Heads Lifting and compression
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From: Coppell,TX
Heads Lifting and compression Is head lift directly related to cylinder pressure, or is it linked to something else?
If its cylinder pressure, anyone know about where the different types of head studs give out?
If its cylinder pressure, anyone know about where the different types of head studs give out?
Well today a customer of ours dynoed a 370 LS1 with standard ARP studs and AFR heads. The turbo used is our new S78. At 24-25 psi the coolant was starting to pressurize. Looks like our customer is going to the bigger studs.
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From: Loganville, GA
Originally Posted by JZ 97 SS 1500
Well today a customer of ours dynoed a 370 LS1 with standard ARP studs and AFR heads. The turbo used is our new S78. At 24-25 psi the coolant was starting to pressurize. Looks like our customer is going to the bigger studs.
How does the coolant start to pressurize and what do the (size of the) studs have to do with it? And how would you avoid the spikes in cylinder pressure? I would think it's pretty hard to avoid if you've got a turbo and there's no true way around it.
I have an idea to the answer on each question of mine, but they're probably not truly correct.
When you upgrade to larger studs, what happens and what else is needed? Also, I don't think I can figure out how detonation would lift a head (even though I know it does). What (mechanically/physically) happens to the head when you run into detonation? I know and understand detonation, but pretty much I only see it damaging pistons and every other part below it.
Sorry for being a such a rookie and thread hijacker, but I never grew up with the car knowledge some people did.. hopefully the answer to my post will further answer the thread starters question
Last edited by mahhddgtp; Jan 28, 2006 at 02:51 AM.
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In theory/practice, you spark a motor for peak cylinder pressure to occur ~10 ATDC for best torque. The amount of spark lead you need to achieve that is a function of charge temp, fuel octane, AF ratio, compression ratio, chamber design, etc etc....
The problem is, if you over spark, have a mixture than burns fast, etc, you increase cylinder pressure to quickly and reach peak pressure early. Now you might get lucky and this happens after TDC, not so bad. Since the piston is already on the way down.
The big problem is if you reach peak while the piston is still moving up. You have the cylinder pressure from combustion fighting the static compression force of the piston itself. As you compress the burning mixture is begins to burn even quicker. You now end up with uncontrolled combustion resulting it huge pressure spikes. This is often the audible sound you hear that we call detonation.
Now this is my crude understanding from hanging around the people that really know what's going on.
simple graph on page 2, reasonable read for those interested
The problem is, if you over spark, have a mixture than burns fast, etc, you increase cylinder pressure to quickly and reach peak pressure early. Now you might get lucky and this happens after TDC, not so bad. Since the piston is already on the way down.
The big problem is if you reach peak while the piston is still moving up. You have the cylinder pressure from combustion fighting the static compression force of the piston itself. As you compress the burning mixture is begins to burn even quicker. You now end up with uncontrolled combustion resulting it huge pressure spikes. This is often the audible sound you hear that we call detonation.
Now this is my crude understanding from hanging around the people that really know what's going on.
simple graph on page 2, reasonable read for those interested
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