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2011-2014 Mustangs
Engine/Tuning
5.0 Coyote Valve Spring Upgrade: Brands, size, and price
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<blockquote data-quote="Shaun@AED" data-source="post: 13846705" data-attributes="member: 32381"><p>I'm going to try to keep this explination as simple as possible so everyone can follow it.</p><p></p><p>First off lets discuss what valve float is.</p><p>The simple answer is valve float is the roller follower losing contact with the camshaft lobe.</p><p>Valve Loft is the roller follow flying off the camshaft lobe at peak lift. Valve Loft is used in some racing where limits on camshaft lift and duratoin are impossed. Valve Loft typically requires asymetric lobe profiles with very aggressive opening ramps that throw the follower off the lobe at peak lift and softer closing profiles to 'catch' the follower without causing the follwer to bounce.</p><p>To be 100% clear, we will not achieve valve Loft in one of these Coyote / Roadrunner engines with the current line of off-shelf camshafts. Therefore this post will focus on valve float, which is the valve bouncing on the valve seat as seen in the video link I posted above.</p><p></p><p>When does valve float (bounce) happen? By definition it is when the valve closes.</p><p></p><p>Now that we are clear what valve float actually is and when it occurs, lets look at the contributing factors:</p><p>1. RPM</p><p>2. Aggressive cam lobe profiles</p><p>3. Low spring pressures</p><p>4. Pressure differnetials on valve</p><p></p><p>The biggest contributing factors will be RPM and camshaft lobe design coupled with spring pressure.</p><p></p><p>Lets talk about spring pressures for a moment. Why is seat pressure important? Because valve float is the valve bouncing on the seat, it is NOT the roller follower flying off the end of the camshaft lobe (loft). At peak lift spring pressues are MUCH higher and there is virtually no pressure differential across the face of the valve, so 'Boost' is irrelevent when it comes to Open Spring pressure.</p><p>Higher seat pressures are used to control the valve from bouncing on the seat.</p><p></p><p>Aggressive lobe profiles like CompCams XE series greatly contribute to valve float when coupled with RPM. I think we can all agree on this so I will not discuss it further.</p><p></p><p>Low spring pressure obviously contributes to valve float. As stated above in another post it is quite common for springs to lose 10% pressure during they normal useful life.</p><p></p><p>Pressure differentials across the valve (Boost).</p><p>To answer this appropriately we need to look at when valve float occurs. As stated above valve float is the physical bouncing of the valve on the seat when it closes. During the 4-cycle combustion process we have 2 valve closing events. Intake valve closing and exhaust valve closing.</p><p>Based on the valve events of a Typical boosted coyote at *X* RPM I will now plot the valve closing events.</p><p></p><p>Intake Cam timing at -20</p><p>Intake valve @ .050" on the closing ramp is at 44.5 degrees After bottom Dead center.</p><p>Intake Valve @ .004" (considered fully closed) happens at 69 degrees Ater bottom Dead center.</p><p></p><p>Exhaust Cam timing at 10</p><p>Exhaust valve @ .050" on the closing ramp is at 7.5 degrees Before Top Dead Center.</p><p>Exhaust Vavle @ .004" happens at 18.5 degrees After Top Dead Center.</p><p></p><p>Now that we know WHERE in the combustion cycle each valve will 'bounce', we can look at the pressure differential at these points to determine of if Boost will affect things.</p><p></p><p>Intake valve:</p><p>As the intake valve is closing the piston has already reached the bottom of the bore and is on it's way back up. The incoming airflow has been filling the cylinder (aided by boost) and at a certain point we need to close to valve to 'catch' all the incoming air before the piston starts to push the airflow back into the intake manifold.</p><p>By definition of the TiVCT OP talbes (optimum performance) the goal here is to optimize the intake valve closing event to trap as much of the aircharge in the cylinder as possible. This means we close the intake valve JUST before pressure in the cylinder exceeds pressure in the intake manifold. IE pressure differential across the intake valve is very little and therefore valve float on the intake side from 'boost' is not likely, even under very high boost conditions.</p><p></p><p>Exhaust valve:</p><p>As the exhaust valve is closing the piston is just passing the top of the cylinder bore (TDC). The intake valve has just opened and ideally the incoming intake aircharge pushes out the remaining exhaust (scavenging), and it does help having an exhaust system that pulls the intake aircharge into the cylinder as well. This is the case with both Super charged and All Motor setups, therefore 'boost' does not affect exhaust valve float on these applications.</p><p>Turbocharging on the other hand will have exhaust pressure before the turbine (exhaust side of the turbo). How much depends on the kit as a 'whole', but you MUST have exhaust backpressure and Heat in order to spin the exhaust turbine. Turbo's run on heat and pressure differentials. More pressure on one side of the turbine than the other. We are all clear on this yes?</p><p>Now, the question is does pressure in the exhaust before the turbine contribute to valve float? Given location of the piston moving down the bore as the exhaust valve closes the answer is YES. Even though the intake valve is opening and there is boost behind it, there is still a low pressure zone developing in the cylinder. The intake valve is not yet open enough to flow a significant amount of airflow to fill the cylinder, let alone match the pressure on the other side of the exhaust valve. This is where Boost affects valve spring pressure, and once again it does not occur at peak lift and therefore spring pressure at peak lift is irrelevant.</p><p></p><p>I hope this clears some things up for you guys.</p><p></p><p>-Shaun</p><p>AED</p></blockquote><p></p>
[QUOTE="Shaun@AED, post: 13846705, member: 32381"] I'm going to try to keep this explination as simple as possible so everyone can follow it. First off lets discuss what valve float is. The simple answer is valve float is the roller follower losing contact with the camshaft lobe. Valve Loft is the roller follow flying off the camshaft lobe at peak lift. Valve Loft is used in some racing where limits on camshaft lift and duratoin are impossed. Valve Loft typically requires asymetric lobe profiles with very aggressive opening ramps that throw the follower off the lobe at peak lift and softer closing profiles to 'catch' the follower without causing the follwer to bounce. To be 100% clear, we will not achieve valve Loft in one of these Coyote / Roadrunner engines with the current line of off-shelf camshafts. Therefore this post will focus on valve float, which is the valve bouncing on the valve seat as seen in the video link I posted above. When does valve float (bounce) happen? By definition it is when the valve closes. Now that we are clear what valve float actually is and when it occurs, lets look at the contributing factors: 1. RPM 2. Aggressive cam lobe profiles 3. Low spring pressures 4. Pressure differnetials on valve The biggest contributing factors will be RPM and camshaft lobe design coupled with spring pressure. Lets talk about spring pressures for a moment. Why is seat pressure important? Because valve float is the valve bouncing on the seat, it is NOT the roller follower flying off the end of the camshaft lobe (loft). At peak lift spring pressues are MUCH higher and there is virtually no pressure differential across the face of the valve, so 'Boost' is irrelevent when it comes to Open Spring pressure. Higher seat pressures are used to control the valve from bouncing on the seat. Aggressive lobe profiles like CompCams XE series greatly contribute to valve float when coupled with RPM. I think we can all agree on this so I will not discuss it further. Low spring pressure obviously contributes to valve float. As stated above in another post it is quite common for springs to lose 10% pressure during they normal useful life. Pressure differentials across the valve (Boost). To answer this appropriately we need to look at when valve float occurs. As stated above valve float is the physical bouncing of the valve on the seat when it closes. During the 4-cycle combustion process we have 2 valve closing events. Intake valve closing and exhaust valve closing. Based on the valve events of a Typical boosted coyote at *X* RPM I will now plot the valve closing events. Intake Cam timing at -20 Intake valve @ .050" on the closing ramp is at 44.5 degrees After bottom Dead center. Intake Valve @ .004" (considered fully closed) happens at 69 degrees Ater bottom Dead center. Exhaust Cam timing at 10 Exhaust valve @ .050" on the closing ramp is at 7.5 degrees Before Top Dead Center. Exhaust Vavle @ .004" happens at 18.5 degrees After Top Dead Center. Now that we know WHERE in the combustion cycle each valve will 'bounce', we can look at the pressure differential at these points to determine of if Boost will affect things. Intake valve: As the intake valve is closing the piston has already reached the bottom of the bore and is on it's way back up. The incoming airflow has been filling the cylinder (aided by boost) and at a certain point we need to close to valve to 'catch' all the incoming air before the piston starts to push the airflow back into the intake manifold. By definition of the TiVCT OP talbes (optimum performance) the goal here is to optimize the intake valve closing event to trap as much of the aircharge in the cylinder as possible. This means we close the intake valve JUST before pressure in the cylinder exceeds pressure in the intake manifold. IE pressure differential across the intake valve is very little and therefore valve float on the intake side from 'boost' is not likely, even under very high boost conditions. Exhaust valve: As the exhaust valve is closing the piston is just passing the top of the cylinder bore (TDC). The intake valve has just opened and ideally the incoming intake aircharge pushes out the remaining exhaust (scavenging), and it does help having an exhaust system that pulls the intake aircharge into the cylinder as well. This is the case with both Super charged and All Motor setups, therefore 'boost' does not affect exhaust valve float on these applications. Turbocharging on the other hand will have exhaust pressure before the turbine (exhaust side of the turbo). How much depends on the kit as a 'whole', but you MUST have exhaust backpressure and Heat in order to spin the exhaust turbine. Turbo's run on heat and pressure differentials. More pressure on one side of the turbine than the other. We are all clear on this yes? Now, the question is does pressure in the exhaust before the turbine contribute to valve float? Given location of the piston moving down the bore as the exhaust valve closes the answer is YES. Even though the intake valve is opening and there is boost behind it, there is still a low pressure zone developing in the cylinder. The intake valve is not yet open enough to flow a significant amount of airflow to fill the cylinder, let alone match the pressure on the other side of the exhaust valve. This is where Boost affects valve spring pressure, and once again it does not occur at peak lift and therefore spring pressure at peak lift is irrelevant. I hope this clears some things up for you guys. -Shaun AED [/QUOTE]
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5.0 Coyote Valve Spring Upgrade: Brands, size, and price
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