Valve Spring Pressure vs Boost

Discussion in 'PSI Superchargers Tech Questions' started by TOL, Jul 2, 2020.

  1. TOL

    TOL Active Member

    Joined:
    May 18, 2005
    Messages:
    1,267
    Likes Received:
    15
    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.
     
    #1
  2. nitrowannabe

    nitrowannabe Member

    Joined:
    Oct 9, 2006
    Messages:
    414
    Likes Received:
    20
    Is fuzzy logic a useful tool in understanding the valve train design of an 11,000 RPM blown hemi ?
     
    #2
  3. rpt

    rpt New Member

    Joined:
    May 24, 2013
    Messages:
    20
    Likes Received:
    1
    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)
     
    #3
  4. Ron C

    Ron C Jr. Dragster

    Joined:
    Mar 4, 2005
    Messages:
    501
    Likes Received:
    1
    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.
     
    #4
  5. Mike Canter

    Mike Canter Top Dragster
    Staff Member

    Joined:
    Mar 10, 2004
    Messages:
    4,485
    Likes Received:
    153
    But that cam card does not take into account the boost pressure so it may not be what is required.
     
    #5
  6. Ron C

    Ron C Jr. Dragster

    Joined:
    Mar 4, 2005
    Messages:
    501
    Likes Received:
    1
    Tested up to 42 psi boost and the boost had very minimal effect of spring pressure. Don't know above that boost..
     
    #6
  7. TOL

    TOL Active Member

    Joined:
    May 18, 2005
    Messages:
    1,267
    Likes Received:
    15
    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?
     
    #7
    Ron C likes this.
  8. Ron C

    Ron C Jr. Dragster

    Joined:
    Mar 4, 2005
    Messages:
    501
    Likes Received:
    1
    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
     
    #8
  9. Ron C

    Ron C Jr. Dragster

    Joined:
    Mar 4, 2005
    Messages:
    501
    Likes Received:
    1
    I never mentioned Cam Card. And your right that the Cam Card does not take into account a bunch of operational conditions.
     
    #9
  10. Will Hanna

    Will Hanna We put the 'inside' in Top Alcohol
    Staff Member

    Joined:
    May 6, 2003
    Messages:
    6,661
    Likes Received:
    117
    From what I have seen with the developments in valve train technology over the years, the biggest reason why we run a lot of spring pressure in a hemi is trying to keep the lifter on the cam.

    I don't know if there is a hemi out there that is not experiencing some degree of loft at high rpm's. So you need the valve spring to get that lifter back on the cam on the ramp as quickly as possible. The loft/lifter situation gets way better as the cam gets bigger. I have seen 65 mm set ups very stable at very high rpm's. Most cars that have the 65 mm set ups are running seat pressure that you would throw away if you had that seat pressure on a 54 or 60 mm cam.

    As we have started paying attention to valve train, we also started watching the weight of the valve. Companies like Manley have produced hollow stem designs that have proven just as reliable as conventional stem. Titanium locks are another way to get rid of some weight. They aren't that much more expensive vs. a set of steel locks. There are a couple of trade offs with a light valve. Make it too much of a 'nail head' valve and it will be prone to tulip. Also there is a train of thought a bigger margin improves flow.
     
    #10

Share This Page