Building a blonde young beefcake wearing nothing but skimpy shorts named Rocky
#1022
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Is that fab9 someone you know or work with Bryan? I might end up ordering some engine internals from them. More than likely get the Supertech pistons. I like the price of those way more than the Wiesco ones.
#1023
I like the new setup your going with. I have heard some pretty good things about that spring setup. Still can't wait to see a video too. In the next couple months I'm planning on doing a built motor as well. A lot of inspiration has come from you. I just don't have the time to put one together. I've been looking at track speed engineering's motor. Heard or seen good things anyone? Or should I just do the same route you went?
#1031
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Lets say, just to keep it simple my valve is one square inch of surface. It has a factory seat pressure of lets say.. 45LBS return pressure. Then I boost my car to 24PSI. That means there is 24lbs per square inch fighting my valve springs. Leaving me with only 24lbs of seat pressure do do the same job it was supposed to do with 45lbs of seat pressure at 7000rpm... Valves can't close quickly enough so they start to float.
Also this dyno is seriously low. Locally known as the heartbreaker. I just watched a video of my car pulling on a Stage 3 Roush gutted and caged with a 575cal. When earlier that week my car made 310 on that dyno.
Last edited by miatauser123; 04-26-2013 at 02:43 AM.
#1033
It's not Magic. Think of it this way..
Lets say, just to keep it simple my valve is one square inch of surface. It has a factory seat pressure of lets say.. 45LBS return pressure. Then I boost my car to 24PSI. That means there is 24lbs per square inch fighting my valve springs. Leaving me with only 24lbs of seat pressure do do the same job it was supposed to do with 45lbs of seat pressure at 7000rpm... Valves can't close quickly enough so they start to float.
Lets say, just to keep it simple my valve is one square inch of surface. It has a factory seat pressure of lets say.. 45LBS return pressure. Then I boost my car to 24PSI. That means there is 24lbs per square inch fighting my valve springs. Leaving me with only 24lbs of seat pressure do do the same job it was supposed to do with 45lbs of seat pressure at 7000rpm... Valves can't close quickly enough so they start to float.
24psi is not fighting your 45psi springs.
Intake stroke - valve is open, pressure inside combustion chamber is same as pressure in intake manifold. Net pressure on valve = 0
Compression stroke - your engine has compression of 150+ psi. So pressure inside combustion chamber is several times higher than 24psi of boost in intake manifold
Power stroke - Pressure inside chamber is even higher than compression stroke
Exhaust stroke - this is about the only time when the pressure in intake manifold may exceed pressure in the combustion chamber. But the intake valve is not moving at that point, so no float can happen.
In my honest opinion, higher valve spring rates are only required for more aggressive cam/higher rev limiter. I run more boost on 7200rpm limiter. You run less boost on 7500rpm limiter. Your valves float, mine don't. I call bullshit on the "I need stiff springs for high boost" theory.
#1034
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I see what you're saying, but.
I think it's more a matter of the valve cant get it's *** closed fast enough.
Though, i bet what happened was just valve bounce. They were probably getting closed fast enough, but just didn't have enough pressure to keep them from bouncing on the seat.
I think it's more a matter of the valve cant get it's *** closed fast enough.
Though, i bet what happened was just valve bounce. They were probably getting closed fast enough, but just didn't have enough pressure to keep them from bouncing on the seat.
#1035
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You absolutely need stiffer springs for more boost pressure. The net pressure does not equal out because the valve is open. You can't just think of it as one pressurized system.
There is air velocity to consider and more importantly volumetric efficiency. There are very directional things happening. IT's literally 20psi blowing AT the back of the valve INTO the cylinder.
My example is not accurate above, it was just an example. You are correct that we must consider the pressure on both sides of the valve but more boost absolutely equates to an increase in seat pressure.
My example was based on the older theory that still hold some truth. Volumetric efficiency is the key to the equation..
If for example my engine is running 20psi and has a volumetric efficiency of 100% when the piston reaches the bottom of the intake stroke and the intake valve closes there will be 20psi on both sides of the valve surface. So 20 on the intake manifold side and 20 in the cylinder side. Since the air pressure is the same on both sides there is no additional force trying to keep the valve open.
But if the engine has a volumetric efficiency of only 50% there will be 20-psi pressure on the manifold side but only 10-psi on the cylinder side when the valve closes, because the cylinder did not completely fill, the pressure of 10-psi will be present across the valve head. If the intake valve has a surface area of 1 square inch a force of 10 pounds will be trying to open the valve thus reducing the valve spring pressure by 10 pounds.
Make sense? So basically what I've just realized is that I probably went a little overkill on my seat pressure.
There is air velocity to consider and more importantly volumetric efficiency. There are very directional things happening. IT's literally 20psi blowing AT the back of the valve INTO the cylinder.
My example is not accurate above, it was just an example. You are correct that we must consider the pressure on both sides of the valve but more boost absolutely equates to an increase in seat pressure.
My example was based on the older theory that still hold some truth. Volumetric efficiency is the key to the equation..
If for example my engine is running 20psi and has a volumetric efficiency of 100% when the piston reaches the bottom of the intake stroke and the intake valve closes there will be 20psi on both sides of the valve surface. So 20 on the intake manifold side and 20 in the cylinder side. Since the air pressure is the same on both sides there is no additional force trying to keep the valve open.
But if the engine has a volumetric efficiency of only 50% there will be 20-psi pressure on the manifold side but only 10-psi on the cylinder side when the valve closes, because the cylinder did not completely fill, the pressure of 10-psi will be present across the valve head. If the intake valve has a surface area of 1 square inch a force of 10 pounds will be trying to open the valve thus reducing the valve spring pressure by 10 pounds.
Make sense? So basically what I've just realized is that I probably went a little overkill on my seat pressure.
#1036
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No matter how you look at it, you have more RPMs and more pressure on the back of the intake valve than what the Mazda engineers designed it for. I agree with tighter springs as a preventative measure.