Stage One Air Flow

July 30, 2021
by Bob Thoma

So, you just purchased that new—or at least new to you—V-twin motorcycle. Now let’s assume even though it may be used, it is basically in bone stock condition—meaning stock air cleaner and stock exhaust. Your buddies tell you it sounds like a pooch! We all know we can’t have that, and you start thinking about some upgrades. After all, half the fun of owning a new motorcycle is making it your own—modifying it with the addition of chrome, pegs, etc. My personal favorite is enhancing the performance and sound. And this starts with a new air cleaner and upgraded exhaust. Most people would call this upgrade a “stage one” which as far as I can tell has been derived from dealership accessories catalogs, so for now we just use that moniker.

We all have those friends who are more than willing to tell you their favorite brand of air cleaners or exhaust. So, you may or may not take their advice, and you begin your search. You log-on to denniskirk.com and woah, there is a plethora of different air cleaner styles, shapes, prices, etc. It can be overwhelming. And you’re not even thinking about the exhaust or fuel delivery yet. (Something you’ll also need to address after changing the airflow characteristics of your motor.)

Unless you are a die-hard gear head looking for all out performance, you will likely put appearance at the top of your list. Some like a completely modified, custom look and others prefer the stealth approach that uses the stock cover. Either way, there are many options to choose from. Let’s address what I feel are some important things to consider when purchasing a high flow air cleaner.

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Number one would be overall quality in construction and hardware. In my opinion, a well-built air cleaner setup will not only have top quality hardware, but solid construction and engineering that keeps the backing plate screws from being part of the air fuel mixture on top of the piston. A good design is one that will have the outer cover encapsulating the inner backing plate screws so that even if they were to come loose, they could not get into the intake tract.

A few designs use a system that threads through the backing plate and then through the intake to hold the backing plate on. These can vibrate loose and back their way out of the backing plate and on into the combustion chamber causing catastrophic engine damage.

We all know these V-twin bikes have a bit of vibration and trust me I have seen happen. It’s neither pretty, nor inexpensive, when it does.

Another thing to keep in mind is the breather system. Because it relieves crankcase pressure that is built up from expansion, blow by of combustion past the piston rings, and the ever-changing internal pressure from the pistons displacing crankcase volume as they cycle up and down; any air cleaner you choose should have ample passageways for the breather system from the crankcase, to function properly.

You may be asking, “But what about performance?” I have seen the elbow forward style outperform the others consistently on my dyno, but on a “stage one” setup you would see little variance in the high flow systems. Remember, some air cleaners stick out further than others, so depending whether you have forward or mid-controls, and where your legs are where riding, certain styles may not work for you. But if you purchase an extremely open style make sure it has some sort of rain sock should you be one of those riders who doesn’t mind a little rain.

Lastly, a good, washable air cleaner is a must! One you can clean and re-use at every service will save you money over the long haul. And they for the most part are a high flow design as well so there can potentially be a performance increase.

Now if you are lucky, you have narrowed down your air cleaner choices to a select few. Next, you’ll want to address the exhaust. Are you going the “slip on” muffler only route or do you want a full-system—true duals or maybe a 2-into-1 system that you can build on at a later date?

Watch for my next installment as we discuss the various exhaust styles and how they compare in both appearance but more importantly performance.

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Bob Thoma

Some of you are wondering who the hell this guy from Razorback Performance is, some of you may have already had him tune a bike or do performance work on your Harley V-twin motorcycle. So, how did he come to work on these motorcycles?

Back in the late 90’s all a performance tuner had to worry about was a simple ignition and carb. But thanks to our old buddies at the EPA, more stringent standards for exhaust emissions came out and the Motor Company of course had to comply. And this called for a new system to tune a bike when you did performance upgrades—no longer was it as simple as a jet change.

To make a long story short, Bob had one of these early fuel injected bikes and wanted to build a good reliable performance motor.In those days, every “expert” seemed to have a different idea of how to properly tune a fuel-injected bike. And no one could answer the tough technical questions he had. It seemed clear to Bob there was a huge hole in the market for fuel-injection tuning.

After researching various tuning devices, and acquiring a knack for road-tuning, it didn’t take long for his buddies and their buddies to ask them to tune their bikes. He realized that collecting data this way not only had him breaking the speed limits but doing it in an area of dense deer population wasn’t the best idea. So, he purchased a dyno in Florida and the rest is history. His hobby became a job and he created Razorback Performance and Dyno tuning.

Bob resides about a half-hour south of the Twin Cities with his beautiful wife of 35 years, Deb. His shop, south of Eau Claire in rural Whitehall, Wisconsin, is on the same property where he grew up. And he has two kids and two grand kids—with one on the way.