Understanding cam specs
Thread Starter
Safety Car
Joined: Mar 2005
Posts: 4,723
Likes: 11
From: Winnipeg Manitoba, Canada
Understanding cam specs
I'm reading over the specs of my car and am wondering about the cam. I know that everyone always talks about lift and duration, but I have different specs for intake and exhaust. What is the difference, and if someone asks me the lift and duration what do I say. The reason I'm asking is because I believe I need to get my chip reprogrammed. The car is running very rich at idle. Thanks for the help!
Heres the link to the specs.
http://www.compcams.com/Technical/Se...umber=08-501-8
Heres the link to the specs.
http://www.compcams.com/Technical/Se...umber=08-501-8
Team Owner
Joined: Oct 2004
Posts: 81,241
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From: altered state
St. Jude Donor '05
Engine -Present Chevrolet
305ci-350ci
8cyl.
Grind Number CS XR264HR-12
Description
--------------------------------------------------------------------------------
Intake Exhaust
Valve Adjustment 0 0
Gross Valve Lift 0.488 0.495 Total amount valve is raised off the seat
Duration At 0.006 Tappet Lift 264 269 AKA Advertised duration
--------------------------------------------------------------------------------
Valve Timing At 0.006
Open Close
Intake 24 60
Exhaust 70 18
--------------------------------------------------------------------------------
These Specs Are For The Cam Installed At 108 Intake CL
Intake Exhaust
Duration At 0.05 212 218 AKA duration @.050
Lobe Lift 0.325 0.33 Take this # and multiply is by 1.5 (1.5 rockers), should get your total lift noted above. Using 1.6 rockers? Do the same. Lobe Separation 112
305ci-350ci
8cyl.
Grind Number CS XR264HR-12
Description
--------------------------------------------------------------------------------
Intake Exhaust
Valve Adjustment 0 0
Gross Valve Lift 0.488 0.495 Total amount valve is raised off the seat
Duration At 0.006 Tappet Lift 264 269 AKA Advertised duration
--------------------------------------------------------------------------------
Valve Timing At 0.006
Open Close
Intake 24 60
Exhaust 70 18
--------------------------------------------------------------------------------
These Specs Are For The Cam Installed At 108 Intake CL
Intake Exhaust
Duration At 0.05 212 218 AKA duration @.050
Lobe Lift 0.325 0.33 Take this # and multiply is by 1.5 (1.5 rockers), should get your total lift noted above. Using 1.6 rockers? Do the same. Lobe Separation 112
Ex: Take the adv. duration, say 280
minus-
dration @ .050, say 230
=
an intensity factor of 50. They say 48 is pretty damn decent...Lower the number the more agressive the ramp for the most part. Fwiw, less intensity typically are gentler on valvetrain parts and may last longer.....+ and -
My solid roller has an I.F. of 30. Ramps are inverted
Camspeak can get much more technical to the point where I get lost, but these are some basic regurgitated things youll read about a lot. I used to hang out on a Chevelle site where UD Harold, designer of the Lunati Voodoo line is a lot, and some of the discussions would leave me stupified.
Last edited by cv67; Jun 20, 2007 at 07:43 PM.
Large Impressive Member
Joined: Jul 2003
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From: Good health is merely the slowest possible rate at which one can die
St. Jude Donor '04-'05-'06-'07
Thread Starter
Safety Car
Joined: Mar 2005
Posts: 4,723
Likes: 11
From: Winnipeg Manitoba, Canada
Also, a factor called "intensity", simply put a way to see how agressivethe ramps and valve events are.
Ex: Take the adv. duration, say 280
minus-
dration @ .050, say 230
=
an intensity factor of 50. They say 48 is pretty damn decent...Lower the number the more agressive the ramp for the most part. Fwiw, less intensity typically are gentler on valvetrain parts and may last longer.....+ and -
My solid roller has an I.F. of 30. Ramps are inverted
Camspeak can get much more technical to the point where I get lost, but these are some basic regurgitated things youll read about a lot. I used to hang out on a Chevelle site where UD Harold, designer of the Lunati Voodoo line is a lot, and some of the discussions would leave me stupified.
Ex: Take the adv. duration, say 280
minus-
dration @ .050, say 230
=
an intensity factor of 50. They say 48 is pretty damn decent...Lower the number the more agressive the ramp for the most part. Fwiw, less intensity typically are gentler on valvetrain parts and may last longer.....+ and -
My solid roller has an I.F. of 30. Ramps are inverted
Camspeak can get much more technical to the point where I get lost, but these are some basic regurgitated things youll read about a lot. I used to hang out on a Chevelle site where UD Harold, designer of the Lunati Voodoo line is a lot, and some of the discussions would leave me stupified.
Burning Brakes
Joined: Jun 2006
Posts: 1,096
Likes: 28
From: Baltimore MD
Using the cam info the original poster linked to,
Duration @ .050"
212* Intake/218* Exhaust
Gross Valve Lift
.488" Intake/.495" Exhaust (with 1.5 ratio rocker arms)
Personally, I'd simply either include a copy of the actual cam card with the other requested chip info, or provide them with the link you provided us with above.
If you tell them your cam's lift @ .500" is .488" and .495", then he will think you are nuts
, as that doesn't make a bit of sense.
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Obviously, Vader is mixed up, as there is lift at the cam lobe, and gross (or total) lift like you pointed out above, which is the actual lift after multiplying lobe lift times your rocker arm ratio.
Using the cam info the original poster linked to,
Duration @ .050"
212* Intake/218* Exhaust
Gross Valve Lift
.488" Intake/.495" Exhaust (with 1.5 ratio rocker arms)
Using the cam info the original poster linked to,
Duration @ .050"
212* Intake/218* Exhaust
Gross Valve Lift
.488" Intake/.495" Exhaust (with 1.5 ratio rocker arms)
i mean gross lift
Race Director
Joined: Jun 1999
Posts: 14,924
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From: Merritt Ils Fl
An afterthought: A general discussion about SBC cams will almost always assume 1.5:1 rockers when gross lift is discussed. With the increasing popularity of 1.6:1 and even 1.7:1 it might be a good idea to ID the rockers early in the conversation.
