Camshaft Selection: What the catalog descriptions don't tell you.

Loves302Chevy

Loves302Chevy

"One test is worth a thousand expert opinions."
This post was prompted by Jimmy Duncan's post, Frank the Tank: http://garage.grumpysperformance.com/index.php?threads/building-a-s̶t̶r̶o̶n̶g̶-̶3̶5̶0̶-383-for-frank-the-tank….11173/page-26#post-61098

On page 17, as he is taking measurements of his 383 SBC short block to enter into the DCR calculator, he learns that with his 5cc EDV pistons and 64cc heads, his DCR will be too high. Fortunately, he hasn't bought his heads or camshaft yet.

Specifically, I'm looking to discuss in more detail:
  • advancing or retarding the camshaft to adjust your DCR
  • why do nearly all manufacturers grind their camshafts "dual-pattern" with more lift & duration on the exhaust side?
  • why most cams are ground 4 degrees advanced and under what conditions should we install 4 degrees retarded to "undo" this
  • when using the DCR, how do you use it with SOLID lifter camshafts?
  • CompCams THUMPER line of camshafts for more of that "rumpity-rump" sound
 
specifically, I'm looking to discuss in more detail:

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
800-615-ValveTimingIllustration-002.gif


camshaft_diagram.jpg

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

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


why not call the tech dept at all five cam manufacturers linked below, and get their input,
(without discussing or letting anyone at those individual tech departments,know you talked to other sources
.what any other cam manufacturer might have said in any way)
write down the cam specs they suggest, lift duration and lsa,

then average the results and
select the cam thats the closest match, to that average , of the 5 cams that were suggested.

crane (386)310-4875

crower 619.661.6477

erson 800-641-7920

lunati..662-892-1500

ISKY 323.770.0930

what your basically trying to do is to maximize operational compression,
over the useful rpm range
(this maximizes the torque curve efficiency,)
but, while keeping that cylinder pressure under the detonation threshold

related info
http://garage.grumpysperformance.com/index.php?threads/semi-fool-proof-cam-sellection.82/

http://garage.grumpysperformance.com/index.php?threads/how-to-read-a-cam-spec-card.1477/

http://garage.grumpysperformance.com/index.php?threads/the-mechanics-of-adv-ret-a-camshaft.4532/

http://garage.grumpysperformance.co...d-high-spring-pressures-don-t-work-well.1489/

http://garage.grumpysperformance.com/index.php?threads/valve-train-clearances-and-problems.528/

http://garage.grumpysperformance.co...e-springs-and-setting-up-the-valve-train.181/

http://garage.grumpysperformance.co...-the-charts-calculators-and-basic-math.10705/

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
  • when using the DCR, how do you use it with SOLID lifter camshafts?
????? not sure of the questions intent here???


  • CompCams THUMPER line of camshafts for more of that "rumpity-rump" sound
EVEN COMP CAMS ADMITS if pressed that they make cams in the other line designs that produce better average and peak power and torque, the THUMPR lines strictly for POSERS, and those more concerned with sounding like they have a radical engine vs having the best performance
 
Last edited:
Thanks Grumpy. Great answers and I've got some links to read.
  • when using the DCR, how do you use it with SOLID lifter camshafts?
????? not sure of the questions intent here???

I'll get back to you with this one, but I might find the answer in the links.
 
I don't think the Opening and closing ramps of a Solid Lifter cam will effect results of Calculated Dynamic Compression Ratio.
Just VE Will.
 
Loves302Chevy said:
  • when using the DCR, how do you use it with SOLID lifter camshafts?
????? not sure of the questions intent here???

I'll get back to you with this one, but I might find the answer in the links.
Click to expand...
Loves302Chevy said:
How might the valve lash for a SOLID lifter camshaft factor
into this problem with the DCR - or does it at all?
Click to expand...
I found this in one of Grumpys links:
The special case of solid lifter cams. Solid cams are usually spec'd at an arbitrary lift value (often .015" or .020") determined by the designer to be a good approximation of the cam's profile. This lift spec is not always correct for a particular cam. The correct lift point to determine the seat to seat timing of the cam is: Lash / rocker ratio + .004". This accounts for the lash. A cam with a .026" lash (given 1.5 rockers) should be measured at .02133" (.026/1.5+.004= .02133"). This cam lash, with seat timing spec'd at .020", is actually a bit smaller than advertised since the valve has yet to actually lift off the seat. How much is the question (.024" lash is the only lash that is correct at .020" with 1.5 rockers). Without knowing the ramp rate, and doing some calculations, or measuring with a degree wheel, it is impossible to know. Again, we have to use the mfg's numbers.
 
Last edited:
LOL Mike.

The Compression Cranking Test Don't Lie.
My Snap On Compression Tester Set Costed me $310.00 Cash.
 
The V/P index is OK.

I don't believe all engines have 100 % VE at cranking speeds as Mopar Victory Claims.
 
87vette81big said:
The V/P index is OK.

I don't believe all engines have 100 % VE at cranking speeds as Mopar Victory Claims.
Click to expand...
I read that. What they are saying is that at cranking, there are no restrictions to the air flow,
therefore 100% VE.
But when you start your engine, your carb is not blocked wide open as when you are doing a
compression test. So in that case, I have to agree with you.
 
Too many Dictations.....No concrete proof.
Too Compression tests done in the car.
No Compression tests done on the engine dyno.

It all ended real world proof after 2007-2008.'

Blah Blah Blah Blah....................No Racing Proof.
 
So if I attached a degree wheel to my crankshaft, and used the air adapter screwed into the
spark plug hole with maybe 15 psi, then I should be able to hear the difference when the intake
valve actually becomes closed, and read the number on the degree wheel. Correct?
 
Loves302Chevy said:
So if I attached a degree wheel to my crankshaft, and used the air adapter screwed into the
spark plug hole with maybe 15 psi, then I should be able to hear the difference when the intake
valve actually becomes closed, and read the number on the degree wheel. Correct?
Click to expand...

? Not following what you wish to accomplish Mike.'
Camshaft lobe spec checks are done with a Crankshaft mounted degree wheel & a dial indicator.'
You already know how to Degree in Camshafts.
 
Thinking about what you wrote...I suppose you could check with 15 psi air pressure.
 
Grumpy said:
  • CompCams THUMPER line of camshafts for more of that "rumpity-rump" sound
EVEN COMP CAMS ADMITS if pressed that they make cams in the other line designs that produce better average and peak power and torque, the THUMPR lines strictly for POSERS, and those more concerned with sounding like they have a radical engine vs having the best performance
Click to expand...
I'll bet that the people who use the THUMPR camshafts are the ones who, as kids,
made VROOM, VROOM sounds while playing with their toy cars.:D
 
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