super charged valve spring pressure

[cjshaker]

I always thought the finger video wass showing the return pulse wave from the moving column of air hitting the closing valve, not reversion.

My bad for using the wrong terminology. Mr. Conley and Mr. Patrick did a better job of putting into words, what I was trying to get across. That's a LOT of momentum for a valve to stop. And like Brent said, since we typically don't like to over-pressure on springs, for obvious reasons of wear and stress, I think you reach that point of "not enough" fairly quickly.

[jayb]

One of the things that tends to muddie the waters when talking about SOHC valve spring pressure is that the original factory valves were really, really light, hollow stem and less than 100 grams each.  The factory spring pressure was about 110 on the seat and 300 over the nose, and with the big ramps on the factory cams the engines would go to 7500+ RPM with that package.  When I was running the Manley custom valves that I used as SOHC replacements, the intake weighed almost 150 grams, and the exhaust was about 145 if I recall correctly.  With an aggressive lobe from Comp I needed 240 on the seat and 600 over the nose to get to 7000 RPM; it needed more to go higher.  Bill has some of the spintron data on the testing he did for me, which is pretty impressive actually.

Ferrea makes a lighter weight valve, around 120 grams if I recall correctly, and they won't need as much spring pressure to go to 7500 RPM, something like 175 on the seat and 450 over the nose.  But those valves flow poorly compared to the Manleys, and cost a bunch of horsepower in a max effort application.

I think the springs Leny needs will depend on the cam profile, the weight of the valves, and how much boost he wants to run.  Leny, can you give us that information?

[Joe-JDC]

If you think of the boost as time instead of psi, then the amount of air/fuel goes in much quicker under boost.  On the SBF valves which are much lighter than FE valves, it is not uncommon to increase seat pressure 20-45# for boosted applications, as I stated earlier.  Experience over theory.  Joe-JDC

[Leny Mason]

cam # is LH C5AE-6A274-A RH C5AE-6250-C Dennis sent me the specs a while ago 22-40-58-4 @.100" cam lift, 328/328 Dur112 O/L Theoretical .565" lift at zero lash and 10 # boost  I will weigh the valves and let you know, thanks every one for the input some of it  way over my head. Leny Mason

[turbohunter]

thanks every one for the input some of it  way over my head. Leny Mason

Don't feel like the Lone Ranger Leny. But I must say I love stretching my little noggin like this.

[preaction]

cam # is LH C5AE-6A274-A RH C5AE-6250-C Dennis sent me the specs a while ago 22-40-58-4 @.100" cam lift, 328/328 Dur112 O/L Theoretical .565" lift at zero lash and 10 # boost  I will weigh the valves and let you know, thanks every one for the input some of it  way over my head. Leny Mason

Looks like the factory spec cam info.

[machoneman]

Nice explanation Jay on the unique nature of the Cammer.

I'm still amazed, even with light valves, big ramps, etc. that at only 110 lbs. closed/330 open, the engine would turn 7,500 rpm! Amazing considering it was a near "90 day wonder" as a replacement head design to the existing straight valve FE 427 block. What a replacement!

quote author=jayb link=topic=5679.msg61453#msg61453 date=1519750613]
One of the things that tends to muddie the waters when talking about SOHC valve spring pressure is that the original factory valves were really, really light, hollow stem and less than 100 grams each.  The factory spring pressure was about 110 on the seat and 300 over the nose, and with the big ramps on the factory cams the engines would go to 7500+ RPM with that package.  When I was running the Manley custom valves that I used as SOHC replacements, the intake weighed almost 150 grams, and the exhaust was about 145 if I recall correctly.  With an aggressive lobe from Comp I needed 240 on the seat and 600 over the nose to get to 7000 RPM; it needed more to go higher.  Bill has some of the spintron data on the testing he did for me, which is pretty impressive actually.

Ferrea makes a lighter weight valve, around 120 grams if I recall correctly, and they won't need as much spring pressure to go to 7500 RPM, something like 175 on the seat and 450 over the nose.  But those valves flow poorly compared to the Manleys, and cost a bunch of horsepower in a max effort application.

I think the springs Leny needs will depend on the cam profile, the weight of the valves, and how much boost he wants to run.  Leny, can you give us that information?
[/quote]

[Joe-JDC]

When the piston starts down on the intake stroke, it creates a vacuum, and with the reduced timing, and stuffing more air into the cylinder, it takes more seat pressure to keep the intake valve closed until the camshaft opens it.  Too much boost would slam the valve open too quickly and open up the clearance on the rocker arm to valve stem, causing a pushrod to be thrown.  Increasing the seat pressure assures the lifters open the valve in a controlled manner.  Joe-JDC

[scott foxwell]

When the piston starts down on the intake stroke, it creates a vacuum, and with the reduced timing, and stuffing more air into the cylinder, it takes more seat pressure to keep the intake valve closed until the camshaft opens it.  Too much boost would slam the valve open too quickly and open up the clearance on the rocker arm to valve stem, causing a pushrod to be thrown.  Increasing the seat pressure assures the lifters open the valve in a controlled manner.  Joe-JDC

Except for the fact that most intake valves start opening before the piston reaches TDC.

[CaptCobrajet]

I'm guessing that Mr. Joe Craine is aware of overlap, and the fact that the intake valve is opening before TDC.  He probably also knows that the exhaust port scavenges the system, and that after TDC, when the exhaust finishes closing, and the train is already moving, that the downstroke does pull on the intake port.  So, his statement that boost can nudge on the intake valve is 100% correct.  I like Jay's logic on valve area vs. boost pressure.  Seems like a good way to estimate the need.  I'd bump the number a little just to be safe.

[scott foxwell]

I'm guessing that Mr. Joe Craine is aware of overlap, and the fact that the intake valve is opening before TDC.  He probably also knows that the exhaust port scavenges the system, and that after TDC, when the exhaust finishes closing, and the train is already moving, that the downstroke does pull on the intake port.  So, his statement that boost can nudge on the intake valve is 100% correct.  I like Jay's logic on valve area vs. boost pressure.  Seems like a good way to estimate the need.  I'd bump the number a little just to be safe.

Not going to agree with that...not if the valve is open. And nothing "pulls" on the intake port, especially in a boosted app. If we're going to describe what's going on, lets at least be accurate about it. Atmospheric pressure, or boosted pressure does the work pushing the air from high to low pressure. Sorry...pet peeve of mine.

[CaptCobrajet]

Well, I was writing figuratively about a natural aspirated situation, and then adding boost.  If you don't think the exhaust port pulls a signal on the intake tract during overlap, there is just no point in my trying to convince you.  I don't know you from Adam's house cat, Mr. Foxwell, but I do know that you are fairly new on this forum, and you seem to have a way of attempting to argue with some pretty accomplished guys (absolutely excluding my dumb ass) here, on a regular basis.  I don't wish to argue with you, and I certainly don't care if you agree with anything I post, but there are some guys on here who know a heck of a lot about what they post, and I don't think you help yourself look smart by challenging some of those guys.  Just my opinion.

[Joe-JDC]

It is getting really old having every thing I add to this forum torn apart as if I didn't know what I am talking about.  I am tired of this.  I have a degree in Automotive, Aircraft Maintenance, and Business, and was an Automotive instructor for a Junior College and Master Instructor while serving in the USAF at retirement.  I don't have a habit of posting anything that is conjecture, but from experience.  I have been building and racing Fords since 1962, and bought my first new Ford in 1966.  I respect Jay and his forum members and have always tried to add in a positive way to the folks here, but I will not respond any more to anything you say, Scott.  Joe-JDC

[WConley]

Well, I was writing figuratively about a natural aspirated situation, and then adding boost.  If you don't think the exhaust port pulls a signal on the intake tract during overlap, there is just no point in my trying to convince you.  ...

Blair is absolutely correct.  During the overlap phase, the exhaust flow momentum will create a pressure differential that the intake port sees.  This is especially strong if you have a tuned exhaust primary tube.

Two-stroke engines wouldn't work very well if it wasn't for this...

[scott foxwell]

LOL...OK, Joe.