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23:15:35 - 04/26/2024
Dakota Performance
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93 Dak
Dodge Dakota
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11/14/2004
22:00:09
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 Subject: Cam specs
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Message:
All right, I really need to better understand cam specs. I have a basic understanding but I'm sure there some things I just assume in my thinking.
Maybe someone can clarify these specs for me (I'll use a Comp Cam 604 as an
example):
Duration @.050 210/220 : I know 210 is intake and 220 is exhaust.
210 degrees of what?
Is it 210 degrees out of 360?
220 degrees of what?
@.050 = ?
LSA Lobe Separation Angle 112 degrees:
That would be the distance between the top of the intake and exhaust lobe, which controls the how much time is between the opening and closing of the valves?
Is that what causes overlap and a lumpy idle?
How is performance affected when the LSA is changed in a cam (going from 112 to 108)?
Lift:
That one is pretty straight forward.
Centerline installation:
I read a cam can be advanced or retarded depending on what centerline it's installed on. My 604 is installed on a 108 degree centerline. How would a
106 centerline affect performance? How about a 110 centerline?
Thanks all!
James
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gen1dak
Dodge Dakota
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11/14/2004
22:49:28
| RE: Cam specs
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Message:
220 degrees of crank rotation.
@.050 lift. Generally, a measurement of net duration is taken at .050 lift. Again, generally, this is considered to give a more accurate net duration number.
LSA is the peak point between intake and exhaust lift points. It cannot be changed after the initial grind.
If you take 3 cams with identical specs, except for the LSA, the cam with the lowest LSA, say, 108 degrees, will have the strongest low to midrange power, and the narrowest rpm range. Also, the lumpiest idle, as well as the lowest manifold vacuum. A 110 degree LSA will osften the idle, move best torque to the midrange/upper midrange, and increase the max rpm range a bit, and improve manifold vacuum. A 114 degree LSA will have the smoothest idle and best manifold vacuum, which makes it the most computer-friendly. The power band will be wider than the others, but net power will be slightly less than the others throughout the rpm range. They do tend to meet or exceed the redline power of the other cams with lower LSA's, however. Naturally, different specs of cams can offset things. So, you could have a 108 degree LSA can with less overlap than a 114 degree LSA cam, and a thousand different variable of that theme, and everything in between. So, these specs are used as guidelines, but are not iron-clad.
Centerline refers to peak lift point of the intake lobe in relation to the top-dead-center of the piston. Advancing the cam tends to move the power band down a few hundred rpm's, retarding it will move it up about the same amount, and improve upper rpm power. Unless you are sure you want to do this, install it at the recommended centerline.
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.boB
Dodge Dakota
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11/14/2004
23:09:15
| RE: Cam specs
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Cam shaft design is highly complicated and technical. I could waste a lot of band width here trying to explain all that, and I probably wouldn't do a very good job. Fortunatly, I don't need to.
Go to www.compcams.com Go to the technical section, and then click on "Valve Timing Tutorial" near the bottom. That will get you started.
Then do a google search for anything that isn't clear; you'll get hundreds of web pages to read.
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93 Dak
Dodge Dakota
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11/15/2004
00:26:32
| RE: Cam specs
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Message:
.boB-
I don't want to do "camshaft design", all I wanted was a basic understanding of cam specs so thanks for not doing a 3 page reply :), however, thanks for the Comp Cams web site suggestion.
gen1dak-
Thanks for the basics, that's what I was looking for!!
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