Hot Rod Air: Going For The Flow

Article and Photos By: Daniel Donley – Pandemonium Custom Choppers

Originally Published In The April 2019 Issue Of Cycle Source Magazine


Last months tech article “Pay Attention… Its’ Free” covered preventative maintenance procedures for your air compressor. This article was written out of necessity for the Pandemonium Shop. I recently purchased a few new pieces of equipment to help make life here at Pandemonium a little easier. In doing so, I found a major weak link in the shop. That being my air compressor. My old faithful friend just could not keep up with the air demands of the new equipment. So, out with the old and in with some more new! I installed my new bigger CFM air compressor, but I was still was not getting the CFM that I should be getting so, this made me realize that there is more to it than just the air compressor. I began thinking about it in terms of flow. We port and polish the cylinder heads on our hot rod engines to increase airflow which in turn makes more horsepower. You know the old saying “Horsepower is how hard you hit the wall” Similar to PSI. Torque is “How far you take the wall with you”, similar to CFM.

So, I am going to pass along a few things that I have learned the hard way! CFM, Cubic Feet Per Minute – Is a measurement of Flow that will make your tool work faster. PSI, Pounds per square inch – is a measurement of force that drives your air tool. For this month’s tech I have a fun little project that will cost you a whopping $5 bucks. It will help give you a better understanding of PSI & CFM. And the little things you can do to improve both.

Harbor Freight blow gun modifications 101… Ya, it works ok, but when we are done it will be the sweetest $5 blow gun you have ever owned!

To get things started, remove the air inlet adapter and O-ring. You will notice that the inside diameter of this fitting is very small and CFM restrictive at .195 I.D. What we are going to do is drill out the inside diameter to .250, while you’re at it, drill out your male quick-change adapter, these are very restrictive as well.

Now that the air inlet adapter has been drilled, you can chuck this up into your drill and use a deburring tool and sandpaper to put a smooth radius on the inside diameter. This smooth radius will allow smoother air flow

With this blowgun kit you receive three different length nozzles, great for getting into tight spaces. The inside diameter of the nozzles has a hard edge, this will also need to be smoothed and radiused. Just like your air inlet adapter. As before, se your drill to accomplish this. It’s all about the airflow in and out.

The inside passages of the blowgun are very restrictive also. Inside the air inlet chamber, you will see a hole that I approx. .195 in dia, I used a drill bit the size of .350 to enlarge this passage. This will greatly increase the airflow

You can see the trigger switch assembly, the on off valve that makes the air gun work when you pull the trigger. As you can see, this is also a highly restrictive area by design. The sizing of holes, restrictions or even aluminum in casting flash are all going to limit the amount of flow the tool is capable of producing. With that being said, go ahead and modify this trigger assembly as you see fit to increase the flow. Don’t worry if you mess it up, its only $5, its all about learning!

Restrictions of flow are everywhere in the things we mess with. At the end of the day if it flows well, it will probably work well. Typically, everything can be a little bit bigger, have a smoother radiused edge or an internal weld seam removed. All of which increases flow. High flow fittings and couplers are available for purchase, but I have also noticed with that higher caliber of product also comes a higher price. I figure you already have it and with a few modifications and some time it can be adjusted to perform as well if not better than the expensive counterparts.

This is a fun affordable project and one that doesn’t take much time, even your kids or buddies could give you a hand with it. The whole idea was to give you an understanding of flow and what you can do to increase it.

CFM=Faster the tool will work PSI = Harder it will drive the tool This is not just about a blow gun, it Is about everything that flows! When you do this project in your shop you will see the drastic difference it makes! Now you have some knowledge to make things flow better than they did before. This is one project that I would love to see some of your feedback on! This year is my 8th year writing for Cycle Source and my 97th tech article so if there is something that you would like to me do an article on please call me or email me with your idea.

If you have any questions, please feel free to call me at the shop anytime 419-576-6812

Daniel Donley Pandemonium Custom Choppers

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