Stage II street car Timing chain or Gear drive

Let's look at when the intake valve opens. In a high performance situation, it will typically open before top dead center and as in my case while the exhaust valve is still closing. The overlap period. I can see how the intake pressure would make it easier for the cam lobe to overcome spring pressure to open the intake. Still, I can't see cylinder pressure being so low (vacuum) that it would help suck the valve open before the cam lobe would act to open the valve.

I'm thinking if the pressure on the intake side is 78.5 lbs. and a vacuum pulse in the cylinder is enough to assist the intake pressure to overcome the force of the valve spring... Well, I just don't think that is a problem.
 
I would think that port velocity and valve train weight also come into play. Maybe in a small way, maybe not?

Don, I think your right on with valve closing or opening being the issue. More pressure should = less bounce and more control. Excessive pressure is hard on parts.

Back to the original question, at what point is high spring pressure, along with high RPM, detrimental to timing chain life? At what point is a gear drive the way to go?
Somewhere there should be a shear strength # for the chain. Should be able to calculate pressures, rotational mass and such to see what absolute pressure is actually coming from the valve train.
 
d90dan said:
I would think that port velocity and valve train weight also come into play. Maybe in a small way, maybe not?

Don, I think your right on with valve closing or opening being the issue. More pressure should = less bounce and more control. Excessive pressure is hard on parts.

Back to the original question, at what point is high spring pressure, along with high RPM, detrimental to timing chain life? At what point is a gear drive the way to go?
Somewhere there should be a shear strength # for the chain. Should be able to calculate pressures, rotational mass and such to see what absolute pressure is actually coming from the valve train.
Click to expand...
Add to the picture the valvetrain reverse acceleration problem inherent with our V6s. At high spring pressures, that equals a quickly stretched timing chain.

As a timing chain stretches, the cam timing changes, possibly causing a person to chase their tuneup.

A gear drive never stretches.
 
I think some of you would be surprised how quickly a timing chain stretches in even a moderate street build application.
 
Otto J said:
You have a 2" intake valve(Lets say)
you know have 25PSI (Pounds per square inch) of boost boost pressure
25X2=50. You are now applying 50#s of pressure against the spring.
Hence 250# springs - 50#s against the valve = only a 200# spring.
This is my thought,what do you think?
Click to expand...


a 2 inch valve has 3.14 square inches in area, making the pressure on the valve head 78.5 #'s of pressure against the spring ( not 50#'s )

Remember in school; area of a circle = pie R squared ( 3.14 x 1 ) = 3.14 square inches on a 2 inch diameter valve. 3.14 x 25# = 78.5 ... a 57% increase over 50#

Hence a 250# spring minus 78.5 = a 171.5# spring.

The question still is, I guess; does this matter ?

George

OOOPS, I should have read all of the posts ... sorry Don/ Otto.
 
DonWG said:
An intake valve at rest on its seat with 78.5 lbs. of force trying to open it should stay closed with a valve spring of, let's say 100 lbs. seat pressure. I definitely don't see a problem when the valve is at rest on its seat. The assumed problem has to be while the valve is in motion off of its seat or when coming off or coming to be seated.
Click to expand...
ya your probably right,Im just thinking out loud.
 
oldtimer said:
a 2 inch valve has 3.14 square inches in area, making the pressure on the valve head 78.5 #'s of pressure against the spring ( not 50#'s )

Remember in school; area of a circle = pie R squared ( 3.14 x 1 ) = 3.14 square inches on a 2 inch diameter valve. 3.14 x 25# = 78.5 ... a 57% increase over 50#

Hence a 250# spring minus 78.5 = a 171.5# spring.

The question still is, I guess; does this matter ?

George

OOOPS, I should have read all of the posts ... sorry Don/ Otto.
Click to expand...
IM guessing not as this would mean that some cars have only 30#s or so of spring with my thought.
 
DonWG said:
No. You're right about that. But, it's not 9 to 10 square inches.
Area of a circle is, Pi x radius squared.
3.14 x 1 x 1 = 3.14 square inches of area for a 2" valve.

So 3.14 square inches of area x 25 psi = 78.5 lbs. of force.

The question still exists. With this extra force working on the intake side of the intake valve. Just where in the complete cylcle of the engine does this extra pressure cause the intake valve to be out of the control of the cam lobe?
Click to expand...

Theres a duh moment for ya'. I must have been more tired than I thought,
oops:eek: I was thinking though, I think your right about cylinder vacuum (refering to your later post), I can't remember the conversion from in.hg. to -
psi. but I think its somewhere around 1/5 psi equals 1in.hg. I don't see peak
cylinder vacuum being any more than .5 in.hg at WOT.


One more thought, just an interesting idea I had. @ 25psi of boost, the intake
valve is probably seeing both more and less boost at times, whats displayed on
a boost gauge/map sensor is an average of the pressure in the intake over a
short peirod. The map sensor or boost gauge is not sensitive enough to show
the fluctuations in the manifold (or even in each individual intake runner).
Kinda like engine vacuum in an N/A engine, the only way to see the pressure
fluctuations is to look at manifold vacuum with a pressure transducer and a lab scope, and when you do its more like a crappy signwave than a flat line. I'm rambling, I was just wondering what it would look like to graph boost
pressure with a scope and high quality transducer?:confused: Wonder how great the pulses would be? I'd like to see that....
 
As mentioned in previous post you are not taking into consideration the column of air moving towards that valve at 200 to 300 feet per second with the additional weight of the fuel in it. In your/my case Don with methanol there is 2 times as much weight. This air is trying to push the valve open!!
The spring must also overcome that inertia!! A stage 2 head at 30 psi will need more spring than a stock head because the port volume is so much bigger / thus a heavier column of air has more inertia. Think of opening/closing a door on a windy day!! Yes air can move matter.
I spoke with a Highly respected valve train expert that works with some of the worlds most exotic engines, he wanted all my valve train info/weights ,etc.
He said that at 8000 rpm with 40+ psi and .750 lift that I need 430# on the seat to totally control the valve train at the A/F ratio with methanol I would need to run. Mike:cool:
 
seat pressure is just the start of this,

... where does open pressure consideration enter
(since no one has mentioned this or did I miss it.)
When things get past design parameters is when problems start. Loose contact with a closing ramp and lookout.
Why are there only a few spring winders and so many company's marketing springs?
Rockwell (and a couple of others) makes springs for a lot of company's & everyone has their own idea of what makes a good spring.
Spring design is a cloak and dagger business.
Designers have patented or hidden everything from the wire formula and the processing it goes through to the winding procedures (beehive).. and the finish processes are endless.
Warren Johnson is the professor for good reason.
Manton, K-Motion, PSI, etc., the list seems endless, then add builders ideas (lapped seats to a mirror finish, x-ray, conversion processes, coatings, cryogenics, etc..
all of this to keep things in touch/control.
 
95' regal gs said:
Theres a duh moment for ya'. I must have been more tired than I thought,
oops:eek: I was thinking though, I think your right about cylinder vacuum (refering to your later post), I can't remember the conversion from in.hg. to -
psi. but I think its somewhere around 1/5 psi equals 1in.hg. I don't see peak
cylinder vacuum being any more than .5 in.hg at WOT.


One more thought, just an interesting idea I had. @ 25psi of boost, the intake
valve is probably seeing both more and less boost at times, whats displayed on
a boost gauge/map sensor is an average of the pressure in the intake over a
short peirod. The map sensor or boost gauge is not sensitive enough to show
the fluctuations in the manifold (or even in each individual intake runner).
Kinda like engine vacuum in an N/A engine, the only way to see the pressure
fluctuations is to look at manifold vacuum with a pressure transducer and a lab scope, and when you do its more like a crappy signwave than a flat line. I'm rambling, I was just wondering what it would look like to graph boost
pressure with a scope and high quality transducer?:confused: Wonder how great the pulses would be? I'd like to see that....
Click to expand...
In my particular case, if I remember right, it calculates to be as high as 5 or more psi worth of pressure during the + side pulse wave. :eek: That's on top of the average boost pressure.
 
BlownV6 said:
As mentioned in previous post you are not taking into consideration the column of air moving towards that valve at 200 to 300 feet per second with the additional weight of the fuel in it. In your/my case Don with methanol there is 2 times as much weight. This air is trying to push the valve open!!
The spring must also overcome that inertia!! A stage 2 head at 30 psi will need more spring than a stock head because the port volume is so much bigger / thus a heavier column of air has more inertia. Think of opening/closing a door on a windy day!! Yes air can move matter.
I spoke with a Highly respected valve train expert that works with some of the worlds most exotic engines, he wanted all my valve train info/weights ,etc.
He said that at 8000 rpm with 40+ psi and .750 lift that I need 430# on the seat to totally control the valve train at the A/F ratio with methanol I would need to run. Mike:cool:
Click to expand...

But Mike, don't forget that if the cam timing is setup for maximum effort, the flow will be in reversion at around the time of the intake valve closing. If the cam is perfectly timed, the flow will be stagnant at the point of the intake closing. That is the only way of packing as much mixture into the cylinder as possible. That, of course, would only occur within a very short rpm band.
 
GARY HARVEY said:
... where does open pressure consideration enter
(since no one has mentioned this or did I miss it.)
When things get past design parameters is when problems start. Loose contact with a closing ramp and lookout.
Why are there only a few spring winders and so many company's marketing springs?
Rockwell (and a couple of others) makes springs for a lot of company's & everyone has their own idea of what makes a good spring.
Spring design is a cloak and dagger business.
Designers have patented or hidden everything from the wire formula and the processing it goes through to the winding procedures (beehive).. and the finish processes are endless.
Warren Johnson is the professor for good reason.
Manton, K-Motion, PSI, etc., the list seems endless, then add builders ideas (lapped seats to a mirror finish, x-ray, conversion processes, coatings, cryogenics, etc..
all of this to keep things in touch/control.
Click to expand...
Valve toss is how I phrased it in an earlier post. I still have to believe that the assumed problem is occurring at the nose of the cam (toss, but can't see how) or at the closing of the intake valve (bounce). I'm leaning way towards the closing point, but I still can't picture how the intake pressure is affecting the situation. I understand that with a properly tuned cam, the flow should be reversing into the intake tract just at the point of the intake valve closing, so I can't see intake column momentum being the problem. I also understand that the cylinder pressure is also higher by the same amount as in the intake and the cylinder pressure will climb dramatically as soon as the intake valve has touched the seat, since the piston will be well on its way of moving upward at this point.
 
It would be great if someone in Redwood City knew the cam design guru living in that area and could get him to give up a few of his thoughts on this subject.
 
Just as bad as having too little spring pressure for a particular camshaft is having the spring go into harmonics. You could have enough pressure and just have a bad match of spring and camshaft, and still have problems.

The vids would be much more interesting if working pressures were actually going on too.
 
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