Performance And Efficiency
Writer: Steve Taylor
PERFORMANCE. Performance is the most recognizable word when it comes to making your bike respond quicker. There are MANY so called "performance" parts available for your bike that if you were to actually believe all the horsepower claims that the part manufacturers make, you would have a rocket. Aftermarket parts manufactures, and even the factory, all claim that 'If you install this part on your bike you will see a 5% horsepower gain". They know that by just mentioning an increase in horsepower that people will buy their product. Reminds me of the traveling Snake Oil salesmen who would travel around the country claiming their product would cure what ails you. Only the faces have changed.
The truth is performance parts have not changed much over the years. You can't re-invent the wheel. The basics have remained consistent throughout the years. To better understand a motor's performance, think of it as an air pump, or compressor pump. The more air that the pump (or motor) takes in AND expels, the more power you would see. A small versus big concept. This is why American V-Twin owners are always contemplating the big cubic inch theory. More cubic inches equal more power, or so you would think.
There are many ways to attack the performance issue, all of which work. How WELL will they work? Well that depends on a variety of internal issues. You cannot and should not expect that every "performance" part that you install will give you an increase in power. Performance parts have to "agree" with each other, which is what separates the novice motor builder and the professional motor builder. A "mix 'n match" approach does not work. Don't be brainwashed into thinking that if you install the new fangled air breather and the fancy exhaust on your bike that you will be the first to arrive at the bar and be the envy of your riding partners. Truth is you HURT the performance. But hey, it sure sounds good going down the road and everyone asks you questions about your new "performance" parts. Another thing, don't just take the word of someone that installs parts without knowing what they are doing. Of COURSE they will say "Oh yeah, this thing runs great since I installed the new XYZ exhaust and the new X19 air breather, just listen to it!". Yeah, sure looks cool and it IS louder. For some reason people equate loud with fast. Probably a carry-over mind set from the 1930s. A less restrictive exhaust is a good idea, unless you know what you are doing when it comes to exhaust/air breather selection. Don't shoot from the hip when it comes to part selection. Do your homework.
EFFICIENCY. Although not nearly as common a word as performance, it is probably equal to or even more important. Remember the Samson and Goliath theory. Just because you have a 125,000 cubic inch motor don't think that you have the fastest, badest, V-Twin to hit the street. Historically, Harley’s probably having the most inefficient running motor. The biggest reason, the design. To be more specific, head design. If you look at the V-Twin motor, what do you see? I'll tell you what I see. I see a 45 degree twin cylinder motor sharing a common lower end that has not changed. The 45 degree design hasn't changed since it's inception in the 20's. What HAS changed is the head design. Every motor manufacturer out there realized a long time ago that the key to efficiency lies in head design. Look at Harley's history. There were Flatheads, then Knuckleheads, then Panheads, then Shovelheads, then Evolution heads, now Twin Cam heads. With the exception of minor modifications to the lower end, the only thing that keeps changing is the heads. Why you ask???? There's power (efficiency) in them there heads. Harley heads are sand cast, and are probably the cheapest way to make a set of heads. After that they get machined. Like a "one-size-fits-all" application. Truth is, all internal combustion motors (Harley's) run a bit differently, especially the older ones. The reason is attributed to how well the heads flow the fuel in, as well as out. It is tough to maintain any performance/efficiency consistency with sand cast heads.
Efficiency equals performance. If you want REAL performance out of your motor, consider sending your heads to a shop that specializes in head porting, Jerry Branch, Baisley Performance, etc. I also offer the service. There are two types of head porting. One is what is called CNC porting the other is hand porting using a flow bench. CNC porting is when head ports are set up on a milling machine and the heads are cut using a pre-written program designed by someone who has experimented with head flow characteristics. Once optimum flow is reached a program is written for the milling machine. Truly a one-size-fits-all concept but superior to any stock set of heads for your motor. I believe in the hand porting method myself because although it requires a lot more time and patience the net result is more horsepower because the heads are flowed to your particular application, like Dresser, or Softail, Dyna, etc. All of which require a different flow design. You can actually tune the heads to match your bike and riding habits.
An 80" Evo powered bike with more horsepower than an 88" Twin Cam? Of course, that’s easy. Fun too, and not much money spent much to the chagrin of the T/C owners. An 88" Twin Cam with more horsepower than a new 96"? That’s easy stuff too. Efficiency is the key here. How well the motor utilizes the fuel and air mixture is the key to unlocking the horsepower that is already there.