Camshaft design

[Stan Weiss]

Erland, it looks like your seating velocity is too high and the valve is beating the seat. You can see the big difference in velocity at the lash point between your two cams. What is the cam velocity at seating? Cam pro plus should even give you a seating velocity in Inchs/sec I believe.

Erland,
Does your software produce a report like this? While most do use inch/sec I happen to programed fps.

Stan

C:\Program_Files\Microsoft_Visual_Studio\VB98\CARFOR\cmm\COMP161.CMM
RA_Ratio_=_1.65___Lash_=_0.0000__RPM_=_7500__Smooth_=_NO

_______I_N_T_A_K_E
_______Valve_Lift________Velocity______Acceleration_______Jerk___________Velocity_fps
__1___0.00000000000
__2___0.00084448650___0.00042224325___0.00021112163___0.00010556081___1.58341218750
__3___0.00087986250___0.00001768800__-0.00020227763__-0.00020669963___0.06633000000
__4___0.00098648550___0.00005331150___0.00001781175___0.00011004469___0.19991812500
__5___0.00116928900___0.00009140175___0.00001904512___0.00000061669___0.34275656250
__6___0.00143172150___0.00013121625___0.00001990725___0.00000043106___0.49206093750
__7___0.00176563200___0.00016695525___0.00001786950__-0.00000101888___0.62608218750
__8___0.00216871050___0.00020153925___0.00001729200__-0.00000028875___0.75577218750
__9___0.00264952050___0.00024040500___0.00001943287___0.00000107044___0.90151875000
_10___0.00324802500___0.00029925225___0.00002942363___0.00000499538___1.12219593750
_11___0.00402484500___0.00038841000___0.00004457887___0.00000757762___1.45653750000
_12___0.00503066850___0.00050291175___0.00005725087___0.00000633600___1.88591906250
_13___0.00630118500___0.00063525825___0.00006617325___0.00000446119___2.38221843750
_14___0.00784494150___0.00077187825___0.00006831000___0.00000106837___2.89454343750
_15___0.00965037150___0.00090271500___0.00006541838__-0.00000144581___3.38518125000
_16___0.01171849800___0.00103406325___0.00006567412___0.00000012787___3.87773718750
_17___0.01409646150___0.00118898175___0.00007745925___0.00000589256___4.45868156250
_18___0.01683922350___0.00137138100___0.00009119963___0.00000687019___5.14267875000
_19___0.01998915600___0.00157496625___0.00010179262___0.00000529650___5.90612343750_______Cam_Calls_for_0.021"_hot _lash
_20___0.02358071100___0.00179577750___0.00011040563___0.00000430650___6.73416562500
_21___0.02760826200___0.00201377550___0.00010899900__-0.00000070331___7.55165812500

[Erland Cox]

I guess so.
I will try to get better aquainted with the program in the weekend.

Erland

[Stan Weiss]

Erland,
If the program you have does not produce a report with the valve speed information. I would be happy to do that for you. Just email me the lift data file(s), rocker arm ratio and what RPM to use.

Stan

[Erland Cox]

CA



CV



Erland

[Erland Cox]

Last weekend I got my engine together and retested with the new camshaft.
267-14,6mm i and 264-14mm ex versus 267-15,3mm in and 267 ´-14,6mm ex. both 105 degrees LCA.
Previous best was 251,6hp and 296Nm.
Now I got 255,7 hp and 299 Nm.
So now I have to figure out my next step.
I have a reversion problem just before 4000 rpm.
So I guess that the engine does not like more overlap.
Shortening the header makes the problem worse and making it longer takes it away but I lose top end hp.
I have a 105 degree LCA cam with 275-16mm in and 267-15,3mm out.
And I am thinking about trying to widen the lobe separation of the cam I have now to see what happens.
How much does 1 degree of lobe separation do?
Is there any difference with 1 dregree or I must use more?
I was thinking of trying 108 degrees LCA.
Duration at 0,050" on the valve. OHC bucket operation.

Erland

[Stan Weiss]

What is being talked about is the seating velocity of your valve. The charts you supplied show the lifter cam velocity. Since this is in metric unit I would say it is showing mm/deg. The seating velocity of the valve will change with RPM and in metric should be mm /second. Here is the math for 7500 RPM.

► 7500 RPM / 60 (Seconds per minute) = 125 - Crankshaft rotation's per Second

► 1 / 125 = 0.008 - Time for one crank Rotation

► 0.008 / 360 = 2.222222222222222E-005 - Time for one crank degree of Rotation

► 1 / (2.222222222222222E-005) = 45000 - How many units per second.

Velocity mm/deg * 45000 = Velocity / second @ 7500 RPM

Example using my above post

C:\Program_Files\Microsoft_Visual_Studio\VB98\CARFOR\cmm\COMP161.CMM
RA_Ratio_=_1.65___Lash_=_0.0000__RPM_=_7500__Smooth_=_NO

_______I_N_T_A_K_E
_______Valve_Lift________Velocity______Acceleration_______Jerk___________Velocity_fps
_19___0.01998915600___0.00157496625___0.00010179262___0.00000529650___5.90612343750_______Cam_Calls_for_0.021"_hot _lash
_20___0.02358071100___0.00179577750___0.00011040563___0.00000430650___6.73416562500
_21___0.02760826200___0.00201377550___0.00010899900__-0.00000070331___7.55165812500

► 0.00157496625 * 45000 / 12 (inches to Feet) = 5.9061234375

Stan