Cam and Ramp Speed talk
10-07-2002, 10:39 PM
#1
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Cam and Ramp Speed talk Ok... i understand how the duration works and it's at .050 etc... (the numbers given) but... how are the ramp speeds measured? Are these numbers usually given out freely by cam manufacturers?
I read that faster ramp speeds means lower peak power? true? is this a general rule of thum or does it depend on the duration?
Also what are these XE-R lobes i've been reading about?
I read that faster ramp speeds means lower peak power? true? is this a general rule of thum or does it depend on the duration?
Also what are these XE-R lobes i've been reading about?
10-08-2002, 06:14 PM
#2
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Re: Cam and Ramp Speed talk Yeah, I am curious about the Hendrick Motors also. They said the retainer.....aren't they titanium.--Doubt they broke. I just hope if the #24 can't pull it off this year, maybe the #48 can. I would HATE to see either Tony Stewart or Rusty win it.
10-09-2002, 12:55 AM
#4
TECH Fanatic
Re: Cam and Ramp Speed talk Good question!
If by "ramp speed" you mean how fast the lift occurs or how "steep" the cam lobes are, it's called "cam velocity" and measured in inches of lift per degree of cam rotation. It is independent of cam (engine) rpm, which isn't always ovbious.
Cam velocity generally is the basic limiting factor in lobe design; the cam/lifter interface can only handle so much "velocity" and live. With flat lifters, lifter diameter determines it; if you try to get too much velocity, the edge of the lifter digs into the lobe. With roller lifters, it's things like side loads on the lifter bores which limit the durability.
Do cam manufacturers usually quote these numbers? Rarely, if ever, in public. One reason is that many end users don't understand their significance, and various other things also enter into the picture.
You can compare the relative 'velocity' of cams crudely by dividing the lobe lift (valve lift divided by rocker ratio) by 1/2 of the .050 duration. For example, a 224 degree (@.050) .380 lobe lift cam would calc out to ".0034" while a 244 degree (@.050) .380 lift cam would calc out to ".0031". Therefore the 224 cam would have a higher velocity and would be a more aggressive lobe than the 244. It gets the same lift with less duration.
More aggressive lobes usually give more power with less duration, but they are harder on the valvetrain and often need stronger springs, pushrods, rockerams, etc. and are restricted to lower rpm for good durability. Ot the outer edge, ProStock valve springs may have about 8-10 seconds of life at racing speeds! It's even hard to get a dyno pull on a set of springs. That's BIG time velocity!
As an aside, I wonder why almost all the Hendrick Winston Cup engines lost their valve trains near the end of Sunday's Telladaga race. Lifter velocity, perhaps?
You might not believe what kind of lobes they use on those restricted 7000 rpm engines vs. the unrestricted 9400 rpm mills. Anyone have any "inside" info?
More than you wanted to know, huh?
<small>[ October 08, 2002, 01:12 PM: Message edited by: Old SStroker ]</small>
If by "ramp speed" you mean how fast the lift occurs or how "steep" the cam lobes are, it's called "cam velocity" and measured in inches of lift per degree of cam rotation. It is independent of cam (engine) rpm, which isn't always ovbious.
Cam velocity generally is the basic limiting factor in lobe design; the cam/lifter interface can only handle so much "velocity" and live. With flat lifters, lifter diameter determines it; if you try to get too much velocity, the edge of the lifter digs into the lobe. With roller lifters, it's things like side loads on the lifter bores which limit the durability.
Do cam manufacturers usually quote these numbers? Rarely, if ever, in public. One reason is that many end users don't understand their significance, and various other things also enter into the picture.
You can compare the relative 'velocity' of cams crudely by dividing the lobe lift (valve lift divided by rocker ratio) by 1/2 of the .050 duration. For example, a 224 degree (@.050) .380 lobe lift cam would calc out to ".0034" while a 244 degree (@.050) .380 lift cam would calc out to ".0031". Therefore the 224 cam would have a higher velocity and would be a more aggressive lobe than the 244. It gets the same lift with less duration.
More aggressive lobes usually give more power with less duration, but they are harder on the valvetrain and often need stronger springs, pushrods, rockerams, etc. and are restricted to lower rpm for good durability. Ot the outer edge, ProStock valve springs may have about 8-10 seconds of life at racing speeds! It's even hard to get a dyno pull on a set of springs. That's BIG time velocity!
As an aside, I wonder why almost all the Hendrick Winston Cup engines lost their valve trains near the end of Sunday's Telladaga race. Lifter velocity, perhaps?
You might not believe what kind of lobes they use on those restricted 7000 rpm engines vs. the unrestricted 9400 rpm mills. Anyone have any "inside" info?
More than you wanted to know, huh?
<small>[ October 08, 2002, 01:12 PM: Message edited by: Old SStroker ]</small>
