question on cam durration

[grumpyvette]

my big quesions are these,

whats the difference between running a wild cam and a not as wild cam with longer rockers, if the dynamic compression with both are nearly the same?

what are the pros and cons of running high compression with a lower dcr through the cam or running normal compression with an equal dcr? (on 93 octane)

and does anyone have a quick list of cam company ph #s? i used to have one. ill call them all for recommended cam specs

referance for stock cams

http://www.nastyz28.com/sbchevy/sbccams.php

http://www.chevy-camaro.com/parts/chevy ... es-cam.htm

the cams durration effects both the dynamic compression and the effective rpm band that the cylinders fill efficiently in, while its true a low compression and a mild cam could easily have the same dynamic compression ratio as a high compression and much longer durration cam, combo the effective rpm band would be much differant and the low and high rpm performance would be vastly differant
http://garage.grumpysperformance.co...ectly-and-get-it-to-last-cam-install-info.90/

http://garage.grumpysperformance.com/index.php?threads/calculating-overlap-and-lsa-or-lca-etc.480/

http://garage.grumpysperformance.com/index.php?threads/cam-gear-and-timing-marks-etc.724/#post-1021


First Id point out that nearly everyone occasionally confuses or at least makes the mistake of using the wrong abbreviation, (LSA, and LCA) these are terms,that are almost, at least in many discussions interchangeable. which they are not.
LSA =LOBE SEPARATION ANGLE ........LSA is ground into the cam during manufactured, and can,t change,

http://garage.grumpysperformance.co...lsa-effects-your-compression-torque-dcr.1070/

LOBE SEPARATION ANGLE
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
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
[color:red]LCA =(LOBE CENTER ANGLES)remember lobe center angles can be changed thru indexing the cam when degreeing it in[/color]
ADVANCING / RETARDING CAM TIMING

KEEP IN MIND MANY CAMS ARE FACTORY SET UP TO BE 4 DEGREES ADVANCED if INSTALLED DOT-TO-DOT

ADVANCING.
Begins Intake Event Sooner........................
Open Intake Valve Sooner..........................
Builds More Low-End Torque.......................
Decrease Piston-Intake Valve Clearance....
Increase Piston-Exhaust Valve Clearance...

RETARDING
Delays Intake Event Closes Intake
Keeps Intake Valve Open Later
Builds More High-End Power
Increase Piston-Intake Valve Clearance
Decrease Piston-Exhaust Valve Clearance

keep in mind theres three basic factors that are interlinked in that each has some effect on how the other two will effect the engines power curve
duration controls the number of degrees of rotation the valve takes from the time it lifts off its seat until it re-seats, the is the TIME the valve will be open and effects the rpm range , the cam will most efficiently operate in.
LIFT, controls the distance the valve opens,and combined with the valve diameter limits the valve curtain, so combined with duration in controls potential flow.

LOBE SEPARATION ANGLE will effect how effectively the exhaust can scavenge the cylinders and low rpm reversion pulse strength to some degree thus idle quality, as the period of time while both valves are open at the same time, greatly increases cylinder scavenging.

this charts based on a 350-383 chevy or similar size engine, but its a good rought guide on most engines under 400cid displacement on matching the durration to the intended operational rpm band
IDEALLY you would sellect the horsepower goal, and the displacement,youll work with too reach that goal. then the cylinder heads, intake and exhaust are sellected that supply the necessary flow rates,in that rpm band, you pick the cam too match the intended rpm band,and flow rates and power range for the application, you then match the compression ratio, to the cam timing too maintain the correct dynamic compression ratio, and you sellect the matching drive train and gearing to keep the engine IN the matched rpm band the vast majority of the time.
naturally if your limited to a set displacement or compression ratio the other factors must be sellected with those limits in mind.

heres free cam sellection software to narrow your choices
http://www.compcams.com/Camquest/default.asp

btw once you use it to find that approximate lift ,durration and lsa, you can buy any companies cams with similar specs.
most guys use the terms almost interchangably WHICH THEY ARE NOT in all cases!

LCA =(LOBE CENTER ANGLES)remember lobe center angles can be changed thru indexing the cam when degreeing it in, LSA (LOBE SEPERATION ANGLE) is ground into the cam during its manufacturing process.


CROWER cams
http://www.crower.com/misc/contact.shtml

CRANE CAMS
http://www.cranecams.com/

ENGLE CAMS
http://www.englecams.com/index.php
Tel: (310) 450-0806
Fax: (310) 452-3753

ISKY CAMS
http://www.iskycams.com/

phone: 323.770.0930
fax: 310.515.5730


ERSON
http://pbmperformance.com/store.php?catId=327

Lunati
technical support is availible by phone Monday through Friday 7AM to 5PM CST @
662 892-1500

http://www.popularhotrodding.com/tech/0 ... index.html

 

[grumpyvette]

heres something to read from ISKY
(I don,t agree with everything, and some of what he says goes against what IVE seen, (ESPECIALLY IF NITROUS IS IN YOUR PLANS) but it makes several good points...keep in mind that the EFFICIENCY of the total combos intake and exhaust flow,rates, compression,and gearing and exhaust scavaging at the average and max rpms will dictate the best cam timing required in most cases)

Longer Exhaust Duration: Is this really necessary?

Most stock camshafts from American production V8, V6 and 4 cylinder engines manufactured today are ground with the longer exhaust lobe duration. Or, another way of looking at this is that they are ground with shorter intake durations! The former embraces the viewpoint that either the Exhaust Ports or Exhaust Pipe system is somewhat restrictive, and is in need of an assist. The latter suggests that the intake system is rather efficient and cam timing can be trimmed back a bit with out much sacrifice in power, in order to maximize throttle response and cruising efficiency.

Take your pick here. There is no absolutely correct viewpoint - because both are probably true! In a stock engine running at conservative RPM levels, for the sake of overall efficiency, fuel economy and a quiet smooth running engine, this staggering of intake and exhaust duration is quite common and appropriate.

However, High Performance is another thing entirely. Change one factor, let's say in this case, the exhaust system (installing headers and larger pipes) and you have just negated in most cases, the need for that longer exhaust lobe. Now couple this change with a different intake system and camshaft and you have really scrambled the equation. But, wait just a moment. Why is it that so many people (racers & cam grinders alike) insist on running a cam with longer exhaust duration regardless of what equipment is employed? The answer is "habit". Most of them have been somewhat successful in doing it their way and will probably never change unless virtually forced by circumstances to do so.

Before we go any further however let's review what it actually is we are trying to do with an engine when we attempt to make more power. Our best result comes when we are cognizant of the fact that an engine is basically an air pump. We pump it in and out (although in a different form) and we have problems when one side or the other is restricted. Balance or the equilibrium or flow should be our objective, unless of course we are not trying to make more horsepower!

Example #1 (Oval track racing) Here, I have often observed that the most experienced drivers are those who are most likely to run a single pattern (equal on intake and exhaust duration) cam. Why? Because such cams always, I repeat always make more torque! These veterans have a more educated foot and greater experience in feathering the throttle in the corners. They can therefore, utilize the benefit of added torque, in the lower to mid RPM range, to their advantage.

Their counterparts, the younger drivers on the circuit, generally are not as experienced and may at times actually get "crossed up" in the corners especially with a lighter car or when they are learning the ropes. In their case, a longer exhaust duration is often the more appropriate choice. It will often help them to drive better, more "flat footed" if you will, without consequence. But please for the sake of accuracy, let us be truthful. The benefit comes from an actual bleeding off of low to mid range torque, which is always what happens when Exh. Duration is lengthened, not from any improvement. The improvement, (if any) would come because of an improvement in scavenging at the extreme upper end of the power curve and would usually be marginal at best. Yet the so-called "extra power" potential of a longer Exh. Duration cam is most often why they are touted - power most people are backing away from at the end of the strait away!

Example #2 (Drag Racing) At the drag strip it's a little different and I feel more honest. Here, racers have long enjoyed longer exhaust and longer durations across the board (If I may add specifically for the purpose of "killing" low-end torque) to keep the tires from too easily breaking lose. This has been successful and sometimes actually results in a slight increase in top end power - something you can actually use in drag racing since it is a full throttle endeavor through the lights. Keep in mind here though, it's quite possible that a longer duration cam overall would have done just as well or better. In other words if you needed that longer exhaust for top end, perhaps the intake could have benefited from such a lengthening as well.

One of my favorite expressions is how "The Drag Racing mentality has infiltrated the ranks of Oval Track". Many have crossed over and made the switch in the past 10-15 years and some have brought their preconceived notions about how to cam an engine with them. A few may actually read these concepts and if they do so will at least come away with a better understanding of what they are doing. On the other hand they also could find that this information might actually help their cars to run just a bit faster!

heres more to read
http://www.iskycams.com/degreeing.html

http://www.uucmotorwerks.com/html_produ ... uemyth.htm

http://www.circletrack.com/enginetech/c ... rline.html

http://www.carcraft.com/howto/ccrp_0509 ... rings.html

 

[grumpyvette]

EFI systems that are used at least occasionally at low rpms generally require sensor input to the CPU ( control computer), sensor input that reversion pulses, a good deal of overlap in the cam timing, produced in the intake ports.that tends to produce erratic low rpm data to be used, the wider LCA with a given durration the lower the overlap and the less the sensors are effected, now OBVIOUSLY once you reach a certain point it becomes rather hopeless and you need to compensate with software changes/tweaks but on a basically stock or mildly moddified cam timing the wider LCA tends to smooth out the idle and nullify the reversion pulses in the runners to some extent
on a carb, thats not nearly as critical, and you tend to get a faster responce and build torque a bit fast with the tighter LCA

heres that post
"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 106- 110 degrees on most carb engines and 112-114 degrees on EFI engines because I value a wider torque curve more than a few hp only close to peak rpm, and ther tends to be fewer low rpm tunning issues with efi vs carbs that way


http://www.compcams.com/Technical/TimingTutorial/

http://tru-442.tripod.com/camselect.htm

 

[grumpyvette]

what will the smaller lca do for me? i thought overlap was bad on low compression engines

READ THRU THESE CAREFULLY
http://www.compcams.com/Community/Artic ... 2026144213

http://www.popularhotrodding.com/tech/0 ... index.html

http://www.hotrod.com/techarticles/113_ ... index.html

http://www.circletrack.com/techarticles ... ation.html

viewtopic.php?f=52&t=1070

viewtopic.php?f=52&t=480

viewtopic.php?f=52&t=2782&p=7215&hilit=+overlap#p7215

viewtopic.php?f=52&t=90

viewtopic.php?f=52&t=2782&p=7433&hilit=+overlap#p7433
first EVERYTHINGS A COMPROMISE
the TIGHTER LCA means the valves close earlier than a cam with a similar durration but a wider lcc, so youll have more overlap but also more effective cylinder pressure in the area over the piston on the compression stroke

LOOK heres TWO cams IDENTICAL EXCEPT FOR THE LCA

tight LCA

http://www.cranecams.com/product/cart.p ... il&p=23968

wide LCA

http://www.cranecams.com/product/cart.p ... il&p=24424


heres a chart showing degrees of rotation and piston possition, as you can see the valve on the wider LCA closes 5 degrees later on the wider LCA and the piston can,t compress ANYTHING untill both valves are closed, the tighter lca alows the piston to compress almost a tenth of an inch more cylinder voluum, youll find the tighter lca makes more low and mid rpm power , and in many cases more peak power but has a slightly roughter idle and the power peaks faster in the rpm curve
were not thalking a huge change, maybe 7-8 hp/ft lbs but the tighter lca tends to lope more, idles roughter and be more responcive, keep in mind that if you had sellected a cam with 5-7 degrees more durration on the wider lca the overlap would be similar, but the effective compression would be even worse

http://www.iskycams.com/ART/techinfo/ncrank1.pdf


HERES A CHART
http://www.crower.com/misc/valve_timing_chart.html
LOOK UP YOUR CURRENT CAM, ITS PROBABLY GOT MORE DURRATION AND MORE OVERLAP, BOTH BAD for your low CPR COMBO

EVERYTHINGS A COMPROMISE......BUT KNOWING WHAT YOUR DOING HERE AND WHY, HELPS

read these

http://www.circletrack.com/techarticles/ctrp_0701_camshaft_design_science/overlap_duration.html