super charged valve spring pressure

[scott foxwell]

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...

That's not what Blair said, and I have more respect for him than I do anyone else here. I understand exactly what happens during overlap. It's semantics, but it's also true; nothing is being pulled. A pressure differential is created and high pressure moves to low pressure. Learning this and understanding it helped my understanding of the ICE in a lot of ways.
I'm really sorry so many of you are so thin skinned. Nothing I say is personal yet it sure seems to be taken that way. Lol...you think THAT doesn't get old?

[blykins]

Hey Leny, is this engine stroked?

[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

My exhaust valves weigh 148.7 the intake weigh 165.9 just like Jay's Thanks. Leny Mason

[Leny Mason]

Hey Leny, is this engine stroked?

it is 4.125 stroke  Leny Mason

[plovett]

I agree with Scott that "push" or "pull" is semantics.   Molecules move from higher pressure to lower pressure. It doesn't matter if you call it push or pull.  That's because the higher pressure molecules are closer together and hitting each other with more energy.   It's like a "break" in a pool game.  Molecules that are close together (before the break) are given energy from the cue ball then they move further apart and lose energy.  It's all about increasing entropy in the universe and our inevitable death and dissolution.   We can harness the process to go fast and have fun with our FE's , but we are all going to end up lying in the dirt in the end.  Sorry guys.   

JMO,

paulie

edit:  I didn't meant to leave inertia and kinetic energy out of the picture.  Some of you have mentioned it and it's a player, too.

[plovett]

Sorry again guys, but Inertia......it's analogous to our lives, too.    Inertia is like the decisions we made in the past.  We may realize that they weren't correct and we want to change them, but once we realize they weren't correct, it takes time to change them.  So we try, but it's too late.  physics doesn't let us change incorrect decisions.  The repercussions live with us and we can't go back and fix it.   Same thing with valve events.  There's one perfect set of events and we are not likely to get it right.  Really smart guys can get it close.   No, I'm not drunk or stoned.  Crawling back under my rock.

JMO,

paulie

[jayb]

Hey Leny, is this engine stroked?

it is 4.125 stroke  Leny Mason

Those are heavy valves, Leny.  The cam sounds like it is a copy of the stock cam, which has pretty gentle ramps, but you will need some spring to make those valves follow the lobes.  I think I'd be looking at spring pressures of around 220-240 on the seat, and about 500 open.

[My427stang]

I have an issue with this whole discussion prior to the shiny object of overlap and believe you need a little more closed spring pressure for a blower

- Pressure is acting on the closed valve, period, and that is pounds per square inch, normally atmospheric, but with 14 lbs of boost that's closer to 28 lbs per square inch pushing every direction, including down on the valve which is greater surface area than 1 square inch
- As the valve opens, the differential pushes the air in (same with naturally aspirated and of course a negative exhaust pulse also causes more of a depression causing even more movement)
- The charge continues to move through the valve events, if it equalized, before that, it would slow and likely drop fuel out of suspension, if nothing else it would just stop moving. 
- Even if you COULD time the valve to close at exactly pressure equilibrium, move the throttle and it would no longer be there, it would only be for a specific RPM, load and exhaust harmonic
- The issue is, the valve closes before compression builds to a significant amount, and why we need a slight increase in closed pressure, once the piston comes up, it isn't needed, compression is there, but not at the beginning of the event (this IS what DCR considers as the start of the stroke, now this is not a DCR discussion, but important to understand that you need a closed valve to make compression). 
- The increased closed pressure to prevent bounce, not sealing it shut during peak compression
- Now you could say  that the increased cylinder pressure due to the huffer offsets it, but a valve with 3 square inches of surface area, that would be 28 *3 or 64 lbs, and pre-combustion, I would expect cylinder pressures to be lower than that when the valve initially bounces
- Now, if you already have excess closed spring pressure, OK, but IMO, the minimum closed spring pressure for a blown engine is slightly higher than the closed spring pressure for the same naturally aspirated engine

I'll duck back out, but IMHO, add some closed pressure over an equally spec'd naturally aspirated combo

[plovett]

I remember one time I was having an oil consumption issue with my 428 FE.  It ended up that one of the locating pins we had in the intake manifold and heads was too close to the intake port and had broken through.  It acted like a straw, pulling oil in from the head to the intake port.  The crazy thing is it was just in one port, but the oil moved all over the place.  There was oil from this leak over in the other bank of the engine and the other side of the intake manifold.   This really opened my eyes to how crazy the flow in an intake manifold can be.  It's not a linear and smooth flow from the air cleaner, through the carburetor, and down through the intake ports.   There's a whole lot back and forth chaotic action going on.  I'm not sure, but I think adding boost may change things.  It may make it more chaotic or less, but I bet it changes things.  It'd be amazing if it changed nothing.

JMO,

paulie

[plovett]

I think everybody would agree that experience trumps theory every time.  If our experience (test data) doesn't match our theory, then the theory has to change, not the data.  That's assuming the data is good.  I'm guessing it is in this case.

JMO,

paulie

[Leny Mason]

Hey Leny, is this engine stroked?

it is 4.125 stroke  Leny Mason

Those are heavy valves, Leny.  The cam sounds like it is a copy of the stock cam, which has pretty gentle ramps, but you will need some spring to make those valves follow the lobes.  I think I'd be looking at spring pressures of around 220-240 on the seat, and about 500 open.

Thanks everyone, if my valves are to heavy should I find some lighter ones, if that spring pressure may cause other problems it's not the first time I got the wrong parts. Leny Mason

[jayb]

Those spring pressures shouldn't cause you any trouble.

[Leny Mason]

Thank that will save some money. Leny Mason

[scott foxwell]

I think everybody would agree that experience trumps theory every time.  If our experience (test data) doesn't match our theory, then the theory has to change, not the data.  That's assuming the data is good.  I'm guessing it is in this case.

JMO,

paulie

True, but Physics and math don't lie. If our "experience" doesn't match the math and physics, then we're not looking at the experience correctly and need to go back and re-evaluate. I've had to do this many times. Sometimes the changes we make aren't changing what we think they're changing.

[plovett]

So I wonder what we're missing.  Or did somebody say it already and I just missed it?

paulie