garage creating content, you’ll find me outside, running, canoeing, and traveling. My goal is to empower more people to be self-sufficient.

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