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Why datalog?
https://slantsix.org/forum/viewtopic.php?t=41603		 Page 1 of 1
Author:  GunPilot [ Tue Aug 24, 2010 7:26 pm ]
Post subject:  Why datalog?
The graph below is a datalog of one of my runs on Saturday afternoon at Kearney. It records RPM (yellow), throttle position (purple), manifold pressure (light blue), injector pulsewidth (white) and duty cycle (light green), coolant temperature (dark blue), and air/fuel ratio (dark green).

Looking at the left side of the graph, the purple trace shows the stage, as it goes from near 0% open (idle) to about 5% as I footbrake up for the stage. The RPMS come up also and level off as the converter comes to it's stall (about 1700 rpm, stock). Duty cycle and PW jump around as the Megasquirt tries to compensate for a less than optimal tune at that RPM and manifold pressure.

Once staged, I increased the throttle opening to max (99% in this case. The kickdown rod was preventing that last 1%) and manifold pressure rises to near ambient air pressure (94 KPA) but RPMs stay about the same.

Coolant is above 215 which is where the graph is set to record; it was probably somewhere around 220.

Brake release is shown by a slight decrease in RPMs and the rise up to the 4000 RPM shift point. AFR shows an interesting dive to the rich side at that point - more later on that.

The TF 904 was shifting presicely where I wanted it at 4000 rpm. Manifold pressure at 94, injector duty cycle following RPM. AFR settled down around 13:1.

At the end of the run, shutdown as the throttle plates close and manifold pressure dives with it along with everything else. AFR goes rich as fuel puddles up.

Based on this graph, Lou and I adjusted the pump shot leaner to reduce the over rich mixture at launch, and I leaned the VE tables at the 1700-ish RPM level to smooth the engine and make it run better in that MP and RPM range.

Net result? About a .250 improvement on the next pass.

Datalogging is very cool.

Image
Author:  GunPilot [ Wed Aug 25, 2010 9:27 am ]
Post subject: 
Some more data that can be extracted from the log: The manifold absolute pressure (MAP) line shows that there was never any vacuum in the manifold at WOT. This verifies that my throttle body is not a restriction. I'm running venturi spacers that bring it to about 400 CFM according to the vendor. So, as expected, on a stock motor, 400 CFM is more than enough.

I can watch that graph as mods are made to the motor, and if I see the MAP line coming down, i.e., a vacuum produced in the manifold, then it's time for more TB CFM. BTW Sam, this goes somewhat to your TB sizing question in the other thread. You could use this method (assuming you have not already) to look at TB sizing.
Author:  Dart270 [ Wed Aug 25, 2010 9:31 am ]
Post subject: 
George,

Thanks for posting and telling the story - very cool.

Yes, I have looked for this before when tuning my cars - drop in MAP at higher RPM at WOT. Sam should certainly do this.

Lou
Author:  GunPilot [ Wed Aug 25, 2010 9:59 am ]
Post subject: 
More info - the max injector duty cycle was about 60%. This out of a theoretical max of 100% duty cycle on the injectors. What this means is that my injectors are sized pretty well, at least considering that I want to increase the output of the engine from here. I have that 40% remaining duty cycle to grow with, before the engine needs sufficiently more fuel that I have to change the injectors out to a larger size (flow).

Realistically, once duty cycle goes over 85% or so, it's probably time to think about upgrading.

Watching that duty cycle is an indicator of engine output too. If I make a mod, like head porting, I would expect to see an increase in duty cycle as the controller increases fuel flow to keep AFR correct in an engine that is flowing more air.
Author:  Dart270 [ Wed Aug 25, 2010 11:04 am ]
Post subject: 
What is each of the 4 injectors rated at?

Lou
Author:  GunPilot [ Wed Aug 25, 2010 12:23 pm ]
Post subject: 
Great point Lou. 30 PPH. So, conservatively using a brake specific fuel consumption (BSFC) of .5, the 4x 30 pound per hour injectors can support 240 hp.

I could probably delve into the fueling equation and use the duty cycle, pulse width, and AFR to determine HP all along the graph, but I'll just swag it using ET and the weight of the car and say it was around 100 HP ;)
Author:  Dart270 [ Wed Aug 25, 2010 2:16 pm ]
Post subject: 
That is a good size. For reference, I have 24 lbs/hr X 6 in the '68 Dart and 85 lbs/hr X 2 in the '64 Dart. I am close to the duty cycle limit on the '64 Dart.

Lou
Author:  emsvitil [ Wed Aug 25, 2010 3:12 pm ]
Post subject: 
What's the conversion for O2?

Just wondering what the AF ratio is.



What are you using for the datalogging?
Author:  GunPilot [ Wed Aug 25, 2010 3:31 pm ]
Post subject: 
Quote:
What's the conversion for O2?

Just wondering what the AF ratio is.



What are you using for the datalogging?
I'm using the LC-1 wideband, using 0 to 5 volts, with 0 being rich (about 9:1 AFR) and 5v being lean (over 20:1 AFR) so the AFR in the graph is about 13:1.

I used the datalogger built into the Tunerstudio software. Megatune has it too but I kept losing the file. The graph above was produced with Megalogviewer software.
Author:  Sam Powell [ Thu Aug 26, 2010 8:27 am ]
Post subject: 
With the turbo, the boost number will likely stay the same through the RPM range, and the boost number is the same as the MAP reading. At least I do not see it dropping off on the gauge as I reach higher RPM's. It hangs right at 8. So it seems the thing to do is to get a boost control going and raise the boost until I see either detonation or a drop in map at upper rpms at wot. Does that logic make sense? What am I overlooking here?

Sam
Author:  Dart270 [ Thu Aug 26, 2010 10:32 am ]
Post subject: 
Oh yeah, with a turbo, the wastegate will likely regulate the boost so that the MAP reading does not drop at higher flow/RPM. Maybe that won't work to test your TB.

Lou
Author:  Sam Powell [ Fri Aug 27, 2010 4:43 am ]
Post subject: 
Not to high jack the thread here, but, if I raise boost levels, should I be tweaking the MAP values assigned to the cells in the fuel map. I don't know how they got assigned in the first place. Did you do that Lou? And if I go with MS II I am going to have more cells to divide up the RPM and MAP values into, so I will have to get into that some day. Maybe the Map divisions are set when I selected what type of Map sensor I have.

I am not sure what 8 lbs of boost converts to in KPA. I would think 150. Is that close? It is kind of weird that we ended up with an Imperial system where we combine inches of mercury and lbs of boost. It all seems very disconnected, like the jokes where someone says our two choices are 1 and B. But being a kid in the 50's that is the language that means something to me, and not KPA,. I am sure it easy to find on the internet. This is just kind of out loud gentle complaining about illogical cultural customs.

Sam
Author:  Dart270 [ Fri Aug 27, 2010 5:48 am ]
Post subject: 
You and I would have set those VE table values at high MAP values. Yes, MSII would be a good upgrade to get more resolution on the lower and upper end for tuning.

I agree on the unit craziness. Humans, and especially Americans, are very stubborn. Metric is nicer and easier and everyone else uses it...

101.3 kPa = 1.000 atmosphere = 29.92 in Hg = 14.70 psi
(wikipedia)

So 8 psi of boost is 156 kPa at "standard" sea level, or more like 145-150 kPa under normal conditions.

Lou
Author:  GunPilot [ Fri Aug 27, 2010 12:21 pm ]
Post subject: 
Hijack away fellas. This thread was created to foster this kind of discussion. All good stuff.
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