FAQ
This is a basic question and answer format. I will talk in very simple terms so all can understand. If you need more in-depth answers, then e-mail me at n2ofaster@charter.net These are my opinions and were gained with 30 years of riding, working on and drag racing Harley Davidson motorcycles.
"Q" The first and most often asked question is: Why should I get my heads ported if I only ride on the streets ?
"A" A motor makes it's power form the air that it recieves through the intake. It stands to reason that the more air the motor can get the more power it will produce. A good porting job will result in allowing your bike to run at it's peak and provide you with a smoother ride that performs at the RPM levels that suit your everyday riding needs. A good cylinder head man will ask you a lot of questions about how you ride and where you would like to see an improvement. There is no such thing as a perfect set of heads for everybody. The heads should be tailored to YOUR riding style. You can install bigger cams, bigger carb, and bigger exhaust, but, if the heads do not breath you will not get the results you are looking for.
"Q" So, how can I get more power in the low end RPM range?
"A" I have found that most of my customers want more power in the lower RPM ranges, so they can feel the power through the gears from 0 to about 80 MPH. That way they can count on the increased performance to come into play when they need it or want it the most. This is torque power that continues to provide a "push" through all gears. I can provide you with this without bigger valves. You can use pump gas and actually add longevity to your motor because it doesn't have to work so hard to get to the higher RPM ranges.
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Q. Do i really need compression releases ??? A. Yes. In my opinion these little devices are the best thing to happen to the Harleys in a long time. If your bike is stock then you will not need the releases. If your bike has had work then I would recommend the releases. Why ??? When the factory developed these bikes they had to figure out how much electricity the bike would require to turn over the bike and start it. In the stock form the system will work just fine, but now that you have gone and put in bigger pistons, more compression, bigger cams, ported heads and a better exhaust you have made the motor so much more powerful. Did you do anything to improve the over worked starter system and battery ?? Probably not. With the compression releases all that needs to be done is push the little buttons in and the motor will spin over like there are no pistons in the cylinders. When the motors comes to life the releases will automatically close. The load on the starter and the battery have been greatly reduced which will prolong the life of both components. It is just cheap insurance that the bike will start every time.
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"Q" How do the cams affect my motor ???
"A" Very good question. With a good set of heads the cam can be tailored to YOUR riding style, because it's the cam that dictates where the power will come in and how it will be used. There is a tendecy for people to put in cams that are to big and this hurts overall performance. When choosing a cam choose one that will improve power in the rpm range that you ride in.
"Q" What does velocity have to do with heads and how my motor runs ??
"A" Velocity is how fast the air is moving in the intake track. The faster the air moves, the more can be stuffed into the cylinder and the more power your bike will make.(air = POWER) try and imagine how long the valve is open and how much air has to move to fill the cylinder (6,000rpm = valve will open 50 times per second). A lot of air has to move to make good power, and velocity is the key to success.
"Q" Will putting my bike on the dyno hurt it?
"A" That will depend on the dyno operator and how aggresive he is with the bike. But I would say that 99.9% of the time there is no way a dyno can hurt your bike. The bike sits on a roller drum and accelerates through the gears just like you would when you are driving on the street, it might go a little higher in the rpm's than you would but it will not hurt the bike. If you are revving the bike over 6500 rpm constantly then you could be asking for trouble. For the most part the dyno is a good tool to tell you what is happening with the overall bike.
The EFI bikes can only be tuned on a dyno, any other way is just guess work.
"Q" How do I read a dyno graph ??
"A" Dyno graphs are fairly easy to understand. On the left side of the graph there are numbers going up/down the graph, these are the horsepower numbers, on the right side they are the torque numbers, on the bottom is the rpm that the motor was at. When I do a dyno run I warm up the motor for several minutes to get everything up to operating tempature. When all is hot I roll throttle on and shift up to 5th gear at about 3500 rpm. Now I let the motor idle down to about 1800 rpm and then gradually roll the throttle up until I get to 2100-2200 rpm at that time I start my test and roll the throttle to wide open rather quickly. I use 5th gear because it will show me what is happening through the entire rpm range. Depending on the bike and the test I'm doing I stop the test at 5,500-6,000rpm.
On a good running bike the torque line should go almost vertical and then level off, the horsepower line will go on more of a 45 degree angle from the bottom left to the top right. The horsepower line should be convex in shape which would indicate that it is making good power, If the HP line is concave then the motor is just revving up without really making any power. You'll notice that the lines cross at about 5200 rpm, anything below (left) that cross is torque, and anything above (right) is horsepower. Torque is that push you feel when you first whack the throttle and the horsepower is the ability to continue gaining speed. My favorite saying is: Torque moves the world and horsepower keeps it moving. This is why most HD owners should be more concerned with torque as opposed to horsepower.
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"Q" Why do some dyno graphs dip down between 2,000 and 3500 rpm and then rise up. ?
"A" Usually this an indication of too big of an exhaust system, or too big of a carb or cams. Most people think that bigger is better and to some degree they are correct. However the bigger the carb, cams or exhaust means that the higher you have to rev your motor to notice a differance. Drag pipes are good but only at the drags. At the drags we launch at 5,000 rpm so anything that happens in the lower rpm's is not really important, but, for the street rider, he uses the lower rpm ranges all the time in his/her everyday riding. If the graph has a noticeable dip in the lower ranges then it most likely will not work at it's optimum. Sometimes there is a small dip because the test was done in 5th gear and 2000 rpm is to low to start the run. Also on a dyno there is no wind drag or hills to go up so you will see higher miles per hour than your bike will do on the street. A dyno is a tool for checking overall performance, it is not the reality of riding on the open road.
"Q" What is the differance between dyno power and street power??
"A" A dyno is a great tool for checking out where the motor is making it's power, but it can be misleading. Horsepower is a function of RPM. (torque x rpm Divided by 5252 = horsepower) In order to make big HP numbers the motor must be revved higher in the rpm range, if you never go over 5,000 rpm then you wouldn't be interested in HP. What you want is torque. Most people drive their HD from 2,000 to 4500 rpm so any power numbers above that would not be used by most riders. Where is the maximum number? Do you drive in that range? Look at the graph keeping in mind where YOU ride. Big HP numbers are cool to look at but if you do not drive in that rpm range then why make power there?? Put the power where you drive.
"Q" Where do I get my bike dyno-tuned ??? "A" There is only one person in the New England area that I use and his name is Rob Scwartz of Robs dyno tuning in Gardener Mass. This man has a ton of knowledge about efi's and how they work on your bike, not only Harley's but any bike with EFI. He is very easy to work with and very reasonable on the wallet. You can feel confident that when your bike is tuned it will be right, the first time. Just can't say enough good about the service I get when I bring a bike to be tuned. He can be reached at : www.Robsdyno.com or tel. 978-895-0441 You will not be disappointed He even does house calls, You can go to him or he will come to you. Now that's service !!!! Dyno Tuning: www.Robsdyno.com
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Q. A. Without careful thought about these variables, an exhaust system can yield very disappointing results. On the other hand, a properly designed and tuned exhaust system that is well-matched to the engine can provide outstanding power gains. The distinction between "maximum power" and "maximum performance" is significant beyond general discussion. Realistically, one exhaust system may not produce both maximum power and maximum performance. For a motorcycle to cover "X" distance as quickly as possible, it is not the highest peak power generated by the engine that is most critical. It is the highest average power generated across the distance that typically produces the quickest time. When comparing two horsepower curves on a dynamometer chart (assuming other factors remain constant), the curve containing the greatest average power is the one that will typically cover the distance in the least time and that curve may, or may not, contain the highest possible peak power. In the strictest technical sense, an exhaust system cannot produce more power on its own. The potential power of an engine is determined by the proper amount of fuel available for combustion. However, the efficiency of combustion and engine pumping processes is profoundly influenced by the exhaust system. A properly designed exhaust system can reduce engine pumping losses. Therefore, the design objective for a high performance exhaust is (or should be) to reduce engine-pumping losses, and by so doing, increase volumetric efficiency. The net result of reduced pumping losses is more power available to move the motorcycle. As volumetric efficiency increases, potential fuel mileage also increases because less throttle opening is required to move the motorcycle at the same velocity. Much controversy (and apparent confusion) surrounds the issue of exhaust "back-pressure". Many performance-minded people who are otherwise knowledgeable still cling tenaciously to the old school concept.... "You need more back-pressure for better performance." For virtually all high performance purposes, backpressure in an exhaust system increases engine-pumping losses and decreases available engine power. It is true that some engines are mechanically tuned to "X" amount of backpressure and can show a loss of low-end torque when that backpressure is reduced. It is also true that the same engine that lost low-end torque with reduced back-pressure can be mechanically re-tuned to show an increase of low-end torque with the same reduction of back-pressure. More importantly, maximum mid-to-high RPM power will be achieved with the lowest possible backpressure. Period! The objective of most engine modifications is to maximize the proper air and fuel flow into, and exhaust flow out of the engine. The inflow of an air/fuel mixture is a separate issue, but it is directly influenced by exhaust flow, particularly during valve overlap (when both valves are open for "X" degrees of crankshaft rotation). Gasoline requires oxygen to burn. By volume, dry, ambient air at sea level contains about 21% oxygen, 78% Nitrogen and trace amounts of Argon, CO2 and other gases. Since oxygen is only about 1/5 of air’s volume, an engine must intake 5 times more air than oxygen to get the oxygen it needs to support the combustion of fuel. If we introduce an oxygen-bearing additive such as nitrous oxide, or use an oxygen-bearing fuel such as nitromethane, we can make much more power from the same displacement because both additives bring more oxygen to the combustion chamber to support the combustion of more fuel. If we add a supercharger or turbocharger, we get more power for the same reason…. more oxygen is forced into the combustion chamber. Theoretically, in a normally aspirated state of tune without fuel or oxygen-rich additives, an engine’s maximum power potential is directly proportional with the volume of air it flows. This means that an engine of 80 cubic inches has the same maximum power potential as an engine of 100 cubic inches, if they both flow the same volume of air. In this example, the powerband characteristics of the two engines will be quite different but the peak attainable power is essentially the same. Flow Volume & Flow Velocity One of the biggest issues with exhaust systems, is the relationship between gas flow volume and gas flow velocity (which also applies to the intake track). An engine needs the highest flow velocity possible for quick throttle response and torque throughout the low-to-mid range portion of the power band. The same engine also needs the highest flow volume possible throughout the mid-to-high range portion of the powerband for maximum performance. This is where a fundamental conflict arises. For "X" amount of exhaust pressure at an exhaust valve, a smaller diameter exhaust pipe will provide higher flow velocity than a larger diameter pipe. Unfortunately, the laws of physics will not allow that same small diameter pipe to flow sufficient volume to realize maximum possible power at higher RPM. If we install a larger diameter pipe, we will have enough flow volume for maximum power at mid-to-high RPM, but the flow velocity will decrease and low-to-mid range throttle response and torque will suffer. This is the primary paradox of exhaust flow dynamics and the solution is usually a design compromise that produces an acceptable amount of throttle response, torque and horsepower across the entire powerband. A very common mistake made by some performance people is the selection of an exhaust system with pipes that are too large in diameter for their engine's state of tune. Bigger is not necessarily better and is often worse. Equal Length Exhaust : The effectiveness of equal length exhaust is widely debated. Assuming that an exhaust system is otherwise properly designed, equal length pipes offer some benefits that are not present with unequal length pipes. These benefits are smoother engine operation, tuning simplicity and increased low-to-mid range torque. If the pipes are not equal length, both inertial scavenging and wave scavenging will vary among engine cylinders, often dramatically. This, in turn, causes different tuning requirements for different cylinders. These variations affect air/fuel mixtures and timing requirements, and can make it very difficult to achieve optimal tuning. Equal length pipes eliminate these exhaust-induced difficulties. "Tuning", in the context used here, does not mean installing new sparkplugs and an air filter. It means configuring a combination of mechanical components to maximum efficiency for a specific purpose and it can not be overemphasized that such tuning is the path to superior performance with a combination of parts that must work together in a complimentary manner. In an exhaust system that is properly designed for it’s application, equal length pipes are generally more efficient. The lengths of both the primary and main section of pipes strongly influence the location of the torque peak(s) within the powerband. In street and track performance engines with longer pipes typically produce more low-to-mid range torque than shorter pipes and it is torque that moves a motorcycle. The question is... Where in the powerband do you want to maximize the torque? * Longer pipes tend to increase power below the engine’s torque peak and shorter pipes tend to increase power above the torque peak. * Large diameter pipes tend to limit low-range power and increase high range power. * Small diameter pipes tend to increase low-range power and to some degree limit high-range power. * "Balance" or "equalizer" chambers between the exhaust pipes tend to flatten the torque peak(s) and widen the powerband. Among the more astute and responsible exhaust builders, it is more-or-less understood that pipe length variations should not exceed 1" to be considered equal. Even this standard can result in a 2" difference if one pipe is an inch short and another pipe is an inch long. No exhaust system is ideal for all applications. Depending on their design and purpose, all exhaust systems compromise something to achieve something else. Before performing exhaust changes or modifications to increase performance, it is critical to determine what kind of performance you want. * Do you want the best possible low-end and mid-range power or maximum top-end power? * Will you be using an aftermarket cam with different lift, duration, timing and overlap? * Have you investigated the relationship between torque (force) and horsepower (amount of work within time)? * Do you want a cosmetic exhaust system or a performance exhaust system? What's the big deal about exhaust , long, short, big or small. What is the best for my bike ???
Is there an advantage to polishing the ports ?? The "Porting and Polishing" Myth It is popularly held that enlarging the ports to the maximum possible size and applying a mirror finish is what porting is. However that is not so. Some ports may be enlarged to their maximum possible size (in keeping with the highest level of aerodynamic efficiency) but those engines are highly developed very high speed units where the actual size of the ports has become a restriction. Often the size of the port is reduced to increase power. A mirror finish of the port does not provide the increase that intuition would suggest. In fact, within intake systems, the surface is usually deliberately textured to a degree of uniform roughness to encourage fuel deposited on the port walls to evaporate quickly. A rough surface on selected areas of the port may also alter flow by energizing the boundary layer, which can alter the flow path noticeably, possibly increasing flow. Flow bench testing shows that the difference between a mirror finished port and a rough textured port is typically less than 1%. The difference between a smooth to the touch port and an optically mirrored surface is not measurable by ordinary means. Exhaust ports may be smooth finished because of the dry gas flow but an optical finish is wasted effort and money.The reason that polished ports are not advantageous from a flow standpoint is that at the interface between the metal wall and the air, the air speed is ZERO. This is due to the wetting action of the air and indeed all fluids. The first layer of molecules adheres to the wall and does not move significantly. The rest of the flow field must shear past which develops a velocity profile (or gradient) across the duct. In order for surface roughness to impact flow appreciably, the high spots must be high enough to protrude into the faster moving air toward the center. Only a very rough surface does this. There is so much more information available about how to make good usable power that it can not be discussed in this forum
Do you have a question that is not answered here? Or do you want more information? Please write to me at E-mail n2ofaster@charter.net Dyno tuning: www.Robsdyno.com thank you dan vance
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