918 valve springs?
Thread Starter
Staging Lane
Joined: Feb 2014
Posts: 92
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From: Seguin Texas
918 valve springs? What brands make the 918 valve springs?
I looked on a forum talking about turbos and they were talking about going with 918 springs.
I'm building an all forged engine with ls6 or fast 92 intake with tb to match ls6 cam and going TT.
I looked on a forum talking about turbos and they were talking about going with 918 springs.
I'm building an all forged engine with ls6 or fast 92 intake with tb to match ls6 cam and going TT.
A turbo'ed engine may need a little more seat pressure than the 918's can provide. Remember, whatever PSI your intake tract sees is directly acting against the backside of the intake valve...
Really? Without any explanation? 
Better think again. A 2" diameter valve with 5/16" stem has an area of 3.06 sq in. Put 20# of boost on the backside of that valve and you can subtract ~ 61# from the seat pressure.
Better think again. A 2" diameter valve with 5/16" stem has an area of 3.06 sq in. Put 20# of boost on the backside of that valve and you can subtract ~ 61# from the seat pressure. Unless your valve train is not moving the pressure against the back of the valve has no significant force on the intake valve.
Now the exhaust valve is another story. That is where you will see the back pressure of the turbo system create most of it's havoc.
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In fluid dynamics, Bernoulli's principle states that for an inviscid flow, an increase in the speed of the fluid occurs simultaneously with a decrease in pressure or a decrease in the fluid's potential energy.
Unless your valve train is not moving the pressure against the back of the valve has no significant force on the intake valve.
Now the exhaust valve is another story. That is where you will see the back pressure of the turbo system create most of it's havoc.
Unless your valve train is not moving the pressure against the back of the valve has no significant force on the intake valve.
Now the exhaust valve is another story. That is where you will see the back pressure of the turbo system create most of it's havoc.
Not buying it on the intake though. Let's say you have a sealed port, the valves are on springs with 100# seat pressure. Now pressure up that port to 100# and see what happens. Think the valves will remain closed? I know they won't. I also know whatever pressure is in that port will act directly against the valve and it's associated spring regardless if it's stationary or moving. But how would I know, I only spent 35 years working with fluid dynamics in the oil industry...
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Agreed on the exhaust valves, you have as much as double the boost pressure in the exhaust tract. Trying to open a valve against that added pressure is a b!tch.
Not buying it on the intake though. Let's say you have a sealed port, the valves are on springs with 100# seat pressure. Now pressure up that port to 100# and see what happens. Think the valves will remain closed? I know they won't. I also know whatever pressure is in that port will act directly against the valve and it's associated spring regardless if it's stationary or moving. But how would I know, I only spent 35 years working with fluid dynamics in the oil industry...
Not buying it on the intake though. Let's say you have a sealed port, the valves are on springs with 100# seat pressure. Now pressure up that port to 100# and see what happens. Think the valves will remain closed? I know they won't. I also know whatever pressure is in that port will act directly against the valve and it's associated spring regardless if it's stationary or moving. But how would I know, I only spent 35 years working with fluid dynamics in the oil industry...
Agreed on the exhaust valves, you have as much as double the boost pressure in the exhaust tract. Trying to open a valve against that added pressure is a b!tch.
Not buying it on the intake though. Let's say you have a sealed port, the valves are on springs with 100# seat pressure. Now pressure up that port to 100# and see what happens. Think the valves will remain closed? I know they won't. I also know whatever pressure is in that port will act directly against the valve and it's associated spring regardless if it's stationary or moving. But how would I know, I only spent 35 years working with fluid dynamics in the oil industry...
Not buying it on the intake though. Let's say you have a sealed port, the valves are on springs with 100# seat pressure. Now pressure up that port to 100# and see what happens. Think the valves will remain closed? I know they won't. I also know whatever pressure is in that port will act directly against the valve and it's associated spring regardless if it's stationary or moving. But how would I know, I only spent 35 years working with fluid dynamics in the oil industry...
Like I mentioned if you never opened the intake valve it would be an issue. Since we do open it things change. As you are aware, while the valve is open we do not have much pressure at all exerting on the back side of the valve. Now when the valve is closing we are starting to see a pressure increase. Now how fast is this increase compared to the opening and closing events? Not sure but I do know the testing we did on a spintron showed very little on a 2.550" valve.
Now we add in the movement of the piston things change more. The intake valve closes at the same time the piston is on its upstroke. We all know the piston speed is much faster than the valve speed. So we now have combustion chamber pressure starting to exceed manifold pressure by folds.
So my point of it doesn't really matter is very true (on most applications). The few scenarios where I have found this to be an issue is extremely high boost gasoline (well over 25 lbs) and diesel trucks (well over 70 lbs).
Also are you stating that burnellis principle is wrong?
Thread Starter
Staging Lane
Joined: Feb 2014
Posts: 92
Likes: 0
From: Seguin Texas
I'm going to rum 8 psi boost and read on other forum that the guys doing this were running 918 springs. Saw nothing about what valves they were running though
Like I mentioned if you never opened the intake valve it would be an issue. Since we do open it things change. As you are aware, while the valve is open we do not have much pressure at all exerting on the back side of the valve. Now when the valve is closing we are starting to see a pressure increase. Now how fast is this increase compared to the opening and closing events? Not sure but I do know the testing we did on a spintron showed very little on a 2.550" valve.
Now we add in the movement of the piston things change more. The intake valve closes at the same time the piston is on its upstroke. We all know the piston speed is much faster than the valve speed. So we now have combustion chamber pressure starting to exceed manifold pressure by folds.
So my point of it doesn't really matter is very true (on most applications). The few scenarios where I have found this to be an issue is extremely high boost gasoline (well over 25 lbs) and diesel trucks (well over 70 lbs).
Also are you stating that burnellis principle is wrong?
Now we add in the movement of the piston things change more. The intake valve closes at the same time the piston is on its upstroke. We all know the piston speed is much faster than the valve speed. So we now have combustion chamber pressure starting to exceed manifold pressure by folds.
So my point of it doesn't really matter is very true (on most applications). The few scenarios where I have found this to be an issue is extremely high boost gasoline (well over 25 lbs) and diesel trucks (well over 70 lbs).
Also are you stating that burnellis principle is wrong?
Thread Starter
Staging Lane
Joined: Feb 2014
Posts: 92
Likes: 0
From: Seguin Texas
Actually, its "Bernoulli". I fail to see where any of his principle is directly involved in this situation. And you contradicted yourself right before you alluded to his (misspelled) principle by admitting there are circumstances that you "found to be an issue" when we were all unaware of the OP's intended boost level. I'm through...
