How to choose a camshaft
From Crankshaft Coalition Wiki
(Clean up; add text) |
(→Lobe intensity) |
||
| Line 1: | Line 1: | ||
[[File:Comp valve train img.jpg|thumb|right|500px|From Comp Cams]] | [[File:Comp valve train img.jpg|thumb|right|500px|From Comp Cams]] | ||
| − | |||
==Overview== | ==Overview== | ||
| Line 50: | Line 49: | ||
#multiply the results by 2 | #multiply the results by 2 | ||
| − | ===LSA=== | + | ===Lobe separation angle (LSA)=== |
| − | + | The lobe separation angle, sometimes called lobe ''displacement'' angle, is a measurement in ''camshaft'' degrees that states how far apart the maximum lift points of the exhaust and intake lobes are. This number is ground into the cam and can't be altered without physically changing the camshaft lobe profiles. | |
| − | [[File:Las drawing.jpg|thumb | + | [[File:Las drawing.jpg|thumb|left|400px]] <br style="clear:both"/> |
| + | |||
| + | A CHP magazine article comparing identical camshafts except for the LSA (along with comparing open vs. split plenum intakes): [http://www.chevyhiperformance.com/tech/engines_drivetrain/cams_heads_valvetrain/0905chp_camshaft_lobe_separation_angle_performance_test/viewall.html '''Camshaft Lobe Separation Angle Performance Test'''] | ||
====Narrower LSA:==== | ====Narrower LSA:==== | ||
| − | A narrower LSA will ''increase'' overlap. This has a tendency to | + | A narrower LSA will ''increase'' overlap. This has a tendency to increase engine output at lower RPM and decrease engine output at higher RPM. A narrower LSA tend to make less peak power but more average power. |
*Moves torque to lower RPM | *Moves torque to lower RPM | ||
*Increases maximum torque | *Increases maximum torque | ||
| Line 86: | Line 87: | ||
===Overlap=== | ===Overlap=== | ||
| − | + | [[File:Overlap estimator1.jpg|thumb|right|300px|Area '''1''' is for street towing, '''2''' is regular street, '''3''' is street performance, '''4''' is street/strip, '''5''' is race, and '''6''' is Pro race.]] | |
| + | "Overlap" represents the amount of duration in camshaft degrees when both the exhaust and intake valves are open at the same time. For a single cam engine this factor is ground into the cam and can't be changed without physically altering the camshaft lobe profiles. On a dual overhead camshaft (DOHC) engine overlap can be altered with adjustable cam gears. Adjusting one or more cams closer to TDC increases overlap. Increasing duration at the same LSA will increase overlap. Decreasing LSA at the same duration will also increase overlap. | ||
| + | |||
| + | Overlap is usually not found printed out on the cam card, but it's easy to calculate. | ||
| + | *Add the intake opening point BTDC to the exhaust closing point ATDC. | ||
| + | |||
| + | If the intake opening and exhaust closing points aren't known, you can estimate the overlap by using the '''advertised duration''' (or duration @ 0.050" lift, etc.) and the '''lobe separation angle'''. | ||
| + | *Add the intake and exhaust durations, | ||
| + | *Then divide the results by 4, | ||
| + | *Then subtract the lobe separation angle, | ||
| + | *Then multiply the results by 2 | ||
| + | *The result is the overlap <br style="clear:both"/> | ||
Overlap and LSA are closely tied together. Increasing overlap contributes to a race cam's choppy idle, along with the intake valve closing point and the exhaust valve opening points. The extra time the valves are open at the same time causes what is called ''reversion'', which is a situation in which the exiting exhaust gasses are partially pushed back up into the intake runner at low speeds. This causes big fluctuations in vacuum and uneven fuel metering if a carb is used (EFI metering isn't affected but reversion can still be a problem). Once the engine reaches higher RPM, the overlap is helpful since it adds to the time the cylinder can be filled with air/fuel mixture. Also, a tuning effect can come into play where the fast-moving exhaust gasses create a slight vacuum which helps to pull in more air/fuel mixture and remove more spent exhaust gasses from the cylinder, which is called ''scavenging''. Overlap also has a large impact on the amount of intake manifold vacuum an engine makes. Less overlap allows more idle vacuum, and vice versa. | Overlap and LSA are closely tied together. Increasing overlap contributes to a race cam's choppy idle, along with the intake valve closing point and the exhaust valve opening points. The extra time the valves are open at the same time causes what is called ''reversion'', which is a situation in which the exiting exhaust gasses are partially pushed back up into the intake runner at low speeds. This causes big fluctuations in vacuum and uneven fuel metering if a carb is used (EFI metering isn't affected but reversion can still be a problem). Once the engine reaches higher RPM, the overlap is helpful since it adds to the time the cylinder can be filled with air/fuel mixture. Also, a tuning effect can come into play where the fast-moving exhaust gasses create a slight vacuum which helps to pull in more air/fuel mixture and remove more spent exhaust gasses from the cylinder, which is called ''scavenging''. Overlap also has a large impact on the amount of intake manifold vacuum an engine makes. Less overlap allows more idle vacuum, and vice versa. | ||
| − | More overlap (less vacuum) can cause tuning headaches with modern OEM engine management electronics and EFI. It can also make tuning a carburetor more difficult. More overlap makes a choppy idle and tends to make peakier power for the same reason as a narrow LSA does. More overlap and the subsequent lower intake manifold vacuum might mean giving up vacuum-driven accessories like power brakes. Some cars even use vacuum to operate the | + | More overlap (less vacuum) can cause tuning headaches with modern OEM engine management electronics and EFI. It can also make tuning a carburetor more difficult. More overlap makes a choppy idle and tends to make peakier power for the same reason as a narrow LSA does. More overlap and the subsequent lower intake manifold vacuum might mean giving up vacuum-driven accessories like power brakes. Some cars even use vacuum to operate the HVAC, headlight covers, door locks, and windshield wipers, so consideration for those devices has to be given if choosing a cam for a vehicle so equipped. If the vacuum produced is insufficient, a vacuum pump can be installed. |
===Lobe intensity=== | ===Lobe intensity=== | ||
| − | One more point about the cam profile is lobe intensity. For a given duration, more lift means the lobe ramps (the opening and closing faces on the sides of the lobe) are steeper (more intensity). That is to say, the cam lobe | + | One more point about the cam profile is lobe intensity. For a given duration, more lift means the lobe ramps (the opening and closing faces on the sides of the lobe) are steeper (more intensity). That is to say, the cam lobe has to accelerate the lifter faster to get to the peak lift within the available amount of duration duration. Faster ramp speed can give more "area under the curve", which usually equates to a broader, less peaky powerband. The downside for flat tappet cams is that the steeper ramps mean they contact the lifter at a greater angle, so the potential for wiping out a cam lobe or lifter is greater. Manufacturers are well aware of this, so they try to design the lobe profiles to optimize power, yet maintain good durability. Cam profiles like the Comp Cams XE-series and Lunati's Voodoo line are both at the edge of how fast the valve can be safely opened and closed. That's why they caution against using a higher ratio rocker arm when using these grinds. More on lobe intensity can be seen [http://www.harveycrane.com/duration.htm '''at this page'''] by Harvey Crane of Crane Cams. |
===Intake centerline (ICL)=== | ===Intake centerline (ICL)=== | ||
| − | This number represents where the intake lobe's peak lift occurs in relation to crankshaft rotation. It is the point of maximum lift of the intake lobe and is measured in ''crankshaft'' degrees. A cam ground "straight up" | + | This number represents where the intake lobe's peak lift occurs in relation to crankshaft rotation. It is the point of maximum lift of the intake lobe and is measured in ''crankshaft'' degrees. A cam ground "straight up" means that the exhaust lobe's peak lift will happen at the same amount of degrees before top dead center, as the intake valve will peak after top dead center if the intake and exhaust durations are the same. ICL is machined into the cam. When cam manufacturers machine the snout of the cam for the cam sprocket, they will drill the holes with the cam slightly advanced, retarded, or straight up. When installed with stock components, the ICL can't be altered. |
Aftermarket timing set gears often have provisions for altering the cam timing by advancing or retarding the cam position in relationship to the crankshaft position. If the cam card shows the LSA is the same as ICL, the cam is said to be ground "straight up." If the ICL is ''less'' than the LSA, it is said to be ground "advanced". If ICL is more than the LSA, the cam is said to be ground "retarded". It is much more common to see a cam ground advanced or straight up than retarded. | Aftermarket timing set gears often have provisions for altering the cam timing by advancing or retarding the cam position in relationship to the crankshaft position. If the cam card shows the LSA is the same as ICL, the cam is said to be ground "straight up." If the ICL is ''less'' than the LSA, it is said to be ground "advanced". If ICL is more than the LSA, the cam is said to be ground "retarded". It is much more common to see a cam ground advanced or straight up than retarded. | ||
| Line 106: | Line 118: | ||
===Phasing the camshaft=== | ===Phasing the camshaft=== | ||
| − | While is is true that you cannot change the lobes of a camshaft after it is ground (unless you weld and re-grind the lobes), you can alter the characteristics of the camshaft in your motor by installing it in either a retarded or advanced position relative to the crankshaft | + | While is is true that you cannot change the lobes of a camshaft after it is ground (unless you weld and re-grind the lobes), you '''''can''''' alter the characteristics of the camshaft in your motor by installing it in either a retarded or advanced position relative to the crankshaft. For instance, if you have determined that you are making too much horsepower down low and can't hook the tires up, you ''might'' want to trade off a little of the lower end power for some higher end power. In this case, you would install the camshaft slightly retarded (although harnessing the power would be the preferred thing to do- a 0.10 second better 60 foot time equates to about a 0.15 second reduction in 1/4 mile ET). |
Although all four events (intake valve opening, intake valve closing, exhaust valve opening, exhaust valve closing) will be affected by changing the camshaft phasing, the most important one will be the intake closing point. If you retard the camshaft, you will be closing the intake later, thus bleeding off some of the cylinder pressure and resulting in less low end power. Vice versa if you advance the camshaft. More bottom end, less top end. A rough estimate is a 4 degree change in cam phasing will change the cranking pressure by 5 psi (advancing increases pressure, retarding decreases pressure). To put that into perspective, a rough estimate says a one point change in static compression ratio (as in going from 9:1 to 10:1, or vice versa) changes the cranking pressure by 20-25 psi. | Although all four events (intake valve opening, intake valve closing, exhaust valve opening, exhaust valve closing) will be affected by changing the camshaft phasing, the most important one will be the intake closing point. If you retard the camshaft, you will be closing the intake later, thus bleeding off some of the cylinder pressure and resulting in less low end power. Vice versa if you advance the camshaft. More bottom end, less top end. A rough estimate is a 4 degree change in cam phasing will change the cranking pressure by 5 psi (advancing increases pressure, retarding decreases pressure). To put that into perspective, a rough estimate says a one point change in static compression ratio (as in going from 9:1 to 10:1, or vice versa) changes the cranking pressure by 20-25 psi. | ||
| Line 112: | Line 124: | ||
Intake centerline can be altered either by the crankshaft grind or the use of a camshaft sprocket that can alter if the cam is installed advanced or retarded. A later ICL (retarded cam timing) will tend to move the power curve upwards, due to closing the intake valve later. With the faster engine speeds, the intake valve can stay open later without the risk of pushing intake gasses back into the intake runners. An earlier ICL (advanced cam timing) will tend to increase low end torque because at low speeds, closing the intake valve sooner will trap more intake air at lower RPM. | Intake centerline can be altered either by the crankshaft grind or the use of a camshaft sprocket that can alter if the cam is installed advanced or retarded. A later ICL (retarded cam timing) will tend to move the power curve upwards, due to closing the intake valve later. With the faster engine speeds, the intake valve can stay open later without the risk of pushing intake gasses back into the intake runners. An earlier ICL (advanced cam timing) will tend to increase low end torque because at low speeds, closing the intake valve sooner will trap more intake air at lower RPM. | ||
| − | Altering the cam timing by advancing or retarding the ICL can fine tune where the power comes on in the RPM band. Altering ICL should be left to those in the know, and most off-the-shelf cams have been designed by cam companies who know what they're doing. Generally speaking a change of more than 4 degrees either way is a good indication that a | + | Altering the cam timing by advancing or retarding the ICL can fine tune where the power comes on in the RPM band. Altering ICL should be left to those in the know, and most off-the-shelf cams have been designed by cam companies who know what they're doing. Generally speaking a change of more than 4 degrees either way is a good indication that a better cam grind could be chosen. |
There is little point in changing the cam phasing arbitrarily. Unless the camshaft is first degreed, so the exact specs are known, changing the cam position relative to the crankshaft is a total shot in the dark, and could just as easily do nothing or even cause the engine to perform worse than if nothing was done. So, before changing the cam phasing, always degree the cam. Degreeing the cam will also show if there were any errors made during the manufacturing of the cam or other valve train components. | There is little point in changing the cam phasing arbitrarily. Unless the camshaft is first degreed, so the exact specs are known, changing the cam position relative to the crankshaft is a total shot in the dark, and could just as easily do nothing or even cause the engine to perform worse than if nothing was done. So, before changing the cam phasing, always degree the cam. Degreeing the cam will also show if there were any errors made during the manufacturing of the cam or other valve train components. | ||
| + | ;Note<nowiki>:</nowiki> Also see [http://www.crankshaftcoalition.com/wiki/Camshaft_install_tips_and_tricks#Adjusting_the_cam_timing_or_.22phasing.22 Adjusting the cam timing, or "phasing"] | ||
==How the cam specs affect engine output== | ==How the cam specs affect engine output== | ||
| Line 125: | Line 138: | ||
==Solid vs. hydraulic camshaft== | ==Solid vs. hydraulic camshaft== | ||
| − | |||
==Flat tappet vs. roller== | ==Flat tappet vs. roller== | ||
| Line 141: | Line 153: | ||
Comp Cams Endure-X roller lifter is designed specifically for street and marine use. The groove directs pressurized oil to the lobes and roller bearings to keep it alive at low rpm, because it is at low RPM that the roller lifter suffers from a lack of lubrication. | Comp Cams Endure-X roller lifter is designed specifically for street and marine use. The groove directs pressurized oil to the lobes and roller bearings to keep it alive at low rpm, because it is at low RPM that the roller lifter suffers from a lack of lubrication. | ||
| − | |||
==Things that can "frag" a camshaft and lifters== | ==Things that can "frag" a camshaft and lifters== | ||
| Line 148: | Line 159: | ||
==Custom cams== | ==Custom cams== | ||
Choosing a cam is often something that seems shrouded in mystery. The manufacturers have a hundred years of technology to draw from and millions of dollars and man-hours expended on the research, development and testing of camshafts. They have used that experience to come up with thousands of lobe profiles and grinds that attempt to cover the whole broad spectrum of engines and applications. It's possible that an off-the-shelf grind might be perfectly fine, but it can't hurt for you to look into a custom designed/ground camshaft if a particular combination falls between what's readily available. Most all the cam companies will set you up with a custom ground cam for a fee. And most companies have tech lines and web sites to help you pick the right grind. Take the manufacturer's expertise and recommendations into account when deciding on a cam. | Choosing a cam is often something that seems shrouded in mystery. The manufacturers have a hundred years of technology to draw from and millions of dollars and man-hours expended on the research, development and testing of camshafts. They have used that experience to come up with thousands of lobe profiles and grinds that attempt to cover the whole broad spectrum of engines and applications. It's possible that an off-the-shelf grind might be perfectly fine, but it can't hurt for you to look into a custom designed/ground camshaft if a particular combination falls between what's readily available. Most all the cam companies will set you up with a custom ground cam for a fee. And most companies have tech lines and web sites to help you pick the right grind. Take the manufacturer's expertise and recommendations into account when deciding on a cam. | ||
| + | |||
| + | |||
| + | ===Another View=== | ||
| + | This is no longer true. There happens to be a mathematical equation that you can use to calculate exact values for valve seat durations, net valve lift, rate of lift and lobe centerlines. It has been around for years, and was written by Dick Jones, used by Mike Jones at Jones Cams, and written into an easy to use and inexpensive camshaft requirement software. It gives you the exact values for valve seat duration, durations @ .014, .016, .018, .020, .050, .100, .200, .300, .400, net valve lift, cam lobe lift, lift @ TDC, lobe centerlines and profile footprint. It takes 3 to 4 minutes and has been proven to be accurate over the past 30 years. There is nothing as accurate. Controlled Induction camshaft requirement software guarantees it. | ||
==Simulation software== | ==Simulation software== | ||
| Line 156: | Line 171: | ||
==Resources== | ==Resources== | ||
| + | *[http://catalog.elginind.com/app/engine_tech.asp?category=Camshaft+Range+Guide Camshaft Range Guide] from Elgin | ||
| + | *[[Media:Cover front only - cam-selection13-17.pdf|Tips on choosing the right cam]] from Crane Cams | ||
| + | |||
| + | ===Compression ratio calculators=== | ||
| + | *[http://www.wheelspin.net/calc/calc2.html Static compression ratio] | ||
| + | *[http://www.wallaceracing.com/dynamic-cr.php Wallace Racing DCR calculator] | ||
| + | *[http://www.empirenet.com/pkelley2/DynamicCR.html Kelly DCR calculator] | ||
| + | *[http://www.uempistons.com/calc.php?action=comp2 KB/Silvolite DCR calculator] | ||
| + | *[http://www.rbracing-rsr.com/comprAdvHD.htm RSR DCR calculator] | ||
| + | {{Note1}} Some dynamic compression rtatio calculators (like KBs) ask for an additional 15 degrees of duration be added to the IVC @ 0.050" lift point figure. This works OK on older, slower ramped cam lobes, but the faster lobe profiles may need to have 25 degrees or more added to be accurate. | ||
| + | |||
| + | {{Note1}}If the intake valve closing (IVC) point isn't known, it can be calculated: | ||
| + | # Divide the intake duration by 2 | ||
| + | # Add the results to the lobe separation angle (LSA) | ||
| + | # Subtract any ground-in advance | ||
| + | # Subtract 180 | ||
| + | This result does not need to have any amount added to the IVC point, like the KB calculator calls for. | ||
| + | |||
| + | ===Dyno simulator=== | ||
*[http://www.compcams.com/camquest/default.asp Comp Cams CamQuest] | *[http://www.compcams.com/camquest/default.asp Comp Cams CamQuest] | ||
| − | + | ||
| + | ===Crankshaft Coalition wiki articles=== | ||
*[[Valve train points to check]] | *[[Valve train points to check]] | ||
| + | *[[Camshaft install tips and tricks]] | ||
*[[Cam and compression ratio compatibility]] | *[[Cam and compression ratio compatibility]] | ||
*[[Adjusting hydraulic lifters]] | *[[Adjusting hydraulic lifters]] | ||
Your Privacy Choices