I run a gear drive on my race engine. They do have to be set up properly or they will literally rattle themselves apart. They are also getting harder to come by for a Buick V6.
Stage II street car Timing chain or Gear drive
- Thread starter WIKEDV6
- Start date
I run a gear drive on my race engine. They do have to be set up properly or they will literally rattle themselves apart. They are also getting harder to come by for a Buick V6.
Just because you run a solid roller cam does not automatically mean that you need a 400lb spring on the seat. There are a lot of factors involved in choosing the correct spring. Valvetrain weight, anticipated rpm, cam lobe profile. The best source you have for choosing the correct spring will be your cam company. They are familiar with the lobe profile on your cam and already know what spring it's going to take to control the valvetrain with that lobe. If they don't know, time to pick a different cam company.
The size of the Turbo and the amount of boost you plan on running plays a HUGE roll in spring requirements.
Let's explore that. I never could understand why that is so.
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?
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?
(2" x 25 psi) I understand that but,...
[Here is where I imagine everyone shaking their head and saying to themselves, "Oh Lord, what is Don going to come up with now?"
The supposedly extra spring pressure is needed mainly to control the valve as you come to the nose of the cam to control toss, and as the valve comes to rest on the seat to control bounce. Any other time, any reasonable amount of spring pressure will keep the valve closed.
I'm trying to imagine this in my head. Why would boost pressure in the intake tract affect valve toss? As the valve is reaching max lift.
As the valve is seating with boost pressure on the intake side, isn't the cylinder pressure also raised to a higher level to balance out the pressure on the intake side?
[Here is where I imagine everyone shaking their head and saying to themselves, "Oh Lord, what is Don going to come up with now?"
The supposedly extra spring pressure is needed mainly to control the valve as you come to the nose of the cam to control toss, and as the valve comes to rest on the seat to control bounce. Any other time, any reasonable amount of spring pressure will keep the valve closed.
I'm trying to imagine this in my head. Why would boost pressure in the intake tract affect valve toss? As the valve is reaching max lift.
As the valve is seating with boost pressure on the intake side, isn't the cylinder pressure also raised to a higher level to balance out the pressure on the intake side?
There is no actual cylinder pressure until both valves are 100% closed,but there is always boost pressure coming in(underWOT)
is it possible is could slow down the valve closing?
Im not thinking it has a much play at full valve opening as valve closing.
is it possible is could slow down the valve closing?
Im not thinking it has a much play at full valve opening as valve closing.
If the cam is properly picked out for the application, flow should be on the verge of reversing or actually has reversed into the intake tract just as the valve is coming to the seat, so I have to imagine that cylinder pressure and intake tract pressure are very close to the same as the valve comes to a close. And as the intake valve closes, cylinder pressure is rising very quickly as the piston is well past bottom dead center and is compressing the charge.
Pick the right cam like Don said, I stepped down on cams and the car picked up huge just beware of cylinder pressures
95' regal gs
Member
- Joined
- Apr 17, 2008
I may be worong here but the actual force on a 2 inch valve @ 25psi would be a lot more than 50#. The surface area of a 2 inch diameter valve would be somewhere between 9.7 and 9.85 square inches, depending on valve stem diameter. So that would equal some 247# of force @ 25psi? I can never remember if its two-pie-r or pie-r-squared for surface area of a circle. Or mabey I've completly missed the point?
Otto, you need to elaborate on that. Loss of 50# of what?
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?
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.
