Tim_C. Posted November 12, 2002 Report Share Posted November 12, 2002 OK, here is what cam companies do to sell cams. For some reason, bigger advertised durations sell cams much better than smaller. Someone in Texas must have put the word out! ;D The advertised duration can be as much as 20 degrees, or even more than what the usable duration really is. What companies do, is gradually slope the lobe as shallow as they can for the first & last .050" of lift on the lobe. After .050", the games in playing with the lobe are over, and you have to shape the lobe within a much smaller window of steepness if you will. In other words, the cam company must go into whatever design lobe they are going for. So, until the lift gets to .050, the lobe can be flattened out on both ends, so the cam company can say, "look at this big duration cam." When really, what happens above .050 lift is where the real figures come into play. So, one should learn to ask a cam seller what the duration is @.050 lift., and know what that figure means. That tells you a lot more than however long they want to stretch out the duration before .050, which varies greatly, and does absolutely nothing for performance. It is just a gimmick to sell cams. Â Tim C. Link to comment Share on other sites More sharing options...
TurboRaider Posted November 12, 2002 Report Share Posted November 12, 2002 OK, here is what cam companies do to sell cams. For some reason, bigger advertised durations sell cams much better than smaller. Someone in Texas must have put the word out! ;D The advertised duration can be as much as 20 degrees, or even more than what the usable duration really is. What companies do, is gradually slope the lobe as shallow as they can for the first & last .050" of lift on the lobe. After .050", the games in playing with the lobe are over, and you have to shape the lobe within a much smaller window of steepness if you will. In other words, the cam company must go into whatever design lobe they are going for. So, until the lift gets to .050, the lobe can be flattened out on both ends, so the cam company can say, "look at this big duration cam." When really, what happens above .050 lift is where the real figures come into play. So, one should learn to ask a cam seller what the duration is @.050 lift., and know what that figure means. That tells you a lot more than however long they want to stretch out the duration before .050, which varies greatly, and does absolutely nothing for performance. It is just a gimmick to sell cams. Â Tim C. Agreed.....Selling at an advertised duration of .002 is a gimick... However there is a real reason for the slow take up ramps... it keeps the valve train from hammering tiself to death. Sounds like you have been measuring some cams with an indicator and a degree wheel? Kevin C Link to comment Share on other sites More sharing options...
Tim_C. Posted November 12, 2002 Author Report Share Posted November 12, 2002 No, I still haven't dug deep enough yet. I need to get a degree wheel. We have been drawing pictures by hand on a piece of paper! And comparing cams I have by using a caliper. What we have found out is by looking at hundreds of cam profiles, & comparing their advertised duration, and duration @.050 cam lift. Many have the same .050 #'s, but way different advertised, & vice versa. Yeah, I guess the more gradual the incline, the smoother the transition, but it seems they get carried away. Tim C. Link to comment Share on other sites More sharing options...
kev Posted November 12, 2002 Report Share Posted November 12, 2002 I was reading up on cam design again the other day. All webpages I found say to look for the duration at .050 versus the advertised duration. They specifically state how the duration at .050 is achieved but no one says how the advertised duration is found. Seems like it is just a number they pull off the top of their heads. Does anyone know the duration at .050 of the TEP cam? My Schneider 284RH cam only has an actual duration of 234 at .050 versus the advertised duration of 284 degrees. I don't know about you but 50 degrees is a large difference in my mind! kev Link to comment Share on other sites More sharing options...
Tim_C. Posted November 12, 2002 Author Report Share Posted November 12, 2002 Well, the advertised duration starts wherever the base circle starts to change, and ends where the base circle goes back to normal. Between those spots is a lot of room for fudging the slope to gain a number that helps to sell the cam. So, from wherever the base circle starts to change, to .050" up the lobe, is where they can say they have enough slope to add into the duration. If I could draw it, I could show a good picture of where the advertised, and .050 start & end. And yes, I think they get away with pulling any number that's close, and showing it as the "Duration" of the lobe. I know both of you guys (kev & turboraider) know more about cam profile charateristics than me, but I'm slowly catching up! 8) Tim C. Link to comment Share on other sites More sharing options...
kev Posted November 12, 2002 Report Share Posted November 12, 2002 Actually I think you know more than me Tim. I had one course in college on Mechanical design in which we spent a few weeks on cam design. However we only designed one lobe, not two lobes for say an intake and exhaust valve. The theory was very limited and is just now starting to sink in while I compare it to a real life situation such as an automobile camshaft. I find something new with cams everytime I open a book or look on a webpage. I am starting to really feel that the myth of a large duration cam = more power is just that, a myth. There are a lot of factors to consider when designing a cam for a motor. The best be it to use the perfect duration which lets the car scream both in high and low rpms. With turbo cars, we can get away with a small duration cam to increase low end performance and let the big turbo do the work for up top. I really feel that 1 psi increase of boost will equal about 30 degrees or so increase of duration on a cam. So turn up the MBC 1 psi and have just as fast of a car as a 294 cam with only a 272 cam but retain tons of low end power/torque. The 272 cam vehicle will blow away the 294 cam in every aspect. kev Link to comment Share on other sites More sharing options...
Boosted_One Posted November 12, 2002 Report Share Posted November 12, 2002 With what you said Kev, I am wondering if TEP cam is a good grind. Like I said Frank was getting really good results with their 270 duration cam Link to comment Share on other sites More sharing options...
Michael_OBrien Posted November 18, 2002 Report Share Posted November 18, 2002 This may sound crazy, but this is what .050 is about. This comes from the 50's and roller cams and V8's. .050 is the point when the lobe lift reaches the center on a roller lifter, and begins actual effective lift. This began the almost universal use of the .050 number by racers. On a flat tappet V8 cam the number is different but the .050 has other uses. This number is also a effective number when figuring lobe centers, as a number on both sides of a lobe. When degreeing a cam it is easy to use the figure to corrolate lift to crank position, or cam timing. The total duration numbers have to do with the just the cam itself. The actual duration is with the number of degrees of effective lift. The numbers vary do to lifter, or follower design, and size. This may be a little confusing but this is why the .050 duration numbers do not add up by simply adding it back into gross duration. Duration on a Turbo, or Supercharged car are just as effective as a naturaly aspirated car, but overlap is the critical issue. Obiviously the longer both valves are open the more boost you send out the exhaust. This is why people are not getting the results they expected from that "big cam", and the smaller one runs better. Schnieder will grind your cam with the Turbo in mind and it will make a difference from the "off the shelf" one. All this may make sense to some that's all I can ask. twomuchmoparjunk 88 Quest, 87 Starion 91 Spirit R/T 70 Satellite 64 Polara Convertible 59 Chevy Biscayne (watch the Honda guys when they hear this 7500 rpm suprise) And many more Link to comment Share on other sites More sharing options...
Tim_C. Posted November 18, 2002 Author Report Share Posted November 18, 2002 This may sound crazy, but this is what .050 is about. This comes from the 50's and roller cams and V8's. .050 is the point when the lobe lift reaches the center on a roller lifter, and begins actual effective lift. This began the almost universal use of the .050 number by racers. On a flat tappet V8 cam the number is different but the .050 has other uses. Â This number is also a effective number when figuring lobe centers, as a number on both sides of a lobe. When degreeing a cam it is easy to use the figure to corrolate lift to crank position, or cam timing. The total duration numbers have to do with the just the cam itself. The actual duration is with the number of degrees of effective lift. The numbers vary do to lifter, or follower design, and size. This may be a little confusing but this is why the .050 duration numbers do not add up by simply adding it back into gross duration. Duration on a Turbo, or Supercharged car are just as effective as a naturaly aspirated car, but overlap is the critical issue. Obiviously the longer both valves are open the more boost you send out the exhaust. This is why people are not getting the results they expected from that "big cam", and the smaller one runs better. Schnieder will grind your cam with the Turbo in mind and it will make a difference from the "off the shelf" one. All this may make sense to some that's all I can ask. twomuchmoparjunk 88 Quest, 87 Starion 91 Spirit R/T 70 Satellite 64 Polara Convertible 59 Chevy Biscayne (watch the Honda guys when they hear this 7500 rpm suprise) And many more That sounds good. Hey, is that '59 Biscayne a Pro Mod car? I saw an 8 second one that was yellow in Grand Junction CO. Tim C. Link to comment Share on other sites More sharing options...
Michael_OBrien Posted November 18, 2002 Report Share Posted November 18, 2002 Hey Tim, No the Biscayne is not a ProMod. The Biscayne is a "Rat Rod" She's a primer black Lowered (hot rod style) driver. It has a Balanced, and Blue Printed small block with a long lopey cam. twomuchmoparjunk 88 Quest 87 Starion 91 Spirit R/T 69 440 Cuda 64 barracuda 40 Plymouth Pickup And many more Link to comment Share on other sites More sharing options...
Shelby Posted November 18, 2002 Report Share Posted November 18, 2002 Hey Tim, No the Biscayne is not a ProMod. The Biscayne is a "Rat Rod" She's a primer black Lowered (hot rod style) driver. It has a Balanced, and Blue Printed small block with a long lopey cam. twomuchmoparjunk 88 Quest 87 Starion 91 Spirit R/T 69 440 Cuda 64 barracuda 40 Plymouth Pickup And many more hey Mike i don't see the rail dragster list'd have'd made up you mind what to drop in it yet or what , you should put up some pic's of your toys for the guys, Tristarion is a little more use'r friendly for pic posting glad to hear that you able to get arround again you should maybe leave the dirt bike rideing to moma , hehe J/K , by the way the wife sounds like a real COOL gal, lucky man Guys if you want to see some of his work check out the pic's of my intake on Tristarion , this is the guy that did the moding to the intake , and a very nice job to , thank you very much for the nice work Link to comment Share on other sites More sharing options...
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