Big Boyz Head Porting  

 

Big Boyz Street Heads

Price Starts at $299

Big Boyz Head Porting is taking a different approach to Harley-Davidson HEAD PORTING. Over the last 15 years I have used many different combinations of components and port designs in the quest for the best flow numbers while keeping port velocity up. In those years I have found that the majority of the motorcycles that were used on the street did not benefit from heads with the larger valves or what I thought was my best port design. All the formulas I have learned are true and the words from the dude that taught me how to port, "Engines run on math" is also true.

"porting the heads will be a compliment to the other performance parts that are installed."

If we're talking about Harleys, lets face it, our beloved V-twin is not a technological marvel. Head porting is not rocket science. Our engines are air pumps. This is the reason we get good gains in power with modifications to the intake and exhaust (carbs and pipes) if the right parts are used. The ports in the heads are part of this air pump. Done correctly, porting the heads will be a compliment to the other performance parts that are installed. If the choice of components is wrong for the operating range of your engine or in other words, the way you ride your bike, you'll never be happy.

"Engines run on math"

Large, long duration cams are not for everyone, big cams are a common mistake for street bikes that rarely see the redline on the tach. The same can be said about valve sizes. Twin Cam engines have the same intake valve as an Evolution engine, yet the exhaust valve on the Twin Cam is smaller than the Evos, and the Twin Cam is 88 cubic inch. Math told me that the exhaust port and valve on the Evolution heads were enough for 80"-96" engines used on the street and years of porting Evos have proven it. Doing the math with Twin Cam engines and taking into account the way that they are operated on the street, I have been using a flow bench tested port design that complements a very wide array of performance parts from the Motor Company and the After market.

If you feel you are going to turn your engine in the high RPM range (6000 +) on a regular basis, you will benefit from bigger cam, larger valve, larger carb type mods. If however you fall into the majority of V-Twin riders that want more usable power lower in the RPM range your stock heads can't be beat. With ported stock heads, good cam choices, the right exhaust system and the proper carb size, a Twin Cam in the 88"-103" range will yield stump pulling torque in the sweet spot of your RPM where your engine spends 95% of its time.

"NOBODY has more research and development money than the Factory."

There is a reason why a stock or near stock Harley engine will give you over 100 thousand miles with routine maintenance. NOBODY has more research and development money than the Factory. My experience has shown me that by using what the factory has given us and improving on it, you can have a bike that's fun when you twist the throttle and has the reliability and longevity of stock. After all the bench racing is over, most of us ride on streets that have speed limits. Having the highest horsepower on paper means nothing if it's in an RPM range that your not comfortable in. Most times at street speeds, the bike that jumps out when the throttle is whacked is the one with a lower peak horsepower but more torque in the midrange.

The same and sometimes better results can be achieved by using my STREET HEADS over Screamin Eagle (H-D) and others. Best of all, by using the heads that came with your motorcycle, you only have to buy the porting. This allows Big Boyz Head Porting to offer this no B.S. head porting for a price that's realistic. Do you need more than what my Street Heads can do? Do you deserve a quality service at a reasonable cost?

Don't pay a high price for your high performance heads.

When dealing with the stock heads it should be understood that the ports start out too big. This fact is proven by the 883's heads with its comparatively tiny ports. With 140 CC.s less than a 1340 Big Twin, a 1200 with 883 heads can produce very similar torque and horsepower numbers. The key to street power is "Velocity". Even after the 883 heads are well ported, they flow close to the same cfm. as a stock unported set of Big Twin heads. Because the port is so much smaller, the velocity is substantially higher. This allow more cylinder fill and thus more torque and horsepower. Making a broad powerband is accomplished by volumetric efficiency. The goal is to pack as much air and fuel into the cylinder over the widest rpm range possible. This is done by meeting the engines design needs with the smallest port we can get away with. This smaller port creates more velocity, which in turn creates more inertia. Visualize the principle of inertia as a moving train of air attempting to pack into any given area before it stops. The faster the train is going, the more force it develops, and the more mass it will pack before it stops. That is what happens in an operating motor. As the cylinder fills it starts to exert forces that want to stop the incoming train of air. The more inertia there is the longer that train continues before being stopped, thus providing more cylinder fill. When one realizes that inertia = velocity squared x volume (cfm.), it becomes apparent that velocity is more important to cylinder fill than volume.

"the only force keeping that cylinder filling, is inertia."

It should be further understood that a set of heads does not act the same on a flow bench as it does on an operating motor. A flow bench has a set pressure at which airflow is measured. An operating engine develops vast and very rapid changes in pressure depending on where the piston is in the cylinder (how fast it is traveling). From the time the piston hits bottom dead center until the time the intake valve closes, the only force keeping that cylinder filling, is inertia. A slow moving large port moving the same cfm of air, as a fast moving small port, will have less inertia and consequently less cylinder fill and power. Thus, fast moving air in a small port may actually fool an operating engine by giving it more air than a slower moving large port that actually flows more volume on a flow bench.

Don't let other shops lead you to believe that flow numbers are the final word in power. Furthermore, don't let someone tell you that you need a certain amount (cfm) of air on a flow bench to meet your design horsepower needs. The odds are that if you do, the numbers given will be more than you need, and your motor will never even use it all unless you are revving it to 7000 rpm. Even then, faster moving ports with less flow will create the same power sooner, with more torque across the entire power range. So, instead, concentrate on obtaining reasonable numbers with the smallest port possible. This means, don't buy heads from anyone who just hogs out the port and achieves big numbers.





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