What real difference does the lsa on a cam make?

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Well, I shipped the cam to the grinders today. I also decided to go with a split cam profile of 224/230 duration at .050 lift, 496/510 lift with a 1.6 ratio rocker and a 112 lobe separation. So far I spent 120 to grind the cam, 18 to ship and another 18 to ship it back. Way more affordable then a new $315 cam from comp. I will likely need longer push rods though, anyone know where I can get magnum push rods in different lengths?
 
StrokerScamp said:
I've also read the Comp Cams site about all of this......I gotta say, I firmly believe they got a lot of it WRONG. Most of what they have on it is completely backwards.
Click to expand...

Simply

Without going into any overlap discussion.....

IF you move your intake lobe closer to the EX, you are closing the intake valve sooner into the compression stroke. (think cam advance) This creates less compression bleed off at low RPM. Moving the lobes closer together, means the EX is open longer into the intake, at lower RPM, this makes for a rich exhaust small, and a bit of rough idle, (think two stroke) because you are using the exhaust to pull intake charge, but the EX and intake charge is not moving fast enough to work as designed. However, in small cams, (like here) moving the EX lobe closer to the intake, other than a rich(ish) rough (ish) idle, will make more low end torque (providing you're not talking about 850RPM) because the power band, comes in harder, quicker. (building more cylinder pressure, because there is not as much compression bleed off through the intake valve.

Of course, 250* duration 600 lift cams follow a totally different set of rules.


And I swear, if people put more cams in motors and less time playing with desktop dyno.........

My dyno, for my engine power theories, is pickup trucks, with stock converters, and 727's, pulling 10,000+ in steep hills, and yes, there is a difference.
 
I'm proud for you. But everybody's dyno is different. ;)
 
StrokerScamp said:
Absolutely. I agree 100%. I am only saying what I have seen and done. There are so many variables there's no way to nail it down.
Yup. I've read their stuff. However the quoted section leaves out (probably purposely due to the confusion it can create) the affects of stroke, rod angle, crank position, port flow, and port balance on potential overlap and lobe placement. Wallace does touch on some of it in the next paragraph:

"
Overlap and Compression- A very common idea, although for the most part incorrect, is that overlap bleeds off compression. Overlap, by itself, does not bleed off compression. Overlap is the angle between the exhaust closing and intake opening and is used to tune the exhaust's ability draw in additional intake charge as well as tuning idle vacuum and controlling power band width. Cylinder pressure is generated during the compression cycle, after the intake valve has closed and before the exhaust opens. Within practical limits, an early intake closing and late exhaust opening will maintain the highest cylinder pressure. By narrowing the Lobe Seperation Angle 'LSA' for a given lobe duration, the overlap increases, but the cylinder pressure can be increased as well. Thus cylinder pressure/compression can actually increase in this scenario, by the earlier intake closing and later exhaust opening. By increasing duration for a given LSA, the overlap will increase, the intake closing will be delayed, and the exhaust opening will occur earlier. This will decrease cylinder pressure, but the decrease/bleed-off of compression is not due to the overlap, it is due to the intake closing and exhaust opening events. "


Wallace is speaking strictly in terms of the camshaft. Which to me is overly generalized for something so critical but I can understand why they'd stay simple as the website is meant as a quick reference guide. And a good one to boot.
My own opinion is if someone is interested enough to ask about it I'd rather consider and talk about it as more of a "case by case" type thing rather than being too general. Leaving things too general leaves the hobbyist/enthusiast/reader a strong potential for those statements to be considered a specific "rule". Because the cam is dependent on the other parts, IMO there is no hard fast rule unless you remove variables to simplify the choices. That's why I said talk to the grinder. They should be less general and the recommendation should reflect a more complete selection of "inputs".
Click to expand...
 
dodgetkboy78 said:
Of course, 250* duration 600 lift cams follow a totally different set of rules.
Click to expand...

I disagree 100%. It's all the same rules, and that's my point. Pulling a trailer or running a Pro Stock car, the physics, and the "rules" are all the same. It's the supporting parts and expected result that differs.
 
dodgetkboy78 said:
I forgot you were the same guy that said Hughes didn't know what they were talking about.............
Click to expand...

..and you're the dude with them damn dancin cats. They're drivin me nuts.


It's all good man. We all do stuff different and have different opinions. That's how you learn stuff. Them cats need to stop starin at me though.
 
So let's play a scenario. You have an engine with 11:1 static CR, but you want to run pump gas. You leave it up to your engine guy to pick the cam to run the fuel without detonation. He picks a cam with .266/.268 duration @ .050 and a 105 LSA. If the lower LSA pumps up cylinder pressure, why would he have chosen that LSA when static CR is already fairly high? I guess it's mostly about dynamic CR? That's what was just ordered for my motor and didn't know much about LSA when he told me. The tech at comp cams and my engine guy came up with that combo. I thought that was pretty tight so I've been trying to read around to find out why that particular setup was chosen. I'll ask him later about it but wanted to hear some thoughts from you guys on that.
 
All things being the same in a cam grind, except the Lobe Separation Angle itself.......... a 108-LSA will close the intake valve sooner then a 110 -LSA

.....for example.

If you wanted to run a cam with a given duration that compliments your compression and or the type of fuel you wanted to use ---but the rpm band was a little low for your liking ---and you wanted a little more higher rpm engine.
....instead of running a cam with 230@50 duration ground on a 110 LSA...
you could run a 234@50 on a 108 and the intake valve would close at the same time giving you the same cylinder pressure as the smaller cam.

Your rpm band would be higher and more narrow BUT.....in the end.. will make more torque and power.

If you look at most racing cams they are on the tight side.

Engines with high compression,great flowing heads and bigger cubic inches change the formula and more power with a wider LSA.

Cams with a tighter lsa are a little harder to tune and can run very radical.

If your running none ported stock heads and stock compression you want a tighter LSA.

Here is a way to get your engine in the ball park..

Example...318 cubic inches divided by 8 cylinders is 39.75
Take that number....39.75 and divide it by the size of the intake valve
39.75 divided by 1.78(stock 318 valve size) = 22.33

Find the number on the chart and this is the best LSA for a lower compression stock headed engine.
 

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Subscribed. I'm having issues with which roller cam to run on my 90 5.9 roller as well. All this info is really good.
 
[FONT=Verdana, Arial, Helvetica, sans-serif]Tighten [SIZE=-1](smaller LSA number)[/SIZE][/FONT]
[FONT=Verdana, Arial, Helvetica, sans-serif]Moves Torque to Lower RPM[/FONT]
[FONT=Verdana, Arial, Helvetica, sans-serif]Increases Maximum Torque[/FONT]
[FONT=Verdana, Arial, Helvetica, sans-serif]Narrow Power band[/FONT]

[FONT=Verdana, Arial, Helvetica, sans-serif]Builds Higher Cylinder Pressure[/FONT]

[FONT=Verdana, Arial, Helvetica, sans-serif]Increase Chance of Engine Knock[/FONT]

[FONT=Verdana, Arial, Helvetica, sans-serif]Increase Cranking Compression[/FONT]

[FONT=Verdana, Arial, Helvetica, sans-serif]Increase Effective Compression[/FONT]

[FONT=Verdana, Arial, Helvetica, sans-serif]Idle Vacuum is Reduced[/FONT]

[FONT=Verdana, Arial, Helvetica, sans-serif]Idle Quality Suffers[/FONT]

[FONT=Verdana, Arial, Helvetica, sans-serif]Open Valve-Overlap Increases[/FONT]

[FONT=Verdana, Arial, Helvetica, sans-serif]Closed Valve-Overlap Increases[/FONT]

[FONT=Verdana, Arial, Helvetica, sans-serif]Natural EGR Effect Increases[/FONT]

[FONT=Verdana, Arial, Helvetica, sans-serif]Decreases Piston-to-Valve Clearance[/FONT]

[FONT=Verdana, Arial, Helvetica, sans-serif][/FONT]
 
[FONT=Verdana, Arial, Helvetica, sans-serif]Widen [SIZE=-1](larger LSA number)[/SIZE][/FONT]
[FONT=Verdana, Arial, Helvetica, sans-serif]Raise Torque to Higher RPM[/FONT]

[FONT=Verdana, Arial, Helvetica, sans-serif]Reduces Maximum Torque[/FONT]

[FONT=Verdana, Arial, Helvetica, sans-serif]Broadens Power Band[/FONT]

[FONT=Verdana, Arial, Helvetica, sans-serif]Reduce Maximum Cylinder Pressure[/FONT]

[FONT=Verdana, Arial, Helvetica, sans-serif]Decrease Chance of Engine Knock[/FONT]

[FONT=Verdana, Arial, Helvetica, sans-serif]Decrease Cranking Compression[/FONT]

[FONT=Verdana, Arial, Helvetica, sans-serif]Decrease Effective Compression[/FONT]

[FONT=Verdana, Arial, Helvetica, sans-serif]Idle Vacuum is Increased[/FONT]

[FONT=Verdana, Arial, Helvetica, sans-serif]Idle Quality Improves[/FONT]

[FONT=Verdana, Arial, Helvetica, sans-serif]Open Valve-Overlap Decreases[/FONT]

[FONT=Verdana, Arial, Helvetica, sans-serif]Closed Valve-Overlap Decreases[/FONT]

[FONT=Verdana, Arial, Helvetica, sans-serif]Natural EGR Effect is Reduced[/FONT]

[FONT=Verdana, Arial, Helvetica, sans-serif]Increases Piston-to-Valve Clearance[/FONT]
 
GTMOPAR: Subscribed. I'm having issues with which roller cam to run on my 90 5.9 roller as well. All this info is really good.
I can tell you,a mild Magnum 360,with a [email protected],114 lobe center,284 advertised,.491 lift(1.6 rockers) IS MILD. Sounds like a stock 340 cam.800 in drive,21" of vacuum. Too mild,for my tastes.Lotsa torque.
 
frosty_the_punk said:
[FONT=Verdana, Arial, Helvetica, sans-serif]Tighten [SIZE=-1](smaller LSA number)[/SIZE][/FONT]
[FONT=Verdana, Arial, Helvetica, sans-serif]Moves Torque to Lower RPM[/FONT]
[FONT=Verdana, Arial, Helvetica, sans-serif]Increases Maximum Torque[/FONT]
[FONT=Verdana, Arial, Helvetica, sans-serif]Narrow Power band[/FONT]

[FONT=Verdana, Arial, Helvetica, sans-serif]Builds Higher Cylinder Pressure[/FONT]

[FONT=Verdana, Arial, Helvetica, sans-serif]Increase Chance of Engine Knock[/FONT]

[FONT=Verdana, Arial, Helvetica, sans-serif]Increase Cranking Compression[/FONT]

[FONT=Verdana, Arial, Helvetica, sans-serif]Increase Effective Compression[/FONT]

[FONT=Verdana, Arial, Helvetica, sans-serif]Idle Vacuum is Reduced[/FONT]

[FONT=Verdana, Arial, Helvetica, sans-serif]Idle Quality Suffers[/FONT]

[FONT=Verdana, Arial, Helvetica, sans-serif]Open Valve-Overlap Increases[/FONT]

[FONT=Verdana, Arial, Helvetica, sans-serif]Closed Valve-Overlap Increases[/FONT]

[FONT=Verdana, Arial, Helvetica, sans-serif]Natural EGR Effect Increases[/FONT]

[FONT=Verdana, Arial, Helvetica, sans-serif]Decreases Piston-to-Valve Clearance[/FONT]

[FONT=Verdana, Arial, Helvetica, sans-serif][/FONT]
Click to expand...

OK, so...
Smaller lsa increases overlap. Shouldn't this lower compression at low rpm and raise it at high rpm? I would have predicted peak torque moving to higher rpm, and lower cranking compression.

When I think too much about cams my brain hurts and I start getting basic principles backwards. Then I give myself a head slap and it hurts even more. I knew I should not read this thread. :banghead: :D

So tell me if that's why some of this seems backwards to me.
 
A camshaft with a narrow 107 LSA is installed with the peak of the intake lobe at 107 ATDC
A camshaft with a wider 114 LSA is installed with the peak of the intake lobe at 114 ATDC.

This is assuming the camshaft is not retarded or advanced for tuning.

Int centre + exh centre / 2 = LSA

basically widening the LSA equates to later intake valve events. the intake valve closes later during compression stroke. this lowers dynamic compression ratio regardless of valve overlap.
 
Abodybomber said:
GTMOPAR: Subscribed. I'm having issues with which roller cam to run on my 90 5.9 roller as well. All this info is really good.
I can tell you,a mild Magnum 360,with a [email protected],114 lobe center,284 advertised,.491 lift(1.6 rockers) IS MILD. Sounds like a stock 340 cam.800 in drive,21" of vacuum. Too mild,for my tastes.Lotsa torque.
Click to expand...

Hey bomber, I bought a roller cam off of a member brand new and I'm regretting buying it. I jumped the gun a bit before I researched it a bit. The motor is actually an LA roller. I'm thinking of having it reground as a good option. I want the lopey idle and I'm not going to spin it to the moon everytime I take it out. Probably going to be 9.0-9.5-1 iron heads opened up a bit and stock bottom end. With these specs what do you guys think I should do?
482/496 lift
216/222 @ 50
Centerline 119
37 degrees of overlap
I know its small but would this be a good candidate for a regrind? Which route would you guys go?
 
Should be regrindable. Give Oregon Cams a call. About 120-150.00. You will need ,custom push rods.
 
clinteg said:
So let's play a scenario. You have an engine with 11:1 static CR, but you want to run pump gas. You leave it up to your engine guy to pick the cam to run the fuel without detonation. He picks a cam with .266/.268 duration @ .050 and a 105 LSA. If the lower LSA pumps up cylinder pressure, why would he have chosen that LSA when static CR is already fairly high? I guess it's mostly about dynamic CR? That's what was just ordered for my motor and didn't know much about LSA when he told me. The tech at comp cams and my engine guy came up with that combo. I thought that was pretty tight so I've been trying to read around to find out why that particular setup was chosen. I'll ask him later about it but wanted to hear some thoughts from you guys on that.
Click to expand...

I am in a similar situation. I bought a cam that was basically just used on a few dyno pulls. Called comp and they said it is almost perfect for what I am trying to do. Engine is a 422, flattops, zero deck, and the heads will be around 72-75cc. Here are the specs with 1.6 rockers:
275/288 adv
250/254@. 050
104 lsa
Intake open 36.5
Intake closes 58.5
Exhaust open 71
Exhaust close 37
Overlap 73.5
101 cl
I would think this would be working against me trying to run pump gas, but they said it is really close to what they would recommend.
 
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