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Camshafts. What do you really know about them? Frankly, for the most part we know that they are critical to making power and torque by properly timing and sizing the engine's intake and exhaust events. Often referred to as the brain of the engine, there is a lot of mystery surrounding camshaft design, their creation and how that affects performance and durability. COMP Cams touts itself as the absolute leader in valve train technology. We knew they would be a great source of information so we asked them some basic and more advanced camshaft questions relative to their use in drag racing applications. COMP Cams has a large number of on-staff, full-time engineers so knew we had a great place to get the right information first hand. We know that they know their stuff as COMP has been a dominant force in everything from sportsman/bracket class through Pro Class competition for many years. The answers we received taught us a lot about camshafts. In addition, their CAM HELP tech line (1-800-999-0853) is a great place to answer your personal questions, so if you don't see your answer here, don't hesitate to give them a call. |
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1. I have an idea of what powerband I want my motor to produce. How should I go about selecting a camshaft? Many variables determine the power band of an engine, including: cubic inch, cylinder heads, intake manifold, camshaft specifications and the list goes on. The most important aspect of selecting a camshaft is to have your specific rpm "goal" in mind before you begin to select engine components. When selecting a camshaft it is important that you have determined the weight of your vehicle, transmission type, converter stall speed, rear end ratio, engine displacement, compression ratio, normally aspirated or turbo/supercharged induction. Each of these parameters will affect cam choice and the more accurate the information - the better your new camshaft will perform. And remember, larger cubic inch engines require more duration because they require more air/fuel mixture to fill the larger displacement cylinders. The best way to select a camshaft is to ask an expert to help you select the right camshaft based on not only the size of the engine, but the entire combination of parts. 2. What is the difference between intake centerline and lobe separation? These two terms are often confused. Lobe separation angle is simply what it states: the number of degrees separating the peak lift points of the intake and exhaust lobes. Lobe separation can not be changed after the cam has been initially ground. In contrast, the intake centerline spec is the position of the centerline (or peak lift point) of the intake lobe in relation to top dead center of the piston. This can be adjusted when degreeing the camshaft. For example, if your camshaft has a 110-degree lobe separation specification and you install it 4-degrees advanced, then the intake centerline spec is 106-degrees. A few general rules of thumb here: A tighter lobe separation results in a peakier powerband. Likewise: A wider lobe separation produces a broader powerband. In addition, if you advance the centerline you create more bottom end power. Retard the centerline and you net more top end power 3. My motor is currently normally aspirated, but I plan on adding a power adder. Will my N/A camshaft work in a power adder application? Normally aspirated engines require different kinds of camshafts than those with power adder to work at optimum efficiency. Generally, power adder applications require a wider lobe separation and a larger split between the intake and exhaust duration compared to a N/A camshaft. A few important points: * All power adders are different and so are the cams. Variables of the combination are very important to consider, such as: How much boost or how much nitrous? * Nitrous creates a lot of cylinder heat, requiring more exhaust duration to help evacuate the cylinder. The amount of nitrous used will affect what camshaft is selected. If you choose the wrong specs you won't see consistent gains once you increase the nitrous shot. * Superchargers also create increased cylinder heat and tend to work more efficiently with a wider lobe separation. * Turbochargers have come a long way in design and technology. Once again, many variables can be considered, but in general you don't need a very large camshaft and the intake and exhaust duration should be tighter than a N/A camshaft. 4. How does increasing or decreasing duration affect my engine performance? Duration has a tremendous amount of affect on an engine's performance personality. Lower duration camshafts will produce more torque in the lower rpm range while camshafts with larger duration specs will sacrifice some low rpm torque for upper rpm power. There is a common thought that for each 10-degree change in duration, the powerband of the engine moves up or down in the rpm range by 500 rpm. 5. I currently run a solid flat tappet camshaft. Is it really worth the investment to upgrade to a solid roller camshaft system? The simple answer to this question is yes, if it's in your budget. Solid roller designs use the latest and most advanced profiles we offer. Among the benefits are reduced valve train friction, higher engine rpm capability and use of faster ramp profiles, which generate higher power and torque by snapping the valve open and closed more quickly. The result is more area under the curve resulting in better performance. Solid roller camshafts and related component technology has come a long way in the last 10 years, today a proper solid roller set-up can be durable and offer previously unattainable performance. COMP Cams offers a high quality, Endure-X lifter which features a tool steel axle, EDM Oil Injection and precision sorted needle bearings. These Endure-X lifters are available for a variety of engines with different off-sets and lifter body heights. 6. How does compression ratio affect camshaft selection? The key fact to watch here is cylinder pressure. If you have a lower compression motor, say 9.5:1, and you use a camshaft that is fairly large (increased overlap between lobes allowing both the intake and exhaust valves to be open at the same time) then you will bleed off cylinder pressure and in effect - power and torque. On the other hand, if you're running a high compression motor and your engine has a minimal amount of overlap, the cylinder pressures can go sky high - which for racing engines is far less of a problem than street-bound engines, but none the less should be a calculated execution and not one happened upon by accident. In addition, the type of cylinder head and quality of fuel are another consideration. If you try to stick with pump gas, the rule of thumb is to limit compression to 10:1 with cast iron heads and 11:1 compression with aluminum heads. 7. I have heard some stories about people having issues with flat tappet break-in. What does COMP Cams offer to help reduce the chances of flat tappet failure? Due to federal legislation, motor oils no longer contain certain anti-scuffing agents that are essential to flat tappet designs. While incorrect spring pressure and not following proper break-in procedure are often the culprit, the changes in oil formulation have brought the need for additional steps to be added to the break-in process. COMP Cams has two ways to ensure proper break-in of flat tappet camshafts. COMP Cams Engine Break-In Oil Additive (Part #159) ensures that the camshaft will have the lubricant it needs to seat the camshaft journals and lobe/lifter surfaces. This lubricant is poured into the engine crankcase after the camshaft and lifters have been coated with the initial break-in lubricant supplied with the camshaft. Step two is COMP Cams new nitriding procedure. Recently COMP invested in a nitriding machine, the first of its kind in the US owned by a major aftermarket camshaft manufacturer. Nitriding actually hardens the surface of the camshaft and tappet face by injecting nitrogen "needles" into the metal. The result is an ultra-hard surface on the face of the camshaft lobes and lifter face, which greatly improves the performance and break-in process for flat tappet cams. This process is an additional charge for COMP Cams camshafts but for many extreme duty applications, it virtually ensures proper break-in and increased durability. 8. I'm switching to fuel injection. Do I need to change my camshaft? Yes, factory fuel injected engines require wider lobe separation specs than carbureted engines to decrease the overlap, yielding a more efficient combustion process and increased vacuum. This is important because modern ECUs require certain vacuum parameters to operate properly. In addition, camshafts, such as the XFI line, take advantage of the high velocity EFI-style cylinder head intake ports, intake manifolds and combustion chamber designs, resulting in dramatic improvement in performance durability with today's fuel injected engines. With racing engines using aftermarket stand-alone computers, this dynamic is much less part of the considerations when selecting a camshaft. 9. What pushrod length do I need and which style pushrod is best for my application? Pushrod length and rocker arm geometry are critical to an engine's performance. Pushrod length should always be measured in any racing engine because no two engines are exactly the same. The net result of various factors, including quality of engine machine work, cylinder head casting variances, camshaft base circles sizing and other elements all affect rocker arm geometry and precise pushrod length. As for the pushrod diameter required, that depends on the application. COMP Cams offers pushrods in various diameters, material, lengths and wall thicknesses to meet your specific needs. If you need a mental picture of the real dynamics affecting your pushrods, think of this: the pressure being applied to your pushrod when the engine is running at high rpm is the same as if your entire car's weight was being supported by a single pushrod. Now, think about how important it is to find the right pushrod, and you'll know just why winning racers don't skimp when buying the best quality pushrods they can find. The general rule of thumb is to use the largest diameter pushrod your engine will accept. 10. How does lash setting affect the powerband of my motor? Adjusting your valve lash by adding or subtracting a few thousandths of an inch will respectively reduce or increase a camshaft's duration, thus affecting the engine's performance. Running a tighter valve lash (reducing the amount of space between the rocker tip and the valve stem) will make the cam profile larger (more duration) and increase your top end power. Loosening the valve setting does just the opposite by promoting bottom end power and torque which will improve your 60-foot times. Although the overall effect is obviously never as dramatic as making a camshaft swap, knowledgeable racers have successfully used this tuning tip to win races when either of these results is desired. The rule of thumb here - 0.004-inch of lash movement from the factory rating equated to two degrees of duration when measured at 0.050-inch lift. |
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