Author Topic: Question on Relative Air Density readings  (Read 12315 times)

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Offline stay`tee

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Question on Relative Air Density readings
« on: March 25, 2014, 02:23:33 AM »
i would assume that in automotive EFI Computers the maximum RAD would be read as 100*, what would be the minimum RAD setting for "trim" purposes, :?,, is there an Industrie Standard regarding these settings, ?,,
« Last Edit: March 27, 2014, 11:27:50 AM by Seldom Seen Slim »
First Australian to ride a motorcycle over 200mph at Bonneville,,,

Offline JimL

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Re: Question on Ralitave Air Density readings,,
« Reply #1 on: March 26, 2014, 11:38:30 PM »
Density Altitude is pretty much "automatically" covered by the use of hot-wire anemometer Mass Airflow Meters on our cars.  The ECUs have a positive/negative 40% fuel trim correction available (actually..more, but the check engine light comes on!)  It lives based on what it sees from the wide-band air-fuel ratio sensor.  Additional oxygen sensing is performed after the cat to fine tune cruise performance at whatever altitude we are driving. MAFs give the intake air temp very accurately by the data read from their Wheatstone bridge circuit.  Many modern cars, that have an outside air temp on the dash, are actually getting that number from the engine ECU, not from a separate temp sensor.

Modifying MAF systems is tricky because you can get outside of the design range of the stock hot-wire MAF.    MAF systems for blown engines can require some pretty expensive shapes to cover enough range of air measurement.  The problem is that hot-wire systems are most responsive at their lower air flows, and get less "fine" as you get to the max capacity of measurement.  That sensitivity at lower flow, to small changes, is what makes them wonderful for emission control vehicles.  It also makes them a great tool for your lung doctor...but thats another dizzying story that aint as much fun as racing.

The MAP systems (absolute manifold pressure) also tell the efi what available air is seen in the manifold, but not as accurately at low throttle openings.  If the car is a non-turbo or non-supercharged (with a standard MAP sensor), it will be very accurate up to a maximim of positive 4.3 psi in the manifold.  The silicone sensing plug will cave in at about that level.  Blown/turbo MAP sensor vehicles often have 2-3 bar sensors (2-3 times atmospheric pressure).  When you run higher "bar" sensors, you can adjust for more boost, but you lose data points in the wide range mapping.  Most of us use MAP systems for racing because they are simple, durable, and cost a lot less. 

The MAP systems had to have separate air temp sensors, which you find plugged into the side of the air filter box.  For a dashboard thermometer, another sensor was used behind the grill, ahead of the radiator.

If you are running EFI, in feedback control, you will pretty much get "as good as you get".  The last cars I saw with an altitude sensor in the ECU were the old P7 type systems with a vane type AFM.  They only checked for "over 4300 feet" or "under" because there were different standards for "high altitude emissions" back then.  I think there are some altitude sensors still used, but dont know for sure.

Aside from having enough injector capacity for the target HP, you probably wont get in trouble on your EFI tuneup unless you get too big on your injectors.  If you cannot run at fairly low (or idle) rpm...at minimum 1.5 millisecond injector duration, you will have trouble.

Intake air temp + manifold absolute pressure ( + intake plenum temp for blown/turbo) = about right for DA

Hope this wasnt too muddy, and it was what you were looking for.  If not, "dont shoot the piano player...he's doin' the best he can...". (I saw that sign on a piano in an old saloon in Colorado...how true it is.)

JimL

Offline stay`tee

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Re: Question on Ralitave Air Density readings,,
« Reply #2 on: March 27, 2014, 02:49:38 AM »
Thankyou Jim, i think that you have given me the answer i was lookin for in your second sentance, "positive/negarive 40%",, the following information given, i will have to digest and maybe questions will arise from there,,
one of the reasons i initally asked is because my bike is running on Menthanol with a PC over the standard computer (reads MAP and Temp), at Gairdner (RAD mid,low 90's, bike dynoed/tuned at 94) it works fine, but last year at Bonneville(RAD around low 80's),?, well, i question the fuel trim,, from what you say, the way i see it is that with gasoline you could see up to 40% trim (at Bonneville's altitude), however with Menthanol this trim would equate to maybe 20%??,, (given the differing A/F ratios),, am i on the right track here,?, im ol'skool, this white man magic stuff looses me at times, LOL :-)   
First Australian to ride a motorcycle over 200mph at Bonneville,,,

Offline grumm441

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Re: Question on Ralitave Air Density readings,,
« Reply #3 on: March 27, 2014, 06:51:56 AM »
Hey Ron
Are you going to stick with the standard ECU or are you going for something more adjustable
G
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https://www.dlra.org.au/rulebook.htm

Offline stay`tee

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Re: Question on Ralitave Air Density readings,,
« Reply #4 on: March 27, 2014, 07:11:01 AM »
Hey Ron
Are you going to stick with the standard ECU or are you going for something more adjustable
G


 trying to determine if i have enough tunablity within the PC111, given "worst case air", for Methanol at Bonneville,,
First Australian to ride a motorcycle over 200mph at Bonneville,,,

Offline JimL

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Re: Question on Ralitave Air Density readings,,
« Reply #5 on: March 27, 2014, 10:49:19 AM »
I dont know how much your bike ECU is programmed like our OBD II cars.  The real question is:  What size injectors on what size cylinder, and what is the horsepower target per cylinder?

When we ran our roadster on 435cc injectors, I burned it down running in the 180 mph range.  With everything the same, but 550cc injectors, it ran the same speeds with no damage.  That was the same ECU in both cases (actually a standard, factory, Toyota WRC computer as used by the WRC rules in those days).  Generally, 500cc/min on a 500cc cylinder was capable of roughly 100 hp.  We didnt have enough cam, turbo, or plenum to actually reach 400 hp on that 2000cc 4-cylinder roadster.

For my bike EFI, the folks in Torrance have specd' 45 lb/hr injectors to allow up to about 75 hp per cylinder.  Because it is only 340cc per cylinder, it wont make that 75 number.  

All in all, this is remarkably close to my old 1988 WRC ECU which was really programmed for about 300 hp from four 500cc cylinders....which was the upper safe limit on the standard 435cc injectors required by those old rules.  WRC today is a whole different animal, and the cars are no longer required to run factory stock fuel injection systems.

There are certainly some sharper folks on here, about what you and I are trying to learn, but these notes give an idea of where we are.  Curiously, this is all very much like Mikuni carb jetting where the jet number tells you the fuel flow rate of the main jet orifice size.  Running my bike on 41mm Mikunis, unblown, with 230 mainjets....gets me about 40 HP per cylinder (2 cylinders) worth of time slips (usually around 160 mph).

Pretty interesting parallel between carbs and efi, dont you think?  In the end, its just mixing air and fuel at the right ratio.

JimL
« Last Edit: March 27, 2014, 11:14:30 AM by JimL »

Offline maj

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Re: Question on Relative Air Density readings
« Reply #6 on: March 27, 2014, 04:38:06 PM »
Ronnie your starting to get to the same questions i did just before changing to a standalone ecu on the 750
when you change injectors you end up with different opening and closing times (latency)to what the std ecu is programmed for ,
 
So for example if you converted a stock bike to methanol and calculated you need a 2.5x injector size change to flow the same amount of fuel
so you fit the exact size injectors , but find in the low rpm stuff the bike is running lean, through the mid range its not bad but rich up top
because your new injectors take longer to open and on small duty cycle numbers its a major part of that

then add in your various sensors all making the ecu vary its output duty cycle to suit the conditions its programmed for , but this now is multiplying the systems innacuracy

Then you put a powercommander on and correct the fueling based on TPS  , but you have only corrected it in a given temp and pressure range  that it was tuned in

When i retuned my bikes at Scotts last yr the standalone on the 750 only needed a couple of runs and minor adjustments,and it read same at 4500ft as here at 600
but the busa with its factory ecu needed many runs and a lot of adjusting to be correct
i now have 2 ecus 1 with my Aussie tuneup  and a second for Bonneville

The difference with the standalone ecu is you tell it the changes in injector characteristics , and you can adjust the correction factors
I was intending to put a standalone on the busa now for my methanol conversion, but think i will run out of time with everything else going on and will revert back to E8D and the Bonneville ecu

I would suggest you book into Scotts and we plan to get the bikes into the US a few days earlier

Offline firemanjim

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Re: Question on Relative Air Density readings
« Reply #7 on: April 08, 2014, 04:40:20 PM »
"I would suggest you book into Scotts and we plan to get the bikes into the US a few days earlier "
or he loads everything he owns in the container and moves over! :cheers:
Bonneville 2001,2002,2003,2004,and NO stinking 2005,DLRA 2006, next?
Well,sure can't complain about 2008--6 records over 200 and 5 hats from Bonneville,Bubs, and El Mirage for the team!