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Author Topic: Volumeteric Efficiency vs Load with pics  (Read 1536 times)
mister t
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« on: March 11, 2018, 02:17:29 PM »

So I decided to plot chart my engine's VE by hand over a WOT pull and this is what I found.

It looks like engine VE is an exact mirror of the engine's measured load as well as the engine's torque curve.
MAF AND VE LINE PLOT by zimbu themonkey, on Flickr

Here's my engine VE compared to measured Load
VE vs LOAD S4 by zimbu themonkey, on Flickr

As it pertains to Motronic, this should mean that the closest relation to VE would be KFMIOP would it not?

Maybe that's obvious to some of the more knowledgeable members here, however I've never seen any references to where VE would be represented in Motronic (since Load in Motronic is basically arbitrary).

EDIT: what I'm trying to do here is determine what maps are the closest representations of either predicted or actual VE. Reason being is that I find it much easier to tune something when I have a 3D representation of what the engine is doing. Then, everything else follows from that model. Make sense?
« Last Edit: March 11, 2018, 07:21:49 PM by mister t » Logged
prj
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« Reply #1 on: March 11, 2018, 04:45:32 PM »

Uhmm newsflash - VE on ME7 is KFURL, KFPRG and KFPBRKNW.
IOP has nothing to do with pressure to load conversion.
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mister t
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« Reply #2 on: March 11, 2018, 06:44:42 PM »

Uhmm newsflash - VE on ME7 is KFURL, KFPRG and KFPBRKNW.
IOP has nothing to do with pressure to load conversion.

Couple of comments;

1) To clarify the purpose of my original post, I was trying to ID the maps which give us the most direct view of the engine's VE and/or predicted VE. My reason for doing so is that I find it easier to tune something when I can conceptualize a starting point in 3D. From there, I find it much easier to basically build everything around it.

2) I'm dealing with a naturally aspirated engine, so in my case, there's really no pressure conversion to take into account.

3) Couple of questions regarding the maps you mentioned above. I searched the S4 tuning wiki and found that the map sets you reference are for cam changeover effect on requested boost.

KFPBRK - Correction factor for combustion chamber pressure
KFPBRKNWS - Correction factor for combustion chamber pressure when NWS active
KFPRG - Internal exhaust partial pressure dependent on cam adjustment when sumode=0
KFURL - Conversion constant for ps->rl dependent on cam adjustment when sumode=0


I do realize that just because they're not labeled as VE per-se, they could still be representative of VE. However when I read the description of the maps in plain English, it seems on the surface that what they're concerned with is the residual exhaust fraction of the combustion cycle which is left in the chamber after blow down as a result of things like reversion due to overlap, exhaust restrictions on account of the turbine, etc...

Now, I realize that residual exhaust is a portion of VE measures, it doesn't seem to me that it's a very direct measure of VE. Put otherwise, any inferences you could make about VE would require further calculation (as in you would need to work backwards for a bit to say "my engine is working at X% VE at this point")

Is my line if reasoning making any sense here? I realize it's kind of convoluted.

I also want to be clear that I'm not trying to argue or prove you wrong. I also want to be clear that I don't mind someone pointing out that I'm wrong about something SO LONG AS I end up getting pointed in the right direction. Really, what I'm doing is just working this all through in my head and responses from members such as yourself are quite a valuable part of the process. However I need to ask questions along the way.

With that said, wouldn't it make more sense that your IRL and IOP maps would be the closest approximations of VE? Bearing in mind that IRL is your target cylinder filling (or, in other words, target volumeteric efficiency) and IOP is basically the torque which results from that cylinder filling?

If I break it down a little further, the definition of volumeteric efficiency is the ratio of the volume of fluid actually displaced by a piston or plunger to its swept volume

By definition then, isn't VE most closely related to IRL (and by extention, IOP?)

If I'm wrong, then hey so be it. Wouldn't be the first time lol.

« Last Edit: March 11, 2018, 07:16:28 PM by mister t » Logged
nyet
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« Reply #3 on: March 11, 2018, 10:35:43 PM »

no, torque is a percentage of an almost arbitrary 100% value
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prj
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« Reply #4 on: March 12, 2018, 04:08:47 AM »

I don't think you understand what VE is Smiley

Why write a wall of text when I told you what is VE in ME7?

IRL/IOP is torque to load and back. Nothing to do with volumetric efficiency of the engine whatsoever.
rl_w is AFTER the VE calculation is already done. VE in digital engine control is pressure to load plain and simple.
As for the maps, it's irrelevant what they are called. KFURL is multiplicative VE line (Schluckgerade for scientific term in German), KFPRG is additive offset, KFPBRK/NW is multiplicative correction at different loads.
« Last Edit: March 12, 2018, 04:11:03 AM by prj » Logged
nubcake
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« Reply #5 on: March 12, 2018, 03:04:12 PM »

no, torque is a percentage of an almost arbitrary 100% value

I guess, it was originally supposed to be a percentage of MDNORM. Smiley
But in reality quite often it's way off, yea.
« Last Edit: March 12, 2018, 03:50:00 PM by nubcake » Logged
mister t
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« Reply #6 on: March 12, 2018, 04:16:39 PM »

I don't think you understand what VE is Smiley

Why write a wall of text when I told you what is VE in ME7?

IRL/IOP is torque to load and back. Nothing to do with volumetric efficiency of the engine whatsoever.
rl_w is AFTER the VE calculation is already done. VE in digital engine control is pressure to load plain and simple.
As for the maps, it's irrelevant what they are called. KFURL is multiplicative VE line (Schluckgerade for scientific term in German), KFPRG is additive offset, KFPBRK/NW is multiplicative correction at different loads.

No, I'm pretty sure I understand what VE is lol Wink

So what I want to know is how is it that IOP IRL has nothing do to with VE when my VE curve is a mirror image of my calculated load which is a mirror image of my actual torque curve?

I'll note that you state (quite accurately) that VE in digital engine control is pressure to load. If that's the case, then would you not agree that in a N/A engine, where pressure is constant (read: ambient barometric pressure) that the resulting calculated load would be a VE curve?

Just think of it in terms of basic algebra. When you have a constant on both sides of the equation you cancel them out and the answer to the problem is whatever remains.

*Bear in mind that we're talking about a N/A engine here. I understand that when you introduce forced induction into the mix, VE curves get weird and wonderful.*

EDIT: I should clarify, for Motronic's purposes IN A N/A ENGINE , is 'pressure' defined as ambient atmospheric pressure, the differential pressure across the throttle plate or both (I do know that there is a calculation for MAF and MAF across throttle plate).

If that's the case, then it would make sense that WOT calculated load would be a mirror image of VE, whereas part throttle calculated load would be less representative of true VE as the throttle plate becomes more of a restriction, thus skewing 'pressure' in the calculation.
« Last Edit: March 12, 2018, 04:26:01 PM by mister t » Logged
nyet
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« Reply #7 on: March 12, 2018, 05:32:17 PM »

One more time, 100% torque is an arbitrary concept to convey whatever the driver "expects" 100% to feel like.

In general, it is assumed to be something close to "actual" torque that a motor can potentially produce. This (somewhat, but not exactly) mirrors not the pressure to load process, but actual engine efficiency at converting a given airmass (load) into a percentage of that total "possible maximum" torque at that operating point. It may resemble the VE map, but not because it is VE itself, but because VE somewhat resembles overall engine *thermal* efficiency.

I think you are completely misunderstanding what "torque" is here.

is 'pressure' defined as ambient atmospheric pressure, the differential pressure across the throttle plate or both (I do know that there is a calculation for MAF and MAF across throttle plate)

Pressure is generally manifold pressure, regardless of N/A or FI or whatever.

From that and VE, you can calculate load, or the mass of air per cylinder expressed as a percentage of the amount of air mass at standard pressure and temperature that the cylinder can hold.

The pressure behind the throttle plate is immaterial with respect to calculating load, unless you do further TB modeling to calculate the pressure drop across the TB to get... drum roll.. MAP.
« Last Edit: March 12, 2018, 05:38:16 PM by nyet » Logged

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prj
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« Reply #8 on: March 13, 2018, 05:52:42 AM »

The failure of comprehension is strong with this one.

VE = pressure->load
IRL/IOP = load->torque

Nothing in common whatsoever.

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mister t
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« Reply #9 on: March 14, 2018, 11:44:32 PM »

One more time, 100% torque is an arbitrary concept to convey whatever the driver "expects" 100% to feel like.

In general, it is assumed to be something close to "actual" torque that a motor can potentially produce. This (somewhat, but not exactly) mirrors not the pressure to load process, but actual engine efficiency at converting a given airmass (load) into a percentage of that total "possible maximum" torque at that operating point. It may resemble the VE map, but not because it is VE itself, but because VE somewhat resembles overall engine *thermal* efficiency.

I think you are completely misunderstanding what "torque" is here.

Pressure is generally manifold pressure, regardless of N/A or FI or whatever.

From that and VE, you can calculate load, or the mass of air per cylinder expressed as a percentage of the amount of air mass at standard pressure and temperature that the cylinder can hold.

The pressure behind the throttle plate is immaterial with respect to calculating load, unless you do further TB modeling to calculate the pressure drop across the TB to get... drum roll.. MAP.


Nyet, thank you for what I see as a very well thought out response to my query.

Just to be clear, what you're saying is that while there may be a CORRELATION between my VE measurements and measured load, it's not CAUSAL.

You also seem to be saying that the IOP map is (as it name suggests) a measure of optimal torque. However in practice, the actual torque output (and measured load) can vary based on any number of combustion efficiency factors (AFR, ignition timing, air density, etc...) therefore IOP is not a reliable indicator of VE.

Is that what you were trying to say or did I miss the mark?
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mister t
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« Reply #10 on: March 14, 2018, 11:58:54 PM »

The failure of comprehension is strong with this one.

VE = pressure->load
IRL/IOP = load->torque

Nothing in common whatsoever.



Well, maybe if the people who allegedly understand it would actually explain it, then I wouldn't have comprehension issues...

One thing I learned as a National Development Luge Coach is that if my athletes weren't understanding something, the first place I looked was in the mirror....

To wit, look at your answer vs Nyet's.

Nyet obviously took the time to try and explain things to me, your answer is a pissy 2 line blurb that does nothing to address my questions.

As I've said a million times, I accept that you know more about this than I do and I've been giving you a pass on a lot of condescending/pissy responses because you may very well be of some use to me.

However, if you plan to keep responding condescendingly without actually answering my questions, then I'm going to loose my patience.

Seriously man, for as much as you know, why don't you actually try and help people out without being a dick about it. It's really unnecessary and quite frankly, it makes you sound like someone who got beat up on the playground for being too smart and now you've got a chip on your shoulder.

Let it go and play nice. Encouraging members to post up novel ideas is what's at the core of this forum.

I've heard quite a few people remark that they get turned off this place because of condescending attitudes. If you really care about this forum, then maybe re-evaluate your way of responding to people.

Anyway, just a thought. However I hope you take it to heart as I really think you have a lot to offer. I've seen some of your threads and you've got mad skills man *thumb-up*
« Last Edit: March 15, 2018, 12:08:38 AM by mister t » Logged
prj
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« Reply #11 on: March 15, 2018, 05:32:18 AM »

You're not entitled to any of my help.
I say exactly as much or as little as I want, and IDGAF what you think about that.

All these snowflakes thinking that the world owes them something.
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mister t
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« Reply #12 on: March 15, 2018, 11:48:01 PM »

You're not entitled to any of my help.
I say exactly as much or as little as I want, and IDGAF what you think about that.

All these snowflakes thinking that the world owes them something.

I agree that i'm not entitled to your help. That's precisely the reason I've been giving your unnecessarily condescending answers a free pass, because some of them have been useful.

However, the fact that you know more than I do DOES NOT give you any right to make condescending posts with little to no useful information in them just to remind us of how much you know.

What i find especially irritating is when i take a great deal of time to post up empirical information which address someone's counterpoint and they can't be bothered to read it. I did this in the RS4 thread and your response was:

I don't have time to read this.
But my data is based on personal experience on my dyno.

0.75 timing pull "controls" nothing at all in any engine - why, I already wrote.
Do as you want and melt your shit if you want to, not my problem.


While i maintain my position that that my efforts were not solely to address your arguments, I still find it quite disrespectful that you simply couldn't be bothered to read it since it was primarily geared towards providing you a thorough, respectful and well thought out response to your argument.

So, while I honestly do appreciate your help and if you're going to offer it please do so.

However, if your posts are just going to be for the purposes of stroking your ego by pointing out what others don't know relative to you, then please take them elsewhere.

Trust me, while I have NO interest in making an enemy out of you, you do NOT want to make an enemy out of me... I've handled you with kid gloves and treated you with a great deal of respect so far (and i hope it stays that way, I really do).

Much like your 'snowflake' comment, while you ARE useful, you're not so special and unique that it makes you immune to criticism, expectations of appropriate social conduct, nor are you indispensable. There's always someone who knows as much or more than you who IS willing to share that knowledge (i.e. Daz RIP)
« Last Edit: March 16, 2018, 12:44:24 AM by mister t » Logged
prj
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« Reply #13 on: March 16, 2018, 02:09:52 AM »

Again, I don't have time or interest to read random page long ramblings on the internet.
Especially by someone who has a lot to say but actually knows very little of the basics.

It's simply not a good use of my time.

As for what you think of me, again IDGAF.
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mister t
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« Reply #14 on: March 16, 2018, 11:31:00 PM »

You know what, I'm saying let's let cooler heads prevail.

Consider this my handshake
« Last Edit: March 17, 2018, 02:23:26 AM by mister t » Logged
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