Correction Factor Limits 1

[Craighell]

I read in a Superflow manual that dyno test correction factors out side of =/-7% were generally not regarded as useful (meaningful). My Dynojet manuals have no mention of upper and lower limits and even detail a 1.18 CF for the purpose of explaining the maths. Is there an SAE paper or some other "official" document stating the recognised upper and lower limits of CFs?

Thanks,
Craig

 

[MaxRaceSoftware]

Is there an SAE paper or some other "official" document stating the recognised upper and lower limits of CFs?
------------------------------------

There maybe other papers i'm not aware on Correction Factors

The SuperFlow manual list a few different SAE correction formulas , ....There maybe other SAE papers i'm not aware on Correction Factors that list upper or lower correction limits .

The only thing i've noticed was as temperature (CAT)
dropped below 40 deg F ....it seems like the SF correction
factor was too conservative ?

Alan Patterson of Patterson Racing told me he noticed
the same tendency .

In southern Louisiana , it usually doesn't get
colder than 40 deg F for many days .

Other parts of the country could probably use a different weather correction formula below 40 deg F

Larry Meaux (meauxracing@mindspring.com)
Meaux Racing Heads
MaxRace Software
ET_Analyst for DragRacers

http://www.mindspring.com/~meauxracing/

 

[MaxRaceSoftware]

is the DynoJet weather correction factor something like this ???

DynoJet_CF= 1.18 * (29.92/ABP) * ((((SQR ( CAT +460) / 537 )) - .18

--------------------------------------------------------

i have some formulas i developed off the "old" Weather Correction Chart
that Stuska dyno were using ....i haven't compared Stuska correction to
SAE/SuperFlow ...maybe it might give accurate results over a greater range limit ??
i think DynoJet , Land & Sea , or DTS use different weather corrections also ?

SuperFlow uses the following formula ;

Weather_CF = (29.92 / ( Baro_Press - Vapor_Press )) * ((( 459.7 + CAT ) / 519.7 )^.5)

Corrected_HP = Weather_CF * UnCorrected_HP


in the above there is missing the effects of SuperFlow Friction HP Correction ...
i left it out !!

CAT = Carb Air Temperature in degrees F
STP = Standard Temperature and Pressure
and STP to SuperFlow means = 29.92 BP , 60 deg. F , and 0 % Rh


Below is some weather calculation source code
If you input the dry bulb temperature in degrees F
you will get the corresponding saturation pressure
..then all you have to do is multiply
the Relative Humidity % percent times saturation pressure
to calculate the vapor pressure that you will subtract
from the barometric pressure .

' at 0 deg C 2.036020696 inches Hg = 1 psi

' at 60 deg F 2.041778886 inches Hg. = 1 psi

' Note EXP in QBasic is same as the INVERSE LNx keys on a hand calculator
' Note EXP in QBasic replaces e 2.718281828 ^ number
' EXP in QBasic is the inverse function of the natural log
' it calculates e raised to a specified power

' ===================================================

' Copy - Paste this in QBasic
' QBasic , QuickBASIC computer program
VIEW PRINT: COLOR 15, 1: CLS
start:
LOCATE 5, 5
PRINT USING "Dry bulb = ###.## "; dryf;
LOCATE 5, 30
INPUT dryf$: IF LEN(dryf$) > 0 THEN dryf = VAL(dryf$)

dryr = 459.67 + dryf
satp = 29.9213 / (EXP((671.67 - dryr) * 35.913 * (dryr ^ -1.152437)))

LOCATE 8, 5: PRINT USING "Saturation pressure =###.###### psi "; (satp / 2.036020696 )
LOCATE 9, 5: PRINT USING "Saturation pressure =###.###### inches Hg "; satp
LOCATE 10, 5: PRINT USING "Saturation pressure =###.###### mm Hg "; satp * 25.4

GOTO start

'================================

The above formula "mirrors" the Smithsonian Meteorological Tables/Charts
from -60 deg.F to 212 deg.F and well past to as much as .00001 accuracy
in inches Hg.


-Meaux saturation pressure curve formula--

dryr = (dry bulb temperature deg.F) + 459.67 '<--conversion to Rankine

Psat = 29.9213 / (EXP((671.67 - dryr) * 35.913 * (dryr ^ -1.152437)))


The above { Meaux saturation pressure curve formula } is copyrighted
(c)1995 by Larry Meaux/MaxRace Software, All Rights Reserved.


i would just use the 1 to 9 Loop ...its faster and as accurate as 1 to 25 Loop
......you can delete the 1 to 25 Loop out of code
...... i just included it so you could see that option

'-----------------------------------------------------------------------------------------

'======== Copyright (c) 1995 Larry Meaux , All Rights Reserved ==============
'| |
'| Program Name: REVERSE.BAS , QBasic/QuickBasic version |
'| Date: Sept 29,1995 |
'| Time: 1:00 pm |
'| Purpose: Compute temperature from dewpoint vapor pressure or |
'| from saturation pressure (all in inches Hg.) |
'============================================================================

WIDTH 80 '<--set screen to 80 columns , default
SCREEN 0 '<--set to text screen , default
KEY OFF '<--turn-off 25th line GW-Basic's menu text
VIEW PRINT '<--enable printing on 25th line
LOCATE , , , 7, 7 '<--set cursor to default shape
COLOR 15, 1 '<--bright white on blue
CLS '<--clear entire screen

start:
LOCATE 3, 5
PRINT &quot;Input choices: dewpoint,vapor, or saturation pressure in inches Hg.&quot;;
LOCATE 5, 5
PRINT USING &quot;Pressure inches Hg.= ##.###### &quot;; psat;
LOCATE 5, 38
INPUT psat$: IF LEN(psat$) > 0 THEN psat = VAL(psat$)
IF psat = 0 THEN psat = .5216 '<--default value if no input, (60 deg.F)

x = LOG(29.9213 / psat) '<--29.9213 inches Hg. at sea-level at 59 F
b = psat
a = 672 '<- 672 Rankine, (672 = 460 + 212) , 212 F = boiling pt. H2O
c = 35.9381# '<- Constant , 35.913 works with 671.67 and 459.67 (original)
d = -1.152437# '<- Constant , best constant value for d,(-1.152437 orig.)

logicloop:
FOR cnt = 1 TO 25 '<---- 25 is best value for number of loops
t1 = x - (a - b) * c * (b ^ d)
b = b + t1 / (a * c * d * b ^ (d - 1) - c * (d + 1) * b ^ d)
NEXT cnt

dry1 = psat
FOR cnt = 1 TO 9
dry1 = ((x + (c * (dry1 ^ (-.152437)))) / (a * c)) ^ -.867726392#
NEXT
dryb = (dry1 - 460)



LOCATE 10, 5
psatf = b - 460 '<-Fahrenheit conversion from Rankine degrees (459.67 orig.)
PRINT USING &quot;Temperature =####.#### deg.F (####.#) (2nd formula=####.####)&quot;; psatf; psatf; dryb

GOTO start
------------------------------------------------------------
Larry Meaux (meauxracing@mindspring.com)
Meaux Racing Heads
MaxRace Software
ET_Analyst for DragRacers

http://www.mindspring.com/~meauxracing/

 

[Craighell]

Thanks Larry,

Yeah, you hit the Dynojet correction factor formula on the nose. They claim it is the 1990 SAE formula. They assume 85% mechanical efficiency. I know Superflow uses a much more complex method of calculating efficiency and factors that into the power output figures. At least that's what I understand from their self published docs.

I know the later SAE formula should be best and thus limit the amount of deviation, but it seemed that Superflow was implying that some one else (SAE, EEC ?) had determined that the error stack up was too great beyond 7% (>1.07 CF or <0.93 CF) to use the results for anything other than simple comparrison.

When using my Stuska for sled motors, The CF was always high (~10% - 15%) but CFs were always similar. Basically I was testing sled motors in the fall and winter so the hottest temps were about 35 deg F and coldest = 0 deg F.
As soon as I tested a bike on the Dynojet (model 150 inertia) at 45 deg, we got good results and noted the CF (printed on the documents). Later testing at reasonable temps put the corrected values out the window compared to the 45 deg F runs. The result was my dry, 40 - 45 deg tests with 1.08 CF were not at all like my humid 85 deg 1.02 CF runs. Even with the CF applied the HP levels varied considerably.

I realize there are numerous variables involved (tire temp, drive line - chain - belt temp, etc) but this alone seemed to confirm that the published Superflow limits are certainly good measure if not accepted by the SAE.

If anyone else notices an &quot;official&quot; publication of recomended upper and lower limits, I'd certainly appreciate hearing about it. I started using this + or - 7% window as my &quot;house rule&quot; and sometimes it raises the hairy eyebrow when I suggest repeating the test under conditions more in line with SAE standard (to keep the CF under 7%).

Thanks, Larry for the detailed reply. I appreciate your taking the time and devoting the effort to my issues.

Craig @ Hell Fire

 

[MaxRaceSoftware]

Craig, i'm glad to hear me and Patterson weren't the only people to notice the correction factors effects below 40 deg F


In southern Louisiana, weather can change drastically
in just a couple of hours .

i've had some days where we had a thouroughly sorted out Super Stock combination on the dyno...and a cold front came thru ...the dyno room weather would change pretty drastically..the uncorrected HP might go up 20+ HP in the room...but the &quot;Corrected HP&quot; would be the same or within half a HP ....very good correction...i have to be thankful for SAE and SuperFlow !! but i did notice when deg F temps dropped below 40 in the room with a similiar Barometric increase, the SAE/SF correction factor was starting to be too conservative .

Some of this might be being caused by the dyno fan in the room ...the windchill goes up turning on the dyno fan !!
Cools the headers off pretty quick though

Let me know if you want any algorithms for the Stuska
correction ??


Larry Meaux (meauxracing@mindspring.com)
Meaux Racing Heads
MaxRace Software
ET_Analyst for DragRacers

http://www.mindspring.com/~meauxracing/