Someone who understands engine theory a bit better...
When I try to calculate the theoretical flow capacity of the 1zz I get to about 215 CFM.
Assuming 82% efficiency, should see a real world CFM of 185.
Now,when I average up my maximum airflow over quite a few drives, as measured by the MAF in a stock setup, I get a number of 114g/s,which equates to 215.
That means I'm running at 100% efficiency... Hmm... Not convinced...
What am I missing?
Edit:
Good explanation in the post below here:
https://www.mr2roc.org/forum/index.php?msg=822006
When it comes to flow capacity the engine is simply an air pump.
As long as there are no leaks, there is no reason why air in should not exactly equal air out.
How come that most cars sr said to run about 80-85% volumetric efficiency?
Quote from: shnazzle on February 8, 2020, 12:09How come that most cars sr said to run about 80-85% volumetric efficiency?
Because there are flow losses. It is after all ´driven´ by súcking in air through a filter and then pushing it out through another restriction. There is a pressure difference needed to drive the flow, hence the volume pumped is less than the swept cilinder volume.
How sure are you that the number indicated is the actual air mass? In other words is the value calibrated?
Quote from: Petrus on February 8, 2020, 12:14Quote from: shnazzle on February 8, 2020, 12:09How come that most cars sr said to run about 80-85% volumetric efficiency?
Because there are flow losses. It is after all ´driven´ by súcking in air through a filter and then pushing it out through another restriction. There is a pressure difference needed to drive the flow, hence the volume pumped is less than the swept cilinder volume.
How sure are you that the number indicated is the actual air mass? In other words is the value calibrated?
I'm not at all.
Could be aged MAF. But you would hope Toyota calibrated it.
Hence my suspicion.
Quote from: shnazzle on February 8, 2020, 12:30I'm not at all.
Could be aged MAF. But you would hope Toyota calibrated it.
Hence my suspicion.
For the ECU and all tuning purposes it is all relative. X signal air means y fuel etc.
Toyota will have calibrated that for sure.
How the signal relates to the real volume is basically irrelevant other than for an additional dial.
There are ways of extrapolating the swept air vuloume by calculating from the fuel used and the fuel air ratio.
It is not very important though other then for knówing.
More important is the effect of any modifications. Like the fuel flow rate increasing with the same ratio.
Or the CFM indicated increasing etc.
A 10% increase in fuel flow with constant ratio should equate to 10% more energy pushing the pistons down, the crank and eventually the wheels thus the car, thus basically 10% more performance.
And then you change the ignition advance, messing up the logic by adding a variable in the efficiency of both the burn and the push (effective duration) on the piston.
My understanding is that you should be able to get to or beyond 100 volumetric efficiency at peak torque.
Where does that 80-85% come from?
Quote from: jonbill on February 8, 2020, 13:27My understanding is that you should be able to get to or beyond 100 volumetric efficiency at peak torque.
Where does that 80-85% come from?
It's a safe assumption, taking into consideration moderate tuning, aging, etc etc.
Theoretically, riding intake/exhaust pulses you COULD get 100% or more.
What I'm saying is that I find it unlikely this is the case for my stock engine, stock intake, 200 cell cat, zero mani and tte exhaust.
Unless it is... In which case; happy days
It would be interesting to see a VE table from a 1zz.
VE?
Volumetric efficiency?
All above my station, but every day is a school day.
Quote from: jonbill on February 8, 2020, 22:13It would be interesting to see a VE table from a 1zz.
If I could have one wish from Toyota, including free services for life and 20% discount on parts, I'd forego that for a copy or their calibration tables.
With VVTi and 4 valves per cylinder, I don't see any reason why you shouldn't see something close to or slightly above 100% VE. Only the long stroke makes it difficult to get more. Peak VE will be where peak torque is.
Quote from: ChrisGB on March 30, 2020, 22:28With VVTi and 4 valves per cylinder, I don't see any reason why you shouldn't see something close to or slightly above 100% VE. Only the long stroke makes it difficult to get more. Peak VE will be where peak torque is.
That's just it. If I'm hitting 100% VE, it would assume that my 100k mile engine is still hitting factory levels of peak torque.
With normal wear and tear it just seems unlikely, even with my "performance" mods.
Quote from: shnazzle on March 30, 2020, 23:08Quote from: ChrisGB on March 30, 2020, 22:28With VVTi and 4 valves per cylinder, I don't see any reason why you shouldn't see something close to or slightly above 100% VE. Only the long stroke makes it difficult to get more. Peak VE will be where peak torque is.
That's just it. If I'm hitting 100% VE, it would assume that my 100k mile engine is still hitting factory levels of peak torque.
With normal wear and tear it just seems unlikely, even with my "performance" mods.
Wear will possibly reduce power / torque by losing a little compression and some increased blow by, but unless your inlet ports and valves are coked up, the VE should be mostly the same as when it was new. The inlet and exhaust gases move through spaces which, hopefully, don't wear out!
Quote from: ChrisGB on March 30, 2020, 23:18Quote from: shnazzle on March 30, 2020, 23:08Quote from: ChrisGB on March 30, 2020, 22:28With VVTi and 4 valves per cylinder, I don't see any reason why you shouldn't see something close to or slightly above 100% VE. Only the long stroke makes it difficult to get more. Peak VE will be where peak torque is.
That's just it. If I'm hitting 100% VE, it would assume that my 100k mile engine is still hitting factory levels of peak torque.
With normal wear and tear it just seems unlikely, even with my "performance" mods.
Wear will possibly reduce power / torque by losing a little compression and some increased blow by, but unless your inlet ports and valves are coked up, the VE should be mostly the same as when it was new. The inlet and exhaust gases move through spaces which, hopefully, don't wear out!
I do mean the VE vs theoretical VE of course.
I understand that, as you say, unless those spaces have somehow been coked up, the theoretical CFM produced is the same. But, VE being a % of that theoretical, surely 100% means that compression is perfect as well?
Or am I getting that wrong?
Speaking from experience of having the engine in bits, pound to a penny your inlet manifold will be an oily mess inside and your valves and combustion faces will be carrying a film/coating of carbon so your available cc won't be "factory spec".
Quote from: Call the midlife! on March 31, 2020, 07:01Speaking from experience of having the engine in bits, pound to a penny your inlet manifold will be an oily mess inside and your valves and combustion faces will be carrying a film/coating of carbon so your available cc won't be "factory spec".
Exactly. Hell even just going off the muck in the throttle body, the intake mani has to be a mess.
Having said that, it gets a yearly intake clean with two cans of EGR cleaner so it might not be all too bad. How many people do that?
That's why I had my catch can (before it just leaked everywhere).
And having thought about it, I had my compression check done at AK and it was spot on. So, I guess it is POSSIBLE that my engine's quite clean.
Still not 100+ VE clean though so I still feel like I'm missing something
Quote from: shnazzle on March 31, 2020, 07:32Quote from: Call the midlife! on March 31, 2020, 07:01Speaking from experience of having the engine in bits, pound to a penny your inlet manifold will be an oily mess inside and your valves and combustion faces will be carrying a film/coating of carbon so your available cc won't be "factory spec".
Exactly. Hell even just going off the muck in the throttle body, the intake mani has to be a mess.
Having said that, it gets a yearly intake clean with two cans of EGR cleaner so it might not be all too bad. How many people do that?
That's why I had my catch can (before it just leaked everywhere).
And having thought about it, I had my compression check done at AK and it was spot on. So, I guess it is POSSIBLE that my engine's quite clean.
Still not 100+ VE clean though so I still feel like I'm missing something
I'll stand to be corrected here but dirty/carbon coated head and piston faces would probably up your compression values anyway, assuming your cylinder walls and rings were making a good seal?
Quote from: Call the midlife! on March 31, 2020, 08:10Quote from: shnazzle on March 31, 2020, 07:32Quote from: Call the midlife! on March 31, 2020, 07:01Speaking from experience of having the engine in bits, pound to a penny your inlet manifold will be an oily mess inside and your valves and combustion faces will be carrying a film/coating of carbon so your available cc won't be "factory spec".
Exactly. Hell even just going off the muck in the throttle body, the intake mani has to be a mess.
Having said that, it gets a yearly intake clean with two cans of EGR cleaner so it might not be all too bad. How many people do that?
That's why I had my catch can (before it just leaked everywhere).
And having thought about it, I had my compression check done at AK and it was spot on. So, I guess it is POSSIBLE that my engine's quite clean.
Still not 100+ VE clean though so I still feel like I'm missing something
I'll stand to be corrected here but dirty/carbon coated head and piston faces would probably up your compression values anyway, assuming your cylinder walls and rings were making a good seal?
I believe you're right. My values were a bit elevated. So that would suggest the valves etc are a bit mucky
Quote from: shnazzle on March 31, 2020, 07:32And having thought about it, I had my compression check done at AK and it was spot on. So, I guess it is POSSIBLE that my engine's quite clean.
Still not 100+ VE clean though so I still feel like I'm missing something
Apologies for the delayed reply, been trying to salvage me business.
I'm wondering if you are confusing VE with airflow? Peak airflow would be at peak power assuming everything is set up correctly. Peak airflow = peak fuel burn = peak work done = peak power.
This will be a nominal figure and if numerically scaled on the ECU would probably be measured in grams / second or similar rather than CFM. The MAF sensor is highly unlikely to be calibrated to read from 0 to 100% where airflow is between 0 and 100%. The reading range will be a part of the full range of the sensor.
When everything is running optimally, your peak air draw should stay very close to the amount drawn when the engine is new. Things that could significantly reduce that figure could be a blocked air filter, blocked exhaust or severely coked up inlet valves (particularly a problem in direct injection engines). Assuming these things have not happened, your peak airflow should stay very similar to when the engine is new. I'm not sure that spotlessly clean and shiny inlet tracts flow any any better than slightly dirty ones. Very smooth surfaces can actually reduce flow slightly.
Of course, the older engine can be down on power, but this is mostly going to be energy lost to blow by, reduced combustion efficiency from tired ignition components, or ignition timing being pulled due to head / valve / piston crown fouling induced detonation.
Volumetric Efficiency or VE is something quite different. Imagine a cylinder of 500cc. If your intake cycle gets 500cc of air into the cylinder (at STP or Standard Temperature and Pressure) that is said to have achieved 100% VE. With two valve per cylinder road engines, they tend to top out at around 85% VE, so your 500cc cylinder will ingest up to 425cc of air at peak torque. Four valve per cylinder engines can, if well set up, achieve up to 125% VE, so your 500cc cylinder could ingest up to 625cc at peak torque. This is achieved by clever intake and exhaust pulse control that effectively uses resonances in the system to cram more air in than natural airflow would allow, hence the term tuning! For an easy to read grounding in how this stuff works, I'd recommend "4 Stroke Performance Tuning" by A. Graham Bell.
Hope this clarifies!
Quote from: ChrisGB on April 7, 2020, 19:58Quote from: shnazzle on March 31, 2020, 07:32And having thought about it, I had my compression check done at AK and it was spot on. So, I guess it is POSSIBLE that my engine's quite clean.
Still not 100+ VE clean though so I still feel like I'm missing something
Apologies for the delayed reply, been trying to salvage me business.
I'm wondering if you are confusing VE with airflow? Peak airflow would be at peak power assuming everything is set up correctly. Peak airflow = peak fuel burn = peak work done = peak power.
This will be a nominal figure and if numerically scaled on the ECU would probably be measured in grams / second or similar rather than CFM. The MAF sensor is highly unlikely to be calibrated to read from 0 to 100% where airflow is between 0 and 100%. The reading range will be a part of the full range of the sensor.
When everything is running optimally, your peak air draw should stay very close to the amount drawn when the engine is new. Things that could significantly reduce that figure could be a blocked air filter, blocked exhaust or severely coked up inlet valves (particularly a problem in direct injection engines). Assuming these things have not happened, your peak airflow should stay very similar to when the engine is new. I'm not sure that spotlessly clean and shiny inlet tracts flow any any better than slightly dirty ones. Very smooth surfaces can actually reduce flow slightly.
Of course, the older engine can be down on power, but this is mostly going to be energy lost to blow by, reduced combustion efficiency from tired ignition components, or ignition timing being pulled due to head / valve / piston crown fouling induced detonation.
Volumetric Efficiency or VE is something quite different. Imagine a cylinder of 500cc. If your intake cycle gets 500cc of air into the cylinder (at STP or Standard Temperature and Pressure) that is said to have achieved 100% VE. With two valve per cylinder road engines, they tend to top out at around 85% VE, so your 500cc cylinder will ingest up to 425cc of air at peak torque. Four valve per cylinder engines can, if well set up, achieve up to 125% VE, so your 500cc cylinder could ingest up to 625cc at peak torque. This is achieved by clever intake and exhaust pulse control that effectively uses resonances in the system to cram more air in than natural airflow would allow, hence the term tuning! For an easy to read grounding in how this stuff works, I'd recommend "4 Stroke Performance Tuning" by A. Graham Bell.
Hope this clarifies!
It most certainly does. First and foremost; I sincerely hope your business is ok, or will be OK. It's tough times for the self-employed or business owners. Definitely wishing you all the best.
So taking what you said, really 100% VE, on our engines with VVTi and 4 valves per cylinder, is quite bad.
But, that's based on the MAF signal, which as you say, may not be calibrated for the full VE range. So, 100% VE might actually be higher. The only way to measure VE then is to have a calibrated device that accurately measures the actual airflow.
Why is the MAF no calibrated to be true?
Putting head briefly above the parapet.
I think CGB is saying it will be true, for the range it is calibrated for.
If 0 = no air and 100 = air.
Not much point calibrating to measure a vaccum. If there is no air. Engine starting will be the least of your worries.
So anything below a set target does not need to be measured. But between whatever the range is. Will be accurate.
Ducking back down quickly.
Quote from: Ardent on April 7, 2020, 22:07Putting head briefly above the parapet.
I think CGB is saying it will be true, for the range it is calibrated for.
If 0 = no air and 100 = air.
Not much point calibrating to measure a vaccum. If there is no air. Engine starting will be the least of your worries.
So anything below a set target does not need to be measured. But between whatever the range is. Will be accurate.
Ducking back down quickly.
On that note, how does the car measure manifold pressure? Is there a sensor I don't know of? That shows vacuum on the "gauge"
Part of the PCV system?
I'm sure there's a vacuum hose comes off the inlet manifold to the small assembly that clips into the air feed pipe, near the MAF.
Quote from: shnazzle on April 8, 2020, 08:50Quote from: Ardent on April 7, 2020, 22:07Putting head briefly above the parapet.
I think CGB is saying it will be true, for the range it is calibrated for.
If 0 = no air and 100 = air.
Not much point calibrating to measure a vaccum. If there is no air. Engine starting will be the least of your worries.
So anything below a set target does not need to be measured. But between whatever the range is. Will be accurate.
Ducking back down quickly.
On that note, how does the car measure manifold pressure? Is there a sensor I don't know of? That shows vacuum on the "gauge"
The standard car doesn't measure manifold pressure.
Quote from: Carolyn on April 8, 2020, 18:48Quote from: shnazzle on April 8, 2020, 08:50Quote from: Ardent on April 7, 2020, 22:07Putting head briefly above the parapet.
I think CGB is saying it will be true, for the range it is calibrated for.
If 0 = no air and 100 = air.
Not much point calibrating to measure a vaccum. If there is no air. Engine starting will be the least of your worries.
So anything below a set target does not need to be measured. But between whatever the range is. Will be accurate.
Ducking back down quickly.
On that note, how does the car measure manifold pressure? Is there a sensor I don't know of? That shows vacuum on the "gauge"
The standard car doesn't measure manifold pressure.
Indeed. So it has to be a calculated value.
Quote from: shnazzle on April 7, 2020, 20:46So taking what you said, really 100% VE, on our engines with VVTi and 4 valves per cylinder, is quite bad.
But, that's based on the MAF signal, which as you say, may not be calibrated for the full VE range. So, 100% VE might actually be higher. The only way to measure VE then is to have a calibrated device that accurately measures the actual airflow.
Why is the MAF no calibrated to be true?
I think you are still confusing VE with airflow. VE is very specifically the amount of mixture in the cylinder at the time the valves are both closed at the end of an induction cycle. For a 500cc cylinder, this would be 100% if there is 500cc of mixture in there. This has very little to do with airflow. The VE changes depending on the various physical attributes of the engine and its load condition. It is generally a guide to how effectively an engine is setup and it's peak value will only occur at a very limited speed and load range.
It is difficult to explain, but this may make sense... Imagine your 500cc single cylinder engine as an air pump. At full throttle lets assume that the engine as a system draws in 500cc of air for every intake stroke. You'd think that this would mean 100% VE. However, what happens if some of this air gets down the exhaust port before the exhaust valves close? If 10% goes down the exhaust port, the engine has pulled 500cc per intake cycle, but VE is only 90%. Another loss could be that some of the air gets pushed back into the inlet system as a pulse before the inlet valves close, eg 5%. It has still pulled 500cc for that intake stroke, but another 5% is sitting in a higher pressure area in the inlet system, you are now down to 85% VE.
On the subject of air metering, the MAF consists of two elements. A hot wire assembly, which is cooled by inlet air, the more it is cooled, the more airflow it reports. A thermistor, which tells the ECU how warm the air is. So if you know the cooling effect and the air temperature, you can easily work out how much fuel to add. MAF specifically refers to Mass Air Flow, so it is done by weight. For any number of reasons, the airflow metering system could be non linear in output, so the readings would need to be scaled electronically. It is not unusual to have sensors with a full range value of say 0-5v being used between 1v and 4v to represent minimum and maximum output within their application.
VE is a slippery concept to pin down and not easy to measure directly.
Quote from: Petrus on February 8, 2020, 12:14Quote from: shnazzle on February 8, 2020, 12:09How come that most cars sr said to run about 80-85% volumetric efficiency?
Because there are flow losses. It is after all ´driven´ by súcking in air through a filter and then pushing it out through another restriction. There is a pressure difference needed to drive the flow, hence the volume pumped is less than the swept cilinder volume.
How sure are you that the number indicated is the actual air mass? In other words is the value calibrated?
Have a look at this folks:
https://www.motor.com/magazine-summary/driveability-corner-june-2003/
Quote from: SV-3 on April 10, 2020, 14:06Quote from: Petrus on February 8, 2020, 12:14Quote from: shnazzle on February 8, 2020, 12:09How come that most cars sr said to run about 80-85% volumetric efficiency?
Because there are flow losses. It is after all ´driven´ by súcking in air through a filter and then pushing it out through another restriction. There is a pressure difference needed to drive the flow, hence the volume pumped is less than the swept cilinder volume.
How sure are you that the number indicated is the actual air mass? In other words is the value calibrated?
Have a look at this folks:
https://www.motor.com/magazine-summary/driveability-corner-june-2003/
Peak VE under optimum circumstances is not a usefull perspective for modern road cars. Air filtration, sound regulations and catalists are but three real world restrictions lowering VE for an n.a. engine.
The about 10 extra hp the 1ZZ in the SW30 pumps out with the cats and restrictions in the muffling removed is a good example.
Take the air filter into account ánd the proven limited flow though the head.
And remember the MAF mod and the OEM inlet elbow.
Monitoring and tuning for VE from the MAF ís usefull though. Just not as an accurate real value measuring instrument.
It is as with apps on the mobile phone for tuning purposes. Gréat comparative tools, just not for real numbers.
Quote from: ChrisGB on April 8, 2020, 23:43Quote from: shnazzle on April 7, 2020, 20:46So taking what you said, really 100% VE, on our engines with VVTi and 4 valves per cylinder, is quite bad.
But, that's based on the MAF signal, which as you say, may not be calibrated for the full VE range. So, 100% VE might actually be higher. The only way to measure VE then is to have a calibrated device that accurately measures the actual airflow.
Why is the MAF no calibrated to be true?
I think you are still confusing VE with airflow. VE is very specifically the amount of mixture in the cylinder at the time the valves are both closed at the end of an induction cycle. For a 500cc cylinder, this would be 100% if there is 500cc of mixture in there. This has very little to do with airflow. The VE changes depending on the various physical attributes of the engine and its load condition. It is generally a guide to how effectively an engine is setup and it's peak value will only occur at a very limited speed and load range.
It is difficult to explain, but this may make sense... Imagine your 500cc single cylinder engine as an air pump. At full throttle lets assume that the engine as a system draws in 500cc of air for every intake stroke. You'd think that this would mean 100% VE. However, what happens if some of this air gets down the exhaust port before the exhaust valves close? If 10% goes down the exhaust port, the engine has pulled 500cc per intake cycle, but VE is only 90%. Another loss could be that some of the air gets pushed back into the inlet system as a pulse before the inlet valves close, eg 5%. It has still pulled 500cc for that intake stroke, but another 5% is sitting in a higher pressure area in the inlet system, you are now down to 85% VE.
On the subject of air metering, the MAF consists of two elements. A hot wire assembly, which is cooled by inlet air, the more it is cooled, the more airflow it reports. A thermistor, which tells the ECU how warm the air is. So if you know the cooling effect and the air temperature, you can easily work out how much fuel to add. MAF specifically refers to Mass Air Flow, so it is done by weight. For any number of reasons, the airflow metering system could be non linear in output, so the readings would need to be scaled electronically. It is not unusual to have sensors with a full range value of say 0-5v being used between 1v and 4v to represent minimum and maximum output within their application.
VE is a slippery concept to pin down and not easy to measure directly.
Gotcha. Thanks Chris. That explains it perfectly. Two completely different concepts and explains a lot of questions I had about Helen's standalone map.
So, is there any way to measure VE actually? Or, do you just aim to get peak torque and it is what it is? Whether it's 100% VE, or 125%,or 85% is irrelevant I guess.
Quote from: shnazzle on April 10, 2020, 19:31So, is there any way to measure VE actually? Or, do you just aim to get peak torque and it is what it is? Whether it's 100% VE, or 125%,or 85% is irrelevant I guess.
Tricky Patrick. Temperature change in the inlet tract also messes up the ´real´ volume.
In itself metering the fow through a tube is a good base for calculation but again, it is flów metering and then calculation the quantity of air, compensating for variables such as temp.
Yes, the actual value is not important nor the goal is it?! For a given egine set up you mess with the variables to get max. flow over a wide as possible rev range with max torque and hp the resiltants.
Quote from: Petrus on April 11, 2020, 11:09Quote from: shnazzle on April 10, 2020, 19:31So, is there any way to measure VE actually? Or, do you just aim to get peak torque and it is what it is? Whether it's 100% VE, or 125%,or 85% is irrelevant I guess.
Tricky Patrick. Temperature change in the inlet tract also messes up the ´real´ volume.
As explained by Mr Boyle.
Quote from: Joesson on April 11, 2020, 11:45Quote from: Petrus on April 11, 2020, 11:09Quote from: shnazzle on April 10, 2020, 19:31So, is there any way to measure VE actually? Or, do you just aim to get peak torque and it is what it is? Whether it's 100% VE, or 125%,or 85% is irrelevant I guess.
Tricky Patrick. Temperature change in the inlet tract also messes up the ´real´ volume.
As explained by Mr Boyle.
Frankie?? I've not heard his opinions on VE...🤓
Quote from: Call the midlife! on April 11, 2020, 12:52Quote from: Joesson on April 11, 2020, 11:45Quote from: Petrus on April 11, 2020, 11:09Quote from: shnazzle on April 10, 2020, 19:31So, is there any way to measure VE actually? Or, do you just aim to get peak torque and it is what it is? Whether it's 100% VE, or 125%,or 85% is irrelevant I guess.
Tricky Patrick. Temperature change in the inlet tract also messes up the ´real´ volume.
As explained by Mr Boyle.
Frankie?? I've not heard his opinions on VE...🤓
Frankie Boyle, four letter, rather than four syllable words are apparently more his forte. I had no knowledge of Frankie Boyle until I looked at the www. However, I do believe that Roberts words will endure longer than Frankie's
Quote from: shnazzle on April 10, 2020, 19:31Gotcha. Thanks Chris. That explains it perfectly. Two completely different concepts and explains a lot of questions I had about Helen's standalone map.
So, is there any way to measure VE actually? Or, do you just aim to get peak torque and it is what it is? Whether it's 100% VE, or 125%,or 85% is irrelevant I guess.
I think the only way you could home in on a value would be to measure a known quantity of fuel and air flow, adjust whatever variable inlet and exhaust parameters you can, optimise the ignition timing and gather information like unburnt HC / CO EGT / torque etc. To be fair, there are bags of calculations you can make when designing your engine and these generally get you into the right ball park.
The fun starts once you start adding boost. It is possible to have a huge airflow and relatively poor VE if inlet charge goes down the exhaust port. This is an issue for people boosting the 2zz by large amounts IIRC. Cams need changing to keep the charge in!
The problem with gases is that they are elastic. Volume, in a dynamic environment, is all over the place and pretty meaningless. In a liquid, mass and volume are much easier to tie down.
In rocketry, we only ever measure mass. That isn't always easy either.
Quote from: Carolyn on April 13, 2020, 18:41The problem with gases is that they are elastic. Volume, in a dynamic environment, is all over the place and pretty meaningless. In a liquid, mass and volume are much easier to tie down.
In rocketry, we only ever measure mass. That isn't always easy either.
So very true! Mind you, it is that elasticity that makes it possible to cram in more than 100% cylinder volume with good design. When that tune all comes together it just sounds "right". Four stroke setup is tricky, two stroke even more potential, but trickier still.
I'd really love to know more about rocket engines. Do they, like a well set up petrol engine, have that grin inducing sound that tells you when everything is just "right"?
Quote from: ChrisGB on April 13, 2020, 18:56Quote from: Carolyn on April 13, 2020, 18:41The problem with gases is that they are elastic. Volume, in a dynamic environment, is all over the place and pretty meaningless. In a liquid, mass and volume are much easier to tie down.
In rocketry, we only ever measure mass. That isn't always easy either.
So very true! Mind you, it is that elasticity that makes it possible to cram in more than 100% cylinder volume with good design. When that tune all comes together it just sounds "right". Four stroke setup is tricky, two stroke even more potential, but trickier still.
I'd really love to know more about rocket engines. Do they, like a well set up petrol engine, have that grin inducing sound that tells you when everything is just "right"?
Not really.. Mind you they do leave you rather deaf - at least the ones I worked with did. The exhaust plume, (colour, steadiness and shock-waves) is where that satisfaction is to be had.
Quote from: Carolyn on April 13, 2020, 19:07Quote from: ChrisGB on April 13, 2020, 18:56Quote from: Carolyn on April 13, 2020, 18:41The problem with gases is that they are elastic. Volume, in a dynamic environment, is all over the place and pretty meaningless. In a liquid, mass and volume are much easier to tie down.
In rocketry, we only ever measure mass. That isn't always easy either.
So very true! Mind you, it is that elasticity that makes it possible to cram in more than 100% cylinder volume with good design. When that tune all comes together it just sounds "right". Four stroke setup is tricky, two stroke even more potential, but trickier still.
I'd really love to know more about rocket engines. Do they, like a well set up petrol engine, have that grin inducing sound that tells you when everything is just "right"?
Not really.. Mind you they do leave you rather deaf - at least the ones I worked with did. The exhaust plume, (colour, steadiness and shock-waves) is where that satisfaction is to be had.
I'd assumed that loud is good and louder is better. Something on my bucket list it to get to see a launch from Cape Kennedy, Baikonur or Kourou.
I can see the satisfaction in seeing / feeling shock waves is always visceral!
Quote from: ChrisGB on April 13, 2020, 19:23Quote from: Carolyn on April 13, 2020, 19:07Quote from: ChrisGB on April 13, 2020, 18:56Quote from: Carolyn on April 13, 2020, 18:41The problem with gases is that they are elastic. Volume, in a dynamic environment, is all over the place and pretty meaningless. In a liquid, mass and volume are much easier to tie down.
In rocketry, we only ever measure mass. That isn't always easy either.
So very true! Mind you, it is that elasticity that makes it possible to cram in more than 100% cylinder volume with good design. When that tune all comes together it just sounds "right". Four stroke setup is tricky, two stroke even more potential, but trickier still.
I'd really love to know more about rocket engines. Do they, like a well set up petrol engine, have that grin inducing sound that tells you when everything is just "right"?
Not really.. Mind you they do leave you rather deaf - at least the ones I worked with did. The exhaust plume, (colour, steadiness and shock-waves) is where that satisfaction is to be had.
I'd assumed that loud is good and louder is better. Something on my bucket list it to get to see a launch from Cape Kennedy, Baikonur or Kourou.
I can see the satisfaction in seeing / feeling shock waves is always visceral!
I got that just from watching the top fuel drag bikes at Santa Pod. Never experienced such a visceral rumble before that.
Watching a launch would be epic
Quote from: shnazzle on April 13, 2020, 19:44I got that just from watching the top fuel drag bikes at Santa Pod. Never experienced such a visceral rumble before that.
Watching a launch would be epic
Go and see top fuel dragsters if you like a bit of noise!
https://youtu.be/EhzTvN4UEKY
The last comment reminded me about this, feel free to remove it or reposition it as necessary Patrick, just thought it might appeal..
Quote from: Call the midlife! on April 15, 2020, 22:33https://youtu.be/EhzTvN4UEKY
The last comment reminded me about this, feel free to remove it or reposition it as necessary Patrick, just thought it might appeal..
We saw those at the pod as well!
I remember having a good look at one and saying a CBR600 engine with a turbo and NOS was absolutely mental.
.... Which it is.
Thread revival;
Was reading another forum and someone else was struggling with the concept of VE.
His struggle was around an example of a 5L engine being 100% VE if it displaced 5L of mixture through one cycle. So the cylinders filled perfectly. Nothing up the intake, nothing out the exhaust,perfect valve timing, nothing blowing. Each cylinder filled with all the mix it could, to be compressed at whatever rate the engine allowed.
But, then went on to say, if it only sucked in 2.5L of mixture, because of an intake restriction (throttle body) would it have a VE of 50%?
This is where things got funny
The cylinders were still filled with 5L of mix. But that mix was 50% as dense.
So in that case... What's the VE? Is it still 100%?
Quote from: shnazzle on July 10, 2020, 00:46Thread revival;
Was reading another forum and someone else was struggling with the concept of VE.
His struggle was around an example of a 5L engine being 100% VE if it displaced 5L of mixture through one cycle. So the cylinders filled perfectly. Nothing up the intake, nothing out the exhaust,perfect valve timing, nothing blowing. Each cylinder filled with all the mix it could, to be compressed at whatever rate the engine allowed.
But, then went on to say, if it only sucked in 2.5L of mixture, because of an intake restriction (throttle body) would it have a VE of 50%?
This is where things got funny
The cylinders were still filled with 5L of mix. But that mix was 50% as dense.
So in that case... What's the VE? Is it still 100%?
That's why, in rocketry, everything is done by mass not volume. Guess what - the car uses a MASS airflow meter.