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Old 09-08-2012, 03:01 AM   #651
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Would you mind elaborating?

Load is basically just MAF / RPM, so I don't see how corrections are going to make much difference. I can't figure out what you're getting at. There are corrections that affect fueling in response to delta-load, but that's a whole other ball of wax...
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Old 09-11-2012, 12:44 PM   #652
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Quote:
Originally Posted by NSFW
Would you mind elaborating?

Load is basically just MAF / RPM.
Not quite. Load is maf/rev. RPM has a time component which is not present in load. I know I am nitpicking but its worth mentioning
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Old 09-11-2012, 01:49 PM   #653
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Quote:
Originally Posted by Ziggyrama View Post
Not quite. Load is maf/rev. RPM has a time component which is not present in load. I know I am nitpicking but its worth mentioning
MAF = kg/s
RPM = 1/s

MAF/RPM = (kg/s)/(1/s) = kg/s*s = kg.

In other words, no time component
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Old 09-11-2012, 04:06 PM   #654
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Quote:
Originally Posted by AruisDante View Post
MAF = kg/s
RPM = 1/s
MAF/RPM = (kg/s)/(1/s) = kg/s*s = kg.

In other words, no time component
RPM = rev/min which in units might boil down to 1/time, but you have to divide by 60 to get to that point which is pretty important. Also maf is generally measured as g/s not kg/s on these cars. While revolutions might not seem like a unit to you, it's important because the ecu needs to make a comparison between the 2 axes. So load boils down to g/rev and the way it compares that to RPM, without the /rev in the definition of load you really can't make a comparison to anything. But yes not really a time component. Just related to time through revolutions.
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Old 09-11-2012, 04:18 PM   #655
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Quote:
Originally Posted by kakarot09 View Post
RPM = rev/min which in units might boil down to 1/time, but you have to divide by 60 to get to that point which is pretty important. Also maf is generally measured as g/s not kg/s on these cars. While revolutions might not seem like a unit to you, it's important because the ecu needs to make a comparison between the 2 axes. So load boils down to g/rev and the way it compares that to RPM, without the /rev in the definition of load you really can't make a comparison to anything. But yes not really a time component. Just related to time through revolutions.
is there a particular reason you wanted to confuse things?
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Old 09-11-2012, 06:26 PM   #656
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Quote:
Originally Posted by ride5000 View Post
is there a particular reason you wanted to confuse things?
It's really not confusing.
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Old 09-12-2012, 04:13 AM   #657
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Nor was it the slightest bit enlightening...

I'm still curious how Clark's special tables bend the laws of physics, though.
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Old 09-12-2012, 12:53 PM   #658
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Quote:
Originally Posted by kakarot09 View Post
It's really not confusing.
It's unnecessarily complicated. A revolution isn't a unit. It's just what we are defining as one cycle. 1RPM is very well defined as 0.016Hz, or 0.016 s^-1 (or heck, 0.105 rad/s). If you want to think of it that way, an RPM is 0.016 Rev/s, but it's still all the same thing mathematically.

Maf/rev, however, is not the same thing mathmatically, because that would be g/s (or g/(s*rev) if you want). Therefore, MAF/RPM is the mathematically correct representation.

Last edited by AruisDante; 09-12-2012 at 12:59 PM.
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Old 09-12-2012, 01:11 PM   #659
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Quote:
Originally Posted by kakarot09 View Post
It's really not confusing.
sorry man. perhaps english is not your first language, but these two sentences are pure ****:

"While revolutions might not seem like a unit to you, it's important because the ecu needs to make a comparison between the 2 axes. So load boils down to g/rev and the way it compares that to RPM, without the /rev in the definition of load you really can't make a comparison to anything."

i understand you think you're helping, but stuff like this overly verbose and convoluted explanation utterly misses the point:

load is basically maf/rpm. pump in a couple of conversion factors and the resulting unit is grams.

that's it.
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Old 09-12-2012, 02:02 PM   #660
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Lol ok, well I'm sorry if it was confusing, my bad. I agree that it basically boils down to grams but it is necessary for the /rev to be there. Without it there is no basis for comparison to anything.
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Old 09-12-2012, 02:51 PM   #661
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Except it's not, mathematically, because every other parameter you're dealing with (spark, fuel, etc) is also per-revolution. So it's implied. Load is essentially the amount of air, in grams, that needs to be fueled/sparked against. If you were fueling or sparking more than once per revolution, then yes, you would need some more conversion factors to get the appropriate load.

To bring it a step further, load is essentially telling you the maximum torque potential of that motor at that RPM. In a perfect system, if you had a constant load between two RPM ranges you would be able to generate constant torque between those two RPM ranges (assuming the AFR is constant and ignition timing was adjusted appropriately for RPM). In a real system however the load will change based on the volumetric efficiency curve of the engine for a given RPM thanks to good old fashion physics, and so you wind up with non-constant load across RPM.

Last edited by AruisDante; 09-12-2012 at 03:01 PM.
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Old 10-03-2012, 03:23 PM   #662
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FYI, difference between EJ207 AVCS and EJ255/257 AVCS:

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Old 10-05-2012, 06:16 AM   #663
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Quote:
Originally Posted by AruisDante
Except it's not, mathematically, because every other parameter you're dealing with (spark, fuel, etc) is also per-revolution. So it's implied. Load is essentially the amount of air, in grams, that needs to be fueled/sparked against. If you were fueling or sparking more than once per revolution, then yes, you would need some more conversion factors to get the appropriate load.

To bring it a step further, load is essentially telling you the maximum torque potential of that motor at that RPM. In a perfect system, if you had a constant load between two RPM ranges you would be able to generate constant torque between those two RPM ranges (assuming the AFR is constant and ignition timing was adjusted appropriately for RPM). In a real system however the load will change based on the volumetric efficiency curve of the engine for a given RPM thanks to good old fashion physics, and so you wind up with non-constant load across RPM.
You would not want your car to make constant torque value across entire rpm range. You do not need max power all the time. Energy that would not be turned into kinetic energy would have to be dissipated another way, as in heat. You'd end up with 5mpg economy and a giant ball of heat that would likely destroy the car in short order.
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Old 10-05-2012, 09:57 AM   #664
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Quote:
Originally Posted by Ziggyrama View Post
You would not want your car to make constant torque value across entire rpm range. You do not need max power all the time. Energy that would not be turned into kinetic energy would have to be dissipated another way, as in heat. You'd end up with 5mpg economy and a giant ball of heat that would likely destroy the car in short order.
If by that you mean at all throttle positions, then of course. The whole point of a throttle (in the physical sense) is that it drastically affects the VE curve of the engine for that particular RPM and thus changes the load. But flat torque at full throttle from say 2500RPM to redline? That would be the holy grail of engine tuning.

As an example, here's a dynograph of a stock Honda S2000:


Besides the bump at around 6250RPM when VTECH kicks in, it's pretty much a flat torque curve.

Now turbocharged cars are pretty much never going to do that unless you intentionally don't max it out in the lower RPM's. But I was simply using that to illustrate my point about what load represents. If you want to see a turbo car that comes close, here's a 2012 GTR:


It's basically flat from 3500-5250, and I bet if you looked at the engine map there is a constant load between those two points.

Last edited by AruisDante; 10-05-2012 at 10:03 AM.
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Old 10-05-2012, 01:36 PM   #665
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^^^ Agreed, although torque curve can look flat, as you described in turbocharged cars too. IT is definiitely possible given the right blower and cam profile. There are many variables involved but it's doable. For example, if I had a snail that could keep up with my EJ257 above 4800RPMs, I could continue to increase the flow such that my torque curve is flat as RPMs increase. Would I want to do that? It depends on many things.

I think we're digressing here a bit.

I just reread this:

Quote:
Originally Posted by AruisDante View Post
...
To bring it a step further, load is essentially telling you the maximum torque potential of that motor at that RPM.
I don't want to split hairs here but that is not accurate. Load typically goes in lockstep with torque output at the given moment. It is not the max potential of torque. That is some theoretical limit that the engine could achieve given perfect condition. I am having a hard time quantifying max torque potential actually. But I definitely know that it is not load
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Old 10-12-2012, 11:18 PM   #666
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"Real" load is measured in peak cylinder pressure and brake mean effective pressure. Since lab-grade combustion analysis equipment costs as much as most people's cars, we're left quibbling over this stuff.

Quote:
Originally Posted by AruisDante View Post
Now turbocharged cars are pretty much never going to do that unless you intentionally don't max it out in the lower RPM's. But I was simply using that to illustrate my point about what load represents. If you want to see a turbo car that comes close, here's a 2012 GTR:

It's basically flat from 3500-5250, and I bet if you looked at the engine map there is a constant load between those two points.
Most new turbo engines have flat torque curves from about 1800-5500rpm. Have you looked at the dyno curves on new BMW (M5) and Audi (S8) twin turbo V8's?
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Old 11-18-2012, 07:32 AM   #667
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I did some 4th gear pulls in my 2005 STi yesterday. The ONLY thing that I changed in the maps between the pulls was AVCS targets. I did the pulls back to back on the highway. Traffic was light here on the "mostly speed limit ignored" Italian highway right by my house. I have a VF39, stock airbox with silicon after MAF and turbo inlet, catted TBE, 08+ STI intercooler, and stock header/UP. For the boost tables, my target boost is the heavier red line. For AFR I have an Innovate LC-1. Anyway, screen shots of the results are below.

Boost for AVCS values 0, 5, 10, and 15


Boost for AVCS values 20, 25, 30, 35, and 40


MAF for AVCS values 0, 5, 10, and 15


MAF for AVCS values 20, 25, 30, 35, and 40


AFR for 0, 10, 20, 30, and 40


Although boost was higher with more AVCS in the upper RPM range, MAF readings showed the same or less airflow. So although 0 AVCS had the lowest boost, it also had essentially the "best" airflow since it was the same as 5, 10, and 15 but boost was lower. For my setup, aside from AVCS at 0 and 5, spool was the same. Part of that is going to be due to my boost targets for spool-up. I have a different boost target than Cobb in the spool-up region (2200-3300RPM). If you compare them to Cobb's OTS stage 2, I hit 17# at ~3300RPM and Cobb hits 17# at ~3200RPM but the ramp up to 17# is different.

AFR's were identical for every run.
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Old 11-18-2012, 11:12 AM   #668
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I also did some fuel economy testing some time ago using 30 and 40 degrees advance. I did data runs on the same stretch of road back to back only changing the AVCS values. Since I am in Italy and the speed limits around here are 80 and 100 KPH (if they are even followed) I did the tests at 50 and 62 MPH. Here are the screen shots of the results with all the calculations. 40 degrees advance definitely had better fuel economy. I also did a data run at 50 MPH (on a later day though) using an AFR of 15.0 for closed loop fueling.

50 MPH


62 MPH


If you are wondering why I have 5th and 6th gear I will tell you. In a fuel economy thread I read about people claiming our cars will get better fuel economy between 2500 and 3000 RPM vs a lower RPM. In other words, do not cruise at 50 MPH in 6th (2000RPM) instead use 5th (2500RPM). I think I proved that concept completely wrong, as I expected, since 999 times out of 1000 a lower RPM will provide better fuel economy over a higher RPM.
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Old 11-19-2012, 08:48 AM   #669
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^^^ Thumbs up for data!

It makes total sense that you have less boost at the topend at less Intake advance and flow more g/s.
The engine is LESS restrictive which means you will flow more air for the same boost and since you use a more or less fixed WGDC it means that you will have less boost for more airflow.

Jasper.

Last edited by jkopinga; 11-19-2012 at 08:55 AM.
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Old 11-19-2012, 02:54 PM   #670
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@jebjkey, it makes sense. Advancing intake valve at high load opens the valve too early such that the piston is still moving up and slowing the charge down. Also, you have to consider when intake valve closes. If you advance too much, you will move the closure too close to piston's BDC which at high load is not beneficial. In that scenario, you want to close it sometime after BDC because the air rushing in has momentum and can compress against the piston and be trapped in the chamber as it starts to move up. Another point to consider here is that when you advance intake, you create overlap with exhaust valve which in FI applications is not desirable.

Single AVCS STIs are simpler in the way you can tune this and your options are more limited. Dual AVCS really helps in certain scenarios. But that is a story for another time

Lastly, I really hate when people talk about spool and boost as measures of performance. These things are so subjective and typically their interpretation is wrong. For example, more boost earlier in RPM range is typically considered to be a good thing, except that most of the time, more pressure in the intake is a representation of lower VE which "looks" better but it most likely is costing you power. Bad, bad, bad.
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Old 11-19-2012, 04:26 PM   #671
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Quote:
Originally Posted by Ziggyrama View Post
@jebjkey, it makes sense. Advancing intake valve at high load opens the valve too early such that the piston is still moving up and slowing the charge down. Also, you have to consider when intake valve closes. If you advance too much, you will move the closure too close to piston's BDC which at high load is not beneficial. In that scenario, you want to close it sometime after BDC because the air rushing in has momentum and can compress against the piston and be trapped in the chamber as it starts to move up. Another point to consider here is that when you advance intake, you create overlap with exhaust valve which in FI applications is not desirable.

Single AVCS STIs are simpler in the way you can tune this and your options are more limited. Dual AVCS really helps in certain scenarios. But that is a story for another time

Lastly, I really hate when people talk about spool and boost as measures of performance. These things are so subjective and typically their interpretation is wrong. For example, more boost earlier in RPM range is typically considered to be a good thing, except that most of the time, more pressure in the intake is a representation of lower VE which "looks" better but it most likely is costing you power. Bad, bad, bad.
In your last paragraph, some of the oranges and apples got mixed up in my opinion. Working with my fuel, for example, with no changes to AVCS or anything else, I have found earlier spool and more consistent boost habits. I don't consider that a reduction in VE when it produces more power/torque.

In addition, I have found that some overlap with the exhaust has definitely been beneficial to me. It is all about the quantity, and the blend.

Following all the blanket statements in this thread leads nowhere but a circle of frustration.
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Old 11-20-2012, 09:42 AM   #672
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^^^ non of my statements were meant as blanket rules. Please do not read them as such. They were meant for the scenario described by jebjkey: mid to high rpm, high load situations. Valve overlap is desirable in some scenarios.
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Old 11-20-2012, 03:36 PM   #673
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Quote:
Originally Posted by Ziggyrama View Post
^^^ non of my statements were meant as blanket rules. Please do not read them as such. They were meant for the scenario described by jebjkey: mid to high rpm, high load situations. Valve overlap is desirable in some scenarios.

Gotcha. Should have considered the source.
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Old 11-20-2012, 03:53 PM   #674
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jebjkey, can you attach the Excel files? It's hard to figure out what line is what, when you're kind of color blind. And thanks for testing and sharing your findings.
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Old 11-21-2012, 01:33 AM   #675
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