So I just wanted to clarify some dyno mis-conceptions. It has been brought to my attention that some people have been doubting or maybe more so questioning some of the dyno results they have seen. Also, there are some people that have been doubting or questioning the results from some tunes they have recieved from myself and my company so I just wanted to clear up a few things.

Now there are few standards used in the dyno world for gathering HP and TQ numbers, UNCORRECTED, SAE and STD. Uncorrected is NEVER accepted in the world of dynoing and tuning as it does not factor in any weather conditions etc. Now here is where the big debate comes...is between SAE and STD. SAE (Society of Automotive Engineers) is the MOST ACCURATE AND WIDELY ACCEPTED FORM OF MEASUREMENT when it comes to the world of dynoing. Here is some more info I have gathered between the two.....

A lot of people have been asking about SAE .vs STD Dyno numbers so I thought this would help. Most people know that showing STD numbers read higher but not many know why. SAE represents more realistic standard conditions, STD artificially boosts numbers.

Identifying Your Correction Factor:
Dynojet:
If you look at a dynojet graph in the upper right corner, you will see where it says the correction method being used. The options are SAE, STD, Uncorrected and a few not needed for discussion. You will also notice a smooth factor (up to 5) which dyno operators use to make the power curves and any other data displayed, such as AFR, seem more accurate and smooth. You will also see AFR graphs scaled DOWN to hide flaws in the curve.

MD:
A Mustang Dyno ONLY uses SAE Corrections. Smoothing can also be controlled as well as scale for the Graphical Outputs.


Overview:
Most of the stated horsepower numbers are “Corrected” values. The correction standards were developed to discount the observed horsepower readings taken at different locations and weather conditions. It is obvious that an engine builder in Colorado could not produce as much horsepower as a shop at sea level. There is just less oxygen for the engine to burn at the higher altitude. What are less obvious are the other weather condition effects on the engine. So in order to compensate for this all advertised horsepower is “corrected” to several different industry standards.

SAE:
"SAE (Society of Automotive Engineers), USA. 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.

STD:
STD is Another power correction standard determined by the SAE. 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."



Here is some quick math (using assumptions and round numbers):

STD:
Air Temperature: 60F
Absolute Pressure: 29.92 inches Hg
Relative Humidity: 0%

Relative Horsepower : 104.8%
Air Density: 1.223kg/m3
Relative Air Density: 99.8%
Density Altitude: 67feet
Virtual Temperature: 60F
Vapor Pressure: 0 inches Hg
Dyno Correction Factor: .955

SAE:
Air Temperature: 77F
Absolute Pressure: 29.23 inches Hg
Relative Humidity: 0%

Relative Horsepower : 100%
Air Density: 1.157kg/m3
Relative Air Density: 94.4%
Density Altitude: 1952feet
Virtual Temperature: 77F
Vapor Pressure: 0 inches Hg
Dyno Correction Factor: 1

Now with that said... keep that in mind when you see a dyno chart because there are some folks on here who's dyno numbers alot of you have been in awe over who may not have been telling the whole truth as they have tweeked the numbers with an STD correction factor etc.

We at SMG HAVE ALWAYS and WILL ALWAYS been using and posting our charts and numbers in SAE correction. So those of you who have done business with us in the past or some of you looking to do business with us can expect to see SAE correction factors and nothing else.

Hope this helps clear up some miss-conceptions about dyno numbers and the comments on some of the results from our tunes.

Also feel free to do some of your own research on the difference between SAE and STD by google-ing Dynojet SAE vs. STD there are some good posts and threads about it out there and what is more widely accepted and which is not.

So, some of you may have known we dyno'd and tuned a SS/TC this past weekend.... and if you took our SAE numbers and changed them to STD the numbers went up by over 12 whp and 11 wtq.

Just FYI.

Again like i said above, you will only see SAE correction numbers and charts posted from SMG as it is the more true and accurate results.

 

bump

 

Great post! Thanks for clearing that up for everyone

 

bump for good information

 

std does not always boost numbers by 4%. two dyno runs from 8 months apart will be different when bringing them back up for comparison at a later date. sae will skew both numbers.

uncorrected is the exact numbers the car is doing right then and there for those conditions.

 

sae will give you a number so that you can dyno in january, then comeback in the summer and produce very similar numbers, hence the truest numbers

but ill say this again, what is exeptable to you isnt always what is wideley exepted in the dynoing industry

 

open a magazine and tell me what correction factor they dyno in.

also, your statement about january vs summer is not true.

correction factors are nothing more than percentages. plus or minus depending on temperatures.

 

you just said the same thing i did, january here is 15-30 degrees, summer is 60-100, thank you.

 

std. simple correction

90 degree's on day

20 the next.

what happens?

OMG the same thing as std.

who knew.

 

my only question about dynos is

How do I know the TQ value is correct? Seems to me that this value is the main unknown when figuring HP.....

 

The torque value is a calculation that is made directly from the HP the car made. The hp is calculated by how fast your car can accelerate a fixed weight (being the dyno drum itself) and then torque is figured from that. I will try and dig up the actual formula for you asap.

As far as the correction factors go... Both Area and glen are correct. SAE and STD will both vary on how much they correct depending on the day and STD will not always scew the numbers by 4% all the time... sometimes it can be by more, sometimes it can be less. The simple examples in the first post were just to give an idea of what the correction factors are based off of.

The Idea behind the correction factors were so that if you dyno'd your car in januray, you wouldnt go back in july and see your car lost 15hp due to the hot humid conditions like what we would see here in Mass. The idea was to have a corrected number so that dyno results would remain the same.

an uncorrected number IS what the car did make that given day in those given temps and conditions however, it is seldomly taken as a real number as far as dyno numbers are concerned and most dyno's will have their correction factor set to SAE as it is the industry standards (such as we do here at SMG.) Most all dyno results you will see listed in magazines, as we have done for articles etc we have put into print mags, will be in SAE unless otherwise noticed.

as far as pulling past dyno results up and reviewing them at a later date, the correction factors will not change as the weather conditions for those specific pulls are saved in the information per pull. So referencing pulls at a later date will not change anything. Hope this helps out some, and thanks to all who have posted in the thread as we have been able to gather alot of useful info.

Also, there are some good threads over on the LS1tech forum about this very topic, might be some goof references for all of you as well. Thanks everyone!

 

wow, that just make it more complicated then. I'm sure its some complex calculus problem filled with centrifical equations and what nots... so weight is the key, weight of the drums and weight of the car. Basically no calibration required...... lol

 

Weight of the car is not a factor... just the fixed weight of the drum itself... Im looking for the calculation right now...

 

Do the size of the tires come into play at all?

 

Different tire sizes can alter your effective gear ratios, which can technically skew numbers, but it should be very minor.

 

ok so here are some of the basic calculations...

Hp= torque x rpm / 5252

tq= hp x 5252 / rpm

Now that is the most common way to figure hp and torque, now what im trying to find is the actual velocity calculation for the rate of acceleration of the drum, which is how it would be figured on an interia chassis dyno.

OK here is the torque or "force" calculation.

Force (tq) = mass x acceleration

here is a very good link of another dyno shop that has posted up some of the calculations and has written some good explainations on how the calculations are figured on the chassis dyno... hope this helps out clear some of the calculation trivia up http://www.bristoldyno.com/info/whatis.htm

Ebristol, tom is right... it will effect your overall effective gear ratio... and it theoretically could vary your dyno results but it would be a minimal change and probably would not be a huge effect.

 

theres an even better solution, don't use dynojets and you wont have to worry about correction factors

 

unfortunately every chassis dynamometer uses corrections factors to ensure day to day weather changes don't greatly effect results.

 

subscribed to read later

 

click for formulas

 

Just realized i left the link out on th previous post... so i added it in.