Valve Spring Pressure vs Boost

This is maybe going to sound like a weird dumb question, but here goes.......... Don't shoot me too hard!

There seems to be a lot of controversy over what intake valve spring pressures to run in the face of high boost pressures in the intake runner. Some say just run what the cam manufacturer recommends. Some say add spring rate, or else the valves won't be controlled proper. Some use a rough rule of thumb to add X pressure for Y boost, especially if taking an existing boosted engine from an old boost level to a new much higher boost level. Others say just try what 'ya got and see if it works, which seems a bit unscientific.

Seems to me like a confusing topic with fuzzy logic.

Anyone want to jump in with some thoughts?

Thanks.

 

Is fuzzy logic a useful tool in understanding the valve train design of an 11,000 RPM blown hemi ?

 

I don't know why it is used to rate the spring with a pressure while the spring creates a force. Then it should be rated with newton, kilos, pounds or what ever force unit.
From PSI to pound the conversion is one to one since the standard gouge used is a 1 inch square in area.

Anyway, going into the topic, I have no smart idea but I would say that you should estimate the force applied to the valve at a certain intake pressure and then compare it with the spring force.

Changing the intake pressure and left the rest the same I would keep constant the delta between valve and spring forces.

How much is the right amount of "delta" is the real question because I think it depends on valvetrain geometry, weight, RPM etc.
What also counts a lot in high RPM applications I think is the ringing of the valve (resonance)

 

Some think of this in a static port condition which is incorrect. There's a bunch more dynamics going on on both sides of the valve under boost and operating condition. Run the spring pressure the cam/valve train call for. It works.

 

Tested up to 42 psi boost and the boost had very minimal effect of spring pressure. Don't know above that boost..

 

Thanks guys, appreciate all the commentary. Let's put some bookmarks around this topic..........

So lets say you have a screw blown hemi that turns 10,000 rpm.

You put the whole wiggly mess on a Spintron machine, and it confirms that for the mass/inertia/mechanics involved, you need to have an intake valve spring with X spring force. A certain force on the seat, and an obligatory force full open. That's kind of calculable up front, and easy to test on the Spintron. It is also what the cam companies will do.

So lets say you then use the same hardware, but in an environment of 60 psig boost in the intake runner. Same spring pressure? More spring pressure? How much more spring pressure? I think RonC hit the nail on the head when he said it is all related to the "pressure differential" within the intake port, or across the valve head.

So lets say you then use the same hardware in a compound turbo application where the intake runner boost is 120 psig or more. Same spring pressure? More spring pressure? How much more spring pressure?

Seems to me to be a very confusing topic, but maybe I'm experiencing cognitive impairment from COVID at the moment?

If you think about the engine cycles, there must be brief periods where the pressure "differentials" across the heads of the valves are affecting the overall dynamics of the valvetrain assembly?

Is this affect significant, calculable, worth worrying about, or not relevant in the big scheme of things?

 

I persued this question a number of years ago and came to the conclusion that the dynamics going on on both sides of the valve pretty much equal themselves out. The old idea that you need to compensate for the boost pressure is mostly based around a static port condition. And if you do the calculations around that idea at fairly high boosts it comes up with a ridiculesly low spring seat pressure that you no for certain cannot work. I tell people concerned about it,.....add 10 psi of spring pressure if it makes you feel better. RPM....Valve Train.....and who actually designed the cam lobe profiles has infinitely more influence on spring pressure than blower boost,........in my opinion

 

I never mentioned Cam Card. And your right that the Cam Card does not take into account a bunch of operational conditions.