Huge dino variations...

[Paul Workman]

A while back, someone posted a source for driving hp corrections for atmospheric conditions. After running just a few scenarios, it hit me like..."Eureka!!" Since I can't seem to locate that link just now, I'll just summarize what it clearly pointed out this way:

The variables deriving Density Altitude are key...make that crutial(!!)...to the dyno's SAE corrected (calculated) hp values! In short, I saw how as little as 20º variation in temperature, along with some humidity changes, could easily skew hp readings on the same car on the same day! (20º between say 8AM and 3:30 PM on a summer day is easily possible.)

How much difference would it make? Well, w/o the calculator at hand, let me say this much: When you have your car dyno'ed, having the barometric pressure, temperature, and humidity numbers that are dialed in at that time is extremely important. 5% error doesn't sound like a lot to some, but at 400 hp, 5% is 20 ponies difference - enough to drive someone trying to set timing on camshafts nutz! (Right Pete?) But, if you have the values used to correct for Density Altitude, and the actual conditions at the time of the test, then theoretically, one could improve the accuracy - especially if the "dialed" numbers are way out, compared to conditions at the time of the run.

Maybe someone can dig that SAE correction link up again, and we could do some what if?? (cuz I gotz ta go ta woik just now!)

P.

[GrayZ]

Isn't Dino the Flinstones, dog??

[bobbyhi]

Originally Posted by ITLGO2

Isn't Dino the Flinstones, dog??

Wuff, wuff..........

[Paul Workman]

Originally Posted by ITLGO2

Isn't Dino the Flinstones, dog??

Yeah, yeah, yeah... I got your Dino right heeyah, bowy!

P.

PS.

Marc told me he had 'em dial in Density Altitude conditions for DENVER COLORADO when he ran the graph on your "500 hp" LT5 here at nearly sea level. (Talk about an ego booster!) JK.

P.

[XfireZ51]

Paul,
Is this the link you're looking for?

http://www.dragtimes.com/da-density-...calculator.php

We should have the mod make that a "sticky". Very useful.

[Paul Workman]

Originally Posted by XfireZ51

Paul,
Is this the link you're looking for?

http://www.dragtimes.com/da-density-...calculator.php

We should have the mod make that a "sticky". Very useful.

I saved that link too, but apparently the hp correction calculator has been removed, or the link is wrong - anyway it isn't there.

What I was referring to was a similar calculator where you entered your Density/Altitude info (baro, temp, humidity, etc) and then the calculator (as I recall) spit out a correction factor, relative to a standard (pressure, temp, humidity, etc).

The format was very similar to the link you posted; making me think they must have pulled it or revised the web site an deleted that one??

I'll look some more.

P.

[Paul Workman]

OK, check it out...

http://wahiduddin.net/calc/calc_hp_dp.htm

Playing with a 20º temp variation from say early morning (at Antioch?) to mid afternoon, it was easy to get an 11hp variation on a dyno reading of 370 (base).

Sooooo... My point in all this is/was that at least some of the dyno reading variations we see, especially in out-door "circus" scenarios, can easily be the result of air density variations throught the day as a function of temp, altitude, etc. In addition, reading up on the Dynojet calibration, there is a cal number stamped on the weighted drum which has to match the value entered in the dyno's computer or the readings can be significantly off. Comments like, "This dyno we call the 'Heart Breaker' ", to me says it reads different than some, and they don't know if the calibration is correct or not..."Air density? What's that?"

Gotta run.

P.

[Pete]

TABLE 1 Correction Standard Air Temp (°F) Relative Humidity (%) Barometric Pressure (in-Hg) Density Altitude (feet)
SAE J607 60 0 29.9284
SAE J1349 77 0 29.235 1962
ECE 77 0 29.235 1962
DIN 68 0 29.92 605
JIS 77 0 29.235 1962
SAE J1995 77 0 29.53 1623


http://www.smokemup.com/tech/weather.php

I guess it all depends which correction you use.

Pete