Does the Comp 212/218 high lift cam have advance ground in?
Nov 13, 2004 | 02:49 PM
#22
Originally Posted by Ryan23silverado
Not picking on you, but this is why I posted that picture in the cam thread. A lot of people on here think that lsa means over lap, but it does not 
the left cam looks like a flat tappet profile to me and the right cam looks like a typical roller profile.
or was this just for an example?
Nov 13, 2004 | 02:57 PM
#24
I think he was just showing that a camshaft with a 112 lsa can have a bunch of different amounts of overlap. This is why you can't say all FI motors need a 114-119lsa. It's all relative to the amount of duration and the valve events being shot for.
Nov 13, 2004 | 03:00 PM
#25
TECH Apprentice
Joined: Apr 2004
Posts: 321
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From: Thousand Oaks, Ca
Originally Posted by moregrip
is this really apples to apples though?
the left cam looks like a flat tappet profile to me and the right cam looks like a typical roller profile.
or was this just for an example?
the left cam looks like a flat tappet profile to me and the right cam looks like a typical roller profile.
or was this just for an example?
Nov 13, 2004 | 08:04 PM
#26
so what you are saying is i can run a 112 lsa cam as long as the valve events are correct and i will not have any bleed of boost? what details overlap if lsa isnt it. duration?
Nov 13, 2004 | 08:46 PM
#27
By looking at Ryans chart, you can see that duration plays a large affect on how and where the valves will overlap.
One thing I'd like to add.
Lets take: Comp 212/218 @ 115 + 0 (We'll use)
It has 38* of overlap @ .006 lift
It has -15* of overlap @ .050 lift
It has -96.5* of overlap @ .200 lift
Take the right camshaft and compare lobes. You can see at the inner sides of the lobe, they overlap. This is where you get 38* of valve overlap @ small amounts of lift. Once the lifter moves up the lobe, there is no valve overlap at all. (ex. -96.6* of overlap @ .200 lift of the valve)
I really don't know what lobe seperation angle is needed. Its up to the cam grinders to decide. Even the above listed camshaft has 38* of overlap @ .006 . Do we widen the seperation even more?
One thing I'd like to add.
Lets take: Comp 212/218 @ 115 + 0 (We'll use)
It has 38* of overlap @ .006 lift
It has -15* of overlap @ .050 lift
It has -96.5* of overlap @ .200 lift
Take the right camshaft and compare lobes. You can see at the inner sides of the lobe, they overlap. This is where you get 38* of valve overlap @ small amounts of lift. Once the lifter moves up the lobe, there is no valve overlap at all. (ex. -96.6* of overlap @ .200 lift of the valve)
I really don't know what lobe seperation angle is needed. Its up to the cam grinders to decide. Even the above listed camshaft has 38* of overlap @ .006 . Do we widen the seperation even more?
Nov 13, 2004 | 10:01 PM
#28
man i widh i knew more. i have been looking for good info on cams. but they usually go to things i cant understand. i was under the assumption that lsa was the killer in boost. maybe not. it might just be the cams that are offered off the shelf that are not set up for fi. so does a low lsa help low end torque as well as a high lsa moving it up. or is that in the same thing as the valve evnt theory. manj do they have camshaft school somewhere.
Nov 13, 2004 | 10:48 PM
#29
The lobe seperation angle is the killer of boost. It judges the amount of overlap.
To keep the same overlap, but with added duration. You would have to widen the lobe seperation angle.
If you look at that chart. Imagine you wanted to keep the same degree of overlap, but you wanted a higher peaking camshaft. Well, you would add duration (add fat) to the lobes but the exhaust and intake centerlines would have to spread farther apart, causing a wider lsa. This would give you idealy, somewhere near the same amount of valve overlap @ a given lift.
ICL + ECL = X /2 = LSA
To keep the same overlap, but with added duration. You would have to widen the lobe seperation angle.
If you look at that chart. Imagine you wanted to keep the same degree of overlap, but you wanted a higher peaking camshaft. Well, you would add duration (add fat) to the lobes but the exhaust and intake centerlines would have to spread farther apart, causing a wider lsa. This would give you idealy, somewhere near the same amount of valve overlap @ a given lift.
ICL + ECL = X /2 = LSA
Nov 14, 2004 | 08:50 AM
#30
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Joined: Feb 2003
Posts: 1,295
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From: NY
Originally Posted by SportSide 5.3
With your radix less overlap.
Most of the camshafts being used are in the negative range. Less than X amount of overlap. And low boost at that.
Take the 212/218 @ 114lsa. It has -13* of overlap relative to top dead center. The exhaust valve closes 7* before the piston reaches the top. And the intake valve opens 6* after the piston has reached the top. So theres a gap there of -13* of overlap.
So worrying about overlap with a smallish camshaft shouldn't be a big concern. Obviously, there wont be any bleeding of boost if there isn't really an "overlap" phaze.
A 220 @ 109 has 1 degrees of overlap relative to TDC.
A 220 @ 113 has -7 degrees of overlap relative to TDC.
Up to the cam grinders to decide when they feel the need to back down overlap in fear of bleeding.
Most of the camshafts being used are in the negative range. Less than X amount of overlap. And low boost at that.
Take the 212/218 @ 114lsa. It has -13* of overlap relative to top dead center. The exhaust valve closes 7* before the piston reaches the top. And the intake valve opens 6* after the piston has reached the top. So theres a gap there of -13* of overlap.
So worrying about overlap with a smallish camshaft shouldn't be a big concern. Obviously, there wont be any bleeding of boost if there isn't really an "overlap" phaze.
A 220 @ 109 has 1 degrees of overlap relative to TDC.
A 220 @ 113 has -7 degrees of overlap relative to TDC.
Up to the cam grinders to decide when they feel the need to back down overlap in fear of bleeding.
212/218 557/562 114+4
Ryan23silverado= "I found this, but I'm not sure if it works...
"If you have the duration at .006,add the intake and exhaust duration,divide by 4,subtract the LSA and multiply by 2,that will give overlap."
"If you have the duration at .006,add the intake and exhaust duration,divide by 4,subtract the LSA and multiply by 2,that will give overlap."
265 + 271 /4=134-114=20 X 2 = 40 overlap???