Can someone (who really knows what they are talking about as opposed to repeating hearsay) explain the differences between the various dynamometers?

How do they compare to each other? What is their individual accuracy levels and repeatability? What are the meanings of STP and SAE corrected values? Is there a standard to which all are compared to determine their respective accuracies? Hoe can results from various dynos be evaluated?

 

RANDOM THOUGHTS:
All chassis dynos measure torque by reverse calculating torque from the time between speed changes of of the rolling drum.

The problems are: weight of the drum is not an exact match with the cars weight and engines respond differently when not loaded to real world conditions [no air speed drag and lighter drum]. Tire changes with brand, tread depth, and pressure temp, etc..

Dyno Jets are always optimistic as the dyno runs accelerate too fast.
Mustangs use the exact vehicle weight in formula and an eddy brake to add resistance to the drum to compensate for lack of weight and wind resistance with speed. If you know the typical quarter mile time you set the eddy brake near this number so the acceleration time is increased to approximate it [~~14 sec quarter mile ]. Create real world conditions

As the speed increases the Mustang eddy resistance increases [for example wind resistance [HP required to overcome] increases 4 times when you double speed.

What counts is real world on the highway acceleration time not what some machine in a closed enviroment say it Could Might Should be.

Trying to figure flywheel HP from a Dyno [any dyno] is full of errors and guess work. The act of trusting manufacturers lab engine dyno numbers [to start with] and trying to create a correction factor for RW power is all about averages.......every engine is different at different rpms. The number might be close at HP peak rpm but not at torque peak rpm or redline.

The thing most don't understand is that most of the friction losses are in the rear diff and half shafts and the tire road interface......what gets hotter the diff and the tires in a dyno run.

The road is not smooth like the dyno roller drum so tires on the road perform differently due to cooling air flow and increased heat from road roughness........these things are not considered on any dyno.

For minor mods which don't change things more than 10%, you DO NOT add the correction factor back to the increase.

IF stock 260 yields 210 RW, then a modified 20 RW increase is just 280 not 284 at flywheel........there is no multiplicative effect in small power increases.

The only way to really know what flywheel power is, is to pull the engine and put it on a lab engine dyno. Load it till the engine stops accelerating and measure the required load power.

Tuning an engine on a Dynojet is iffy because of the faster than real world acceleration! A CORRECTLY SET UP Mustang is safer due to correct acceleration time but still there are errors compared to the road just more precise.

Why I never accept most dyno graphs as anything more than a feel good sheet of paper [accurate to 5% or 10%] what really counts are dozens of quarter mile runs to average out launch and shift errors.

 

Because the air density changes with temperature, pressure, and humidity.

"The STP (also called STD) standard is another power correction standard determined by the SAE. This standard has been stable for a long time and is widely used in the performance industry. Power is corrected to reference conditions of 29.92 InHg (103.3 kPa) of dry air and 60 F (15.5°C). Because the reference conditions include higher pressure and cooler air than the SAE standard, these corrected power numbers will always be about 4 % higher than the SAE power numbers. Friction torque is handled in the same way as in the SAE standard. Once again, this means the STP corrected power displayed by your SuperFlow test system will be more accurate than power numbers obtained using a default Mechanical Efficiency of 100% or 85%. "

"The SAE standard applied is a modified version of the SAE J1349 standard of June 1990. Power is corrected to reference conditions of 29.23 InHg (99 kPa) of dry air and 77 F (25°C). This SAE standard requires a correction for friction torque. Friction torque can be determined by measurements on special motoring dynamometers (which is only practical in research environments) or can be estimated. When estimates must be used, the SAE standard uses a default Mechanical Efficiency (ME) value of 85%. This is approximately correct at peak torque but not at other engine operating speeds. Some dynamometer systems use the SAE correction factor for atmospheric conditions but do not take mechanical efficiency into consideration at all (i.e. they assume a ME of 100%). SuperFlow uses a more sophisticated algorithm for calculating friction torque, based on a summary of thousands of friction power tests performed by the automotive industry. This proprietary algorithm estimates friction torque as a function of piston speed and engine displacement.
The "SAE corrected" power numbers indicated by your SuperFlow system are thus more accurate estimates of engine power output under reference conditions than what other systems using no ME correction or using a fixed ME of 85% will provide.

Relative humidity can change oxygen density in air by 2.2% -8% from zero to 100% depending on temperature [spread get worse at 100F].
http://wahiduddin.net/calc/calc_hp.htm

Notice from the above calculator how a REAL 260 HP SAE engine can decrease to 231 HP at 130F and increase to 281 HP at 30F assumming barometer and humidity [50%] stay the same.Changing quarter mile times by more than 0.5 seconds.

 

Q45tech

I recently had a dyno run on a Superflow dyno. My mods can be viewed in the My Ride section. The ECU has been reflased by TS in anticipation of the installation of a Crawford V5 plenum, but the plenum was not on yet at the time of the run. Accordingly, the engine was running rich.. A/F ran 12.6 -12.8 throughtout the rpm range. I plan to run the dyno again after the plenum is installed.

The dyno setup apparently has software that also provides equivalent Dynojet (DJ) results. Here are the numbers:

Torque:

SAE 244.4
STP 254.2
DJ 268.8

HP:

SAE 220.0
STP 228.8
DJ 242.0

Which numbers reflect reality and which should be used for comparison purposes?

Can an estimated crank HP number be extrapolated from these results?

How does a Superflow dyno compare with a Mustang dyno?

 

Q45,

Why do dyno's mostly graph the horsepower and torque curves from 3k+ rpms? Why not lower rpms if the car won't stall in the desired gear? Ultimately, I guess I'm trying to figure out what the curve would look like from idle to 3.5k rpms since that is the range that the engine is in most of the time.

<font color=blue>2004.5 Coupe ^ 5AT ^ DG/W ^ Z Tube</font color=blue>

 

My car is a 5AT. Dynos for the AT are usually run in third or fourth gear, preferrably fourth.

It's not possible to run the engine WOT in fourth gear below about 3800 rpm because it will downshift. So typically, the car is run up to that rpm in fourth, the data recording is started and WOT applied at that point.

 

I have had it in manumatic in 4th at approximately 1500 rpms and opened it up... it did not downshift. Then we have the issue of manual transmissions... why not do it there where it's guaranteed not to downshift?

<font color=blue>2004.5 Coupe ^ 5AT ^ DG/W ^ Z Tube</font color=blue>

 

Nothing says you cannot run a zero to 150 mph on a Mustang dyno showing the EXACT equal to on the road performance on a MUSTANG DYNO.

You just experiment with the eddy brake friction to equal the road air friction. Do some stopwatch timing [drag strip] etc and dial in 30,50,60, 80, quarter times 120 etc, then create an equation that follows these ---then read the torque at each rpm in each gear.

You may end up with a 3-4 hour [$400] dyno bill to get everything down pat.

Nice graphs that show everything including the shift times rise and falls, torque convertor response, etc.

Most people just want some graphs to show their friends or boast on INET or at club meets. They really don't care for precise expensive data logging and the mathematics involved.

What do most dyno runs have to do with the real world?

Most of the time the car with 30-50 RWHP more and nearly equal weight will be faster in the quarter mile. That cannot be said of 5,10, 15, even 20 RWHP differences, as the dyno errors come into play.

Magazines don't compare test new cars on dyno they head to head time them in acceleration.......on the track/on the road.

 

Doesn't one really care more about how the engine performs in the first 3 gears than how it might perform from 100-150 mph on some dyno that is no where near real world conditions. There is so little accelerative stress from lack of wind resistance the numbers may be meaningless.

When you have bank payments to make on a dyno you will say/print/graph almost anything to get enough business in to make the payments. If people don't get gains why would they come back and pay you again"?

 

http://www.aatuning.com/dyno/default.asp
http://www.aatuning.com/dyno/MustangVsDynojet.asp

Mustangs site explains it pretty well without half truths
http://www.mustangdyne.com/Articles/...article-01.htm

 

This is so very true Q45 Tech...so sad too, but so very true. I have gotten into it with a few dudes regarding my 87 GT and not giving me bull$hit numbers and they had the nerve to get indignant and act like on one pulls this crap.

John
03.5 G35 5AT 14.2 @ 96.4
10 Wire Grnd Kit
K&N CAI w/Injen HS
UR UD CP
NISMO Mid Pipe
Crawford V 5.0
TS
350 Z 170F Thermostat
02 Maxima SE 4AT 14.5 @ 95
87 Mustang GT 13.2 @ 107