Please explain this card to me
Thread Starter
TECH Enthusiast
Joined: Mar 2004
Posts: 647
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From: Australia
Please explain this card to me Here is a cam doctor for a stock LS1. I know how to read a cam card, but there is one thing that I don't understand. It seems to me the valve duration is longer than the cam duration, by around 16* at all points. Is this normal?
http://ourworld.cs.com/ls1info/LS1-data-2.jpg
This is taken from the cam sticky above.
cam duration - intake
0.004_284.3
0.02__226.8
0.05__197.8
0.1___167.1
0.2___113.1
valve duration - intake
0.004_278.6
0.02__236.7
0.05__213.2
0.1___190.0
0.2___156.6
Am I reading this right? In that even though the stock cam is small, it is yielding the equivalent of a 213-226 at the valve?
http://ourworld.cs.com/ls1info/LS1-data-2.jpg
This is taken from the cam sticky above.
cam duration - intake
0.004_284.3
0.02__226.8
0.05__197.8
0.1___167.1
0.2___113.1
valve duration - intake
0.004_278.6
0.02__236.7
0.05__213.2
0.1___190.0
0.2___156.6
Am I reading this right? In that even though the stock cam is small, it is yielding the equivalent of a 213-226 at the valve?
Originally Posted by MNR-0
Here is a cam doctor for a stock LS1. I know how to read a cam card, but there is one thing that I don't understand. It seems to me the valve duration is longer than the cam duration, by around 16* at all points. Is this normal?
http://ourworld.cs.com/ls1info/LS1-data-2.jpg
This is taken from the cam sticky above.
cam duration - intake
0.004_284.3
0.02__226.8
0.05__197.8
0.1___167.1
0.2___113.1
valve duration - intake
0.004_278.6
0.02__236.7
0.05__213.2
0.1___190.0
0.2___156.6
Am I reading this right? In that even though the stock cam is small, it is yielding the equivalent of a 213-226 at the valve?
http://ourworld.cs.com/ls1info/LS1-data-2.jpg
This is taken from the cam sticky above.
cam duration - intake
0.004_284.3
0.02__226.8
0.05__197.8
0.1___167.1
0.2___113.1
valve duration - intake
0.004_278.6
0.02__236.7
0.05__213.2
0.1___190.0
0.2___156.6
Am I reading this right? In that even though the stock cam is small, it is yielding the equivalent of a 213-226 at the valve?
it looks like at .050 198-213
depends on the ratio of the rocker. Most SBCs(LSx included) use a rocker arm ratio higher than one to one, so valve lift and duration will be higher than cam lift and duration.
Thread Starter
TECH Enthusiast
Joined: Mar 2004
Posts: 647
Likes: 0
From: Australia
So you are saying the rocker arm ratio is increasing the duration at the valve by 16*? If that is so, then when specifying a cam of 0.050 tappet lift for, say, 216-220 it is in effect generating 232-236 at the valve?
If so, perhaps this explains why such a small cam yields such great results, and that why going bigger suffers the law of dimishing returns as it overcams the LS1.
I didnt think a 1.7:1 ratio increased the valve events by THAT much. Makes it even more difficult knowing what the valve is doing when designing a cam, and perhaps why I have seen so many 232-232 cams build great horsepower after 6000RPM, but perform poorly going by their ET due to decreased pumping efficiencies and sluggishness under 4000RPM.
If this is so, then this must be very important when considering an optimum cam for an engine.
Also, when determing the IVC-EVO valve events that you can't go by the cam card.
I am trying to picture it as a triangle like so:
__/| 0.05/1.5=0.033 equivalent cam lift at the valve
_/_| which is approx. 212 duration going by the cam lift
/__| where measured duration at the valve is 213 (seems to work)
Since cam choice is ALL about valve events, then shouldn't we be factoring in the rocker ratio? Or am I such an idiot that everyone else has been factoring this all along?
If so, perhaps this explains why such a small cam yields such great results, and that why going bigger suffers the law of dimishing returns as it overcams the LS1.
I didnt think a 1.7:1 ratio increased the valve events by THAT much. Makes it even more difficult knowing what the valve is doing when designing a cam, and perhaps why I have seen so many 232-232 cams build great horsepower after 6000RPM, but perform poorly going by their ET due to decreased pumping efficiencies and sluggishness under 4000RPM.
If this is so, then this must be very important when considering an optimum cam for an engine.
Also, when determing the IVC-EVO valve events that you can't go by the cam card.
I am trying to picture it as a triangle like so:
__/| 0.05/1.5=0.033 equivalent cam lift at the valve
_/_| which is approx. 212 duration going by the cam lift
/__| where measured duration at the valve is 213 (seems to work)
Since cam choice is ALL about valve events, then shouldn't we be factoring in the rocker ratio? Or am I such an idiot that everyone else has been factoring this all along?
Last edited by MNR-0; Oct 30, 2005 at 05:50 AM.
Isn't this what you are looking for?
Stock 98-00 trans am cam
Duration@.050 198.86 intake 209.25 exhaust
Lift .498 intake .497 exhausts
LSA 119.45
Stock 01-02 trans am cam
Duration@.050 196.37 intake 208.72 exhaust
Lift .464 intake .479 exhausts
LSA 115.92
Stock 98-00 trans am cam
Duration@.050 198.86 intake 209.25 exhaust
Lift .498 intake .497 exhausts
LSA 119.45
Stock 01-02 trans am cam
Duration@.050 196.37 intake 208.72 exhaust
Lift .464 intake .479 exhausts
LSA 115.92
