Help me understand camshafts...
07-09-2015, 05:10 PM
#1
TECH Addict
Thread Starter
Help me understand camshafts... If this is in the wrong section, feel free to move it.
Now, I am trying to understand camshafts, as the title suggests.
I know a lot of people guard their cam specs, for whatever reason, so I almost am afraid to even ask for help, but here we go.
Believe me, I'm not trying to steal anyone's patent pending secret squirrel cam specs. I'm not the guy cloning your cam just to race you on Saturday night.
I'm literally just trying to understand the effects of different changes.
Duration and lsa are simply byproducts of the actual valve opening and closing events, so I'm not too caught up with those numbers. What the changes to the valve events do IS what I am interested in.
Also, changes in engine architecture and how it effects cam events... I hear about the ls7 cam being stuffed into 4.8's and this confuses me because the ls7 has a 4" stroke, while the 4.8L has a 3.3" throw. It seems that the timing would be all out of whack between the two stroke lengths. Am I wrong? Or does stroke length not come into play because it's based on degrees of rotation?
I don't know ****, but it seems that stroke length would play a huge role in valve timing.
I have already came to the conclusion that I will have a custom grind done when the time comes, but I would at least like to have a rudimentary understanding of the process.
Once again, I'm not trying to impede on anyone's business, but I would greatly appreciate a quick overview of what does what and why.
Opening the intake valve sooner does this.... Closing the exhaust valve later does that... These combined have this effect on the duration and would be better suited for this or that...
There's obviously a good reason that people who are proficient at this get paid to do so, I get that. I'm just looking for an interactive explanation to help me better understand the process.
Low duration tends to be associated with good torque production, why?
Tight separation angles tend to prefer high rpms, why?
I'm not too worried about lobe profiles, or lift. I think I understand those well enough.
Any help will be appreciated. Thanks in advance.
Now, I am trying to understand camshafts, as the title suggests.
I know a lot of people guard their cam specs, for whatever reason, so I almost am afraid to even ask for help, but here we go.
Believe me, I'm not trying to steal anyone's patent pending secret squirrel cam specs. I'm not the guy cloning your cam just to race you on Saturday night.
I'm literally just trying to understand the effects of different changes.
Duration and lsa are simply byproducts of the actual valve opening and closing events, so I'm not too caught up with those numbers. What the changes to the valve events do IS what I am interested in.
Also, changes in engine architecture and how it effects cam events... I hear about the ls7 cam being stuffed into 4.8's and this confuses me because the ls7 has a 4" stroke, while the 4.8L has a 3.3" throw. It seems that the timing would be all out of whack between the two stroke lengths. Am I wrong? Or does stroke length not come into play because it's based on degrees of rotation?
I don't know ****, but it seems that stroke length would play a huge role in valve timing.
I have already came to the conclusion that I will have a custom grind done when the time comes, but I would at least like to have a rudimentary understanding of the process.
Once again, I'm not trying to impede on anyone's business, but I would greatly appreciate a quick overview of what does what and why.
Opening the intake valve sooner does this.... Closing the exhaust valve later does that... These combined have this effect on the duration and would be better suited for this or that...
There's obviously a good reason that people who are proficient at this get paid to do so, I get that. I'm just looking for an interactive explanation to help me better understand the process.
Low duration tends to be associated with good torque production, why?
Tight separation angles tend to prefer high rpms, why?
I'm not too worried about lobe profiles, or lift. I think I understand those well enough.
Any help will be appreciated. Thanks in advance.
07-10-2015, 12:59 PM
#4
TECH Addict
Thread Starter
Ok, I do have questions.
First and foremost, why are people so secretive about cam specs? Every motor/set-up is different and will behave/react differently, so who gives a $#!+ if someone else clones your cam?
Secondly, why don't more manufacturers post the actual valve opening and closing events? We can calculate duration on our own. Or is this related to question one, and all that secret squirrel B.S.?
The lack of information is nothing but annoying. Everyone is caught up in the wrong direction, focusing on the wrong information. Duration and LSA are arbitrary numbers, just the byproducts of the important data... That nobody is willing to share, for whatever stupid reason.
So, without using the words duration or LSA, can we discuss a couple things and their effects on the actual valve opening and closing events
Vehicle weight...? Do heavier vehicles require specifically different valve events than a lighter vehicle? If so, what changes in weight correspond with what changes to the valve events?
Head flow...? Better flowing heads require the valves to be open for a shorter amount of time to achieve the same result. So, how do you know what "side" to shorten most? What I mean by that is, do you open the valves later, or close them sooner?
Overlap...? I don't see this as an arbitrary byproduct. This is important, and can be changed to achieve a desired result. In a naturally aspirated motor, overlap controls exhaust scavenging and the amount of vacuum. In a forced induction engine, overlap is used to control cylinder pressure. How does vehicle weight effect overlap? What effects do better flowing heads have on optimum overlap?
How do you determine where to start opening the intake valve? What factors influence where the intake valve starts to open?
Displacement...? Does engine size influence the valve events? Larger engines use more air, more air takes more time to flow, so do you open the intake valve sooner in relation to top dead center, than say a smaller displacement motor?
Crankshaft stroke...? Given EQUAL DISPLACEMENT AND HEAD FLOW, yet different architecture, would the valve events be different? What changes (to the valve events ) would be necessary/wanted going from a oversquare 353ci motor with a 4.125" bore and 3.3" stroke, to say a 359" undersquare motor with a 3.78" bore and 4" stroke?
Any help would be greatly appreciated.
First and foremost, why are people so secretive about cam specs? Every motor/set-up is different and will behave/react differently, so who gives a $#!+ if someone else clones your cam?
Secondly, why don't more manufacturers post the actual valve opening and closing events? We can calculate duration on our own. Or is this related to question one, and all that secret squirrel B.S.?
The lack of information is nothing but annoying. Everyone is caught up in the wrong direction, focusing on the wrong information. Duration and LSA are arbitrary numbers, just the byproducts of the important data... That nobody is willing to share, for whatever stupid reason.
So, without using the words duration or LSA, can we discuss a couple things and their effects on the actual valve opening and closing events
Vehicle weight...? Do heavier vehicles require specifically different valve events than a lighter vehicle? If so, what changes in weight correspond with what changes to the valve events?
Head flow...? Better flowing heads require the valves to be open for a shorter amount of time to achieve the same result. So, how do you know what "side" to shorten most? What I mean by that is, do you open the valves later, or close them sooner?
Overlap...? I don't see this as an arbitrary byproduct. This is important, and can be changed to achieve a desired result. In a naturally aspirated motor, overlap controls exhaust scavenging and the amount of vacuum. In a forced induction engine, overlap is used to control cylinder pressure. How does vehicle weight effect overlap? What effects do better flowing heads have on optimum overlap?
How do you determine where to start opening the intake valve? What factors influence where the intake valve starts to open?
Displacement...? Does engine size influence the valve events? Larger engines use more air, more air takes more time to flow, so do you open the intake valve sooner in relation to top dead center, than say a smaller displacement motor?
Crankshaft stroke...? Given EQUAL DISPLACEMENT AND HEAD FLOW, yet different architecture, would the valve events be different? What changes (to the valve events ) would be necessary/wanted going from a oversquare 353ci motor with a 4.125" bore and 3.3" stroke, to say a 359" undersquare motor with a 3.78" bore and 4" stroke?
Any help would be greatly appreciated.
Last edited by DavidBoren; 07-10-2015 at 01:09 PM. Reason: I want to learn...
07-10-2015, 02:07 PM
#5
TECH Addict
Thread Starter
Compression...? Besides the physical restraints of ptv clearance associated with flat-top/domed pistons and/or small combustion chambers, what effect does the compression ratio have on the actual valve opening and closing events? I have heard high compression favors big amounts of overlap to bleed cylinder pressure, but that sounds like it's negating the benefits of having high compression in the first place.
Intake lobe centerline...? I get that it is the starting point for the cam. Is this the tool to use, or specific item to change that effects or rather, is effected by the stroke of the crankshaft? Would a longer stroke require the icl to be greater or lesser than that of a shorter stroke?
I have questions for days. Am I asking the wrong questions? Am I asking in the wrong section? Anyone know where I can find this information?
Intake lobe centerline...? I get that it is the starting point for the cam. Is this the tool to use, or specific item to change that effects or rather, is effected by the stroke of the crankshaft? Would a longer stroke require the icl to be greater or lesser than that of a shorter stroke?
I have questions for days. Am I asking the wrong questions? Am I asking in the wrong section? Anyone know where I can find this information?
07-10-2015, 04:26 PM
#6
ill try to answer these as best as i can with what knowledge i have
The reason why you would increase compression is to directly off set the loss of compression from overlap of the cam, yes that is correct. A higher compression motor will have an easier time in the low rpm's with a larger overlap cam then one with low compression. Again if you go back to the video, where he says that the longer that intake valve stays open after BTDC, its generating no compression on the way back up the cylinder. A higher compression engine would be able to generate similar compression to what it was stock, or even more, given the smaller amount of time it has to actually make compression from the bigger cam, thus offsetting the loss.
Ok, I do have questions.
First and foremost, why are people so secretive about cam specs? Every motor/set-up is different and will behave/react differently, so who gives a $#!+ if someone else clones your cam?
Custom spec cams for people that use them exclusively for racing are usually kept secretive for a competitive edge, or if a company has a certain proprietary lobe design that they havent patented they will only advertise certain specs of the cam so that they stay an exclusive dealer of said cam.
Secondly, why don't more manufacturers post the actual valve opening and closing events? We can calculate duration on our own. Or is this related to question one, and all that secret squirrel B.S.?
Usually the opening and closing events are calculated because it would be more time consuming and costly to measure each individual cam on a cam doctor for every buyer. The range that the card usually gives you usually has some margin of error, thats why its important to degree your cam and make sure you have it set to the way its supposed to be cut. If it's off by a large amount it can either be adjusted slightly, or maybe sent back as it could be defective.
The lack of information is nothing but annoying. Everyone is caught up in the wrong direction, focusing on the wrong information. Duration and LSA are arbitrary numbers, just the byproducts of the important data... That nobody is willing to share, for whatever stupid reason.
So, without using the words duration or LSA, can we discuss a couple things and their effects on the actual valve opening and closing events
Vehicle weight...? Do heavier vehicles require specifically different valve events than a lighter vehicle? If so, what changes in weight correspond with what changes to the valve events?
couldnt answer that question directly, cam designer might have more insight into how cams are specced for this
Head flow...? Better flowing heads require the valves to be open for a shorter amount of time to achieve the same result. So, how do you know what "side" to shorten most? What I mean by that is, do you open the valves later, or close them sooner?
single pattern, dual pattern, and reverse split all have their own advantages, again i couldnt tell you specifically what is better for each individual build as i dont have enough experience testing alot of cams on different cars, but I can tell you that speccing your lift is exclusive to comparing against flow numbers of your cylinder head. If your cylinder head flows its best at .600 lift, thats what you want your lift of your cam to be to take full advantage of port flow. I can tell you that port velocity is VERY important in making low end power, and its something that tony mamo discusses in detail in his MMS 220 thread.
Overlap...? I don't see this as an arbitrary byproduct. This is important, and can be changed to achieve a desired result. In a naturally aspirated motor, overlap controls exhaust scavenging and the amount of vacuum. In a forced induction engine, overlap is used to control cylinder pressure. How does vehicle weight effect overlap? What effects do better flowing heads have on optimum overlap?
How do you determine where to start opening the intake valve? What factors influence where the intake valve starts to open?
again both these questions, better suited for a cam designer
Displacement...? Does engine size influence the valve events? Larger engines use more air, more air takes more time to flow, so do you open the intake valve sooner in relation to top dead center, than say a smaller displacement motor?
Crankshaft stroke...? Given EQUAL DISPLACEMENT AND HEAD FLOW, yet different architecture, would the valve events be different? What changes (to the valve events ) would be necessary/wanted going from a oversquare 353ci motor with a 4.125" bore and 3.3" stroke, to say a 359" undersquare motor with a 3.78" bore and 4" stroke?
Stroke and bore (essentially displacement) are the single most important factor in choosing your cam because they go hand in hand with how it will make power in both the low end and top end. Engines are big air pumps, and the longer the stroke and bigger the bore, the more efficient it will be at sucking in large volumes of air, that's the reason for the saying "no replacement for displacement". It's also directly related to why a small cam will sound lopey on a 4.8 and it will sound like a stock cam on a 6.0. A 6.0 engine is able to run alot more efficiently on a baby cam because it can pull in a much higher volume of air for the given specs.
Any help would be greatly appreciated.
First and foremost, why are people so secretive about cam specs? Every motor/set-up is different and will behave/react differently, so who gives a $#!+ if someone else clones your cam?
Custom spec cams for people that use them exclusively for racing are usually kept secretive for a competitive edge, or if a company has a certain proprietary lobe design that they havent patented they will only advertise certain specs of the cam so that they stay an exclusive dealer of said cam.
Secondly, why don't more manufacturers post the actual valve opening and closing events? We can calculate duration on our own. Or is this related to question one, and all that secret squirrel B.S.?
Usually the opening and closing events are calculated because it would be more time consuming and costly to measure each individual cam on a cam doctor for every buyer. The range that the card usually gives you usually has some margin of error, thats why its important to degree your cam and make sure you have it set to the way its supposed to be cut. If it's off by a large amount it can either be adjusted slightly, or maybe sent back as it could be defective.
The lack of information is nothing but annoying. Everyone is caught up in the wrong direction, focusing on the wrong information. Duration and LSA are arbitrary numbers, just the byproducts of the important data... That nobody is willing to share, for whatever stupid reason.
So, without using the words duration or LSA, can we discuss a couple things and their effects on the actual valve opening and closing events
Vehicle weight...? Do heavier vehicles require specifically different valve events than a lighter vehicle? If so, what changes in weight correspond with what changes to the valve events?
couldnt answer that question directly, cam designer might have more insight into how cams are specced for this
Head flow...? Better flowing heads require the valves to be open for a shorter amount of time to achieve the same result. So, how do you know what "side" to shorten most? What I mean by that is, do you open the valves later, or close them sooner?
single pattern, dual pattern, and reverse split all have their own advantages, again i couldnt tell you specifically what is better for each individual build as i dont have enough experience testing alot of cams on different cars, but I can tell you that speccing your lift is exclusive to comparing against flow numbers of your cylinder head. If your cylinder head flows its best at .600 lift, thats what you want your lift of your cam to be to take full advantage of port flow. I can tell you that port velocity is VERY important in making low end power, and its something that tony mamo discusses in detail in his MMS 220 thread.
Overlap...? I don't see this as an arbitrary byproduct. This is important, and can be changed to achieve a desired result. In a naturally aspirated motor, overlap controls exhaust scavenging and the amount of vacuum. In a forced induction engine, overlap is used to control cylinder pressure. How does vehicle weight effect overlap? What effects do better flowing heads have on optimum overlap?
How do you determine where to start opening the intake valve? What factors influence where the intake valve starts to open?
again both these questions, better suited for a cam designer
Displacement...? Does engine size influence the valve events? Larger engines use more air, more air takes more time to flow, so do you open the intake valve sooner in relation to top dead center, than say a smaller displacement motor?
Crankshaft stroke...? Given EQUAL DISPLACEMENT AND HEAD FLOW, yet different architecture, would the valve events be different? What changes (to the valve events ) would be necessary/wanted going from a oversquare 353ci motor with a 4.125" bore and 3.3" stroke, to say a 359" undersquare motor with a 3.78" bore and 4" stroke?
Stroke and bore (essentially displacement) are the single most important factor in choosing your cam because they go hand in hand with how it will make power in both the low end and top end. Engines are big air pumps, and the longer the stroke and bigger the bore, the more efficient it will be at sucking in large volumes of air, that's the reason for the saying "no replacement for displacement". It's also directly related to why a small cam will sound lopey on a 4.8 and it will sound like a stock cam on a 6.0. A 6.0 engine is able to run alot more efficiently on a baby cam because it can pull in a much higher volume of air for the given specs.
Any help would be greatly appreciated.
Compression...? Besides the physical restraints of ptv clearance associated with flat-top/domed pistons and/or small combustion chambers, what effect does the compression ratio have on the actual valve opening and closing events? I have heard high compression favors big amounts of overlap to bleed cylinder pressure, but that sounds like it's negating the benefits of having high compression in the first place.
Intake lobe centerline...? I get that it is the starting point for the cam. Is this the tool to use, or specific item to change that effects or rather, is effected by the stroke of the crankshaft? Would a longer stroke require the icl to be greater or lesser than that of a shorter stroke?
I have questions for days. Am I asking the wrong questions? Am I asking in the wrong section? Anyone know where I can find this information?
Intake lobe centerline...? I get that it is the starting point for the cam. Is this the tool to use, or specific item to change that effects or rather, is effected by the stroke of the crankshaft? Would a longer stroke require the icl to be greater or lesser than that of a shorter stroke?
I have questions for days. Am I asking the wrong questions? Am I asking in the wrong section? Anyone know where I can find this information?
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07-10-2015, 09:57 PM
#8
no problem, my knowledge is a bit limited but this should certainly help give you a basic understanding. I've always questioned on how you could know what specs work best on a build without doing direct comparisons of multiple cams or having some sort of simulator to plot and predict possible good combinations. I use desktop dyno 2003 for alot of stuff but its a dated program and the numbers usually dont match up as well.
07-24-2015, 02:10 PM
#9
TECH Addict
Thread Starter
Ok, I would like to come back to this discussion. So please bear with me, and remember, I'm stupid.
I went forth and studied. But with new information, comes new questions.
I learned that cam lift is or should be directly related to the heads you are using peak flow lift numbers. If peak head flow happens at .500" of valve lift, then the cam (and rockers) should be designed to achieve that lift value at the correct time.
The "correct time" is dictated by when/ where the piston is traveling at its fastest, which is when the conrod is perpendicular to the crank.
Your rod ratio determines where/ when this takes place. And the optimal rod ratio is dependent upon the flow characteristics of your heads.
Example:
2v heads fill the cylinder slower than 4v heads. So, 2v heads respond better to higher rod ratios. And 4v heads to lower rod ratios, respectively.
Without any specifics, you can determine when/ where the conrod is perpendicular to the crank using trigonometry and nothing more than the rod ratio. To simplify this, because I know none of you want to do trigonometry calculations today, with rod ratios closer to 2:1, the rod is perpendicular to the crank at about 80° ATDC, and again at ~80° BTDC. With lower ratios, angles change at a faster rate so this event happens sooner, it is closer to 70° ATDC.
If the piston is traveling its fastest at 80° ATDC, this is where you need to have your optimal head flow valve lift for best naturally aspirated cylinder filling.
And if peak lift isn't achieved until the lobe centerline, and peak lift needs to occur at ~80°... Why is the intake lobe centerline at ~110°?
I don't understand that. Wouldn't you want your lobe centerline pretty much aimed directly at where the piston is traveling its fastest? Otherwise, you have to "program" more lift into your cam, so you're getting whatever lift is optimal for your heads before reaching the centerline of the lobe.
What would happen if you had a ~80° ICL with a ~2:1 rod ratio?
I have more to ask, but let's get this answered before moving on.
Thoughts, comments, or explanations for why the intake lobe centerline isn't aimed at where/ when the piston is traveling at its fastest.
Any insight into the relationship between cam profile and rod ratios?
I went forth and studied. But with new information, comes new questions.
I learned that cam lift is or should be directly related to the heads you are using peak flow lift numbers. If peak head flow happens at .500" of valve lift, then the cam (and rockers) should be designed to achieve that lift value at the correct time.
The "correct time" is dictated by when/ where the piston is traveling at its fastest, which is when the conrod is perpendicular to the crank.
Your rod ratio determines where/ when this takes place. And the optimal rod ratio is dependent upon the flow characteristics of your heads.
Example:
2v heads fill the cylinder slower than 4v heads. So, 2v heads respond better to higher rod ratios. And 4v heads to lower rod ratios, respectively.
Without any specifics, you can determine when/ where the conrod is perpendicular to the crank using trigonometry and nothing more than the rod ratio. To simplify this, because I know none of you want to do trigonometry calculations today, with rod ratios closer to 2:1, the rod is perpendicular to the crank at about 80° ATDC, and again at ~80° BTDC. With lower ratios, angles change at a faster rate so this event happens sooner, it is closer to 70° ATDC.
If the piston is traveling its fastest at 80° ATDC, this is where you need to have your optimal head flow valve lift for best naturally aspirated cylinder filling.
And if peak lift isn't achieved until the lobe centerline, and peak lift needs to occur at ~80°... Why is the intake lobe centerline at ~110°?
I don't understand that. Wouldn't you want your lobe centerline pretty much aimed directly at where the piston is traveling its fastest? Otherwise, you have to "program" more lift into your cam, so you're getting whatever lift is optimal for your heads before reaching the centerline of the lobe.
What would happen if you had a ~80° ICL with a ~2:1 rod ratio?
I have more to ask, but let's get this answered before moving on.
Thoughts, comments, or explanations for why the intake lobe centerline isn't aimed at where/ when the piston is traveling at its fastest.
Any insight into the relationship between cam profile and rod ratios?
07-27-2015, 10:54 AM
#10
TECH Addict
Thread Starter
Am I asking this in the wrong section
Or is camshaft design theory just something nobody talks about
Given the amount of camshaft related questions and topics, I thought there would be more interest in this.
And honestly, given that we have vendors that post on here who literally design cams, and know the answers to my questions, I'm surprised that nobody has taken the time to even try help me understand.
I'm not forgetting about you, spawne32, thank you for your response.
If it's against the rules to discuss camshaft design theory here, does anyone know any creditable places such matters may be openly discussed?
Or is camshaft design theory just something nobody talks about
Given the amount of camshaft related questions and topics, I thought there would be more interest in this.
And honestly, given that we have vendors that post on here who literally design cams, and know the answers to my questions, I'm surprised that nobody has taken the time to even try help me understand.
I'm not forgetting about you, spawne32, thank you for your response.
If it's against the rules to discuss camshaft design theory here, does anyone know any creditable places such matters may be openly discussed?
07-27-2015, 01:53 PM
#11
Your right, but i couldn't tell you why it is what it is. I'm sure alot of these smaller cam vendors sell profiles based on comparison and just testing designs, and have no real math or data to support the reasoning, they just know that it makes power on a dyno. Probably the reason why your not getting the answers that your looking for.
08-04-2015, 11:05 PM
#12
Speaking of ICL, you are basically talking advance. An interesting topic for sure.
Hey, I have the ability to put together software, if you come up with anything interesting. I have been thinking about it lately and would love to create a cool project that could be distributed to site users as a learning tool and one for discussion. Was thinking graphic driven setup to move crank with mouse, etc.
Hey, I have the ability to put together software, if you come up with anything interesting. I have been thinking about it lately and would love to create a cool project that could be distributed to site users as a learning tool and one for discussion. Was thinking graphic driven setup to move crank with mouse, etc.
08-04-2015, 11:40 PM
#13
TECH Addict
Thread Starter
I understand that a lot of actual lobe profiles are proprietary. But a visual representation, showing the lobe change with changes to duration and lift and lobe separation would be very beneficial, at least I would have really found it useful when I was first looking into this stuff. I since have a better understanding, but a graphic simulator would still be fun, useful, and helpful.
That's not my forte, but I will help any way I can.
That's not my forte, but I will help any way I can.
08-04-2015, 11:43 PM
#14
TECH Addict
Thread Starter
Oh, and yes, intake lobe centerline is absolutely advance. You are trying to accomplish peak valve lift at peak piston velocity, which is between 70 and 80 degrees after/before top dead center. You have to "lead the target" and that is why you see ICL's around 110 degrees. That 30° difference is a combination of piston speed and the fact that valves cannot open/close immediately.
Last edited by DavidBoren; 08-04-2015 at 11:55 PM.
08-05-2015, 01:51 AM
#15
Oh, and yes, intake lobe centerline is absolutely advance. You are trying to accomplish peak valve lift at peak piston velocity, which is between 70 and 80 degrees after/before top dead center. You have to "lead the target" and that is why you see ICL's around 110 degrees. That 30° difference is a combination of piston speed and the fact that valves cannot open/close immediately.
Martin discusses advance in his sticky. Interesting read.
08-05-2015, 09:09 AM
#16
TECH Addict
Thread Starter
I can definitely see how that would be beneficial. I was assuming cam lift was determined by head flow. Whatever lift peak flow occurs is what you grind as peak lift for the cam.
Obviously err on the side of more lift, but I never thought to grossly overshoot peak head flow lift to hit it twice on the curve. That makes perfect sense.
Obviously err on the side of more lift, but I never thought to grossly overshoot peak head flow lift to hit it twice on the curve. That makes perfect sense.
08-05-2015, 09:46 AM
#17
TECH Addict
Thread Starter
And I have read Martin's sticky post. It has helped me immensely. Also a really good explanation on elgincams website. But I'm still just learning about this stuff and there's a lot to take in.
And about the graphic simulator, I would have the crank run off either a play/pause/fwd/rwd/stop system, or a cell in an active excel table dictating rpms. The table controls would be really nice. You could also have it so you can tell it either the cam or crank degrees and the graphic moves to that spot. The reason I wouldn't want to use the mouse to control the graphic is because the mouse cursor should be a magnifying glass. Just a thought.
And about the graphic simulator, I would have the crank run off either a play/pause/fwd/rwd/stop system, or a cell in an active excel table dictating rpms. The table controls would be really nice. You could also have it so you can tell it either the cam or crank degrees and the graphic moves to that spot. The reason I wouldn't want to use the mouse to control the graphic is because the mouse cursor should be a magnifying glass. Just a thought.
08-05-2015, 03:47 PM
#18
TECH Addict
Thread Starter
It has been discussed in various other threads that the difference in piston speed between a 3.6" stroke and a 4" crank equates to about 5° difference in cam events.
I'm not sure if it's a linear relationship, but would a 3.6" stroke camshaft being used in a 3.3" stroke application be off the same ~5°?
Obviously this difference in valve events of +/- 5° is small enough that people don't mind. Plenty of people using ls6 cams in their 4.8's, or ls7 cams in their 6.2's, but it's essentially a different cam at that point.
Can anyone explain the effects of putting a ls6 cam in a 4.8, or ls7 cam in a 6.2?
If going from a long stroke engine into a short stroke engine, all the events would be "early" by that ~5° (in the case of LS motors) difference. And inversely, if using a short stroke cam in a long stroke application, all the events would be "late"... What effect(s) would this have if all the events are off by the same degree?
I'm not sure if it's a linear relationship, but would a 3.6" stroke camshaft being used in a 3.3" stroke application be off the same ~5°?
Obviously this difference in valve events of +/- 5° is small enough that people don't mind. Plenty of people using ls6 cams in their 4.8's, or ls7 cams in their 6.2's, but it's essentially a different cam at that point.
Can anyone explain the effects of putting a ls6 cam in a 4.8, or ls7 cam in a 6.2?
If going from a long stroke engine into a short stroke engine, all the events would be "early" by that ~5° (in the case of LS motors) difference. And inversely, if using a short stroke cam in a long stroke application, all the events would be "late"... What effect(s) would this have if all the events are off by the same degree?
08-06-2015, 01:12 PM
#19
TECH Apprentice
It has been discussed in various other threads that the difference in piston speed between a 3.6" stroke and a 4" crank equates to about 5° difference in cam events.
I'm not sure if it's a linear relationship, but would a 3.6" stroke camshaft being used in a 3.3" stroke application be off the same ~5°?
Obviously this difference in valve events of +/- 5° is small enough that people don't mind. Plenty of people using ls6 cams in their 4.8's, or ls7 cams in their 6.2's, but it's essentially a different cam at that point.
Can anyone explain the effects of putting a ls6 cam in a 4.8, or ls7 cam in a 6.2?
If going from a long stroke engine into a short stroke engine, all the events would be "early" by that ~5° (in the case of LS motors) difference. And inversely, if using a short stroke cam in a long stroke application, all the events would be "late"... What effect(s) would this have if all the events are off by the same degree?
I'm not sure if it's a linear relationship, but would a 3.6" stroke camshaft being used in a 3.3" stroke application be off the same ~5°?
Obviously this difference in valve events of +/- 5° is small enough that people don't mind. Plenty of people using ls6 cams in their 4.8's, or ls7 cams in their 6.2's, but it's essentially a different cam at that point.
Can anyone explain the effects of putting a ls6 cam in a 4.8, or ls7 cam in a 6.2?
If going from a long stroke engine into a short stroke engine, all the events would be "early" by that ~5° (in the case of LS motors) difference. And inversely, if using a short stroke cam in a long stroke application, all the events would be "late"... What effect(s) would this have if all the events are off by the same degree?
Example #1 has a B x S x R of 4.065 x 3.622 x 6.098
Example #2 has a B x S x R of 3.86818 x 4.0 x 6.734
Both are 376 cubic inches displacement.
How are they the same? Both have the same swept volume that means that every degree of rotation the cubic inch per degree is the same. That means that they should take the same cam specs for a given application. 1500 - 6000 RPM.
Both would have the same torque to the crank at every degree of rotation with the same cylinder pressure all the way through the cycle. So you can't go by just the stroke
08-06-2015, 01:27 PM
#20
TECH Addict
Thread Starter
But in the set dimensions of the typical LS motor, we cannot have a 4" stroke and a 6.7x" rod, so everything is different from a 3.6" crank. The rod ratio with the 4" crankshaft ends up in the 1.5:1 range. Displacement per degree change is different. Piston acceleration per degree will be different.
I should have stated that I was using LS motors as reference for this conversation. In theory, yes, if the rod ratio remains unchanged, then changes to stroke wouldn't change much.
But putting a cam designed for a 4" stroke and 1.5:1 rod ratio in an engine that has a 3.3" crank and a 1.9:1 rod ratio HAS to be different.. right?
I should have stated that I was using LS motors as reference for this conversation. In theory, yes, if the rod ratio remains unchanged, then changes to stroke wouldn't change much.
But putting a cam designed for a 4" stroke and 1.5:1 rod ratio in an engine that has a 3.3" crank and a 1.9:1 rod ratio HAS to be different.. right?