Boosted cyl. pressure?
Unfortunately, most people who have actually tested realtime cylinder pressure put enough money into r&d on their race teams that they aren't about to give out the info. Kind of sucks for the rest of us, but it is understandable.
Force on the valve due to combustion pressure is fairly low by the time the exhaust valve starts to open. A 1000 HP N20 engine will typically see over 2000 psig 'peak' cylinder pressure at approx 15 degrees ATDC. By the time the exhaust valve starts to open your piston is closing on BDC and your cylinder pressure is falling fast~approx 10% or less of peak pressure. The resultant force at the valve is in the hundred(s) lb of range on a 1.6 dia valve, smaller than the peak lift force contribution with a stiff valve spring.
If you want to do a simulation, CSU's Engineering dept has some applets on-line that match up fairly close to re-world results. If you account for differences between NA and boosted; inlet temperature, ignition timing, cyl wall temp, burn time you can get a realistic cylinder pressure profile.
If you want to do a simulation, CSU's Engineering dept has some applets on-line that match up fairly close to re-world results. If you account for differences between NA and boosted; inlet temperature, ignition timing, cyl wall temp, burn time you can get a realistic cylinder pressure profile.
Originally Posted by Nmbr1GMfan
OK, so what if you have the biggest pushrods but it breaks the exh lifter @ 20psi and only 1400hp? we need anothr 10psi to complete this project. Has anyone actually heard of someone testing the cyl. pressure?
Originally Posted by ProdriveMS
I wonder if anyone is even looking at how harmonics play into the situation. If a pushrod and spring have their natural frequencies too close to each other, bad things happen when they both start to resonate at around the same rpm. From valve float, to broken parts, to an inexplicable power dip at a certain rpm. It's complicated because while you can get the natural frquency of a spring, many pushrod manufacturer's dont even know the natural frequency of the pushrods they're manufacturing. Experiments have been done by clamping a pushrod in a fixture with a transducer at the bottom and then striking the pushrod. The trace from the transducer then will give you the natural freqency. In some cases, a monster spring that barely survives isn't always the answer. If a harmonic exists, changing to a different pushrod might fix the problem and allow a milder spring.
Al
Al
