Captain Obvious

So is the damper intended to reduce changes in pressure in the positive, or negative direction, or both? In other words, suppose your fuel rail is supposed to be at 30 psi... Is the damper supposed to provide some temporary volume to swamp out pulses above 30 psi, or supply a transient supply of fuel in the event that the fuel pressure drops below 30 psi? Or both? I've never thought about it that intently before. You got any idea? I mean, who knows what's happening at speed. You got the injectors are opening and closing. They open and fuel goes out, so physics dictates that the pressure must drop. And then they snap shut, probably momentum hammering the fuel rail and sending a very high spike back through the line. And then you have the fact that the pump output is probably not be a perfectly steady pressure either. So what's your take on the damper?

I'm guilty as charged, and I apologize. I would like to be the first to admit that I've offered nothing to help with your original question. I found the topic interesting and got sucked in with the intent of defending the laws of physics. And just when I thought I would be able to resist, something like this happens... Uhhh... No. There exists a temperature (shown on the phase diagram I linked to earlier as Tcr) called the "critical temperature". The critical temperature of a substance is the temperature at and above which vapor of that substance cannot be liquefied, no matter how much pressure is applied. In other words, above Tcr, there can be vapor only. No liquid, and certainly no solid. (Haha! Ignoring superheating, of course.) I'm really trying to give up the physics. Really!! As a matter of fact, thermo was my worst class ever. I absolutely hated it.

Please forgive me for not knowing the intricate details of the Z's FI system, but... You made mention earlier of the batch type injection concept where that all the injectors open at the same time for the same duration. Is that what the 280Z uses?

Nice description of the gradient path, and I'm with you. Assuming the temperature is high enough, somewhere between fuel pump and the intake valve end of the pintle the gasoline will cross the phase change line from liquid to gaseous. Still not sure exactly where, but it seems from yours and others experiences that it's in a place that affects performance for the first few minutes of operation. I'm buying it. My only point of contention is that I'm still not seeing the "superheated" part and we are really running the risk of wandering off into the weeds with this part of the discussion so I will try once and then let it go. I believe the use of the term on the geyser page is a misnomer as well. I know you had to pass thermo, right? Just because you have a hot liquid under pressure does not "superheated" make. That just means you have a hot liquid under pressure. With all imperfections in the rock surfaces and turbulence in the water, I can tell you that there's no superheating in a geyser. It's too unstable for that. You can change phase and flip back and forth across the liquid/gas phase line all day by varying temp or pressure as your theory suggests without ever becoming "superheated". In order for a liquid to be superheated, it has to incorrectly exist in liquid form when conditions place it in the gaseous area of the phase diagram. In other words, your substance is at a temperature and pressure that SHOULD result in a gas, but you are incorrectly a liquid instead. Ask yourself the question "What is keeping it in liquid phase?" If the answer is "Pressure.", then you're not superheated. If the answer is "Uhhhhh... I don't know. It really SHOULD be a gas but it's not!!", then you're superheated. Does that make sense?

You think you're boiling fuel even with a 30 psi rail? So where exactly is it that you think the fuel boils? And do you think it's boiling a little at a time on each injector pulse and blowing only vapor into the manifold, or do you think it's sustained and bubbling back into the rail as FastWoman described? One thing that's completely clear from all of this discussion is that with my carbureted Z, I'm simply screwed... And not that it really matters, but I'm still unclear on why you're bringing the concept of superheating into this... You really don't even need it to support the beliefs under discussion. But in any event, it doesn't detract, it's just probably unnecessary.

STP has nothing to do with this. It's all about vapor pressure at elevated temps. You're nowhere near STP. Also, your use of the term "superheated" has become is a little confusing to me, so it might be prudent to make sure we're talking the same thing... What's your understanding of "superheated"?

Yeah, You're right. I probably should have said "the upper limit on vapor pressure is supposed to be tightly controlled" Research indicates that the intention of the gov't is to reduce the amount of fuel evaporation into the atmosphere as much as possible while still allowing the fuel to work well in application. The way they do this is to dictate an upper limit on the vapor pressure for different locations at different times of the year. How the manufacturers achieve that vapor pressure limit seems to be mostly up to them, including the composition and ethanol content of the fuel. My research turned up two things that always seem to be true: 1) Winter fuel (RFG) is allowed to have a higher vapor pressure than summer fuel, and... 2) California requires a lower vapor pressure than most other states. Of course they are. You remember the difference between "suspensions" and "solutions", don't you? And you mentioned the concept of superheat earlier and I forgot to ask... Why do you think the fuel in the injectors is superheated? Seems difficult to achieve. Have we strayed far enough from the OP's question yet?

I did a little digging into the vapor pressure of gasoline and learned that the petroleum industry and US government have standardized on the "Reid Vapor Pressure (RVP)" test. It specifies a test temperature of 100C and measures the resultant vapor pressure in psi. The vapor pressure is constrained by government regulations and is tightly controlled by industry. The limits change by location and time of year, but from what I found, the vapor pressure of your typical pump gas (at the RVP test temperature of 100 degrees C) is between 5 psi and 11 psi depending on where you live and what season it is. Vapor pressure will decrease as temp goes down and go higher as the temp increases. So how hot do the fuel get and what pressure is it under? Being as how I'm not an ME, it's probably not a good idea to wade into the middle between two of them, but I've never been very bright...:tapemouth

jaltman, Just sent you a PM RE the 73 airbox. Captain

I'm unclear how worn carb parts could increase the oil consumption. The damper oil is nowhere near the venturi and it seems that any worn parts should only make the situation better, not worse. That's more like what I'm thinking... The only way (you should be able) to get oil out of the plunger tube would be to pull it up and out the top. Maybe the plunger check valve disk is in backwards or something? desertmonkey, Did you ever disassemble the brass pieces off the stalk?

That's weird... There isn't supposed to be any way for the damper oil to drain out of the suction piston. Does it go alll the way empty if you don't refill it? Or does it reach a point and level off and stop dropping?

PM back achoo.

Rob, Wow... Talk about coincidence... I've got one that I was going to scrap because the casting is all eaten away and corroded under the EGR valve. If you're positive that you'll never actually want to use it on a car, it's perfect for practice. It's probably off a 77 if that matters. Yours for $1 plus shipping if you want it. PM me offline if you're interested.

Thanks Blue! :beer:That's some great info there. Answered my question, and a few others that I had not even asked (yet)!

Blue, I assume the outer is the one on the left? Does the inner have a seal on the other (hidden) side as well?