LSA selection

[MikeB]

Grumpy,

I read your post that showed Vizard's chart for choosing LSA based on cylinder cubic inches / intake valve diameter. I'm confused as to why all the cam manufacturers grind cams on 110-114 LSA (and a few racing cams at 106-108) if Vizard's theory is correct. :?: And heck, GM has always used even wider LSAs for smooth idles.

If my math is correct, here's what Vizard's chart shows for engines with 2.02" intake valves:
327 cu in: 109 LSA
355 cu in: 107 LSA
383 cu in: 105 LSA

I'd appreciate your comments,

Mike

 

[grumpyvette]

your math is totally correct, keep in mind hes calculating the most efficient LSA to maximize the cylinder fill by maximizing port flow rates, to fill the cylinder,hes not concerned with idle characteristics,emission testing or mileage, just max average POWER, or put a different way at what LSA will I fill the cylinders with fuel/air mix to produce the best horsepower, naturally that assumes all the other factors like duration,lift,port cross section and exhaust scavenging will also be calculated to take full advantage of that potential power range and air flow

if you follow the links and sub links you can find ways to increase power levels.
but keep in mind that the major car manufacturers have different goals in mind than just trying to maximize an engines power potential.
factors like smooth idle, god off idle and low speed acceleration, passing emission testing, long term, durability all tend to factor in at higher goals than maximizing the engines peak power or even average power level in many applications, in most cases the average consumer is much more concerned with having a smooth idle and getting good mileage and having smooth transmission shift from his auto transmission

software like the free comp cams software below[/color]
[/size]

ADDING NITROUS
(ITS SIMPLY ADDING A GREAT DEAL MORE OXYGEN CONTENT TO THE AVAILABLE AIR , in THE CYLINDER ALLOWING YOU TO BURN MORE FUEL EFFECTIVELY THUS PRODUCE MORE CYLINDER PRESSURE OVER THE PISTON< RESULTING IN MORE TORQUE)
ITS use developed similar INCREASED exhaust pressure and INCREASED VOLUMES of exhaust gases, similar too what results in a super charged application, because atmospheric air,run in a N/A engine holds about 21% oxygen and you run a fuel air ratio about 12.6 pounds of air for every pound of gasoline.
with nitrous ADDED theres, up too, about 40% oxygen content available in the same volume of air as you would have with a supercharger at about 15 psi of boost, but without the intake being pressurized and with out the heat and weight a supercharger has, in fact nitrous is injected and radically cools the intake charge making it denser,so to maintain that similar 12.6:1 fuel air ratio your forced to be adding and burning a good deal more fuel,(obviously depending on the percentage of nitrous added to the outside air the engine ingests, vs pure nitrous and fuel which would require a bit more that twice as much fuel to maintain the ideal fuel/air ratio that extra fuel being burnt is where your getting the extra power nitrous used generates, thus the extra exhaust gas volume, you might want to think of nitrous as generating up to twice the volume of exhaust gases from about the same intake volume, thats running and burning extra fuel to generate higher cylinder pressures,up too, twice the oxygen content, means up to twice the fuel being burnt per compression,power and exhaust stroke. thats one reason nitrous cams tend to have, and work better with longer exhaust duration to help blow down the cylinder pressure and volume, but don,t require as wide a LSA as a super charger cam, because they don,t require you trap pressurized intake charge air from exiting the exhaust during valve overlap to the same degree, a supercharger application would benefit from.

http://www.compcams.com/Camquest/default.asp

these may help

viewtopic.php?f=52&t=82

viewtopic.php?f=55&t=58

viewtopic.php?f=52&t=1070

viewtopic.php?f=52&t=3816

viewtopic.php?f=52&t=112

viewtopic.php?f=52&t=2782

 

[Indycars]

Grumpy,

I read your post that showed Vizard's chart for choosing LSA based on cylinder cubic inches / intake valve diameter. I'm confused as to why all the cam manufacturers grind cams on 110-114 LSA (and a few racing cams at 106-108) if Vizard's theory is correct. :?: And heck, GM has always used even wider LSAs for smooth idles.

If my math is correct, here's what Vizard's chart shows for engines with 2.02" intake valves:
327 cu in: 109 LSA
355 cu in: 107 LSA
383 cu in: 105 LSA

I'd appreciate your comments,

Mike

Excellent question, I've been wondering the same thing. I'm building a 400 cu in SBC with the 2.02" intake valve and had noticed the same detail about LSA from Vizard. I wonder what the major cam grinders would say if I asked for a LSA of 104 degrees???

I just haven't gotten around to asking the same question, wanted to re-read to make sure of the details. I will be interested to see what other questions you come up with. I hope to have a few questions in a day or two, after I read that chapter again.

 

[HYPURR DBL NKL]

Isn't most of Visard's stuff on the ragged edge type of building? I would think for a more well rounded type of street/strip car 110 LSA would be plenty, for a mainly strip car 106 LSA should be fine, or am I way off base?

Phil

 

[Indycars]

Isn't most of Visard's stuff on the ragged edge type of building? I would think for a more well rounded type of street/strip car 110 LSA would be plenty, for a mainly strip car 106 LSA should be fine, or am I way off base?

Phil

At this point, I'm not arguing FOR or AGAINST Vizard, just some comments for further discussion.

I don't have an answer to your question, but.......I have his book. The engine that he is referring to in his book needs a 108 degree LCA. Then he says and I quote, "If you are told that the cam you need should have a wider LCA, it is because you are trying to run more duration that the application call for!" If he is right then I need a LCA of 104 degrees for my 400 cu in SBC with 2.02 intake valve. I've looked at CompCams to see what they have with that spec and there's very little choice. This is the mildest cam they list for the SBC. Notice the duration of 255/266 at 0.050.

NOTE: LCA (Lobe Centerline Angle) = LSA (Lobe Separation Angle) It's the same spec.

He goes on to say that compression ratio (CR) has an effect on the LCA. Higher the CR, the more the LCA can be increased, but he doesn't explain. If someone has any comments, please, let's here them.


David Vizard - How To Build Horsepower (Page 104)
http://www.amazon.com/David-Vizards-Bui ... 241&sr=8-2

 

[HYPURR DBL NKL]

I'm no expert, but my understanding has always been that a tighter LSA, also increases overlap which bleed cyl. pressure. This is not ideal for a street car as it would need more compression to compsensate for the cyl. bleed down caused by the cams tight LSA? The more compression you need the less streetable the car becomes. Also my understanding is the tighter the LSA, the more RPM's you need to turn to take advantage of it, hence normally tight LSA's are in race cars? This is a basic explanation, but I am trying to keep the cause and effect simple.

Phil

 

[grumpyvette]

I'm no expert, but my understanding has always been that a tighter LSA, also increases overlap which bleed cyl. pressure. This is not ideal for a street car as it would need more compression to compsensate for the cyl. bleed down caused by the cams tight LSA? The more compression you need the less streetable the car becomes. Also my understanding is the tighter the LSA, the more RPM's you need to turn to take advantage of it, hence normally tight LSA's are in race cars? This is a basic explanation, but I am trying to keep the cause and effect simple.

Phil

THATS PROBABLY one of the MOST COMMON MYTHS
(that overlap with a tight LSA bleeds off compression)

"EXAMPLE, OF A
very common mis- conception, is that a cam which is ground on a 108 degree lobe center. which has more overlap and will reduce your DCR due to greater overlap."

PROBABLY one of the MOST COMMON MYTHS
( is that overlap with a tight LSA bleeds off compression)
Overlap has nothing to due with DCR. A cam with 108 LSA will close the intake valve sooner on the compression stroke and create MORE cylinder pressure than a cam with 112 LSA. That assumes durations and cam lobe designs are the same of course "

this is correct

example
LOOK heres TWO cams IDENTICAL EXCEPT FOR THE LSA,(LOBE SEPARATION ANGLES) assuming both cams are installed with identical LCA (LOBE CENTER LINE ANGLE)remember lobe center angles can be changed thru indexing the cam when degreeing it in, LSA is ground into the cam during manufacture, the tighter LSA of the crane 110921 builds a bit more cylinder pressure and results in slightly more torque over a NARROWER rpm band so its better with a manual transmission, the crane 114681 with its wider LSA tends to work better with an auto trans with its wider torque band but very slightly lower peak torque, the crane 110921 has more overlap and better savaging in the mid rpm band, but it idles rougher at low rpms and that overlap doesn,t help if you use nitrous
COMPARE the TIMING

narrower LSA, more overlap & more effective compression, because the intake valve closes earlier

wider LSA, less overlap & less effective compression, because the intake valve closes later



USING THE .050 LIFT figures, notice that the tighter LSA (LOBE SEPARATION ANGLE)cam CRANES 110921 has the intake close at 45 degrees ABDC while the wider lsa CRANES 114681closes the valves at 50.0 ABDC (the wider LSA results in the valve closing 5 degrees later on the pistons compression stroke, effectively reducing the effective compression ratio

 

[HYPURR DBL NKL]

So the intake valve closing timing is the key to effecting DCR and not LSA(big or small overlap) as I'd always thought?

Phil

 

[grumpyvette]

So the intake valve closing timing is the key to effecting DCR and not LSA(big or small overlap) as I'd always thought?

Phil

yes the combo of static compression,engine displacement,crank stroke, connecting rod length and intake valve close timing are the most critical factors.
pistons can,t compress the cylinders contents until both valves close and the intake valve closes last


youll find this chart very helpful
http://www.crower.com/valve-timing-chart/

 

[Indycars]

LOOK heres TWO cams IDENTICAL EXCEPT FOR THE LSA,(LOBE SEPARATION ANGLES) assuming both cams are installed with identical LCA (LOBE CENTER LINE ANGLE)remember lobe center angles can be changed thru indexing the cam when degreeing it in, LSA is ground into the cam during manufacture,

It's confusing with how everyone uses the TERMINOLOGY! It seems everyone has a different use for the term LCA. Below is the quote from Vizards book(its also in my post above) and he uses the term as the same as LSA. It seems to me that LSA is a better description of the parameter that is ground into the cam and CANNOT be changed without installing a different cam. ICA - Intake Centerline Angle would be good for the value that can be changed when you index the cam during installation.

Then he says and I quote, "If you are told that the cam you need should have a wider LCA, it is because you are trying to run more duration that the application calls for!"

 

[grumpyvette]

LOOK heres TWO cams IDENTICAL EXCEPT FOR THE LSA,(LOBE SEPARATION ANGLES) assuming both cams are installed with identical LCA (LOBE CENTER LINE ANGLE)remember lobe center angles can be changed thru indexing the cam when degreeing it in, LSA is ground into the cam during manufacture,

It's confusing with how everyone uses the TERMINOLOGY! It seems everyone has a different use for the term LCA. Below is the quote from Vizards book(its also in my post above) and he uses the term as the same as LSA. It seems to me that LSA is a better description of the parameter that is ground into the cam and CANNOT be changed without installing a different cam. ICA - Intake Centerline Angle would be good for the value that can be changed when you index the cam during installation.

Then he says and I quote, "If you are told that the cam you need should have a wider LCA, it is because you are trying to run more duration that the application calls for!"

like I said in the beginning the terms have become almost universally MIS-used by nearly EVERYONE
if you UNDERSTAND the true meaning of both LSA and LCA that statement is both confusing and meaningless

Lobe Separation Angle (LSA) is NOT the same as Lobe Centerlines (LC), although the two are directly connected.

The Lobe Centerline Angle is measured as the degrees that the crankshaft rotates BETWEEN the exhaust valve’s maximum lift point (aka: Exhaust Centerline) and the intake valve’s maximum lift point (aka: Intake Centerline). Check the lead illustration in this story from COMP Cams to show this effect. The highest lift points on the lobes are referred to as the cam “Lobe Centerlines” and are usually ground somewhere between 102 and 122 crankshaft degrees. Since Lobe Centerline is referenced in relation to crankshaft degrees as well, it can be moved around, depending on where you install the cam.
you can advance or retard the lobe centerline but not make it wider or narrower

When you degree the cam, you’re usually checking to see if it’s installed at the cam manufacturer’s recommended Intake Centerline point. Let’s say your cam manufacturer recommends installing the cam at a 112-degree Intake Centerline. Using the degree wheel you check the intake’s highest lift point to be exactly at 112-degrees. That means you’ve now installed the cam “Straight Up”. If the degree wheel shows an intake max lift point of 110-degrees, the cam is now INSTALLED 2-degrees advanced from the manufacturer’s settings. If the degree wheel showed an installed position of 114-degrees, the cam is now INSTALLED 2-degrees retarded.

Lobe Separation Angle, on the other hand, is ground into the cam and it cannot be changed (see red arc in illustration). To check your LSA you calculate it by adding the intake and exhaust Lobe Centerline figures together and dividing their sum by two (Ex: 112 intake Centerline + 116 exhaust Centerline = 228 / 2 = 114-degree LOBE SEPARATION ANGLE).

There’s more. These are also the figures used to indicate how much the cam’s intake lobe was ground “advanced” or “retarded” from the factory. To find intake lobe advance/retard, simply subtract the Intake Lobe Centerline from the Lobe Separation Angle (i.e.: LSA 114 – IC 112 = 2-degree advance). This difference is how far advanced or retarded your cam was ground at the factory, 2-degrees in our example here. You cannot change Lobe Separation Angle because it is ground at the factory. But you can advance or retard the cam in relation to the crank when it’s degreed-in."

 

[Indycars]

Grumpy,

if you UNDERSTAND the true meaning of both LSA and LCA that statement is both confusing and meaningless

Are you referring to the statement by Vizard that I quoted, or something I said. Not sure exactly which statement you are referring to. Could you clarify for me.....thanks!

 

[grumpyvette]

Grumpy,

if you UNDERSTAND the true meaning of both LSA and LCA that statement is both confusing and meaningless

Are you referring to the statement by Vizard that I quoted, or something I said. Not sure exactly which statement you are referring to. Could you clarify for me.....thanks!

sorry for the confusion I was referring to this statement, VISARD MADE that you QUOTED

""If you are told that the cam you need should have a wider LCA, it is because you are trying to run more duration that the application calls for!"

a cam can not have a "WIDER" or "NARROWER"..."LCA" you can advance or retard the LCA (LOBE CENTER-LINE ANGLE) in relation to the crank rotation , but you can,t make it "wider"
you can have a cam ground with a WIDER LSA (LOBE SEPARATION ANGLE) but thats fixed and not something that changes once the cams manufactured

 

[Indycars]

I don't disagree with you about the definition of LCA, but I'm certain that when he says LCA, it is the same thing that we call LSA. See graphic below, taken from same book quoted earlier. Aside from Vizard use of the term LCA, his points about selecting a camshaft could still be valid. I think LSA describes the camshaft parameter very nicely and will continue to use LSA.

Note: In graphic below: lobe centerline angle (LCA) (6)

 

[grumpyvette]

thats the problem with some of these discussions,
the TERMS USED mean different things to different people, in different discussions


LSA=LOBE SEPARATION ANGLE

LCA =LOBE CENTER-LINE ANGLE

that and the fact that they can both be the same thing ,(IF the cams installed strait up,) as opposed to having the cam installed either advanced or retarded , where they will NOT BE!

LOBE SEPARATION ANGLE, IS GROUND INTO THE CAM CORE WHEN ITS MANUFACTURED, YOU can INDEX THE CAM ADVANCING AND RETARDING ITS LOCATION IN RELATION TO THE PISTON IN ITS STROKE, IN THE BORE BUT THE LOBE SEPARATION ANGLE REMAINS CONSTANT,
EXAMPLE
if YOU ADVANCE THE INTAKE LOBE 4 DEGREES YOU'VE ALSO ADVANCED THE EXHAUST LOBE 4 DEGREES.
ADVANCING THE CAM 4 DEGREES TENDS TO LOWER THE WHOLE TQ CURVE ABOUT 170-200RPM, RETARDING the CAM 4 DEGREES TENDS TO RAISE THE WHOLE TQ CURVE ABOUT 170-200RPM.
IF YOU NEED MORE THAN THAT MUCH ADJUSTMENT YOU PROBABLY NEED A DIFFERENT CAM
your LCA or LOBE CENTER ANGLE will change with any changes in indexing, degreeing in the cam,or moving the cam rotation with the cranks rotation .

Above 114 Deg. = Extremely Wide
114-112 Deg. = Wide
112-110 Deg. = Moderately Wide
110-108 Deg. = Moderate
108-106 Deg. = Moderately Tight
106-104 Deg. = Tight
Below 104 Deg. = Extremely Tight

VARYING LOBE SEPARATION ANGLE (CONSTANT)Tighten.................................................Widen
Moves Torque to Lower RPM.................Raise Torque to Higher RPM
Increases Maximum Torque..................Reduces Maximum Torque
Narrow Power Band..............................Broadens Power Band
Builds Higher Cylinder Pressure............Reduce Maximum Cylinder Pressure
Increase Chance of Engine Knock.........Decrease Chance of Engine Knock.
Increase Cranking Compression...........Decrease Cranking Compression
Increase Effective Compression............Decrease Effective Compression
Idle Vacuum is Reduced........................Idle Vacuum is Increased
Idle Quality Suffers...............................Idle Quality Improves
Open Valve-Overlap Increases.............Open Valve-Overlap Decreases
Closed Valve-Overlap Increases...........Closed Valve-Overlap Decreases
Natural EGR Effect Increases................Natural EGR Effect is Reduced
Decreases Piston-to-Valve Clearance...Increases Piston-to-Valve Clearance

ADVANCING / RETARDING CAM TIMING (LCA)will change with any changes in indexing
ADVANCING...............................................RETARDING
Begins Intake Event Sooner........................Delays Intake Event Closes Intake
Open Intake Valve Sooner..........................Keeps Intake Valve Open Later
Builds More Low-End Torque.......................Builds More High-End Power
Decrease Piston-Intake Valve Clearance....Increase Piston-Intake Valve Clearance
Increase Piston-Exhaust Valve Clearance...Decrease Piston-Exhaust Valve Clearance

http://www.hotrod.com/techarticles/engi ... index.html

viewtopic.php?f=52&t=480

http://www.stockcarracing.com/techartic ... index.html

http://www.hotrod.com/techarticles/engi ... index.html

http://www.chevyhiperformance.com/techa ... index.html

http://www.popularhotrodding.com/tech/1 ... index.html

http://cochise.uia.net/pkelley2/Overlap.html

viewtopic.php?f=52&t=480&p=1666#p1666

 

[Indycars]

If we can get past Vizard terminlogy, I would like to understand why Vizard’s concepts work or don’t work. So I used my DynoSim5 software to model the engine I’m building. The camshaft I picked to use as my baseline is the Crower 0471, spec shown below. The camshaft I used for Vizard was a modified Crower 0471 to agree with his way of picking the specs, also shown below. I changed the LSA from 110 to 106, then I shortened the duration until I had the same overlap of 69 degrees. Now the DynoSim5 software has a spec that shows how aggressive the lifter acceleration is, so I used that to reduce the lift until I had the same rate. This was needed because it would be more aggressive if it obtained the same lift with a shorter duration.

Engine Specs:
Size: 401 cu in
Bore: 4.125”
Stroke: 3.750”
Rod Length: 6.0”
Carb: 750 cfm
Comp Ratio: 10.6 to 1
Manifold: Dual Plane
Exhaust: Small Tube Primaries, No Mufflers

Vizard’s cam seems to have more area under the torque curve from 1000 to 6200 RPM. It is higher until the RPM reaches 4300 and then it crosses over the other cam going below it now.

I’m not understanding everything that is happening, just too many variables changed for me sort thru all their effects. Maybe someone can give me some insight into why those changes had the effects they did. I debated whether to even post this, because I know it’s going to be hard to follow. So I’m not sure anyone will have the time and background to sort thru this information. I would just like to know if his way thinking has merit.

Is this even a fair comparison??? Comments???

Below is the original Crower 0471 specs

Now the cam specs for the modified Crower in DynoSim5 (Next 2 Pictures)

DynoSim5 Comparison Graph Below

 

[grumpyvette]

FIRST, Ive just got to say!
DARN IMPRESSIVE COMPUTER WORK and GOOD QUESTION!

theres several factors at work, but the basic concept is based maximizing the port & runner flow rates and velocities DURING the max cylinder draw and time limitations,due to the piston dropping away from TDC , and air flow inertia,and closing the valves at the point that will maximize the trapped volume of fuel/air mix , in the cylinder..

you might want to think of it as maximizing ,the process of filling a glass of water under the faucet, in your sink, it doesn,t too much matter how much water flows, or the pressure,as long as its enough to fill the glass in a set time frame.what matters is how full the glass gets, too little flow and the glass can,t fill, too much flow and much of its wasted , or splashed out and the glass never gets full, move the glass into or out of the flow during the process and its sure to hold less that the max

READ THESE, threads but keep in mind that at 6000rpm those cylinders are filling and burning and exhausting their contents at a rate of 50 TIMES PER SECOND
viewtopic.php?f=55&t=4131&p=10975&hilit=volumetric#p10975

viewtopic.php?f=52&t=322&hilit=volumetric

viewtopic.php?f=53&t=3893&p=10304&hilit=volumetric#p10304

viewtopic.php?f=56&t=1303&p=2822&hilit=coke+can#p2822

 

[Indycars]

Grumpy,

Hey.....thanks! for the compliment!!!

So which cam would you pick when looking at the graph above and the specs below???

Engine Specs:
- Block: Dart SHP
- Size: 401 cu in
- Bore: 4.125”
- Stroke: 3.750”
- Rod Length: 6.0”
- Heads: Brodix IK200, 70 cc Chamber
- Rockers: Full Roller - Steel
- Carb: 750 CFM
- Comp Ratio: 10~10.5 to 1
- Manifold: Dual Plane
- Exhaust: 1 5/8" Primaries, 3 1/2" Collector
- Max RPM: 6200
- Scat Forged Rotating Assembly with Mahle Flat Top Pistons

Car Specs:
- Weight: 1800 lbs
- Rear Gear: 3.7 to 1
- Tire Dia: 28 inches
- Trans: TH350 with high stall converter
- Application: High Performance Street

 

[grumpyvette]

http://www.lunatipower.com/Product.aspx?id=1990&gid=289

just for grins can you throw this choice with the others as a third choice, on that graph above?

 

[Indycars]

Your wish is my command !!!

So which cam would you pick now ???