Some time ago I saw a link on this forum to a good article on cams. Most info I have come across cover lift and durration but not much on lobe centers and the effects different lobe centers have on the engine.
I did a search for lobe centers and didn't find much. Anyone refer me to an article/s?
What got me interested was while this forum was down I came accross a post on the Calook forum about 112 making a good bit more power over the commonly used 108. There was not info though as to what other changes the cam might like, or its effect on engine temps and so on. Its a big enough subject that my questions could go on an on, so any info out there?
Thanks
Ron
Lobe centers
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rcb78
- Posts: 2406
- Joined: Mon Jul 10, 2000 12:01 am
Lobe centers
That's James2 saying that over there. He may or may not agree with my point of view on this but here goes. To me it appears that the wider lobe centers simply give the effect of higher compression, among other less significant things. They create less overlap compared to a cam with a 108 degree lobe center meaning less compression is bled off. Granted it will change cam timing to some degree, but the compression change is what stands out to me. Soooo, then why not just bump CR instead? I'm not trying to argue the point, that's just how I interpret it, anyone want to set me straight then feel free. I leave it alone on the CLF cause I'm not much for debating. --Ryan
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danimal
- Posts: 958
- Joined: Wed Jun 13, 2001 12:01 am
Lobe centers
widening the lsa effectively milds the cam... unless you are running boost... in most cases, 108 will make more power on an n/a motor than 112... that's why most vw cams are standard-ground at 108 to begin with 
see if this helps any: http://members.accesstoledo.com/fastlarry1/caminfo.htm
dan
oceanstreetvideo.com
see if this helps any: http://members.accesstoledo.com/fastlarry1/caminfo.htm
dan
oceanstreetvideo.com
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JohnConnolly
- Posts: 3336
- Joined: Thu Apr 13, 2000 12:01 am
Lobe centers
the larger the LC the less "overlap" the engine has. Overlap is when both valves are open at the same time. A 112 LC has 8 degrees less overlap then a 108LC cam.
There are pros and cons to the overlap issue, I'll try to cover the basics here.
Overlap is the time when you can have the exhaust SUCK the intake into the combustion chamber. The problem is overlap is also when you can get REVERSION UP thru the intake (from the exhaust). When you have a turbo application, wider LC prevents the exhaust pressure (it is pressurized under boost) from blowing back up the intake, which is why wider LCs are better on boosted applications.
GENERALLY, smaller LCs will have more power at lower RPM, and higher LCs will have more power at higher RPM, all else being the same. The reason why is apparant if you look at a cam card for the same cam, one on 108 and one on 112, for example.
Larger LCs open the intake later, and close it later, which is the same thing as "retarding" the camshaft (which moves the powerband upwards).
The 121/125 Web grind is an awesome grind off road on 105LCs, it moves the powerband DOWN a bit, with a lot of overlap it pulls hard but peters out sooner.
The other issue you have to watch out for with larger LC cams is cylinder pressure. You do get more cylinder pressure with more LC, and this can bring you over the detonation threshold if you don't account for it. We run more LC on our squishy applications, but we can get away with more cylinder pressure because the squishy chambers dont' detonate, so more pressure is more power! Obviously every engine is different, and it's possible (POSSIBLE, not always) that you can just run less timing to hold off the detonation, just know what you are doing.
I believe that more LC would work well on "restricted" intake systems, since you can't get a lot of intake IN, you use more LC to get more from what you already have.
many other "high tech" chambers and engine designs run LCs in the 116-118 range, which removes all overlap from the engine dynamics (exhaust scavenging, and sucking in the intake disappears). While this seems to be backwards to "progress", there are advantages to this when used with a lot of other associated engine mods/specs, but I won't go into it here, it's too complex and we are pushing into this arena now and I don't want to give away the farm.
Hope this helps clear it up a little bit.
John
Aircooled.Net Inc.
There are pros and cons to the overlap issue, I'll try to cover the basics here.
Overlap is the time when you can have the exhaust SUCK the intake into the combustion chamber. The problem is overlap is also when you can get REVERSION UP thru the intake (from the exhaust). When you have a turbo application, wider LC prevents the exhaust pressure (it is pressurized under boost) from blowing back up the intake, which is why wider LCs are better on boosted applications.
GENERALLY, smaller LCs will have more power at lower RPM, and higher LCs will have more power at higher RPM, all else being the same. The reason why is apparant if you look at a cam card for the same cam, one on 108 and one on 112, for example.
Larger LCs open the intake later, and close it later, which is the same thing as "retarding" the camshaft (which moves the powerband upwards).
The 121/125 Web grind is an awesome grind off road on 105LCs, it moves the powerband DOWN a bit, with a lot of overlap it pulls hard but peters out sooner.
The other issue you have to watch out for with larger LC cams is cylinder pressure. You do get more cylinder pressure with more LC, and this can bring you over the detonation threshold if you don't account for it. We run more LC on our squishy applications, but we can get away with more cylinder pressure because the squishy chambers dont' detonate, so more pressure is more power! Obviously every engine is different, and it's possible (POSSIBLE, not always) that you can just run less timing to hold off the detonation, just know what you are doing.
I believe that more LC would work well on "restricted" intake systems, since you can't get a lot of intake IN, you use more LC to get more from what you already have.
many other "high tech" chambers and engine designs run LCs in the 116-118 range, which removes all overlap from the engine dynamics (exhaust scavenging, and sucking in the intake disappears). While this seems to be backwards to "progress", there are advantages to this when used with a lot of other associated engine mods/specs, but I won't go into it here, it's too complex and we are pushing into this arena now and I don't want to give away the farm.
Hope this helps clear it up a little bit.
John
Aircooled.Net Inc.
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James2
- Posts: 3148
- Joined: Fri Mar 16, 2001 12:01 am
Lobe centers
I was the one pushing 112 lobe centers.
Ryan is correct, it does have the same effect as raising compression, but it does more then that.
Despite what others have said about the wider lobe cutting off power at high rpm, the oppisite can be true (like John said)if you have the right conditions.
The wider lobes does reduce overlap, but it also retards timing, moving the power higher in the rev range. This can be a win win situation, with the reduced overlap creating more torque in the lower rpms and the retarded timing producing more peak power.
The biggest advantage to me is being able to run a smaller cam AND get the same peak power as a larger cam. The benifit of this is unbelievable low end torque, with little or no loss of peak power. to do this, the cam must be further retarded when installed.
So what is better? if I was looking for total peak HP, the closer lobe centers might be better. But if you want a wide power band, then the wider lobe center is better.
Rule of thumb is closer the lobe centers, the closer the torque and HP peak will be together, creating a narrow peaky power band. Wider lobe centers have the torque peak and hp peak further apart, creating a wider power band.
The ACVW world is behind when it comes to cams. If you look at a cataloge for Chevy cams, you will see cams ground on lobe centers from 106 to 116!
yet in the ACVW world it two ways. 108 for N/A and 112 for forced induction.
I basically got tired of debating it, though it was fustrating because I know I'm right.
Others have been doing it, just they are smarter then me and realize there is no benifit in spreading the word. Why beat your head against the wall, when there is nothing to gain?
Ryan is correct, it does have the same effect as raising compression, but it does more then that.
Despite what others have said about the wider lobe cutting off power at high rpm, the oppisite can be true (like John said)if you have the right conditions.
The wider lobes does reduce overlap, but it also retards timing, moving the power higher in the rev range. This can be a win win situation, with the reduced overlap creating more torque in the lower rpms and the retarded timing producing more peak power.
The biggest advantage to me is being able to run a smaller cam AND get the same peak power as a larger cam. The benifit of this is unbelievable low end torque, with little or no loss of peak power. to do this, the cam must be further retarded when installed.
So what is better? if I was looking for total peak HP, the closer lobe centers might be better. But if you want a wide power band, then the wider lobe center is better.
Rule of thumb is closer the lobe centers, the closer the torque and HP peak will be together, creating a narrow peaky power band. Wider lobe centers have the torque peak and hp peak further apart, creating a wider power band.
The ACVW world is behind when it comes to cams. If you look at a cataloge for Chevy cams, you will see cams ground on lobe centers from 106 to 116!
yet in the ACVW world it two ways. 108 for N/A and 112 for forced induction.
I basically got tired of debating it, though it was fustrating because I know I'm right.
Others have been doing it, just they are smarter then me and realize there is no benifit in spreading the word. Why beat your head against the wall, when there is nothing to gain?
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Plastermaster
- Posts: 2762
- Joined: Sun Sep 30, 2001 12:01 am
Lobe centers
Thanks for the info guys.
James, does your Desk Top Dyno factor in different lobe centers? If so what are some figures for what it does down low and up high on a given engine, say a popular combo like 2275 9:1 CR 48 IDAs Etc.
Ron
James, does your Desk Top Dyno factor in different lobe centers? If so what are some figures for what it does down low and up high on a given engine, say a popular combo like 2275 9:1 CR 48 IDAs Etc.
Ron
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James2
- Posts: 3148
- Joined: Fri Mar 16, 2001 12:01 am
Lobe centers
yes, you can change lobe centers in DTD.
On some combo's it will make a big change on others nothing. Typical is 4-5 ftlb gain across the entire rpm range.
DTD will also run every combination of intake and exhaust opening and closing points, keeping the top ten hp producing combinations.
Ideal cam for my motor was on a 114 degree lobe center.
I took a lot of kidding and slack from people because this is all done in the computer and wasn't done on a real dyno.
I now have a running engine using the cam that DTD picked. I was hoping to get jake to dyno it, but he is busy.
I should get it to the track by next Friday.
Car wieghs 1850-1875( i need to wiegh it, I've lost wieght since last year and so has the car).
If my motor makes 170 hp, which is what DTD dyno says, then the car should turn a very low 13. If it does, then I will consider the cam a success.
I could have followed the proven combinations for a 2275 and gotten 170 hp. I wanted to do something different and get 2275 like power from a 1915.
I like it when people tell me it won't work, it's just that much better when it does!!
On some combo's it will make a big change on others nothing. Typical is 4-5 ftlb gain across the entire rpm range.
DTD will also run every combination of intake and exhaust opening and closing points, keeping the top ten hp producing combinations.
Ideal cam for my motor was on a 114 degree lobe center.
I took a lot of kidding and slack from people because this is all done in the computer and wasn't done on a real dyno.
I now have a running engine using the cam that DTD picked. I was hoping to get jake to dyno it, but he is busy.
I should get it to the track by next Friday.
Car wieghs 1850-1875( i need to wiegh it, I've lost wieght since last year and so has the car).
If my motor makes 170 hp, which is what DTD dyno says, then the car should turn a very low 13. If it does, then I will consider the cam a success.
I could have followed the proven combinations for a 2275 and gotten 170 hp. I wanted to do something different and get 2275 like power from a 1915.
I like it when people tell me it won't work, it's just that much better when it does!!
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Marty
- Posts: 5802
- Joined: Fri Nov 16, 2001 12:01 am
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Plastermaster
- Posts: 2762
- Joined: Sun Sep 30, 2001 12:01 am
Lobe centers
I have looked over all this for the past couple of days to digest it all. If you look at the link Dan refered me to, toward the bottom it lists the effects of tighter and wider LCs. According to it the wider LC moves the max torque to a higher rpm, and also broadens the power band which implies that you do this without a loss down low. That sounds good but it also says you reduce the maximum torque. (doesn't say how much but enough to mention I guess. It also says it will reduce cylinder pressure and reduce chance of engine knock. John said the opposite. I would agree with John because it seems to me reducing overlap reduces the time both valves are open (less pressure goes out the intake valve) however it also reduces the time both valves are closed which could then reduce pressure...So really I dont know what to think. Both valves are closed on the compression stroke, but not as long with wider LCs so not as much pressure is built up. What is critical here but I cant visualize it is WHEN this overlap takes place. Any more help would be appreciated!
Thanks
Ron
Thanks
Ron
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melbatoast
- Posts: 181
- Joined: Thu Mar 28, 2002 12:01 am
Lobe centers
stockers run wide lobe center angles.
114+
why? best of all worlds.
idle quality and torque.
what else could anyone want?
------------------
arlan
--------
you see these?
they are my carkeys.
you will never get these.
114+
why? best of all worlds.
idle quality and torque.
what else could anyone want?
------------------
arlan
--------
you see these?
they are my carkeys.
you will never get these.
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James2
- Posts: 3148
- Joined: Fri Mar 16, 2001 12:01 am
Lobe centers
It's hard to generalize what the reduced overlap may do. It could help, or hurt depending on the engine.
The overlap uses the exiting exhaust to help pull the intake charge into the cylinder, which is a good thing.
The problem is you can have to much of a good thing. The exhaust can actually pull part of the intake charge out of the cylinder. Leaving less in there to burn and make power.
This is also where the alterd cam timing helps. Once the cylinder is full, you want to "close the door". If the valve stays open, the intake charge reverses and goes back up the intake. That's why I think smaller cams with the wider lobes will work so well. it in effect slams the door close on the cylinder once it is full.
On efficent setups with decent heads, large extractor exhaust and good carbs, that extra overlap is not needed. This is where the wider lobe centers really help. in this case the wider lobe center will make more torque and more peak hp.
Where you have a restriction on the intake, you might be better off with more over lap, and the narrower lobe center would be better.
Every motor is different. Thats why cam grinders offer so many grinds.
I just think it's silly to say that they all need to be on 108 lobe centers.
Why won't you alter the lobe center, just like you would duration and lift to best fit a particular motor? Saying 108 degree lobes is the end all be all, would be like saying 250 duration is perfect for every motor.
<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Plastermaster:'s hard to gem
<B>I have looked over all this for the past couple of days to digest it all. If you look at the link Dan refered me to, toward the bottom it lists the effects of tighter and wider LCs. According to it the wider LC moves the max torque to a higher rpm, and also broadens the power band which implies that you do this without a loss down low. That sounds good but it also says you reduce the maximum torque. (doesn't say how much but enough to mention I guess. It also says it will reduce cylinder pressure and reduce chance of engine knock. John said the opposite. I would agree with John because it seems to me reducing overlap reduces the time both valves are open (less pressure goes out the intake valve) however it also reduces the time both valves are closed which could then reduce pressure...So really I dont know what to think. Both valves are closed on the compression stroke, but not as long with wider LCs so not as much pressure is built up. What is critical here but I cant visualize it is WHEN this overlap takes place. Any more help would be appreciated!
Thanks
Ron </B><HR></BLOCKQUOTE>
The overlap uses the exiting exhaust to help pull the intake charge into the cylinder, which is a good thing.
The problem is you can have to much of a good thing. The exhaust can actually pull part of the intake charge out of the cylinder. Leaving less in there to burn and make power.
This is also where the alterd cam timing helps. Once the cylinder is full, you want to "close the door". If the valve stays open, the intake charge reverses and goes back up the intake. That's why I think smaller cams with the wider lobes will work so well. it in effect slams the door close on the cylinder once it is full.
On efficent setups with decent heads, large extractor exhaust and good carbs, that extra overlap is not needed. This is where the wider lobe centers really help. in this case the wider lobe center will make more torque and more peak hp.
Where you have a restriction on the intake, you might be better off with more over lap, and the narrower lobe center would be better.
Every motor is different. Thats why cam grinders offer so many grinds.
I just think it's silly to say that they all need to be on 108 lobe centers.
Why won't you alter the lobe center, just like you would duration and lift to best fit a particular motor? Saying 108 degree lobes is the end all be all, would be like saying 250 duration is perfect for every motor.
<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Plastermaster:'s hard to gem
<B>I have looked over all this for the past couple of days to digest it all. If you look at the link Dan refered me to, toward the bottom it lists the effects of tighter and wider LCs. According to it the wider LC moves the max torque to a higher rpm, and also broadens the power band which implies that you do this without a loss down low. That sounds good but it also says you reduce the maximum torque. (doesn't say how much but enough to mention I guess. It also says it will reduce cylinder pressure and reduce chance of engine knock. John said the opposite. I would agree with John because it seems to me reducing overlap reduces the time both valves are open (less pressure goes out the intake valve) however it also reduces the time both valves are closed which could then reduce pressure...So really I dont know what to think. Both valves are closed on the compression stroke, but not as long with wider LCs so not as much pressure is built up. What is critical here but I cant visualize it is WHEN this overlap takes place. Any more help would be appreciated!
Thanks
Ron </B><HR></BLOCKQUOTE>
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FUgly
- Posts: 377
- Joined: Tue Jun 18, 2002 12:01 am
Lobe centers
James what would be the result of running a 112 LC and further retarding the cam say 2, 4 degrees?
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Plastermaster
- Posts: 2762
- Joined: Sun Sep 30, 2001 12:01 am
Lobe centers
There is really so much to play with in cam choice. Aside from lift, duraration, and Lobe Centers, there is also split durration cams which fits or doesn't fit with the engine. The combinations are endless with one change always effecting something else. You can plug in a set of parameters or engine specs and then pick out the best cam. On the other hand but maybe backwards, you can pick a cam and design an engine around it. It may be backwards but the point is that you can find different engine combos to behave pretty much the same. The DTD must be lots of fun. Rather than taking the approach of compensating for this with that, Can you tell DTD you want such an such a power curve, complete with tq and Hp numbers and have it configure an engine for you? What are the minimum specs it needs to work with? Can you give it a power curve and displacement only?
Thanks
Ron
Thanks
Ron
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James2
- Posts: 3148
- Joined: Fri Mar 16, 2001 12:01 am
Lobe centers
you would have a cam a lot like mine 
<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by FUgly:
James what would be the result of running a 112 LC and further retarding the cam say 2, 4 degrees?<HR></BLOCKQUOTE>
<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by FUgly:
James what would be the result of running a 112 LC and further retarding the cam say 2, 4 degrees?<HR></BLOCKQUOTE>
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FUgly
- Posts: 377
- Joined: Tue Jun 18, 2002 12:01 am
Lobe centers
"Ahhhh So" said da young grasshopper. Can ya run the DTD for me? Mahalo's