supercharger camshaft lobe separation

One thing to note is that the valve angle has a lot to do with exhaust scavenging, obviously you will get maximum scavanging if the exhaust and intake valves had ‘line of sight’ i.e. Its a vintage car with long stroke engine 110mm stroke. Lobe separation angle (LSA): This is the number of degrees between maximum intake lobe lift and maximum exhaust lobe lift, also expressed in degrees. IO 23BTDC EO 44BBDC It includes lobe lift, net valve lift, timing points at the advertised duration, duration at 0.050-inch lift, lobe separation angle, and the installed intake centerline. Installing a camshaft designed specifically for a supercharged engine is best. I've wondered this myself, as I have a sbf dart block 9.5 deck out to 454, and the short block was built to n/a specs with a comp cam .600 lift, 110.0 lobe separation, hyd roller. At low rpm with no or low-boost levels, the best camshaft selection would be the same as a normally aspirated engine, meaning that it would have a tighter lobe separation than a camshaft used with a positive displacement blower, and installed a few degrees more advanced. The Lobe Separation Angle (LSA) is the distance between the centerlines of the intake and exhaust lobes on the camshaft. So we see here that the end result here a lop-sided camshaft with a conservative duration, high lift cam on the intake side, and a normal duration, high lift cam on the exhaust with minimal lobe separation angle and minimal (but not necessarily no) overlap. So what happens here is that if your valve train isn’t light enough and well controlled (Through proper valve springs or hydraulic lifting and damping) to operate that rapidly then lift will give you improved performance at lower rpms (where there is a lot of time to move the valve to peak lift) but reduced performance at higher rpms, where there are more rounds per minute and so less time per round, and thus less time to go up the steep ramp and push the valve out to full extension. All of our cams have been in house designed and tested to make more power than … Install cam straight up. Make sure that at this new lift, that there is still enough clearance between the valve (at full extension) and the cylinder (at top dead center) to prevent any catastrophic mechanical failure. What happens here is that we get a cylinder that filled for 30* of overlap with exhaust air, and then filled for another 210* (of the original 240* of duration for a typical street cam) with fresh air. Of course, when cruising and thus not building boost, nothing more than a normal camshaft is required. You can calculate the LSA using the centerlines of the intake and exhaust lobes. The Lobe Separation Angle (LSA) is the distance between the centerlines of the intake and exhaust lobes on the camshaft. The use of the proper supercharger optimized cam shaft can go a long way towards supercharger […] The other part of phenomenon that relates to timing intake valves with respect to exhaust valves is the duration of time where both valves are absolutely closed, which is your power stroke. The result is the intake valve closing further into the compression stroke thereby reducing dynamic compression which will most significantly effect low end power. A supercharger can overcome inadequacies in a stock cam up to about 4,500-5,000 rpm. Sometimes people take a car that starts off with a 9000 rpm redline, has an 11.5:1 compression ratio, and a 280* duration camshaft, and an aggressive naturally aspirated-esque timing curve and decide to supercharge it for more power. if the valves were separated by an angle of 180*. Lift is how far or how deep the valve opens into the cylinder. Depending on where the pistons is in the stroke, and where we are in the combustion cycle, then opening the valves will exploit the pressure difference between the cylinder and the intake and exhaust manifolds. © Copyright 2020 by Total Car Diagnostics. Camshaft tuning is an essential part of supercharger tuning. Advancing the exhaust cam both opens and closes the exhaust valves sooner. IC 34ABDC EC 7ATDC. If so, the exhaust air can directly pull in new air. These blower and turbo camshafts from COMP Cams are available in a variety of mild-to-aggressive styles. Support phone: (+61) 401 605 241. Valve Lift INT 0.623 - EXT 0.623 . “The cam timing for the intake cam would ideally be retarded which would move the intake cam opening event farther away from the exhaust valve closing event so as to reduce or eliminate overlap, and as a side effect the power stroke duration will increase by retarding the intake cam which can also compensate for the lost power from the duration reduction.” The effect upon power stroke when retarding the intake is stated incorrectly. According to the Comp Cams catalog, “The lobe separation angle (LSA) is equal to 1/2 the angle in crankshaft degrees of rotation between the maximum exhaust … You will typically find that performance with a blower will not be significantly enhanced below these speeds with a cam change. Avoid any cam with more than 30-degrees of overlap. Some cards also include overlap and valvespring specs. This is quite possibly the most crucial element of supercharger camshaft selection, since the supercharger cannot push more air in if there is already exhaust gases in the cylinder. If we had a high flow exhaust system installed, then it may not be beneficial to advance the exhaust cam, a high flow exaust system that is optimized for our engine’s power requirements can clear the combustion chamber of all it’s gasses very efficiently. Opening the exhaust valve sooner slightly reduces the power stroke, but at the same time it reduces overlap and makes better use of our supercharger. Additional duration, increasing overlap by opening the intake valve earlier and closing the exhaust valve later, is commonly found on performance camshafts. Nitrous and supercharger cams generally employ very similar profiles because both do their best work at high rpm. An interactive camshaft calculator where engine builders can see how valve overlap (and boost efficiency) is affected by a camshaft’s physical design. For a street motor, this approach is a good compromise. This separation determines where peak torque will occur within the engine’s power range and … Therefore the biggest obstacle to overcome when selecting a cam profile, is selecting the Lobe Center. The net result is something like 16psi of boost so 2psi (or about 12%) of our power was wasted. If the supercharger is geared to 7psi of boost for example, then during overlap, the cylinder sees 7psi of boost on the intake side, and 10psi of back pressure on the exhaust side, the net result is that air will flow from the high pressure zone (the exhaust) to the lower pressure zone (the intake) and so your cylinder will start to fill with exhaust gases. I have taken valve timing at 10 thou (which is valve clearance for this engine) and at 40 thou, which is how some others setup these cams. The high and low pressure pulses created by the design and runner lengths of the intake and exhaust manifolds.It would make sense to open the intake valve just as the reflected pressure waves in the intake manifold reach the intake valve as a high pressure portion of the wave, thus opening the valve at this high pressure point gives a ‘ram air’ effect through volumetric efficiency resonance tuning increasing air ingestion which increases power. 10 thou clearance Overlap is the amount of time in degrees that the intake and exhaust valves are open at the same time, and excess amounts of it can work against your supercharger by allowing exhaust backpressure to negate supercharger pressure while the valves are open. Finally, if we would like to get more flow from the intake cam, there is still the option of using a higher lift camshaft (with a steeper profile due to the decreased duration) with supporting valve train modifications to make sure valve float doesn’t occur at higher rpms. While increasing pressure in the intake manifold can shove more air into the cylinder, that air may well go to waste if the engine itself is not set up to accommodate the blower. Camshaft Article In another section, I explained how cams work, powerbands based on duration and how important valve lift is. The decision to reduce the intake cam duration rather than split the duration reduction between the intake and exhaust cams, is that the intake cam will flow air under pressurized conditions (due to the addition of the supercharger and the increase in intake manifold pressure) and so at a reduced intake cam duration the engine will still be able to get it’s full share of intake air. It does add power but it doesn’t shift the power curve up or down as radically as changing cam duration does, and so in most aftermarket applications we really want a cam to give us peak power at a certain rpm range and so we care much more about the best duration (and some added lift). Lobe separation is 113 degrees, which is appropriate for a forced-induction engine. But, often the existing camshaft works surprisingly well, and those with lobe separation angles between 112 to 116 degrees are ideal. The piston position inside the cylinder. Lobe separation is the angle in camshaft degrees between the maximum lift points of the intake and exhaust valves. How to use MGI’s Camshaft Calculator When shopping for camshafts from different manufacturers, enter each of their supplied cam card specs into MGI’s Camshaft Calculator. Rowe studied engineering, philosophy and American literature at Central Florida Community College. (This information should be listed on your Cam Card. Acquire a cam with more exhaust lift and duration. The camshaft timing card included with your cam provides the essential specifications for installing your cam correctly. (This information should be listed on your Cam Card. As the rotation continues, the exhaust valve will close and overlap will end, and the intake valve will stay open for the remainder of the intake stroke (for the rest of the duration of your intake cam), and the rest of the cylinder will fill with fresh air. Lobe Separation 112+Adv. How is it measured? Having a high duration exhaust cam, a low back pressure exhaust system and a no overlap what so ever camshaft means that we are giving the exhaust gas plenty of time to exit they cylinder, the intake valve still hasn’t opened (because the we have decide to retard it, or use a conservative cam with less duration) and so the supercharger is not pushing any new fresh air in yet, now the cylinder is void and so some of the exhaust gas can revert back into the cylinder, then the exhaust valve will close, and then the intake valve will open only to find the cylinder already partially filled with exhaust gases. The perfect top mount supercharger camshaft for your LS engine . Specify your cam with the wide lobe separation angle to ensure the lowest possible overlap. Similarly the more overlap we have, the harder the supercharger will have to work because of what we explained earlier about either exhaust reversion into the intake, or the supercharger pressurizing the exhaust. Camshafts orchestrate the valve opening and closing events in the engine and decide whether what comes out of our motor is beautiful high power music, or a mess of dysphonics. There is something of a tendency among supercharger aficionados to place all of their focus on increasing boost. Lobe Separation or Lobe Center is simply the distance between the peak opening points on the Intake and Exhaust lobes. Valve Lift INT 0.605 - EXT 0.624 . Most performance cams use more lift and duration on the intake side to pull more air in; you will want to utilize a cam with exhaust lift and duration at least ten percent higher than the intake. Conversely, you would have the least possible scavenging if you had valves that were at a narrow angle (zero degrees at the extreme) between each other, so that the air would essentially have to make a U turn to come in through the intake and get pulled out the exhaust. In this case it is OK to sacrifice some supercharger high rpm efficiency for preventing high-load & low-rpm detonation. It’s important to note that with all of these changes in cam selection , overlap, power stroke duration, and cam timing, that the power stroke duration is effected and if it is effectively shortened then we may need to retune the car’s timing advance on the dyno (for increased advance) to regain losses in duration of the power stroke (again this against popular thinking of never to advance timing on forced induction cars, if we have a shortened power stroke, or an application with significant overlap then it may be necessary to do so).

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