## Correction Factor Limits

## Correction Factor Limits

(OP)

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

Thanks,

Craig

## RE: Correction Factor Limits

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

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/

## RE: Correction Factor Limits

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 "Input choices: dewpoint,vapor, or saturation pressure in inches Hg.";

LOCATE 5, 5

PRINT USING "Pressure inches Hg.= ##.###### "; 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 "Temperature =####.#### deg.F (####.#) (2nd formula=####.####)"; psatf; psatf; dryb

GOTO start

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

Larry Meaux (meauxracing@mindspring.com)

Meaux Racing Heads

MaxRace Software

ET_Analyst for DragRacers

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

## RE: Correction Factor Limits

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 "official" publication of recomended upper and lower limits, I'd certainly appreciate hearing about it. I started using this + or - 7% window as my "house rule" 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

## RE: Correction Factor Limits

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 "Corrected HP" 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/