001mustang

my goal is minimum stress on push rod at max lift; PR tip far from fulcrum at max lift.

i also like max roller tip acceleration when valve starts to open; PR tip close to fulcrum.

does that sound reasonable?

i think my current RA pics match my goal; correct?

kalli

i also like max roller tip acceleration when valve starts to open
if i understand this right I'd say no according to the mid lift theory. that's where you want it.
and on another note, if you have qucikest accelleration on opening you have quickest decceleration on closing, which causes the valves to bang into their seats. not good either

001mustang

Valve slamming shut is not my concern due to relaxed ramp profile past 0.05" lift. Cam is designed to land valve easy.

Most severe ramp profile is near lobe peak. This is where valve changes direction and where problems occur. Lifters like to jump lobe past max lift like its a ski ramp. Stressed lifters like to wipe off the cam lobe peak if given half a chance.

If your geometry is set up w/ mid lift at advertised RA ratio then max lift will occur at geometry which offers less duration at max lift.

Geometry can effect life span of valve train as well as performance.

Problem I'm having is the magnum roller tips don't have a clear fulcrum center point.

I am interested in finding a good valve train geometry book or link.

kalli

there were fantastic articles at mid-lift.com. very detailed. I am convinced a year ago I read the whole lot, now it seems they charge for the info ...
I'll keep searching. Have a look there. I read a lot of good info there which made sense to me, but I don't have much experience.

001mustang

thanks.
i'll take a look.
i have a book which has a few statements that seem backwards to me.
have a procedure for calculating position based on valve tip to pushrod pivot.
seems to me it should be to rocker arm tip axle not valve tip?
when i study the drawing it seems wrong.

001mustang

leaning towards this geometry

kalli

based on what I have read in the past (this is a bit cloudy as some time ago and I cannot find the documents) is what you want to achieve is that exactly at that point you have half the cam lift, you have half the max valve opening. This should always be the case when you have the adjustment right. However let's say you take a shorter pushrod, the rocker will be sitting lower and therefore not sitting straight at midlift. the rocker will be at an angle. i believe that will cause exactly what you planned. the rocker will open "faster" at valve opening and "slower" at max lift. the reverse is true for pushrods being too long. I believe this midlift theory specifies that if you want reduced valve wear and increase power you should have the correct geometry for that including correctly sized pushrod.
Further, if there is let's say a ski-jump tendency, wouldn't that indicate poorly picked valve springs? i cannot imagine this happening with the correct spring pressure. and maybe here again it depends on where the quickest accelleration of lift is, which again I belive should be mid lift.

Sorry I can't be of any help here. Not an engine builder :-(

mr_velocity

I was at a wedding probably 10 years ago and sitting next to me at dinner was Danny Jesel. We talked an hour about rocker geometry, wish I remembered half of what he said. Next time I won't drink so much.

001mustang

most any cam, given enough rpm will cause ski jump effect.

after market cams w/ specified springs don't float the valves until well above specified operating range.

most likely...if you bought a matched cam spring set ...the springs will be stronger than required for cams operating range...leaving a few ponys on the table while reducing valve train life...still...better for the average joe than having undersized springs and floating valves...richy rich speed racer can seek springs which float valves just above rev limit.

if one is blessed w/ time they could measure lobe lift from 0.01" to max lift.
weigh lifters, PR, RA and calculate valve float speed.

i just ordered a jewelry scale and will weigh my lifters b4 installing...one rainy day i may calculate my valve float rpm...when i win the lotto i will install minimum tension springs.

67mustang302

Rocker geometry is primarily about valve/guide survival. You need the geometry correct so the side loading on the valve stem/guide is minimal. Otherwise if they wear too much, the valve doesn't seat squarely after a while and the head bends during seating, and you break the valve. Rocker geometry can and does have an effect on acceleration at the rocker tip, but it's relatively minimal and is secondary to valve train survival.

Valve acceleration etc is controlled through the cam lobe profile. Get a custom cam from a good grinder, they're designed to get off the seat fast, get up towards max lift fast, stay at/near max lift as long as they can, close fast, and then ease down onto the seat at the last moment to not bounce. All while maintaining a controllable valve train.