Old Crane

[Daves69]

Different ramps.

When the ramp is shallow it can hide allot of duration on both sides of the lobe..

Is it possible for the close ramp to "linger" open before the valve seating occurs in design? As in the lobe not ground symmetrical adding to duration? Does/would that make sense?

 

[rumblefish360]

Is it possible for the close ramp to "linger" open before the valve seating occurs in design? As in the lobe not ground symmetrical adding to duration? Does/would that make sense?

The closing ramp that closes the valve has a given rate as per lobe design. It doesn’t just drop the valve closed. It also doesn’t “Pause” or go super slow just before the valve contacts the seat.

Lobes can be ground symmetrical or non symmetrical. If it adds duration, it should be easily found in the specs or seen on a cam doctor measuring/tracking the lobe.
BUT....

From how I’m reading your question & description, the answer is No. That makes zero sense. It would not be seen anywhere.

There is no reason to slow the valve rate closing to add duration during this time in the events as the engine is running. It would lessen the dynamic compression and hurt the intake charge allowing it to escape through the exhaust valve even more so than what normally is going on.

Ideally, the quicker you can open and close the valve the more power you can make. The amount of overlap also has a play in this. This is a very tricky and build dependent thing. Not even close (as not in this universe close) to a one item or spec fits all. There are just to many variables to consider and contend with for the target goal.

You could generalize a certain something about a cam for a given parameter for a certain goal. Cam companies do this with there shelf cams. Are they the best for what could be done for a target of max power? Max mileage? Boost? No, but there a general cam cut to do what most people are looking to do and will do it well, not best.

One thing I have experienced with my manual trans is they really like a centerline if 108 or 106 for my street performance builds. It works better than the 110 a whole lot. Conversely, my auto trans cars like the 110, though with power brakes, I like the 112 center line or even the 114. This does give up a bunch down low. This is also why you see old school cams companies recommend what seems to be a high compression ratio for the given cam. It’s to help make up the lack of low end torque through cylinder pressure. About 3% in power per 1 point rise in ratio is about right for street, street/strip - street driven cars. This is a lot of torque down low. But impossible to make up.

Go through a old Crane catalog and note there suggested engine guide lines. You’ll find in addition to a raised compression, a higher gear ratio and/or torque converter than what you normally currently see.

 

[Daves69]

...….From how I’m reading your question & description, the answer is No. That makes zero sense. It would not be seen anywhere. There is no reason to slow the valve rate closing to add duration during this time...……………….

Got it.
Thanks again for you time and explanation!

 

[rumblefish360]

I was afraid I was getting a bit long winded.
Perhaps to much babbling....

 

[wyrmrider]

rumble
UDHarrold kept adding polydine curves to his designes
he may have had several between the closing profile and the clearance ramp
some of his early short designs only had 4 total symetrical