HI!... I notice some guys post dyno #'S IN std (standard) and other guys post dyno #'s in SAE. Which is the more accurate #'s? Which is the more prefered way of recording your dyno #'s? I made a few dyno runs last weekend at WALSH MOTORSPORTS in WIXOM MICHIGAN for A/F #'s and the graphs say STD (standard). Thanks.

 

SAE is more accurate. STD tends to inflate the numbers.

-Don

 

SAE corrects the power measurement to a standard air temperature and barometric pressue. (77 deg F and I forget the pressure) In theory if you test on a 90 degree day , or a 50 degree day or a high pressure day/low pressure day if you correct to SAE you shoud end up with the same #'s all other things being equal. For a chassis dyno, thats a huge stretch given variability in vehicle mounting, i.e. friction on the rolls.

For engine only dyno type stuff, SAE correction works pretty well.


What some call STD is likely just the uncorrected number.

If you ran it on a cold day with high BP you'll get a good STD #...
If you ran it on a hot day, low BP you get a bit worse STD #...
In theory, the SAE correction would get you to the same SAE # for both runs all else being the same.


Thats why its used by the OEM's.

 

Actually STD is corrected also.

SAE is corrected to 29.23 InHg of dry air and 77 F.

STD is corrected to 29.92 InHg of dry air and 60 F.

Pretty obvious, correcting to a higher pressure and lower temperature is always going to give a bigger number. The old rule of thumb is that STD is about 4% higher than SAE. They would both be equally accurate, just different.

Some dynos will show uncorrected or raw HP numbers, these of course vary wildly depending on conditions, especially from forced induction vehicles.

For the other pilots out there, I'm sure you all remember that standard temperature and pressure (STP) is 29.92 InHg and 59 F. I don't know why there has to be so many different standards.

 

SAE.

 

WIXOM????

where? I'm in Howell.
I didn't know there was a shop in Wixom.

www.miloc.org/forum stop by and say hi

 

HI!... l-menace : Here ya go :

http://ddperformance.com/aboutus.htm

 

Ah yes. Thanks for the reminder. I think I saw STD calculation from a superflow system about 12 years ago.

I've been dealing with uncorrected/SAE for so long now I had forgotten.

Thanks for the clarification.

Neal, if you want consistent before and after runs make sure you go back to the same place. Chassis dynos are notorious for their variability due to vehicle mounting among other things...

You see the posts all over this place...everyone's trying to compare #'s. Tires, gear, strap down force, temperature, humidity, correction factors etc etc blow most of the comparisons out the window.

Then again, you're not going back there with a simple airbox mod looking for 2 hp. That's like looking for fly-poop in pepper.
You'll be heading back with 100+ hp. So you shouldn't be too concerned about that.

What you should plan for is if you are doing mods, get the dyno for a 1/2 or 1 day so you can make changes right on the dyno and re-run, or at least have the same person strapping you down to the dyno. You can do things like mark where your tires end up on the rolls and try to get it back to the exact same spot. Also, when they strap it down, measure the back bumper so you can duplicate the strap down force as closely as possible.
Same day testing on rolls helps with air temp/humidity/BP. Reduces that variability. Correction factor to SAE doesn't have to deal with big temp or BP swings that way either. Also make sure you do multiple runs of same config.

I'm starting to rant...I'll stop now.

Lots of little things to consider when you head back to the rolls.

Happy rollin'

 

HI!... Thanks guys. One thing I did notice while I was at the dyno was that during all my runs, that my truck was bouncing quite a bit in the rear on the rollers during a run. The guys at WALSH MOTORSPORTS strapped the truck down with 4 straps in front and 4 straps in the rear but they strapped it down by hooking to the rearend housing it'self and not the fram. Would this "BOUNCING" effect skew the #'s? I plan to go back to the same dyno after MIKE TROYER finishes with my new program on my SUPERCHIP.