calculating overlap and lsa, or lca etc.

grumpyvette

Administrator
Staff member
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
........ you can,t select just a DURATION, LSA, or LIFT without making sure that clearances and the valve train geometry match, and the duration and lift will effect the cams operational power band, as will displacement, compression, head and intake flow rates and othe factors like the cars drive train gearing,
LSA (LOBE SEPERATION ANGLE) alone is NOT the main factor that causes problems its the combination of duration,lift,LSA and valve train acceleration
a good tuner can compensate for a great deal, and yes if your willing to make compensating changes in the sensors or the programing you can run the tighter LSA, but it WILL REQUIRE changes to run a tighter 110 LSA once the duration has increased to the point that it effects the sensor data feeding to the CPU, tighter LSA tends to increase OVERLAP and increase intake runner reversion pulse strength, but your compression ratio, displacement and exhaust scavenging efficiency also effect the sensor data
Isky claims that the Comp XE cams violate the 47.5% rule. The 47.5% rule applies to flat tappet cams for SBCs with 1.5 rockers but the concept is still the same for other configurations where the designs are "on the edge" or "over the edge" for lobe intensity. For 1.5 ratio SBCs, the duration at .050 must exceed 47.5% of the total valve lift or your asking valve train problems. For example, take a Comp Cams Magnum 280H, with 230 duration and, 480 lift...230/.480 = 47.9% which exceeds 47.5% therefore would not pose a threat to components. We do not regularly hear about the older, safer HE and Magnum designs rounding off lobes anywhere near as often as the XE cam designs. Unfortunately, some of the Comp Cams XE dual pattern lobes break this 47.5% rule on the intake side so they are likely to be problematic. The design has "steeper" ramps that are too quick for durability and reliability according to other cam manufacturers. They will wipe lobes in a heart beat especially if you have not followed the proper break-in procedure. Other designs are more forgiving during break-in and less likely to fail.
craneq2.gif

flatvsroller.jpg

FlatVsRollerChart.gif

Fig5LiftCurve_HydSolidRoller800.jpg

lsadig.jpg

camshafts_valve-overlap.jpg

52840207_534888543669820_3557515544351473664_n.jpg



camcomp.jpg

the chart above can be used as a rough guide to match cam duration at .050 lift and static compression in engines obviously other factors come into play so its only a rough guide
viewtopic.php?f=99&t=4458&p=12155#p12155

LSA is ground into the cam during manufactured, and can,t change,

LCA= LOBE CENTER ANGLE
LCA =(LOBE CENTER ANGLES)remember lobe center angles can be changed thru indexing the cam when degreeing it in,
http://69.20.53.62/faq_valvetrain.php

READ THESE







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

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

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

http://garage.grumpysperformance.com/index.php?threads/port-speeds-and-area.333/

http://victorylibrary.com/mopar/cam-tech-c.htm
0607phr_11_z+camshaft_basics+lobe_centerline_angle_determination_chart.jpg

FROM PAT KELLY
"There are a couple different ways to calculate the overlap of the cam.

1) The easiest way is to add the intake opening times to the exhaust closing time. Seat to seat times (advertised duration) must be used. .050" durations or timings will not give the correct overlap.

Example:
Comp Cams EX268H
Adv dur: int 268º, exh 280º
110 LSA, 106 ILC (4º advance)
Valve timing @ .006"
intake opens @ 28º BTDC
Intake closes @ 60º ABDC
Exhaust opens @ 76º BBDC
Exhaust closes @ 26º ATDC

In this example the overlap is 54º (28º+26º)


2) If the seat to seat opening and closing times are not known, the overlap can be calculated using the advertised duration and the Lobe Separation Angle (LSA). This formula works for both single and dual pattern cams.

Add the intake and exhaust adv durations
Divide the results by 4
Subtract the LSA
Multiply the results by 2

Using the example cam above:
268+280=548
548/4=137
137-110=27
27*2=54
The overlap is 54º


Here's another example:
Comp Cams XE294H
Adv Dur: int 294º, exh 306º
110 LSA, 106 ILC (4º advance)
Valve timing @ .006"
Int opens @ 41º BTDC
Int closes @ 73º ABDC
Exh opens @ 87º BBDC
Exh closes @ 39º ATDC

Adding the int open and exh close times (41+39) the overlap is 80º

Using the formula above:
294+306=600
600/4=150
150-110=40
40*2=80
The overlap is 80º


These are the valve timing overlap ranges that are most likely to work correctly (thanks to David Vizard for providing this):
trucks/good mileage towing 10-35 degs overlap
daily driven low rpm performance 30-55degs overlap
hot street performance 50-75 degs overlap
bracket/oval track racing 70-95degs overlap
dragster/comp eliminator engines 90-115 degs overlap
"



yes reading thru the links, AND SUB LINKS IS WELL WORTH THE TROUBLE,IF YOU WANT TO LEARN,It gives you a great deal more info

https://www.hotrod.com/articles/roller-rocker-ratio-test/

https://www.onallcylinders.com/2018...rease-horsepower-engine-masters-gets-answers/

https://www.hotrod.com/articles/hrdp-1305-rocker-arm-comparo/



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

viewtopic.php?f=52&t=1070

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

http://victorylibrary.com/mopar/cam-tech-c.htm

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

http://www.hotrod.com/techarticles/engi ... z2FeQk91VU

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

viewtopic.php?f=52&t=181

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

viewtopic.php?f=52&t=965

http://www.auto-ware.com/combust_bytes/camspecs.html

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

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

http://www.compcams.com/technical/Catal ... 07/5-7.pdf

http://www.streetracersonline.com/articles/camshafts/

http://victorylibrary.com/mopar/cam-tech-c.htm

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

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

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

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

http://www.projectlt10.com/content/modu ... .php?id=12

116_0403_basic_08_z.jpg


http://www.compcams.com/Technical/TimingTutorial/
800-615-ValveTimingIllustration-002.gif

116_0403_basic_10_z.jpg



this info posted By Mike Petralia may help

LSA and LC

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

The Lobe Separation 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.

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 Upâ€. 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."

LSA_01.jpg

LSAchart6.jpg

dcr.jpg


"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

110921.jpg

110921q.jpg

narrower LSA, more overlap & more effective compression, because the intake valve closes earlier
114681.jpg

114681q.jpg

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


(just enough links to make anyone insane, with calculating related factors)


reading piston burn patterns | Grumpys Performance Garage

http://www.wallaceracing.com/max-rpm2.php

http://www.wallaceracing.com/chokepoint-rpm.php

viewtopic.php?f=80&t=728

http://2.3liter.com/Calc2.htm#MinCross

http://www.wallaceracing.com/max-rpm.php

http://www.wallaceracing.com/header_length.php

viewtopic.php?f=52&t=727

http://www.dartheads.com/engine-calculators/

viewtopic.php?f=87&t=1285&p=2751&hilit=calculators#p2751

http://racingfeed.com/downloads/chevy_flow_data.pdf

http://www.swartzracingmanifolds.com/tech/index.htm

viewtopic.php?f=52&t=322

http://www.wallaceracing.com/ca-calc.php


http://www.wallaceracing.com/calcdchg.php

http://www.enginebuildermag.com/2016/02/theres-no-simple-formula-to-choosing-the-perfect-camshaft/

http://www.wallaceracing.com/area-under-curve.php

viewtopic.php?f=44&t=38

viewtopic.php?f=52&t=480

http://www.wallaceracing.com/curtain-area-calc.php

http://www.wallaceracing.com/calcafhp.php

http://www.wallaceracing.com/lpv.php

http://www.velocity-of-sound.com/veloci ... lator3.htm

viewtopic.php?f=44&t=3733


WATCH ALL THE VIDEOS

http://www.dartheadstv.com/featured_lan ... reset=true
 
Last edited by a moderator:

grumpyvette

Administrator
Staff member
Re: calculating overlap and lca etc.

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

0810chp_07_z+comp_cams_camshaft_technology_insite_tech+camshaft_valve_events.jpg

http://www.webcamshafts.com/pages/cam_glossary.htm...

ok first some facts, on piston to valve contact
the valves reach max lift at a time when the pistons not even neat TDC

heres a typical cam timing on a good hydraulic roller cam for a SBC that IVE used frequently




heres a cam timing chart

http://www.crower.com/valve-timing-chart


heres a crank rotation and piston angle chart
http://www.iskycams.com/ART/techinfo/ncrank1.pdf

simple math shows the intake valve reaches max lift near 118 degrees atdc
when the pistons about 3" down the bore
the exhaust reached max lift while the exhaust valve and piston were also reasonably far apart or almost 2.5" down the bore , valves tend to come closest to pistons at about 10- 20 degrees before or after TDC while not nearly at full lift and the duration and LSA of the cam had far more effect than max lift

you should also keep in mind that a roller cam valve train with the same lift and duration can provide a good deal more port flow and resulting power.

flatvsroller.jpg

FlatVsRollerChart.gif

http://www.race-cars.net/calculators/compression_calculator.html

http://www.projectpontiac.com/ppsite15/compression-ratio-calculator

http://www.wallaceracing.com/dynamic-cr.php

http://www.rbracing-rsr.com/comprAdvHD.htm

http://performancetrends.com/Compression_Ratio_Calculator_V2.3.htm

http://www.wallaceracing.com/cr_test2.php

http://www.pcengines.com.au/calculators/Calculate dynamic Comp Ratio.htm

http://www.csgnetwork.com/compcalc.html

http://www.diamondracing.net/tools/

https://www.uempistons.com/index.php?main_page=calculators&type=comp

https://www.rbracing-rsr.com/compstaticcalc.html
Theory behind valve overlap; since the intake valve is open slightly departing exhaust gas flow creates pressure differential (vacuum) that aids in pulling fresh air/fuel mixture into the cylinder without any of the intake charge passing into the exhaust system. The exiting exhaust gas at TDC that is replaced directly by the intake charge would exceed that which is normally drawn into the cylinder by piston travel alone. Think poor man’s turbocharger/supercharger.

Overlap trails only duration in its ability to produce power. Additional horsepower increases with the appropriate amount of overlap and can easily exceed output from a relatively identical camshaft with a wider lobe separation. Additional duration, increasing overlap by opening the intake valve earlier and closing the exhaust valve later, is commonly found on performance camshafts. Altering the intake valve opening point is typically the most dynamic modified cam timing event followed by exhaust valve closure. Exhaust valve closure is primarily used to regulate the amount of overlap.

As with almost anything engine performance related however, a trade-off exists. Adding overlap can result in poor idle quality (low vacuum), elevated emissions, and poor throttle response until RPM overcomes intake and exhaust reversion.

Increased overlap is beneficial at higher speeds and loads due to exhaust pressure waves drawing in the intake charge while both valves are open. As the piston travels from BDC pushing exhaust gases from the cylinder the intake valve begins to open before BTDC. Application dependent this process may start as early as 50°BTDC on a race application compared to a street vehicle which can be as late as 3° to 5° BTDC. Exhaust valve closure operates in a comparable range ATDC. Adding the intake BTDC to the exhaust ATDC closing events results in crankshaft degrees of overlap.

Typical overlap for a given application as follows; trucks/good mileage towing 10°-35°, daily driven low rpm performance 30°-55°, hot street performance 50°-75, bracket/oval track racing 70°-95°, dragster/comp eliminator engines 90°-115°. Large overlap at lower speeds results in poor emissions and idle quality as the mixture flows directly into the exhaust never burning. High overlap also results in an EGR effect that although beneficial for emissions at part load, reduces power under full load.
 

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grumpyvette

Administrator
Staff member
Re: calculating overlap and lca etc.

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


first EVERYTHINGS A COMPROMISE, in an engine build, the secret is making the correct choices, and you mean LSA not LCA
I use both these cams below (frequently, as they provide excellent hp/tq at low cost in a flat tappet solid lifter cam for SBCs) and let me point out some differances and simularities, both cams work best with about a 10.5-12:1 cpr,in a sbc of 350-406 displacement, both cams work with a 3.73-4.56:1 rear gear in a car that weights less than about 3400 lbs, if your running an auto transmission youll need a 3000rpm-3500rpm stall converter.
in a 350-406 thats set up correctly both cams can get you close to 475 -500 hp N/A if matched to the correct components.
both cams generally work best with a dual plane if the rear gears a 3.54-3.73:1 or you can use a crossram intake but the cams also work acceptably with a single plane if the rear gear is in the 4.11-4.56:1 range

the TIGHTER LSA means the valves close earlier than a cam with a similar duration but a wider lca, 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 LSA,the tighter LSA of the 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 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 110921 has more overlap and better scavaging in the mid rpm band, but it idles rougher at low rpms and that overlap doesn,t help if you use nitrous

tight LSA




wide LSA



heres a chart (BELOW) showing degrees of rotation and piston position, as you can see the valve on the wider LSA closes 5 degrees later on the wider LSA and the piston can,t compress ANYTHING until both valves are closed, the tighter LSA allows the piston to compress almost a tenth of an inch more cylinder volume, you'll find the tighter lca usually makes more low and mid rpm power , and in many cases more peak power but has a slightly rougher idle and the power peaks faster in the rpm curvewere not talking a huge change, maybe 7-8 hp/ft lbs but the tighter lca tends to lope more, idles rougher and be more responsive, keep in mind that if you had selected a cam with 5-7 degrees more duration 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/valve-timing-chart

LOOK UP YOUR CURRENT CAM, ITS PROBABLY GOT MORE DURATION AND MORE OVERLAP, BOTH BAD for your low CPR COMBO

EVERYTHING'S A COMPROMISE......BUT KNOWING WHAT YOUR DOING HERE AND WHY, HELPS

looking at these two diagrams may also help you visualize overlap
cambasics.jpg



800-615-ValveTimingIllustration-002.gif

you might also want to realize that many cam cards give you info at .050 lift figures but the valve don,t seat for about another 13 degrees of duration

.
116_0403_basic_10_z.jpg



read these links

http://www.babcox.com/editorial/ar/eb90252.htm

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

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

viewtopic.php?f=52&t=1070

viewtopic.php?f=52&t=965


CamTimingGear04.jpg

many guys don,t understand that on these multi key timing sets there areTHREE different letters,
on the crank gear and three matching keyway slots.

0 on the cam gear gets lined up with 0 on the crank gear, if the 0 crank key slot is used to index the cam at TDC

0 on the cam gear gets lined up with R on the crank gear, if the R crank key slot is used to index the cam at 4 degrees retarded from TDC

0 on the cam gear gets lined up with A on the crank gear, if the A crank key slot is used to index the cam at 4 degrees ADVANCED from TDC
 

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OK I gotta take this slow if I want to absorb it, calculating overlap with MY cam is throwing me a bit...

214/224 duration @ .050"
280/290 advertised
.443"/.465" gross valve lift
112 LC (lobe center)
INT opens @ -3 closes @ 6
EXH opens @ 47 closes @ -2

The timing values were given to me over the phone since I have misplaced my cam card, idiot.

Anyway if I add my Intake opening and Exhaust closing figures I get -5, which seems wrong somehow.

Gotta tackle this one before moving on it seems...
 

grumpyvette

Administrator
Staff member
http://www.crower.com/valve-timing-chart

if you just know a cams duration at .050 lift and the LSA the chart above will allow you to get the cams timing points within a degree or two

DON,T CONFUSE ADVERTISED DURATION WITH CAM TIMING AT .050 LIFT, you CAN,T MIX THE TWO IN CALCULATIONS, re- read the top of the thread,, pat kelly uses advertized duration not the cams timing numbers
images

your cam has
214/224 duration @ .050"

112 LC (lobe center)

so the intake timing is at intake opens -01 intake closes 35
so the exhaust timing is at
remember theres 180 degrees between tdc and bdc

TAPPET @.050
Lift: ....Opens....... Closes Duration
Intake (-1) ATDC 35 ABDC 214
Exhaust 48 BBDC (-4) BTDC 224

looking at these two diagrams may also help you visualize overlap
cambasics.jpg

800-615-ValveTimingIllustration-002.gif

you might also want to realize that many cam cards give you info at .050 lift figures but the valve don,t seat for about another 13 degrees of duration
valve seat and back face angles ,valve diameter and valve lift and duration effect the flow thru the curtain area

keep in mind that valve may be forced off its seat, too full lift and re-seating 50 plus TIMES A SECOND at near 5500 rpm, so theres very little TIME for gases to move through the very restrictive space between the valve seat and valve edge
vgd4.jpg

Calculating the valve curtain area
The following equation mathematically defines the available flow area for any given valve diameter and lift value:
Area = valve diameter x 0.98 x 3.14 x valve lift
Where 3.14 = pi (π)
For a typical 2.02-inch intake valve at .500-inch lift, it calculates as follows:
Area = 2.02 x 0.98 x 3.14 x 0.500 = 3.107 square inches

porting+valve_area.jpg


LiftCurveAread.gif


  • advancing or retarding the camshaft to adjust your DCR
  • compress_06.jpg
  • when you advance a cam what your doing is moving all the timing points in relation too, the crank rotation, so the valves open and CLOSE earlier, thus the intake valve seats trapping a bit more volume, of fuel/air mix thats going to be compressed as the piston rises toward TDC, remember nothings compressed to be ignited and burn, until both valves seal, as the piston rises on the compression stroke, this increases pressure and heat, boosting lower rpm torque.
  • retarding the valve seating and sealing by retarding the cam timing reduces the volume of gases being compressed at lower rpms but due to inertia and the exhaust scavenging at higher rpms this retarding the cam does not usually have nearly as much effect on upper rpm power due , that it has on the engine at lower rpms due too the lower trapped low speed volume being trapped and burnt, the inertia and scavinging by the exhaust header can actually increase the mass of trapped gases over the piston at a certain designed rpm range
volumetric.gif

exhaustpressure.jpg

EXFLOWZ4.jpg


pistonposition2a.jpg


http://garage.grumpysperformance.co...ng-cam-and-shifting-the-lca.10553/#post-44949

http://garage.grumpysperformance.com/index.php?threads/dynamic-vs-static-compression.727/#post-5575

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


reading piston burn patterns | Grumpys Performance Garage

http://garage.grumpysperformance.co...hanics-of-adv-ret-a-camshaft.4532/#post-12045
  • why do nearly all manufacturers grind their camshafts "dual-pattern" with more lift & duration on the exhaust side?
  • longer exhaust timing on a cam,allows greater time for the exhaust gases to bleed off,this compensates to some extent for a restrictive stock exhaust manifold and exhaust system, but its seldom required or useful with open tuned headers
http://garage.grumpysperformance.co...lsa-effects-your-compression-torque-dcr.1070/

http://garage.grumpysperformance.com/index.php?threads/is-backpressure-hurting-your-combo.495/

http://garage.grumpysperformance.co...-between-shorty-and-full-length-headers.1303/


  • why most cams are ground 4 degrees advanced and under what conditions should we install 4 degrees retarded to "undo" this
cam manufactures learned very quickly that some customers tended to be impressed with ADVERTISED DURATION AND LIFT, this commonly resulted in less informed customers (the vast majority) purchasing a larger and longer duration cam than the engine required, advancing the cam tended to add a little extra low speed drive-ability reducing the number of customer complaints when the larger than needed cam was installed
0607phr_11_z+camshaft_basics+lobe_centerline_angle_determination_chart.jpg

Duration_v_RPM-Range_wIntakeManifold01.jpg

craneq2.gif

camcomp.jpg

lclcomp.png


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

http://garage.grumpysperformance.com/index.php?threads/split-cam-and-cam-suggestion.12294/

http://garage.grumpysperformance.co...bit-of-extra-cam-lobe-exhaust-duration.11080/

http://garage.grumpysperformance.com/index.php?threads/cam-analysis-pointers-by-harvey-crane.10460/

http://garage.grumpysperformance.com/index.php?threads/lca-or-lsa.11523/#post-53156

http://garage.grumpysperformance.com/index.php?threads/cams-explained.324/#post-48613
 
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Very good link to chart from Crowler, things are starting to get clearer for me :)

According to their chart my valve timing would be:
INT opens @ -1 closes @ 35
EXH opens @ 48 closes @ -4

Following Pat Kelly's formula of adding the INT open value to the EX close value I still get -5... What am I missing here?
 

grumpyvette

Administrator
Staff member
crowers chart is a .050 lift from the seated valve cam timing
pat kellys formula is based on seat timing
while not exact you can add 13-15 degrees to the .050 lift timing to get approximate seat timing on each end of the cam lobe ramp, to get a rough guess as to when the cam places the valve close enough to the valve seat to make any flow, thru the port for figuring dynamic compression all but meaningless, keep in mind that even at idle speed the valves completing a, seat to full lift, to seat movement about 6-7 times a second
or use the advertised timing figures

EXAMPLE

heres my cam in my corvette, cam card





seat timing is at about (most exact valve timing)and what pat kelly uses in his calcs
@.004 lift
Lift: Opens Closes ADV Duration
Intake 35.0 BTDC 77.0 ABDC 292 °
Exhaust 83.0 BBDC 37.0 ATDC 300 °


m Timing: TAPPET @.050 (most useful to compare basic cam rpm and power range, between different manufacturers cams)
Lift: Opens Closes Max Lift Duration
Intake 8.0 BTDC 42.0 ABDC 107 230 °
Exhaust 56.0 BBDC 2.0 ATDC 117 238 °



Timing: TAPPET @.050 plus the rough guess 13-15 degree rule
(this is usefull only as a rough guess for dynamic compression calcs)
Lift: Opens Closes Max Lift Duration
Intake 22.0 BTDC 56.0 ABDC 107 258 °
Exhaust 70.0 BBDC 16.0 ATDC 117 266 °
 

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grumpyvette

Administrator
Staff member
FROM PAT KELLY
"There are a couple different ways to calculate the overlap of the cam.

1) The easiest way is to add the intake opening times to the exhaust closing time. Seat to seat times (advertised duration) must be used. .050" durations or timings will not give the correct overlap.

Example:
Comp Cams EX268H
Adv dur: int 268º, exh 280º
110 LSA, 106 ILC (4º advance)
Valve timing @ .006"
intake opens @ 28º BTDC
Intake closes @ 60º ABDC
Exhaust opens @ 76º BBDC
Exhaust closes @ 26º ATDC

In this example the overlap is 54º (28º+26º)


2) If the seat to seat opening and closing times are not known, the overlap can be calculated using the advertised duration and the Lobe Separation Angle (LSA). This formula works for both single and dual pattern cams.

Add the intake and exhaust adv durations
Divide the results by 4
Subtract the LSA
Multiply the results by 2

Using the example cam above:
268+280=548
548/4=137
137-110=27
27*2=54
The overlap is 54º


Here's another example:
Comp Cams XE294H
Adv Dur: int 294º, exh 306º
110 LSA, 106 ILC (4º advance)
Valve timing @ .006"
Int opens @ 41º BTDC
Int closes @ 73º ABDC
Exh opens @ 87º BBDC
Exh closes @ 39º ATDC

Adding the int open and exh close times (41+39) the overlap is 80º

Using the formula above:
294+306=600
600/4=150
150-110=40
40*2=80
The overlap is 80º


lets insert your cams timing figures
2) If the seat to seat opening and closing times are not known, the overlap can be calculated using the advertised duration and the Lobe Separation Angle (LSA). This formula works for both single and dual pattern cams.

Add the intake and exhaust adv durations
Divide the results by 4
Subtract the LSA
Multiply the results by 2

Using the example cam above:
268+280=548
548/4=137
137-110=27
27*2=54
The overlap is 54º


214/224 duration @ .050"
280/290 advertised
.443"/.465" gross valve lift
112 LC (lobe center)


your cams timing figures

280+290=570
570/4=142.5
142.5-112=30.5
30.5x2=61
degrees of overlap


These are the valve timing overlap ranges that are most likely to work correctly (thanks to David Vizard for providing this):
trucks/good mileage towing 10-35 degs overlap
daily driven low rpm performance 30-55degs overlap
hot street performance 50-75 degs overlap
bracket/oval track racing 70-95degs overlap
dragster/comp eliminator engines 90-115 degs overlap "

 
OK, back on this subject with conflicting info

Got your post and math on calculating the overlap with my cam, and can confirm 61 degrees using the overlap calc at Wallace Racing [http://www.wallaceracing.com/overlap-calc.php]

But if I use the Camshaft Lobe Center / Duration Calculator at RBR Racing http://www.rbracing-rsr.com/camshaft.html using the specs for my cam from Crower's valve timing chart http://www.crower.com/valve-timing-chart#112 I get the same -5 I originally came up with. Here is the result of the data entered:

Your 280/290 cam has an Overlap of -5.00 degrees and has in Intake Duration of 214.00 degrees. The Exhaust Duration is 224.00 degrees. The Inlet Cam has an Installed Centerline of 108.00 degrees ATDC. The exhaust cam has an Installed Centerline of 116.00 degrees BTDC.

Why the conflict in info using the same data?
 

grumpyvette

Administrator
Staff member
the crower charts timing is at .050 lift but dynamic cpr is seat to seat timing and the differences are the result in how the lobe ramps are measured or calculated to give the true seat to seat duration

bler57 POSTED THIS
" I just finished a cam swap from an old Lunati solid roller grind: 230/240 @ .050, 288/298 Adv., 108 Lobe sep, .569/.594 lift, to a new VooDoo solid roller; 243/249 @ .050, 273/279 Adv., 110 Lobe sep, .578/.585 lift. I thought I might lose some of the throttle response, idle quality, and vacuum signal of the smaller cam. However, I was rewarded with no change in throttle response, better idle quality, and 1.5" more vacuum at idle. Plus, enough extra power on the top end that I can feel it in the car. It pulls like a freight train from 4K all the way through 7k. Wow, what a difference!! And no perceptible loss on the bottom end either. This is one change that has all positive results. For those that are deciding on a cam that is street-able and will seriously get after it, I would highly recommend the VooDoo solid roller series. Now I need to get it back on a chassis dyno to see what the real difference is."


swapping from a flat tappet cam to a roller cam generally tends to increase the lifter lobe rates and reduce the slower required opening lobe ramp lift rates that kill off crisp throttle response, in some cases, that ofter comes as a surprise to those guys who have only used flat tappet design cams, because it tends to allow more airflow thru the ports between the valve lifting off its seat and re-seating without a significant part of the lift being consumed in basically not effective port flow rate sections of the valve movement



READ THRU THESE THREADS
http://www.idavette.net/hib/camcon.htm


viewtopic.php?f=52&t=2627
 

Grumpy

The Grumpy Grease Monkey mechanical engineer.
Staff member

 
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