David Vizard wrote: ↑Tue Jun 11, 2019 3:40 pm
Many years ago the chief cam designer at Cosworth made a comment that has stuck with me since because it sums up a very basic truth. It went like this;- The valve train can never be any better than the valve spring will allow.
I tend to prioritize the valve spring so that the preloads and dynamic loads are minimized for the application intended.
All to often the recommended catalog springs are over the top. -- Your thoughts on this Mike!
DV
I dont agree with the bold portion of your statement.
It should read: The system can never accelerate the valve faster than the valve spring will allow!
If it is, it should be from poor cam selection, and not valve train inefficiencies.
We are limited by the valve spring, and should not be limited by the efficiency, or lack thereof, of rest of the system!
David Vizard wrote: ↑Tue Jun 11, 2019 3:40 pm
Many years ago the chief cam designer at Cosworth made a comment that has stuck with me since because it sums up a very basic truth. It went like this;- The valve train can never be any better than the valve spring will allow.
I tend to prioritize the valve spring so that the preloads and dynamic loads are minimized for the application intended.
All to often the recommended catalog springs are over the top. -- Your thoughts on this Mike!
DV
I dont agree with the bold portion of your statement.
It should read: The system can never accelerate the valve faster than the valve spring will allow!
If it is, it should be from poor cam selection, and not valve train inefficiencies.
We are limited by the valve spring, and should not be limited by the efficiency, or lack thereof, of rest of the system!
And since we are always looking to increase valve accelerations in under valved engines this:- The system can never accelerate the valve faster than the valve spring will allow! means 'you cannot have a valve train better than the spring will allow' - which is exactly what I said.
David Vizard Small Group Performance Seminars - held about every 2 months. My shop or yours. Contact for seminar deails - davidvizardseminar@gmail.com for details.
David Vizard wrote: ↑Tue Jun 11, 2019 3:40 pm
Many years ago the chief cam designer at Cosworth made a comment that has stuck with me since because it sums up a very basic truth. It went like this;- The valve train can never be any better than the valve spring will allow.
I tend to prioritize the valve spring so that the preloads and dynamic loads are minimized for the application intended.
All to often the recommended catalog springs are over the top. -- Your thoughts on this Mike!
DV
I dont agree with the bold portion of your statement.
It should read: The system can never accelerate the valve faster than the valve spring will allow!
If it is, it should be from poor cam selection, and not valve train inefficiencies.
We are limited by the valve spring, and should not be limited by the efficiency, or lack thereof, of rest of the system!
And since we are always looking to increase valve accelerations in under valved engines this:- The system can never accelerate the valve faster than the valve spring will allow! means 'you cannot have a valve train better than the spring will allow' - which is exactly what I said.
No, you want the ultimate valve train with zero compliance. It is the cams job the send the correct motion, and this acceleration limits.
Mike,
I know that UDHarold even on a full symmetrical cam lobe would use asymmetrical lash ramps to reduce seating velocity. Do you look at RPM range and seating velocity when designing your lash ramps?
I dont agree with the bold portion of your statement.
It should read: The system can never accelerate the valve faster than the valve spring will allow!
If it is, it should be from poor cam selection, and not valve train inefficiencies.
We are limited by the valve spring, and should not be limited by the efficiency, or lack thereof, of rest of the system!
And since we are always looking to increase valve accelerations in under valved engines this:- The system can never accelerate the valve faster than the valve spring will allow! means 'you cannot have a valve train better than the spring will allow' - which is exactly what I said.
No, you want the ultimate valve train with zero compliance. It is the cams job the send the correct motion, and this acceleration limits.
Warp,
It does not matter how good the valve train is it is not possible to outpace the springs capability.
Sorry, but I cannot agree with you here so we may as well politely agree to differ.
DV
David Vizard Small Group Performance Seminars - held about every 2 months. My shop or yours. Contact for seminar deails - davidvizardseminar@gmail.com for details.
Stan Weiss wrote: ↑Wed Jun 12, 2019 12:00 pm
Mike,
I know that UDHarold even on a full symmetrical cam lobe would use asymmetrical lash ramps to reduce seating velocity. Do you look at RPM range and seating velocity when designing your lash ramps?
No.
My lash ramps are based on the velocity of the first 1/4 degree beyond the opening lash ramp, and the last 1/4 degree before the closing lash ramp.
I look at RPM range when designing the lobe profile(before adding the ramps), because the lobe profile is what dictates the seating velocity.
slowing down the closing lash ramp, without changing the velocity/acceleration leading to the lash ramp, wouldn't reduce seat bounce.
And since we are always looking to increase valve accelerations in under valved engines this:- The system can never accelerate the valve faster than the valve spring will allow! means 'you cannot have a valve train better than the spring will allow' - which is exactly what I said.
No, you want the ultimate valve train with zero compliance. It is the cams job the send the correct motion, and this acceleration limits.
Warp,
It does not matter how good the valve train is it is not possible to outpace the springs capability.
Sorry, but I cannot agree with you here so we may as well politely agree to differ.
DV
No problem, but you are acting like the cam is part of the valve train, which it is not.
And since we are always looking to increase valve accelerations in under valved engines this:- The system can never accelerate the valve faster than the valve spring will allow! means 'you cannot have a valve train better than the spring will allow' - which is exactly what I said.
No, you want the ultimate valve train with zero compliance. It is the cams job the send the correct motion, and this acceleration limits.
Warp,
It does not matter how good the valve train is it is not possible to outpace the springs capability.
Sorry, but I cannot agree with you here so we may as well politely agree to differ.
DV
Maybe I should put this another way. As you say, you can't outpace the valve spring. But compliance in the system will change the acceleration of the cam design, and thus outpace the valve spring. Whenever there is flex, it will release at some point, causing undo acceleration that may have not been designed into the cam. To compound this, it rarely happens consistantly from cycle to cycle. Even in some mild applications, with the stiffest valve train, the valves rarely open when you think they are. The more we can limit this the better. IE, the valvetrain can't be "too good"!
No, you want the ultimate valve train with zero compliance. It is the cams job the send the correct motion, and this acceleration limits.
Warp,
It does not matter how good the valve train is it is not possible to outpace the springs capability.
Sorry, but I cannot agree with you here so we may as well politely agree to differ.
DV
Maybe I should put this another way. As you say, you can't outpace the valve spring. But compliance in the system will change the acceleration of the cam design, and thus outpace the valve spring. Whenever there is flex, it will release at some point, causing undo acceleration that may have not been designed into the cam. To compound this, it rarely happens consistantly from cycle to cycle. Even in some mild applications, with the stiffest valve train, the valves rarely open when you think they are. The more we can limit this the better. IE, the valvetrain can't be "too good"!
Warp,
I now realize you are not disagreeing with my original statement . 'The valve train is only as good as the valve spring' means exactly the same as 'you cannot outpace the valve spring' That was a simple straight forward statement on my part to put forward an important factor.
All the other stuff you are talking about is all good but off the point I was attempting to put over as simple as possible IE you can never have a valve train that outpaces the spring so at the end of the day spring selection is critical.
DV
David Vizard Small Group Performance Seminars - held about every 2 months. My shop or yours. Contact for seminar deails - davidvizardseminar@gmail.com for details.
Ok, but you really need to rephrase your saying. It is not the valvetrains fault if the spring is "overpaced", unless the valvetrains is insufficient in design. It is up to the cam design, the valvetrain is just relaying the message. You want the message, good or bad, to be delivered without fault or delay. Which goes back to my original statement to Walter......
If the message is a bad one, or one the spring will not handle, fix the recipient or the message. Dont band aid it with an absorber in the system.
That was my point all along.
Stan Weiss wrote: ↑Wed Jun 12, 2019 12:00 pm
Mike,
I know that UDHarold even on a full symmetrical cam lobe would use asymmetrical lash ramps to reduce seating velocity. Do you look at RPM range and seating velocity when designing your lash ramps?
No.
My lash ramps are based on the velocity of the first 1/4 degree beyond the opening lash ramp, and the last 1/4 degree before the closing lash ramp.
I look at RPM range when designing the lobe profile(before adding the ramps), because the lobe profile is what dictates the seating velocity.
slowing down the closing lash ramp, without changing the velocity/acceleration leading to the lash ramp, wouldn't reduce seat bounce.
Thanks Mike.
I just found a printout from a Comp Cams hydraulic flat tappet cam. This is from sometime ago and I not sure who the designer was. @ 0.050" there is .3 degrees offset. @ Advertised Duration (0.006") there is 1.8 degree offset.
Warp Speed wrote: ↑Wed Jun 12, 2019 1:27 pm
Ok, but you really need to rephrase your saying. It is not the valvetrains fault if the spring is "overpaced", unless the valvetrains is insufficient in design. It is up to the cam design, the valvetrain is just relaying the message. You want the message, good or bad, to be delivered without fault or delay. Which goes back to my original statement to Walter......
If the message is a bad one, or one the spring will not handle, fix the recipient or the message. Dont band aid it with an absorber in the system.
That was my point all along.
Exactly.
The job of the valvetrain is to do what the cam is telling it to do. If the valvetrian is doing what the cam is telling it to do, and that's causing problems, that's the fault of the cam design or the springs.
If the valvetrain is flexing all over the place, and not doing what the cam is telling it to do, and you have a problem, or are down on power, you have no idea if it's because of the cam design, the springs, or the faulty vavetrain.
Stan Weiss wrote: ↑Wed Jun 12, 2019 12:00 pm
Mike,
I know that UDHarold even on a full symmetrical cam lobe would use asymmetrical lash ramps to reduce seating velocity. Do you look at RPM range and seating velocity when designing your lash ramps?
No.
My lash ramps are based on the velocity of the first 1/4 degree beyond the opening lash ramp, and the last 1/4 degree before the closing lash ramp.
I look at RPM range when designing the lobe profile(before adding the ramps), because the lobe profile is what dictates the seating velocity.
slowing down the closing lash ramp, without changing the velocity/acceleration leading to the lash ramp, wouldn't reduce seat bounce.
Do you believe your cam designs are more stable and/or easier on the valve train than what you see with comparable-sized cams from your major competitors?
You are not saying anything I don't agree with but none of that was to do with what I was trying to put over. If the two of you are not getting my point here then my communication skills are in need of a big overhaul!
Let me try again but this time make it more complex!!!!
Let us assume we have a cam lobe with the best dynamics possible and is infinity stiff. In other words it closely approaches the perfect valve train.
Let us now put on the worlds worst valve spring i.e. zero seat preload, zero rate and zero over the nose force. Even though we have a 'perfect valve train' this combination won't even run 1 rpm let alone what we would typically need. At this point the rpm capability of the valve train is totally dependent on the valve spring chosen. So the rpm is totally dependent on the spring's characteristics. In other words the valve train as a whole 'can never be better than the spring it is equipped with' or, as you said Warp, the valve train cannot outpace the springs capabilities.
The points that both of you are putting forward are not in dispute. I was simply attempting to put forth a quick way to summarize the importance of the valve springs selected. i.e. just like the expression:- 'there is no substitute for cubic inches'.
Whether I have made my point or not can we change the subject??? (pleeeeease)
DV
David Vizard Small Group Performance Seminars - held about every 2 months. My shop or yours. Contact for seminar deails - davidvizardseminar@gmail.com for details.
