Dyno SAE correction math

[rrrocketman]

gtstorey: Indeed, that's what I think too. I just made this thread to determine whether or not this was in fact the case.

I recently dyno'd my 2004 MC SS and it reported 317 ft-lbs. Now the car has a 3.5" pulley and some breathing mods BUT... the car is factory rated at 280 ft-lbs and if we add back the 20% drivetrain losses we're looking at 396 ft-lbs being produced by the engine. Now does anybody believe that the 3.8 can produce 400 pounds at the crank with a 3.5" pulley? I don't. So that's why this question about the SAE standard seems relevant to me and should be to others.

[BehindBlueI's]

Originally Posted by rrrocketman

gtstorey: Indeed, that's what I think too. I just made this thread to determine whether or not this was in fact the case.

I recently dyno'd my 2004 MC SS and it reported 317 ft-lbs. Now the car has a 3.5" pulley and some breathing mods BUT... the car is factory rated at 280 ft-lbs and if we add back the 20% drivetrain losses we're looking at 396 ft-lbs being produced by the engine. Now does anybody believe that the 3.8 can produce 400 pounds at the crank with a 3.5" pulley? I don't. So that's why this question about the SAE standard seems relevant to me and should be to others.

Did you ask the facility that dyno'd your vehicle? Is there a correction factor printed on your print out?

[Royal Tiger]

We were always taught in school that math is absolute. There is only right and wrong. However….

A bone stock “400hp” L99 reliably makes 325-330 on a dynojet. So if we figure out that is roughly a 18% loss due to parasitic draw (400 x .82 = 328), yet if we take that 328 average and try to get back our loss to “crank hp” (328 x 1.18 = 387) we are short 13hp. Using a dyno at least gets us an actual number of what the car is truly making. But, there is the caveat that all dynos (as well as ambient conditions) are different. I had my car on two separate dynos (pre build) and they were almost 19hp apart.

[FASTFATBOY]

Originally Posted by joshnmn

That one works.

It says right in the article that the standard is to certify factory engine numbers. So... For instance, GM can claim the LS7 make 505hp, even though it was never on an engine Dyno.

I am pretty sure every engine has to be on an engine dyno for advertised HP, multiples of said engine do.


They did back here in 2011, I doubt they tore down that facility. Computer modeling may have gotten that good though


https://news.pickuptrucks.com/2011/0...g-center-.html




As a general rule 15% loss for a manual trans car is more accurate than an auto's 20% number as factory stock cars go.


405HP C5 Z06 makes 350 ish


505 HP C6 Z06 makes 450 ish


580 hp Zl1 makes 500 ish.




No dyno is the same, no car is the same, but the windows are similar when SAE correction is used

[rrrocketman]

Originally Posted by BehindBlueI's

Did you ask the facility that dyno'd your vehicle? Is there a correction factor printed on your print out?

What's printed on the graph is STD J607 but I had a long convo with the tech about it and he showed me all the settings including SAE. SAE wasn't much different so both probably used the environmental Cf only. The rest of the discrepancy could have been due to the dyno itself. I guess it's not really the point I was trying to make. But not knowing how the formulae are being implemented raises questions when the results are out of whack with expectations.

Royal Tiger: Math is inerrant. The reason you get that discrepancy is because you should never reverse a calculation like that by multiplying by 1.18. If you initially multiplied by 0.82 then you must reverse it by dividing by 0.82. If you do you get what you started with.

[Royal Tiger]

Thanks!

[chevy pilot]

Has no one really ever taken engine to the motordyno and the same car to the wheeldyno ?