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Old 10-20-2006, 12:12 PM   #1
ride5000
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Default effects of IAT on MRP vs LOAD

so over the past few days i've been logging--no surprise there.

one of the things that characterizes this time of year in the NE area is a lot of temperature swings.

i have compiled some of the datalogs and plotted MRP vs LOAD. i have also worked out a best fit linear equation to define this relationship. since i run both an oem ecu and a utec, my goal is to better understand the effects of IAT on tuning with both MAF based and SD based systems.

here are some of the results, in order of IAT:











in tabular form, along with the equations:
10/16 8am 39.2F
.1636x + 2.1016

10/13 8am 42.0F
.1671x + 2.0935

10/17 8am 43.0F
.1627x + 2.0848

10/17 5pm 53.1F
.1591x + 2.029

10/19 8am 55.0F
.1614x + 2.0479

10/13 4pm 55.9F
.1559x + 1.9868

10/19 5pm 64.0F
.1548x + 1.9689

10/12 5pm 68.0F
.1532x + 1.9336

10/18 4pm 71.1F
.1533x + 1.949

Code:
temp	slope	int	int/10
39	0.1636	2.1016	0.21016
42	0.1671	2.0935	0.20935
43	0.1627	2.0848	0.20848
53	0.1591	2.029	0.2029
55	0.1641	2.0479	0.20479
56	0.1559	1.9868	0.19868
64	0.1548	1.9689	0.19689
68	0.1532	1.9336	0.19336
71	0.1533	1.949	0.1949
and the above data graphed:


now, there is a definite source of error in that i was NOT actually logging IAT for these runs. instead i assumed IAT would be similar to the ambient air temp seen at the closest logged temperature station, and that is at TF green airport in warwick, approximately 9 miles south of where these runs were taken. from now on i am actually logging IAT and will update this thread as more data is collected. i suspect some of the scatter in the last chart is due to inaccurate IAT assumptions.

as for analysis, we can see that the left hand end of the trendlines in the MRP/LOAD charts are all in very similar locations. however, the right ends vary inversely according to IAT: the lower IAT is, the higher the LOAD for a given MRP. there is tight correlation between slope and intercept, as would be expected if one end of the trendline is fixed.

i am predicting that as the turbo and IC fall out of efficiency, we will see a drop in the slope: basically, more MRP is needed to net a given increase in LOAD. there doesn't yet seem to be a dropoff so far despite running quite high MRP. logging higher boost pressures will be an issue since i am already maxing out the oem MAP sensor (this is another possible source of error).

there is also an interesting trend in the "vacuum" portion of the plots--it seems like the slope is slightly smaller than that of the "boost" portion. this effect is even more pronounced above 10-12psi, which is my wastegate spring tension. this tends to indicate that VE is generally lower in the vacuum areas. i think a possible source of this stems from the fact that until the turbo spools up and generates positive manifold pressure, the engine has to literally suck air through the filter, intake pipe, and compressor (which is not the case when "on boost").

one of the goals of this exercise is to derive a temperature compensation trend for the SD mode of my utec. the other is to attempt to determine just how far i can push the vf23. as can be seen, increases of MRP up to this point have resulted in very predictable and linear increases in LOAD. it is my hypothesis that the "end of the line" for a turbo/ic combo will be shown by a sharp decrease in "slope" as defined in the first set of graphs.

comments welcomed!

ken
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Old 10-20-2006, 01:35 PM   #2
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Interesting read..
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Old 10-20-2006, 09:13 PM   #3
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Originally Posted by ride5000 View Post
there is also an interesting trend in the "vacuum" portion of the plots--it seems like the slope is slightly smaller than that of the "boost" portion. this effect is even more pronounced above 10-12psi, which is my wastegate spring tension. this tends to indicate that VE is generally lower in the vacuum areas.
Why does this at all suprise you? Under low throttle the engine is sucking at the intake ports against a vacuum and pumping out into atmospheric pressure + backpressure. So the exhaust backpressure is >>>> than the intake manifold pressure.

High (backpressure/intakepressure) ratio = low VE ... or did you mean something else?

Quote:
Originally Posted by ride5000
one of the goals of this exercise is to derive a temperature compensation trend for the SD mode of my utec. the other is to attempt to determine just how far i can push the vf23. as can be seen, increases of MRP up to this point have resulted in very predictable and linear increases in LOAD. it is my hypothesis that the "end of the line" for a turbo/ic combo will be shown by a sharp decrease in "slope" as defined in the first set of graphs.
Absolutely! I would venture to say that it's THE most effective means of determining overal efficiency of a setup with the data available through the stock sensors. Since you cannot calculate real VE with a static MAP sensor, finding trends is a novel solution. Cheers.

Here's something else to consider for normalizing your data: RPM will affect the slope as well as the pressure the MAP sensor "sees" is artificially lowered by the Bernoulli effect of the moving intake gasses. It's probably not a HUGE effect, but it will alter the data to some degree.
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Old 10-21-2006, 11:58 AM   #4
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Would it suit the situation more to analyze the data with two trend lines? One in vaccum and low boost as you said and one above?
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Old 10-23-2006, 08:08 AM   #5
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Would it suit the situation more to analyze the data with two trend lines? One in vaccum and low boost as you said and one above?
yes, i might try that today.

at some point i actually have to do some WORK though!
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Old 10-23-2006, 08:13 AM   #6
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Originally Posted by SaabTuner View Post
Why does this at all suprise you? Under low throttle the engine is sucking at the intake ports against a vacuum and pumping out into atmospheric pressure + backpressure. So the exhaust backpressure is >>>> than the intake manifold pressure.
the thing is, that's also definitely the case when at high boost as well. there IS a narrow range of operation in which the backpressure is indeed lower than the boost pressure, but it's in the low to midrange area. i'd expect the slope to be higher there, but lower at the extremes. so far that's not holding true, at least with my setup/data.

see also: http://bbs.22b.com/cgi-bin/ultimateb...117;p=2#000054
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Old 10-23-2006, 11:11 AM   #7
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Originally Posted by ride5000 View Post
the thing is, that's also definitely the case when at high boost as well. there IS a narrow range of operation in which the backpressure is indeed lower than the boost pressure, but it's in the low to midrange area. i'd expect the slope to be higher there, but lower at the extremes. so far that's not holding true, at least with my setup/data.
What about the throttle? Seems to me having a huge restriction in the system would throw off turbocharger efficiency, and thus VE, just like a restrictive intake, intercooler, or small throttle body.

I'd think of it this way: if increasing the throttle opening, by installing a large aftermarket throttle body, increases VE, why couldn't decreasing the throttle opening, to something veeeeeerry verry small, dramatically lower the VE? Even just lower it a little?

Does that make sense?
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Old 10-23-2006, 11:32 AM   #8
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Quote:
Originally Posted by SaabTuner View Post
What about the throttle? Seems to me having a huge restriction in the system would throw off turbocharger efficiency, and thus VE, just like a restrictive intake, intercooler, or small throttle body.

I'd think of it this way: if increasing the throttle opening, by installing a large aftermarket throttle body, increases VE, why couldn't decreasing the throttle opening, to something veeeeeerry verry small, dramatically lower the VE? Even just lower it a little?

Does that make sense?
yes, i totally agree that the throttle absolutely decreases VE... that's how it works.

but there is no evidence to suggest that the low rpm/low load/-ve mrp areas are at small throttle angles. in fact, just the opposite tends to be true. i have a LOT of lines at <3krpm and >80% tps.
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Old 10-23-2006, 01:58 PM   #9
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Originally Posted by ride5000 View Post
but there is no evidence to suggest that the low rpm/low load/-ve mrp areas are at small throttle angles. in fact, just the opposite tends to be true. i have a LOT of lines at <3krpm and >80% tps.
And this suprises you ... why? Most cars have a much lower VE at low RPM, especially high-ish revving Japanese turbo sports cars.

I used to have a VE map of the old 2.2L N/A, which showed pretty much the same VE behavior I'd expect in the 2.0L, and even 2.5L, Subie motors. Peak VE = ~ 4,000 RPM and in the low 90% range. High 70's below 3,000 RPM or so, and mid 80's towards redline. I wish I still had the paper. It's where I got the vibrational map for the Subie boxer setup. I got it from a post on NASIOC, but don't recal the conversation in which I found it.

Anyway ...

Low RPM = Low VE = Totally expected behavior.

Low Throttle = Low VE = Totally expected behavior.

No mystery here, methinks.
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Old 10-23-2006, 03:34 PM   #10
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Is this the plot?


The text portion talks about a dual resonance intake manifold (primary, secondary) on a 2.0L engine.
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Old 10-23-2006, 04:25 PM   #11
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Quote:
Originally Posted by SaabTuner View Post
Low RPM = Low VE = Totally expected behavior.
high rpm = low ve also = we don't see the behavior. why not?

Quote:
No mystery here, methinks.
methinks you like to oversimplify, and that's ok. you may be satisfied with your answer, but i'm not.
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Old 10-23-2006, 05:42 PM   #12
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Yea you really need a different linear equation for vacuum/boost. The trend is the same but the accuracy of the data suffers. Not like it really matters, its the trend you are looking for.

Basically you found a really complicated way to express what we already know This also works into what I'm looking at...IAT error versus its effect on fuel.
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Old 10-23-2006, 07:00 PM   #13
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Originally Posted by ride5000 View Post
high rpm = low ve also = we don't see the behavior. why not?
Hinted to that explanation in my first post as it is something I've seen frequently in datalogs and discussed here before. See: Bernoulli effect.

To calculate real VE requires total pressure, static pressure and temperature, not just static pressure and temperature. You have to use the difference between the pressures to find dynamic pressure. Once you do that, combined with temperature, you have density and, if you have area, you have volume flow, and implicitly massflow, as well.

There's no solution to a speed-density setup if you have ONLY static pressure and temperature. The gas could be VERY dense, but moving very very quickly. Or it could be less dense, and moving much more slowly. Both would give identical static pressure and temperature readings despite totally different massflows through the SAME pipe.

Quote:
Originally Posted by ride5000
methinks you like to oversimplify, and that's ok. you may be satisfied with your answer, but i'm not.
Well, you know me; I'm always game to have holes poked in my argument. Get on it!

Quote:
Originally Posted by Airboy
Is it this plot?
Sooooort-of. It looked similar to that, if it wasn't that. I lost it when I lost my hard-drive last year. Still have the vibration maps because they were uploaded to photobucket.

-Adrian
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Old 10-24-2006, 08:18 AM   #14
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Quote:
Originally Posted by SaabTuner View Post
Hinted to that explanation in my first post as it is something I've seen frequently in datalogs and discussed here before. See: Bernoulli effect.

To calculate real VE requires total pressure, static pressure and temperature, not just static pressure and temperature. You have to use the difference between the pressures to find dynamic pressure. Once you do that, combined with temperature, you have density and, if you have area, you have volume flow, and implicitly massflow, as well.

There's no solution to a speed-density setup if you have ONLY static pressure and temperature. The gas could be VERY dense, but moving very very quickly. Or it could be less dense, and moving much more slowly. Both would give identical static pressure and temperature readings despite totally different massflows through the SAME pipe.
adrian, does any commercially available EMS used on any car in the world perform such a complicated measurement of manifold pressure?

you seem to have copious amounts of book knowledge, and that's a great asset to the community. however, real-world results don't lie, and i have NEVER seen any evidence that one must take into account the bernoulli effect when calculating manifold pressure in order to effect a stable and predictable AFR while using speed density algorithms. if nobody who either tunes engines or manufactures engine management systems seems to think it's introducing that much error in the equations, then i believe them, despite the theoretical arguments to the current method's inadequacies.
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Old 10-24-2006, 05:49 PM   #15
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Originally Posted by ride5000 View Post
adrian, does any commercially available EMS used on any car in the world perform such a complicated measurement of manifold pressure?

you seem to have copious amounts of book knowledge, and that's a great asset to the community. however, real-world results don't lie, and i have NEVER seen any evidence that one must take into account the bernoulli effect when calculating manifold pressure in order to effect a stable and predictable AFR while using speed density algorithms. if nobody who either tunes engines or manufactures engine management systems seems to think it's introducing that much error in the equations, then i believe them, despite the theoretical arguments to the current method's inadequacies.
If the current method had a solution, you wouldn't NEED an O2 sensor for tuning. If you actually knew the speed of the airflow and its density, you'd have massflow.

Think you could tune an engine to a predictable A/F ratio with just a static MAP, temp and RPM setup without an O2? Heck, you could even have a VE map and you still wouldn't get predictable A/F ratios as the engine speed rose: you'd run lean.

The reason, if you have an O2 sensor, you can tune a static MAP setup is that the error is constant for any given load point. It varies across the ECU's map, but each load point has a constant error. You use the O2 to correct for the error by mapping the resulting A/F ratio for each load point.

You are also only interested in massflow when calculating fuelling. Unfortunately, when calculating VE, you have to be more specific since you actually have to know the volume of the gas going into the engine, and not just the massflow. Even an O2 sensor will not give you sufficient information to solve for volume flow with just static MAP, temp and RPM.

Anyway ...

Next time I'd appreciate it if you'd ask me what I mean by something before dismissing it as lack of "real world experience". It's pretty irritating to be told that every time I argue anything, whether I'm right or not.
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Old 10-25-2006, 10:22 AM   #16
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Quote:
Next time I'd appreciate it if you'd ask me what I mean by something before dismissing it as lack of "real world experience". It's pretty irritating to be told that every time I argue anything, whether I'm right or not.
next time, i'd appreciate it if you'd refrain from argumentatively obfuscating matters, as you're fond of doing, on purely theoretical grounds. perhaps then you wouldn't take comments that your points lack the perspective of empirical evidence so personally. as you asked yourself, why does this at all suprise you?
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Old 10-25-2006, 10:56 AM   #17
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so i did a bit more graphing and crunching.

it seems like the best way to get a handle on the turbo's limits is to set the dependent variable to engine load divided by MAP. this represents a sort of instantaneous "VE" value.

then by graphing load/MAP vs. various independent variables we can see different trends. for example:



the maximum VE occurs right where we expect it to, in the 3k5 to 4k5 rpm range. (interestingly the minumum VE also occurs in that rpm range.) however there does not seem to be much of a trend to the VE vs. RPM plot.



here with VE plotted against TPS we see better correlation... there's a bit more of a distinct shape to the points. however we can see that tps = 100 and tps = 0 both have a lot of VE variation.



the same data looked at from the perspective of MAP being the independent variable. it has slightly better correlation than the TPS chart, but there remains the limitation of the MAP sensor being maxed out, and now it is affecting both the VE calculation AND the X-axis range.

nonetheless we can see a trend emerging--there seems to be two distinct regions: from 7psia to 20psia the VE is increasing steadily at a certain rate, but from 20psia to 37psia that rate decreases. 20psia is ~ 5psig. this trait can also be observed on the first set of graphs.



this has the tightest, clearest pattern yet. it is pretty obvious where the sweet spot of the turbo is in terms of mass flow rate--between 150 and 225g/s.

as a result of these charts i have come to two conclusions:

1) i am not going to be able to squeak much more MAF through this turbo. the VE vs. MAF characteristic is taking a definite dive at 275g/s or so. this is not that surprising as there is a pretty hard limit as to how much air mass a given turbo can flow, and the vf23's choke seems to be in the 275g/s range.

2) the VE vs. MAP characteristic does not show as severe a trailing off at the right hand side of the chart. i take this to mean that my EGBP to MRP ratio has not risen to ridiculous levels. i may be able to increase boost pressure even higher without taking a disproportionate hit in charge temps in the midrange rpms (where MAF is not at a maximum). the only downside here is that i have already exceeded the limit of the stock MAP sensor, and i won't be able to really correlate the data to what i've already collected.

so 26psi here i come.
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Old 10-25-2006, 12:09 PM   #18
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the maximum VE occurs right where we expect it to, in the 3k5 to 4k5 rpm range. (interestingly the minumum VE also occurs in that rpm range.) however there does not seem to be much of a trend to the VE vs. RPM plot.
Looks like "horse" power.
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Old 10-25-2006, 01:05 PM   #19
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Looks like "horse" power.

lol...
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Old 10-25-2006, 05:41 PM   #20
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Ken,

load/map vs TPS you get a lot of variation, as you stated. Does that graph have different gears plotted in it? I would imagine with a different acceleration rate that the VE would seem to change beacuse of the generated load and MAP not increasing/decreasing at the same rate.

Also 26 PSI might be paper possible but what kind of effects is that going to have on the turbo itself in terms of turbine speed? I dunno what its RPM is but it might be pretty high. Makes me want to turn up the VF22 tho . I'm already beating the crap out of it with the way my BOV is setup...might as well spin it out of whack while I'm at it
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Old 10-25-2006, 11:57 PM   #21
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next time, i'd appreciate it if you'd refrain from argumentatively obfuscating matters, as you're fond of doing, on purely theoretical grounds. perhaps then you wouldn't take comments that your points lack the perspective of empirical evidence so personally. as you asked yourself, why does this at all suprise you?
I hadn't intended to be argumentative. You noted that the "VE" doesn't fall as quickly at high RPM as you'd expect. I pointed out that you weren't actually measuring Volumetric Efficiency, because you can't with a static MAP. I was trying to be helpfull.

Anyway, the "VE" versus RPM graph might look very interesting if you only plotted full-load (or full throttle) points. Worth a shot?
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Old 01-10-2008, 10:14 AM   #22
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taken this morning (38*F):



the r^2 is hard to see but it's 0.9844

details of change here: http://forums.nasioc.com/forums/show....php?t=1423468
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Old 01-11-2008, 08:07 AM   #23
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I posted a question in your other thread great info as always ken.
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Old 01-11-2008, 09:03 AM   #24
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I knew I should have stayed in college.
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Old 03-31-2008, 09:44 AM   #25
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44* f, w/synic el headers

after playing with these headers for a while, i have noticed that:

spool is quicker
high flow / high rpm VE is higher

BUT

the vast majority of low-mid range flow VE is unchanged.

this is somewhat surprising to me as i had anticipated higher VE across the board due to improved scavenging, but the data hasn't borne that out.
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