Trmnatr
12-26-2008, 07:56 PM
Hopefully the information below will help you pick out a new camshaft with your new heads/block etc or i hope you learn something from it or maybe it will bring up a question you never thought about asking. Im sure between Carl, Myself and some others we can help
Whats in bold (the last paragraph) is strictly my opinion and what i have found on ALL small blocks from 283cid to 410cid using GM, Ported GM and Dart Iron Eagle/Pro 1 heads
Over the Holidays i did a pretty long reply on another forum explaining a little about camshaft lobe seperation and some of my opinions on a drag race engine (which for me are small block Chevy engines) which i will highlight in bold here,,
1) Cam Duration is your Intake Valve Opening Point + 180 + Intake Valve Closing Point = Duration
Note that the points must all be @.020" or .050" ETC.
2) Lobe lift is how high the lobe lifts the lifter which pushes the pushrod up which works the rocker arms, The rocker arms multiply your lobe lift by the rocker ratio
Example: .4467" lobe lift x 1.5 rocker = .670" valve lift @ o lash, to get actual lift at the valve with a solid you have to minus your valve lash, say the above cam has a valve lash of .012" the "Actual Valve Lift" would be .658". That would be with ZERO deflection,, With a roller cam your gonna have .010" deflection with good parts and this is why some rockers that are suppose to be 1.5 actually show up as 1.51-1.53 on the engine stand
3) Lobe seperation is a degree of usually 104-110 for most stuff, in racing lobe seperations are 102-118 depending on what the application is
Lobe Seperation is the distance between the peak lobe lifts for a given intake and exhaust lobe
I use and prefer tighter lobe seperations in small blocks, I have always been able to run down the track quicker with a tight lobe seperation
In very general terms a tighter lobe seperation will make more peak torque, more overlap, rougher idle, rev quicker and usually make more HP but they are more picky
Usually if someone uses a 250/250 @.050 on a 110 lobe seperation and are thinking about using a 106 lobe seperation they should go up 6-8 degrees in duration to keep the same top rpm with in 200rpm and to make More Torque and More Horsepower however it will have more overlap which will cause a rougher idle
4) Intake and exhaust Centerline,,,
The Intake Centerline is the MAX LIFT point for the given lobe. Samething for Exhaust centerline
If you have a 110 degree lobe seperation with no advance your Intake and Exhaust Centerline or MAX LIFT will be 110
Now if you advance the Intake lobe 4 degrees to 106 intake centerline the exhaust centerline goes opposite to 114 degree intake centerline
If you were to take and retard the intake lobe 4 degrees to 114 intake centerline that will put your exhaust centerline @ 106
Now lets go back to the original 110 degree lobe center wth 4 degrees advance putting the ICL (intake centerline) at 106,, This would put the ECL (exhaust centerline) at 114 degrees
Now take your intake and exhaust center line and add them together,,
106 ICL + 114 ECL = 220/2 = your lobe seperation of 110 degrees
In my opinion, For a high rpm small block i like to have the intake valve open as far as possible at TDC (Top Dead Center) so when the piston starts to draw in air/fuel mix as it goes down the bore we get to peak airflow (due to valve being open about .300" where heads usually start flowing well) when the piston has the strongest signal (the first 90 degrees of the iduction stroke) which will pack more air/fuel mix in the cylinder for more torque and horsepower
Whats in bold (the last paragraph) is strictly my opinion and what i have found on ALL small blocks from 283cid to 410cid using GM, Ported GM and Dart Iron Eagle/Pro 1 heads
Over the Holidays i did a pretty long reply on another forum explaining a little about camshaft lobe seperation and some of my opinions on a drag race engine (which for me are small block Chevy engines) which i will highlight in bold here,,
1) Cam Duration is your Intake Valve Opening Point + 180 + Intake Valve Closing Point = Duration
Note that the points must all be @.020" or .050" ETC.
2) Lobe lift is how high the lobe lifts the lifter which pushes the pushrod up which works the rocker arms, The rocker arms multiply your lobe lift by the rocker ratio
Example: .4467" lobe lift x 1.5 rocker = .670" valve lift @ o lash, to get actual lift at the valve with a solid you have to minus your valve lash, say the above cam has a valve lash of .012" the "Actual Valve Lift" would be .658". That would be with ZERO deflection,, With a roller cam your gonna have .010" deflection with good parts and this is why some rockers that are suppose to be 1.5 actually show up as 1.51-1.53 on the engine stand
3) Lobe seperation is a degree of usually 104-110 for most stuff, in racing lobe seperations are 102-118 depending on what the application is
Lobe Seperation is the distance between the peak lobe lifts for a given intake and exhaust lobe
I use and prefer tighter lobe seperations in small blocks, I have always been able to run down the track quicker with a tight lobe seperation
In very general terms a tighter lobe seperation will make more peak torque, more overlap, rougher idle, rev quicker and usually make more HP but they are more picky
Usually if someone uses a 250/250 @.050 on a 110 lobe seperation and are thinking about using a 106 lobe seperation they should go up 6-8 degrees in duration to keep the same top rpm with in 200rpm and to make More Torque and More Horsepower however it will have more overlap which will cause a rougher idle
4) Intake and exhaust Centerline,,,
The Intake Centerline is the MAX LIFT point for the given lobe. Samething for Exhaust centerline
If you have a 110 degree lobe seperation with no advance your Intake and Exhaust Centerline or MAX LIFT will be 110
Now if you advance the Intake lobe 4 degrees to 106 intake centerline the exhaust centerline goes opposite to 114 degree intake centerline
If you were to take and retard the intake lobe 4 degrees to 114 intake centerline that will put your exhaust centerline @ 106
Now lets go back to the original 110 degree lobe center wth 4 degrees advance putting the ICL (intake centerline) at 106,, This would put the ECL (exhaust centerline) at 114 degrees
Now take your intake and exhaust center line and add them together,,
106 ICL + 114 ECL = 220/2 = your lobe seperation of 110 degrees
In my opinion, For a high rpm small block i like to have the intake valve open as far as possible at TDC (Top Dead Center) so when the piston starts to draw in air/fuel mix as it goes down the bore we get to peak airflow (due to valve being open about .300" where heads usually start flowing well) when the piston has the strongest signal (the first 90 degrees of the iduction stroke) which will pack more air/fuel mix in the cylinder for more torque and horsepower