Virtual Dyno Results Thread

[Hijinx]

vDyno output is only as good as the operators input.

 

[Fasta123]

vDyno output is only as good as the operators input.

what do u mean? I have all the gearing tire size and stuff input from this thread. do all my testing on the same flat road.

on a side note has anyone actually weighed our car? what does it weigh with nothing in it and a full tank of gas?

 

[Hijinx]

If you're doing everything the same, the only other variable should be weather. A decent tail wind, head wind, cold day, hot, muggy day... All of that will change your numbers unless you get the wx data and plug it in for correction. A full tank of gas vs a nearly empty tank would be a negligible change in power.

Edit- don't use the SAE correction; see posts below.

 

[Fasta123]

If you're doing everything the same, the only other variable should be weather. A decent tail wind, head wind, cold day, hot, muggy day... All of that will change your numbers unless you get the wx data and plug it in for correction. A full tank of gas vs a nearly empty tank would be a negligible change in power.

each gallon is like 7lbs of weight that's + or - 70lbs that's like 3-5hp wen I change that on the vdyno. yea id say I'm seeing 210-220 tho. I'm quite happy I'm not sure how accurate the ap torque gauge is tho it never registers as high as my vdyno torque reading

 

[dyn085]

vDyno output is only as good as the operators input.

^ This. V-Dyno is essentially just a math program, so those that don't like it just don't know how to use it properly. If someone is a 'garbage in' sort of person, they're going to get garbage out. On the other side of that coin, there's a reason that all of the tuners use it.

If you question your results, do a few more pulls and ensure that you're making pulls in the opposite direction for comparison. When I have a datalog road I log a few even pulls in one direction and odd in the other, then I can tell if any particular pull is off and can discard it. It's easy to see if something is wrong or incorrect once you've collected a decent amount of data.

Don't forget to avoid using the SAE corrections, the math compensates for a naturally-aspirated motor and will be incorrect with forced-induction numbers.

 

[Hijinx]

Don't forget to avoid using the SAE corrections, the math compensates for a naturally-aspirated motor and will be incorrect with forced-induction numbers.

I wasn't aware of that. Not that I used the SAE corrections. But, it's good to know. Why/how does it produce incorrect numbers in the SAE correction [MENTION=930]dyn085[/MENTION]? I know you said the math would be incorrect, so I guess I'm asking for a source. Just hit me with a TL;DR.

 

[dyn085]

I wasn't aware of that. Not that I used the SAE corrections. But, it's good to know. Why/how does it produce incorrect numbers in the SAE correction [MENTION=930]dyn085[/MENTION]? I know you said the math would be incorrect, so I guess I'm asking for a source. Just hit me with a TL;DR.

Basically, a normally-aspirated engine is less-sensitive to temperature correction and highly sensitive to pressure density. A turbocharger simply speeds up to create the boost level required (in higher altitude/lower density) but is also much more sensitive to ambient temps. The correction is not as far off in lower-elevation than high, but it will be off nonetheless. This is also why actual dyno's run forced-induction cars without correction.

 

[Fasta123]

Yea I never use the sae, yep it's a good math algorithm. I'm assuming that the weather numbers are different for forced induction and na because it doesn't add enough hp in the heat and doesn't take away enough for the cold, there would be an ideal temp tho where both fi and na react the same some small temp range

 

[Hijinx]

Basically, a normally-aspirated engine is less-sensitive to temperature correction and highly sensitive to pressure density. A turbocharger simply speeds up to create the boost level required (in higher altitude/lower density) but is also much more sensitive to ambient temps. The correction is not as far off in lower-elevation than high, but it will be off nonetheless. This is also why actual dyno's run forced-induction cars without correction.

Because SAE is a correction for altitude. Got it.

 

[dyn085]

Because SAE is a correction for altitude. Got it.

Half-correct. SAE includes both temperature and density. Likewise, STD is also incorrect because it uses temperature and density for correction as well, albeit a lower temp and higher density.

The SAE math as of the AUG2004 revision looks like this-

cf=1.176 [(990/Pd)(Tc+273/298)^.5] - 0.176

cf = correction factor
Pd = Pressure, mb
Tc = ambient temp

SAE corrects to 77 degrees, 29.23 inHg with zero humidity whereas STD corrects to 60 degrees, 29.92 inHg with zero humidity.

 

[Hijinx]

Half-correct. SAE includes both temperature and density. Likewise, STD is also incorrect because it uses temperature and density for correction as well, albeit a lower temp and higher density.

The SAE math as of the AUG2004 revision looks like this-

cf=1.176 [(990/Pd)(Tc+273/298)^.5] - 0.176

cf = correction factor
Pd = Pressure, mb
Tc = ambient temp

SAE corrects to 77 degrees, 29.23 inHg with zero humidity whereas STD corrects to 60 degrees, 29.92 inHg with zero humidity.

Ok...bear with me for one more try. Either correction is inaccurate for FI applications because we're more greatly affected by temperatures than density/altitude. And this is because at altitude the turbo will spool faster to meet its ratio.

 

[dyn085]

Ok...bear with me for one more try. Either correction is inaccurate for FI applications because we're more greatly affected by temperatures than density/altitude. And this is because at altitude the turbo will spool faster to meet its ratio.

Correct. Think of it like this: Normally-aspirated engines don't have compressors to make the ambient air hot but also don't have compressors that make the air pressure uniform. Conversely, turbochargers can't guarantee the same charge-air-temps as ambient but can guarantee uniform density (unless it's boosted on the ragged edge).

Supercharged engines are a middle-ground because they can't guarantee the charge-air temps as ambient (like the turbo) but also can't create the same level of uniform boost due to having fixed compressor speeds (unlike the turbo).

 

[Hijinx]

Correct. Think of it like this: Normally-aspirated engines don't have compressors to make the ambient air hot but also don't have compressors that make the air pressure uniform. Conversely, turbochargers can't guarantee the same charge-air-temps as ambient but can guarantee uniform density (unless it's boosted on the ragged edge).

Supercharged engines are a middle-ground because they can't guarantee the charge-air temps as ambient (like the turbo) but also can't create the same level of uniform boost due to having fixed compressor speeds (unlike the turbo).

Thanks, Dyn.

 

[twolf]

^ This. V-Dyno is essentially just a math program, so those that don't like it just don't know how to use it properly. If someone is a 'garbage in' sort of person, they're going to get garbage out. On the other side of that coin, there's a reason that all of the tuners use it.

If you question your results, do a few more pulls and ensure that you're making pulls in the opposite direction for comparison. When I have a datalog road I log a few even pulls in one direction and odd in the other, then I can tell if any particular pull is off and can discard it. It's easy to see if something is wrong or incorrect once you've collected a decent amount of data.

Don't forget to avoid using the SAE corrections, the math compensates for a naturally-aspirated motor and will be incorrect with forced-induction numbers.

lol, I can assure you that I do indeed know how to use it.


The problem is other people don't. And very few people use the same methodology. I'm tired of seeing people post 235whp vDynos and thinking they have the world's highest horsepower stock turbo FiST because they did it wrong. When I see more people using a program incorrectly, I'm just going to say it sucks. Although you're right, if used correctly it's fine.

Like Hijinx said, there are a million different factors that can influence a vDyno's "reading". The only thing more stupid than comparing two dyno charts is comparing two vDyno charts.

 

[Sekred]

Correct. Think of it like this: Normally-aspirated engines don't have compressors to make the ambient air hot but also don't have compressors that make the air pressure uniform. Conversely, turbochargers can't guarantee the same charge-air-temps as ambient but can guarantee uniform density (unless it's boosted on the ragged edge).

Supercharged engines are a middle-ground because they can't guarantee the charge-air temps as ambient (like the turbo) but also can't create the same level of uniform boost due to having fixed compressor speeds (unlike the turbo).

Good explanation Dyn0

I am fimilar with the SAE standard relating to the adjustment for temp and density and how you can't use it for turbo charged engines because the change in charge temps can have such a significant effect on peak HP.
Now Ford quote the STs flywheel horsepower as 197bhp, SAE net, meaning they follow the SAE standard. So how do Ford get a accurate rating for HP? Control the charge temps?. This may explain why we such a large difference in dyno HP reading for stock vehicles.

 

[dyn085]

That's a good question. My assumption would be, if it's anything remotely similar to aviation, that those numbers are achieved during engine/tune certification in a calibrated, climate-controlled room with all of the input parameters and fluids carefully monitored. Admittedly an assumption, but with how stringent the EPA requirements are and with how much money is at stake, I think it's plausible. I would also assume that their engineers are smart enough to have that test conducted at the necessary temps/pressures because of exactly what's outlined above.

 

[Fasta123]

what is everyone using as there cars weight with a full tank of gas? and if the smoothing is within 5hp from 1-6 does that confirm the road your using is flat enough?

 

[Fasta123]

lol, I can assure you that I do indeed know how to use it.


The problem is other people don't. And very few people use the same methodology. I'm tired of seeing people post 235whp vDynos and thinking they have the world's highest horsepower stock turbo FiST because they did it wrong. When I see more people using a program incorrectly, I'm just going to say it sucks. Although you're right, if used correctly it's fine.

Like Hijinx said, there are a million different factors that can influence a vDyno's "reading". The only thing more stupid than comparing two dyno charts is comparing two vDyno charts.

why is that stupid? sure there will be little fluctuations from weather but if all the info about the car is constant, like the gear ratios tire height weight and the road is the same the only variable is the rate at which the car is accelerating within that gear.

 

[StayPuft]

I think you're doing everything you can to keep it consistent and while it's not the best determinant for actual hp/tq it's a good way to track your hp progress as you mod.

People take issue with the virtual dyno alpha guy who walks in with basically stock hardware and 3 gallons of e85 and claims to have 45 rwhp higher than stock.

 

[Fasta123]

I think you're doing everything you can to keep it consistent and while it's not the best determinant for actual hp/tq it's a good way to track your hp progress as you mod.

People take issue with the virtual dyno alpha guy who walks in with basically stock hardware and 3 gallons of e85 and claims to have 45 rwhp higher than stock.

yea I agree, these number are obviously not concrete like a true dyno but I still think there can be some comparison between graphs. I mean in really cool conditions iv been seeing graphs in the 210-220 range which I think is pretty dam impressive in a 2700lb car.