Valve Events
01-12-2006, 05:41 PM
#11
COMPRESSION AND DURATION
Just about any engine would benefit from a prepared cylinder head, a good exhaust system (with a relatively small diameter for street use), and maybe a little larger carburetor. As you increase the RPM band, you'll need to increase the compression ratio and add some more duration to the cam. The more duration you add, the more compression you'll need and that combination will increase the upper mid-range and top-end power. It is very important to keep your combinations balanced; for example, you can not use a 270 degree camshaft with 8:1 compression. 9.5:1 would be a lot better. Conversely, you can not have 10:1 compression and use a cam with only 250 or 260 degrees of duration! As soon as the duration is above 270 degrees, the standard exhaust system will likely restrict the breathing ability of the engine. As a result, it may become difficult to make the idle mechanism work properly due to reduced vacuum and extra exhaust back pressure.
ELGIN CAM DESIGN PHILOSOPHY
You probably have figured out by now that I am not an advocate of extra high lift, unnecessarily long duration, or very high compression for any street driven car. I prefer instead to use maximum velocity in the camshaft design which allows my cams to have more duration at 0.050", 0.100", and 0.200" lift compared to the "Brand X" cams you might get from other sources. As a side benefit of this design choice, it turns out that when you have more duration at 0.200" - 0.300" lift and not as high a cam lift, you end up with a cam lobe with a rounder nose radius which will support higher valve spring loads and therefore will last longer than a "pointed" high lift cam. I learned a long time ago that dwell on the nose, or top, portion of the cam lobe is equivalent to lift provided that you have the valve open far enough when the piston reaches its maximum velocity. On a normally aspirated engine, I have never seen power increased by adding valve lift above and beyond the flow capacity of the head.
You now have all the info you need to make the important performance enhancement choices appropriate for your own application - so there is not much more to say except HAPPY TUNING.
By: Dimitri N. Elgin
Just about any engine would benefit from a prepared cylinder head, a good exhaust system (with a relatively small diameter for street use), and maybe a little larger carburetor. As you increase the RPM band, you'll need to increase the compression ratio and add some more duration to the cam. The more duration you add, the more compression you'll need and that combination will increase the upper mid-range and top-end power. It is very important to keep your combinations balanced; for example, you can not use a 270 degree camshaft with 8:1 compression. 9.5:1 would be a lot better. Conversely, you can not have 10:1 compression and use a cam with only 250 or 260 degrees of duration! As soon as the duration is above 270 degrees, the standard exhaust system will likely restrict the breathing ability of the engine. As a result, it may become difficult to make the idle mechanism work properly due to reduced vacuum and extra exhaust back pressure.
ELGIN CAM DESIGN PHILOSOPHY
You probably have figured out by now that I am not an advocate of extra high lift, unnecessarily long duration, or very high compression for any street driven car. I prefer instead to use maximum velocity in the camshaft design which allows my cams to have more duration at 0.050", 0.100", and 0.200" lift compared to the "Brand X" cams you might get from other sources. As a side benefit of this design choice, it turns out that when you have more duration at 0.200" - 0.300" lift and not as high a cam lift, you end up with a cam lobe with a rounder nose radius which will support higher valve spring loads and therefore will last longer than a "pointed" high lift cam. I learned a long time ago that dwell on the nose, or top, portion of the cam lobe is equivalent to lift provided that you have the valve open far enough when the piston reaches its maximum velocity. On a normally aspirated engine, I have never seen power increased by adding valve lift above and beyond the flow capacity of the head.
You now have all the info you need to make the important performance enhancement choices appropriate for your own application - so there is not much more to say except HAPPY TUNING.
By: Dimitri N. Elgin
01-12-2006, 09:46 PM
#13
In my humble opinion the closing of the intake is the most important valve event and should be looked at first to determine DCR and the consiquent SCR. Here are some excerpts from jrods post that I linked to earlier. All other valve events should be set in relation to this one also how much the heads should be milled.
Dynamic Compression Ratio (DCR) is an important concept in high performance engines. Determining what the compression ratio is after the intake valve closes provides valuable information about how the engine will perform with a particular cam and octane.
Definition: The Compression Ratio (CR) of an engine is the ratio of the cylinder volume compared to the combustion chamber volume. A cylinder with 10 units of volume (called the sweep volume) and a chamber with a volume of 1 has a 10:1 compression ratio. Static Compression Ratio (SCR) is the ratio most commonly referred to. It is derived from the sweep volume of the cylinder using the full crank stroke (BDC to TDC). Dynamic Compression Ratio, on the other hand, uses the position of the piston at intake valve closing rather than BDC of the crank stroke to determine the sweep volume of the cylinder.
The difference between the two can be substantial. For example, with a cam that closes the intake valve at 70º ABDC, the piston has risen 0.9053" from BDC in a stock rod 350 at the intake closing point. This decreases the sweep volume of the cylinder considerably, reducing the stroke length by almost an inch. Thereby reducing the compression ratio. This is the only difference between calculating the SCR and the DCR. All other values used in calculating the CR are the same. Note that the DCR is always lower than the SCR.
I think this is a key point that 99% of people forget when they just get a big cam and throw it in, I also think this is why alot of engines dont perform to peoples expectations.
Details: Long duration cams delay the closing of the intake valve and substantially reduce the running compression ratio of an engine compared to the SCR. The cam spec we are interested in to determine the DCR is the intake closing time (or angle) in degrees. This is determined by the duration of the intake lobe, and the installed Intake CenterLine (ICL) (and indirectly by the Lobe Separation Angle (LSA)). Of these, the builder has direct control of the ICL. The others are ground into the camshaft by the grinder (custom grinds are available so the builder could specify the duration and LSA). Changing the ICL changes the DCR. Retarding the cam delays intake closing and decreases the DCR. Advancing the cam causes the intake valve to close earlier (while the pistons is lower in the cylinder, increasing the sweep volume) which increases the DCR. This can be used to manipulate the DCR as well as moving the torque peak up or down the rpm range.
Dynamic Compression Ratio (DCR) is an important concept in high performance engines. Determining what the compression ratio is after the intake valve closes provides valuable information about how the engine will perform with a particular cam and octane.
Definition: The Compression Ratio (CR) of an engine is the ratio of the cylinder volume compared to the combustion chamber volume. A cylinder with 10 units of volume (called the sweep volume) and a chamber with a volume of 1 has a 10:1 compression ratio. Static Compression Ratio (SCR) is the ratio most commonly referred to. It is derived from the sweep volume of the cylinder using the full crank stroke (BDC to TDC). Dynamic Compression Ratio, on the other hand, uses the position of the piston at intake valve closing rather than BDC of the crank stroke to determine the sweep volume of the cylinder.
The difference between the two can be substantial. For example, with a cam that closes the intake valve at 70º ABDC, the piston has risen 0.9053" from BDC in a stock rod 350 at the intake closing point. This decreases the sweep volume of the cylinder considerably, reducing the stroke length by almost an inch. Thereby reducing the compression ratio. This is the only difference between calculating the SCR and the DCR. All other values used in calculating the CR are the same. Note that the DCR is always lower than the SCR.
I think this is a key point that 99% of people forget when they just get a big cam and throw it in, I also think this is why alot of engines dont perform to peoples expectations.
Details: Long duration cams delay the closing of the intake valve and substantially reduce the running compression ratio of an engine compared to the SCR. The cam spec we are interested in to determine the DCR is the intake closing time (or angle) in degrees. This is determined by the duration of the intake lobe, and the installed Intake CenterLine (ICL) (and indirectly by the Lobe Separation Angle (LSA)). Of these, the builder has direct control of the ICL. The others are ground into the camshaft by the grinder (custom grinds are available so the builder could specify the duration and LSA). Changing the ICL changes the DCR. Retarding the cam delays intake closing and decreases the DCR. Advancing the cam causes the intake valve to close earlier (while the pistons is lower in the cylinder, increasing the sweep volume) which increases the DCR. This can be used to manipulate the DCR as well as moving the torque peak up or down the rpm range.
01-12-2006, 10:07 PM
#14
I just read all the posts I just said the same thing grippys post did but in a different way. I like what sportsides quote said but I dont agree that the exhaust opening in the most important I think it should be matched to the intake events therefore making it second in scope.
I would like to hear some thoughts on the other two valve events. As Ive heard that intake opening greatly effects charge velocity and tq range.
Then there is overlap.
I would like to hear some thoughts on the other two valve events. As Ive heard that intake opening greatly effects charge velocity and tq range.
Then there is overlap.
01-12-2006, 10:10 PM
#15
Originally Posted by 02sierraz71_5.3
I just read all the posts I just said the same thing grippys post did but in a different way. I like what sportsides quote said but I dont agree that the exhaust opening in the most important I think it should be matched to the intake events therefore making it second in scope.
I would like to hear some thoughts on the other two valve events. As Ive heard that intake opening greatly effects charge velocity and tq range.
Then there is overlap.
I would like to hear some thoughts on the other two valve events. As Ive heard that intake opening greatly effects charge velocity and tq range.
Then there is overlap.
01-13-2006, 06:25 PM
#18
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Shaun feels the EVO is important in these type of setups for one main reason. The EFI restricted intake manifold. Throw a 226 lobe or a 236 lobe at one of these setups and it is going to make peak hp @ 6200RPM with a LS6 intake.
Take a look at Kano's setup.
EFI restricted intake + Slow Intake lobe + Fast exhaust lobe + 85% head = no torque until 4000RPM.
Point being, give me a trick intake lobe and let's get the important VE's 'correct'.
Take a look at Kano's setup.
EFI restricted intake + Slow Intake lobe + Fast exhaust lobe + 85% head = no torque until 4000RPM.
Point being, give me a trick intake lobe and let's get the important VE's 'correct'.
Last edited by Sport Side; 01-13-2006 at 06:32 PM.
01-13-2006, 06:33 PM
#19
Originally Posted by Sport Side
I can give you an idea of why Shaun thinks the EVO is so important... Take a look at Kano's dyno graph.
EFI restricted intake, slow intake lobe, fast exhaust lobe, 85% head = no torque until 4000RPM
Looking at the LS6 intake... It doesn't matter if you throw an intake lobe measuring 230*-.630'', or 226*-.590'', you'll still net a 6200RPM HP peak or lower depending on the rest of course. So, when you get a goofed up torque curve, it's not usually the intake lobe that is the problem or the IVC for this discussion. It's where the EVO has been placed.
Yes, the IVO/EVC are very important too. Not every cam needs 4* of advance.
EFI restricted intake, slow intake lobe, fast exhaust lobe, 85% head = no torque until 4000RPM
Looking at the LS6 intake... It doesn't matter if you throw an intake lobe measuring 230*-.630'', or 226*-.590'', you'll still net a 6200RPM HP peak or lower depending on the rest of course. So, when you get a goofed up torque curve, it's not usually the intake lobe that is the problem or the IVC for this discussion. It's where the EVO has been placed.
Yes, the IVO/EVC are very important too. Not every cam needs 4* of advance.
he clearly states: "I choose the EVO based on the IVC" etc. etc.
to me thats says according to him, IVC is most important. Maybe I missed something.
or maybe he is just trying to stress the importance of EVO based your above statement.
01-13-2006, 06:36 PM
#20
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Grippy... I edited the post you quoted me on so I didn't seem like I was attacking 02sierra. It's hard to set the mood when typing.
Yep, that is his point. He's just 'stressing' the importance of where the EVO is plotted relative to the IVC.
to me thats says according to him, IVC is most important. Maybe I missed something.
or maybe he is just trying to stress the importance of EVO based your above statement.
or maybe he is just trying to stress the importance of EVO based your above statement.
Last edited by Sport Side; 01-13-2006 at 06:41 PM.