Spectre

I have reserched the subject for a
while but still cant understand/visualise
the diffrent aspects of a cam..

whats the diffrence with LSA of 109-110-112 ?
how does LSA work with duration ?

lift.. u get the most possible.. end of story right?

suppose u compare 2 cams, same duration..
one 110- the other 112.. in the same engine..
what would the diffence be?

thanks 4 any help

ede

check out lunati or comp cams web site, both have a lot of good tech info

txhotRS

I'm lucky to have a subscription to CHEVY HIGH PERFORMANCE MAGAZINE... they JUST published an article on cam specs... how to read them and all that... let me help you out...
first things first... lift is not everything... DURATION plays a more important role... (always look at the number that says @.050... it's more accurate)
the camshaft rotates so ALL measurements are in degrees (of a full circle-- 360^) HOWEVER, the degrees are specific to the crankshaft, BECAUSE the crank and the cam are connected by the timing chain BUT, the for every turn the crank shaft makes the cam does 1/2 a turn
for example.. if your cam has an intake duration of 210 degrees... that means for 210 degrees (out of a full circle.. 360 degrees) OF THE ROTATION OF THE CRANK the intake valve will be open... this is where lift comes in... say you have a .450 lift ... that means when the cam is turning and opening the valve it will lift up .450 inches at it's MAX height... so the more duration your cam has ... the longer the valve stays open... but the bigger lift you have,, the higher the valve moves... so big duration and low lift is usually BETTER than little duration and high lift... but both are important... whichever combinaiton allows the most air to flow into, or out of the engine...
EVERY cam lobe has a "centerline" which is usually 1/2 EXACTLY of the duration... the measurement between the intake lobe centerline and the exhaust lobe centerline PER cylinder is the LSA (lobe seperation angle)... so the bigger the LSA... the further apart the lobes are and the smaller the LSA, the closer the lobes are...
when the lobes are closer, they create overlap... which is when the intake valve AND the exhaust valve are open at the same time ( for a split second)... when this happens you get that "rumpy rump" engine sound... So when the LSA is smaller (108, 110) you get MORE POWER, but also WORSE MILEAGE, and LESS ENGINE VACUUM. and the opposite for a LARGER LSA (114, 116)...
HERE IS THE PROBLEM.... if you have a vehicle with fuel injection you NEED engine vacuum, therefore you NEED a LSA of 112 OR higher... that's the difference. /.. if you have any other questions ,,, let me know...

Spectre

but i still dont get the LSA..

so big duration and low lift is usually BETTER .. I agree

I understand ur explanation..
But still dont get it.

Suppose u have 2 cams for ur build up.

same lift.. same duration.

Diffrent LSA. (109 vs 112)

How will the powerband be affected?

I cant visualise this lol I have to SEE it

according to what u wrote..

lower LSA (106-109) narrow down the power band (torque curve)?

Overlap isnt good for high rpm ?

Ill keep looking

Thanks for the resume.. ill read it until I can picture it lol

Enkil

Okay, I'm not very knowledgable, so I could just be talking out my **** and not getting ANY of this right, but it's what I've understood of it so far. If I am wrong, someone will smite me down for it and correct me. (Which I don't mind, because then I'll learn too.)

LSA is how far apart the intake and exhaust lobes are, or.. it determines when the exhaust valve starts opening relative to the intake valve.

If there's a lot of overlap, then the exhaust will be open while the intake is, thus some of the a/f mixture could very easily mix or just be shot into the exhaust stream. Little or no overlap would prevent this from happening.

If the a/f mixture had no inertia/momentum, then it would seem to me to be ideal that the intake and exaust valves would never be open at the same time. However, it does... It doesn't start flowing as soon as the valve opens, it has to start speeding up, then it slows down, then it's sped up as it's pushed out again, and the process repeats. Also, the properties of the a/f mixture are different at different engine RPM's. Think of taking a large piece of of posterboard and moving it slowly through the air, then moving it more quickly.

Because the properties of the mix are different at different engine RPM's, what works for low-rpm engines won't necessarily work at higher rpm's. (Think of the TPI cam.) And cams meant for high-rpm engines are usually very rough at idle.

AJ_92RS

Buy this book.



You can click on the picture.

Once you read that book, you'll be the one all YOUR friends come to for questions.

Air_Adam

LSA is the difference, in degrees, between the highest point of the intake lobe and the highest point of the exhaust lobe. Typically, the smaller the angle, the more overlap you will have.

This is were it gets tricky really. Lift is not the deciding factor in picking the proper cam for an engine so much as duration and LSA.

For example, with a power adder like a blower, to get the most out of it, you want almost no overlap because then the 2 valves aren't open at the same time for very long, if even at all. You would want this with a supercharger because it helps "trap" more of the mixture in the cylinder. Overlap is directly related to LSA. The wider the angle is (higher number of degrees), the less overlap you will have.

Overlap isn't necissarily such a bad thing, untill it becomes excessive. Most hi-perf cams from the '60s and '70s (think Z/28 and LT-1) did have a substantial amount of overlap. This went away in the mid-late '70s because of emitions cams being introduced. The emitions cams have very little overlap because that keeps more unburned fuel out of the exhaust system.

At least this is how I was taught that it works.

Spectre

Tnx everybody !

That book look interesting..

Ill go check it out.

grumpyvette

Duration vs overlap ?
your kidding right? thats one of the best questions ask here in quite a while!
ok what your trying to do is keep the DCR as high as the fuel octane will allow and the duration and lift matching the rpm level you want to be most effective in, now lift per deg. of rotation is limited by the max feed ramp angle that the type of lifter your useing will allow without haveing the edge of the lifter contact the surface of the cam lobe as the cam rotates under the lifter and that is limited by the dia. of the cam lobes base circle to lift ratio and the dia. of the lifter or in the case of roller lifters the dia. of the roller wheel. thats why the ford guys have a slight advantage in that stock chevy lifters are 0.842" and fords are 0.874" this allows the ford cam lobes to be slightly more aggressive and thats also why those mushroom base lifters are used in racing engines in classes not allowing roller lifters. now the main idea is to get the valve open as fast as possiable and closed as fast as possiable within the limits the valve train can support in the rpm range you want max power in , since power is basically the engines torque x rpm and the rate at which it can be produced, and torque is basically cylinder pressure times piston surface area times leverage( max crank stroke) times the number of power strokes per minute your looking for max torque at the max rpm your engine can effectively flow air into the cylinders, so your looking for a ballance between the shortest possiable duration to maximize cylinder pressure that keeps the valves open long enough at that rpm level time wise for max air flow to fill those cylinders, ballanced against the least overlap that will provide efficient exhaust scavageing at that rpm level.now alot depends on the cylinder volume versus port flow numbers


DO YOURSELF A BIG FAVOR
buy these FIVE books,AND CAREFULLY READ THEM... it will be the best money you ever spent, read them, and you will be miles ahead of the average guy. and it will save you thousands of hours and thousands of wasted dollars,

HOW TO BUILD THE SMALL BLOCK CHEVEROLET by LARRY ATHERTON&LARRY SCHREIB
.
HOW TO BUILD MAX PERFORMANCE CHEVY SMALL BLOCKS ON A BUDGET by DAVID VIZARD
.
JOHN LINGENFELTER on modifying small-block chevy engines

how to build & modify CHEVROLET small-block V-8 CAMSHAFTS & VALVTRAINS BY DAVID VIZARD

SMOKEY YUNICK,S POWER SECRETS

THE DISPLACEMENT,CYLINDERHEAD FLOW and cam timing and compression ratio are the major factors in how well the basic combo will work, of these watch the compression ratio matches the cam timing, the larger the displacement the better and cylinderheads are one of the most important parts in the whole combo!


if cams are a mystery please take the time to read these, it will get you a good start, ITS THE CAMS VALVE TIMING THAT HAS THE LARGEST EFFECT ON CHANGING THE STATIC COMPRESSION RATIO TO THE DYNAMIC COMPRESSION RATIO (THE ONLY THING THAT TRUELY MATTERS, BECAUSE ITS THE ONLY COMPRESSION RATIO THE ENGINE EVER SEES)

http://www.newcovenant.com/speedcraf...camshaft/1.htm
(read LESSONs 1-8)

http://www.mercurycapri.com/technica...e/cam/lca.html

http://www.wighat.com/fcr3/confusion.htm

http://www.cranecams.com/instruction...in/camfail.htm

http://www.mercurycapri.com/technica...cam/index.html

http://www.idavette.net/hib/camcon.htm

http://www.cranecams.com/master/adjustvt.htm

http://www.centuryperformance.com/valveadjustment.htm

http://www.totalengineairflow.com/tech/valvelashing.htm

http://www.chevytalk.com/tech/engine/Cam_Selection.html

http://www.chevytalk.com/tech/101/Cam_Theory.html

http://www.babcox.com/editorial/ar/ar119736.htm

http://www.mercurycapri.com/technica...e/cam/vtg.html

http://www.symuli.com/vw/camp1.html

http://www.symuli.com/vw/camp2.html

http://home.wxs.nl/~meine119/tech/camqa.html
these are the valve timeing overlap ranges that are most likely to work correctly

trucks/good mileage towing 10-35 degs overlap
daily driven low rpm performance 30-55degs overlap
hot street performance 50-75 degs overlap

the secret if you care to call it that is that youll need to carefully match the engine components to work at both the correct DYNAMIC compression level and airflow level at a particular rpm range, heres places to get ideas
--------------------------------------------------------------------------------
http://www.ryanscarpage.50megs.com/combos1.html

http://www.chevymania.com/dyno/

http://www.airflowresearch.com/dyno/chevy_dyno.htm

http://www.prestage.com/Tech+Info/En...y/default.aspx
--------------------------------------------------------------------------------
your going to need to understand theres TWO types of compression ratios
the first comonly refered to as the engines compression ratio, is the static compression raio
THE STATIC COMPRESSION RATIO if the DIFFERANCE in VOLUME between the cylinders volume with the piston at BDC (BOTTOM DEAD CENTER) and TDC (TOP DEAD CENTER)
Definition: The Compression Ratio (CR) of an engine is the ratio of the cylinder volume compared to the combustion chamber volume. A cylinder with 10 units of volume (called the sweep volume) and a chamber with a volume of 1 has a 10:1 compression ratio. Static Compression Ratio (SCR) is the ratio most commonly referred to. It is derived from the sweep volume of the cylinder using the full crank stroke (BDC to TDC). Dynamic Compression Ratio, on the other hand, uses the position of the piston at intake valve closing rather than BDC of the crank stroke to determine the sweep volume of the cylinder.

DYNAMIC COMPRESSION RATIO
is the volume of the cylinder measured from the point where the valves close, not BDC, the intake valve NORMALLY closes at some point after BDC, and keep in mind the piston compresses NOTHING UNTILL THE VALVES ARE BOTH CLOSED!
PLAY WITH THE CALCULATOR FOR STATIC COMPRESSION BELOW
http://cochise.uia.net/pkelley2/crc.htm
THEN READ THE LINK BELOW AND DOWNLOAD THE DYNAMIC COMPRESSION SOFTWARE
http://cochise.uia.net/pkelley2/DynamicCR.html


things to read

http://www.geocities.com/jgkov/L98Mods.html

http://www.ws6.com/mycar.htm

http://www.eecis.udel.edu/~davis/z2...page021105.html

boogie

so big duration and low lift is usually BETTER than little duration and high lift...

I am no cam guru but i would rather have a short duration cam and higher lift for a street application.

Spectre

-thats one of the best questions ask here in quite a while!

Well Im glad i brought it up..

Im gonna go buy some of those books..

thanks again

grumpyvette

[QUOTE]Originally posted by boogie
[B]so big duration and low lift is usually BETTER than little duration and high lift...

no, youve got it wrong, lift should be reasonably high in its relation to duration and the cylinderheads flow charicteristics have a great deal to do with what lift will work best, the correct duration is a ballance between the time required to allow air to flow thru the ports constantly becomeing shorter as the rpms increase and the LSA in the cams design and how it effects cylinder scavaging from the exhaust and the intake ports ram tuning frequency.
this chart can be used as a rough guide as to the required duration necessary to get full cylinder fills at various rpm ranges

[b]read these lessons (#1-8)
http://www.newcovenant.com/speedcraf...camshaft/3.htm
The LSA, or lobe separation angle, is ground into the cam and cannot be changed. It is the angle that separates the intake and exhaust lobe for a particular cylinder, and is measured in camshaft degrees. The intake lobe centerline is measured in crankshaft degrees. The #1 intake lobe centerline is usually between 100° to 110° ATDC and is what you use to degree the cam. The cam manufacturer will publish the specs for the cam based on a given intake lobe centerline. Comp Cams, for instance, produces a large number of cams with 110_° LSA ground 4° advanced, so they list the specs for the cam with a 106° intake lobe centerline. You can calculate the ILC by adding the intake opening angle in °BTDC, the intake closing angle in °ABDC, plus 180° for the distance from TDC to BDC. Divide by 2 and subtract the intake opening angle and you will have the ILC. For example a 12-430-8 Comp Cam lists IO at 34°BTDC, IC at 66° ATDC, so 34 + 66 + 180 = 280. 280/2 = 140. 140 - 34 = 106° ILC
Figure 3 is a picture of both an intake and an exhaust lobe of a camshaft, seen end-on. It shows the relationship between the lobes, shows the overlap area, and illustrates this next section.
As stated in lesson 2, overlap has a great deal to do with overall engine performance. Small overlap makes low-end torque but less high-end power. Large overlap reduces low-end torque but increases high-end power.
Overlap is determined by two other cam specifications, Duration and Lobe Center Angle.
Duration is the time, measured in crankshaft degrees, that a valve is open. A duration of 204 degrees means that while the valve is open, the crankshaft rotates through 204 degrees.
Duration is measured on two "standards," "advertised duration" and "duration at 0.050"." Advertised duration is measured from when the valve just starts to lift off its seat to when it just touches the seat again. This is measured in different ways by different manufacturers. Some measure when the valve lifter is raised 0.004", some at 0.006", and some at different points yet. So the industry agreed to another standard that was supposed to make it easier to compare cams. In this standard, the duration is measured between the point where the lifter is raised by 0.050", and the point where it is lowered again to 0.050".
The 0.050" standard is great for side-by-side "catalog" comparisons between cams. But if you use engine prediction software on your computer, the software is much more accurate when you can feed it "advertised" duration numbers.
Lobe Center Angle is the distance in degrees between the centers of the lobes on the camshaft.
To increase duration, cam makers grind the lobes wider on the base circle of the cam. This makes the lobes overlap each other more, increasing overlap. More duration = more overlap.
To increase overlap without changing duration, cam makers will grind the lobes closer together, making a smaller lobe center angle. Less lobe center angle = more overlap.
Overlap and duration are the two big factors in cam design. More overlap moves the power band up in the engine's RPM range.
Longer duration keeps the valves open longer, so more air/fuel or exhaust can flow at higher speeds. It works out that increasing the duration of the camshaft by 10 degrees moves the engine's power band up by about 500 rpm.
A smaller lobe separation increases overlap, so a smaller lobe separation angle causes the engine's torque to peak early in the power band. Torque builds rapidly, peaks out, then falls off quickly. More lobe separation causes torque to build more slowly and peak later, but it is spread more evenly over the power band. So a larger lobe separation angle creates a flatter torque curve.
So you can see how a cam maker can tailor the camshaft specs to produce a particular power band in an engine--

Short duration with a wide separation angle might be best for towing, producing a strong, smooth low-end torque curve.
Long duration with a short separation angle might be suited for high-rpm drag racing, with a high-end, sharp torque peak.
Moderate duration with wide separation angle might be best suited for an all-around street performance engine, producing a longer, smoother torque band that can still breathe well at higher RPM.
Remember, there's always a compromise made in this process.

One last item to consider is the lobe centerline. The lobe centerline is the angle of the lobe's center peak, measured in crankshaft degrees when the piston is at Top Dead Center (TDC). In general (but not always), when a cam is installed "straight up," the intake lobe centerline and the lobe separation angle are the same.
The lobe centerline can be altered when the camshaft is installed, by advancing or retarding the camshaft's position in relation to the crankshaft. Advancing the camshaft by 4 degrees will move the power band about 200 RPM lower in the RPM band. Retarding the cam by 4 degrees will likewise move the power band 200 RPM higher in the RPM band. This allows you to fine-tune the engine's performance according to your needs.

personally I try to stay close to 108-110 degrees on most carb engines and 112-114 degrees on EFI engines because the sensors in EFI engines tend to work more acurately with slightly less overlap and I value a wider torque curve more than a few hp only close to peak rpm, but its a compromise,displacemend, dcr and rod length and stroke all effect the correct choice

e-man

With the Lift I read that you should pick the cams lift to the cylinder head flow.If your heads peak flow is at .500 lift you want the lift to be .500-.530. anything more is a waste.Grump am I right or wrong?

Air_Adam

High Duration = Open long time

High Lift = Opens more

Low Duration = Not open long time

Low Lift = Not open much

Just thought I'd say this cuz a few people seemed a little confused.

grumpyvette

your both right and wrong depending on HOW you want to look at it!
let me explain

look at the graph of the cam above and lets say the ports in the cylinder heads your using flow
.100- 50cfm
.200- 80cfm
.3.00- 128cfm
.400-205cfm
.500-230cfm
.600-232cfm
.700-.232cfm
and that cam acctually has a .650 lift instead of a .480 lift as shown
now keep in mind that the heads stop flowing more at just over .500lift so theres no extra flow to be gained at the higher lift BUT the valve passes thru .500 lift TWICE if the valves open to .650 but only once if the cam reaches just .500. if the valves spends only 10 degrees at .500 lift the total port flow will be far less than if the valve passes thru .500 lift on its way to .650 lift 30 to 40 degrees away from where it falls back past .500 lift on its way closed
its very likely that the port flows more total air into the cylinder simply because the valve stays at .500 or higher longer if the valve reachs .650 lift.
put another way more lift above the ports stall point still tends to increase total flow volume thru the port even if the port cant flow effectively at full lift.
the first question most guys ask is "well why not just keep the valve at .500 lift for 40 degrees" the answer is that the cam lobe MUST be a shape the lifter can smoothly follow , especially at higher RPM LEVELS and the valve springs must maintain the lifters contact on that cam lobe, that can only be done with a smooth curved path for the lifter to follow and that requires that the cams ramps and nose be a smooth curve, and a smooth curve cant STOP at any point

BTW READ THIS
http://www.idavette.net/hib/camcon.htm

IT EXPLAINS WHY ROLLER LIFTERS CAN AND DO PRODUCE BETTER POWER DUE TO BEING ABLE TO FOLLOW MORE RADICAL CAM RAMP CHANGES AND HOW THEY LIFT THE VALVE FASTER AND HOLD IT OPEN LONGER FOR ANY GIVEN LIFT