I have always wondered about this and its true impact on dyno plots.

with all the storys of putting it in cups of hot tea etc its always made me curious how much difference does it really make to din or sae corrections.

well I now have a bit of data.

my r33 was dynoed on a dynapack, temp sensor just hung in the dyno cell and recorded 563.3 hub power, then din correction took it to 561.9 so basically took a tiny bit of power away due to the temperature approx. 23d.

my same car in the same tune was dynoed previous to me owning but by the same dyno and operator (who are very good btw) the only difference was the temp sensor was under the bonnet (which I guess some may say is more representative as after all its all about engine intake air temp) but anyways it measured 536.6 hub power then din correction took it to 583.5 !

those 2 senarios went from taking away 1.4 hp to adding on 46.9 hp ! the only data I don't have is the temp reading of the probe for the old run but im guessing in the 40 - 50d area

and that's with no fugeing anything just 2 genuine dyno runs just with the temp sensor at ambient temp in the room or under the bonnet wether bonnet was open or shut again I don't know.

this is all without even considering any tcf to guesstimate flywheel power.


by no means a precise scientific comparisons but it is apples for apples and shows the difference a little temp change has on dyno readouts.

 

that does not surprise me at all mate, I have added 50hp on the dyno by heating probe up to 45c on the thermostat. and that was on a car with 150whp.

 

A topic close to my heart. The amount of absolute garbage Dyno figures out there Is absolutely shocking mate.

The biggest compensator is the intake air temperature, followed by atmospheric pressure, ambient temp and humidity.

Even the tyre pressures, temperatures and strap loading affects the readings significantly and a good Dyno operator will read, monitor and record all these parameters on a car that is going to have regularly tuning done to ensure consistency.

 

I've written a bit about correction factors on my website in a few areas, most notably here:

http://www.motorsport-developments.c...formation.html

And here:
http://www.motorsport-developments.c...ys_Differ.html

But am happy to discuss further on this topic as its an interesting subject people would do well to understand.

 

imagine the power hike stu if the sensor really was put in a fresh cup of tea, double power anyone

 

If I get a suitable car and a spare hour I may do a video of a real run, then one with air probe above the exhaust manifold and then one In a nice cup of tea.
Would make for interesting viewing.

 

stu how much of a difference can you see on the dyno from a low pressure to high pressure day? is it as obvious as temp differences?

 

I guess it needs putting on here now, so i have Copied and pasted it from elsewhere as i certainly don't know it...
This standard assumes intake air temp is the same as ambient.

The SAE J1349 (Jun 90) power correction formula is:
Metric units millibar / deg C CF = 1.180 [ ( 990/Pd) x (( Tc + 273)/(298 )) ^ 0.5 ] - 0.18
in hg / deg F units CF = 1.180 [ ( 29.23/Pd) x (( Tc + 460)/(505)) ^ 0.5 ] - 0.18

Pd = dry air pressure ( ie absolute air pressure minus the contribution of the partial pressure of the water vapor in the air)
Tc = Ambient air temp ( ie temp outside the car, not the intake air temp)

The formula is supposed to give you the hp the car would make if it was at an absolute air pressure of 990 mb (29.92 in hg) 0% humidity and 25 deg Centigrade (77 deg F) outside air temp.

 

Cheers stu, shame I can't understand it though as I'm only studying rocket science at the moment. lol,
It has made it clearer though thanks.

 

No - temperature difference is the biggest factor.
Most dyno cells create their own atmospheric pressure by ridiculous and ill considered use of fans anyway, so the figures are often totally mute. Lol

 

Mate, I wouldn't even know how to enter that formula into a fucking calculator!

 

So really every track day we do or fancy a nice drive then we want to be looking for high pressure, low temp, and high h20 in the air.

 

it sure would mate, id read it that's for sure.
I regularly read your articles itd be another one for me

 

that is a hell of a jump 25% at 45d.

maybe the under bonnet temps were even lower than I thought then.

 

How about the differences in Correction Factors then? Here's a table showing the differences in power at different (simulated I presume) heats on a Dynapack

Air Temp (°C) Peak Power (DIN) Peak Power (SAE)
10 167.0 kW 169.9 kW
35 176.3 kW 186.4 kW
50 185.1 kW 236.9 kW

Source: http://stmtune.wordpress.com/2012/06...9-kw-for-free/

 

If we never had these threads being started on pf then know body would ever be the wiser as to how easy it is to be mugged off by some back street tuner,
So it interests me to gain knowledge from the likes of stu for us dim wits to learn alittle.
Other wise we might as well all stop using this site and just bum wiki into next week.

Back to topic thanks for sharing your wealths of knowledge

 

nice link cheers mate, thats 66 hp just from going from din to sae at 50d ! and 50d im sure would be easy enough with the sensor just located near the engine.

 

I now have the temperature data for the old run, it was 58d.
so 23degress is virtually 0 correction
58 degress is approx. 9%
if the table is linear with the sensor in a cup of tea at say 90d it would correct 18% !
and that's just at din cr, imagine sae cf !

the bottom line is with the sensor in a fresh cup of tea at din cf my 563 hp reading would be about 665 hp !
100hp for free potentially lol

now according to that link added at 50d sae adds another 65hp so it would then be up to 730 hp and potentially more as the sae may correct even further upto 90d.


so in theory theres potentially a 200 hp increase to be had from a 560 hp car from just sae correction and a cup of tea !


that's not accounting for a tcf to get to flywheel power, which is as best as I can find out not a % loss but just 35hp per axle.

it is crazy how easy it would be to get an 800 hp dyno plot for a 600 hp car !


rototest are good they show all the data on the lot showing the measured power and corrected power with temp for each rpm line.

 

Certainly high atmospheric pressure and low air temps are the recipe for high power output yes.

Humidity though is a point for argument though.
Most people say its good for power but I don't think it is, I think it loses power.
Not easy to test I guess but for me, the water molecules take up valuable space that could have been filled with oxygen, so unless your gaining power from cooling the charge somewhat on an engine that is running too close to the knock line I don't see where any appreciable power increase is going to come from.

A Semi Interesting topic I know little about in all honesty.

 

out of interest what was you charge air temp
surely the ambient air temp is only relevant to nasp engines and hiking the figures up on turbo's

 

I don't have the data tony but the intercooler is huge, and I mean huge 4.5" thick and half as big again as an rs500 one, they monitor it and it wouldn't of been ott.

 

Fascinating stuff isn't it? All those hundreds of people who have been screwed over by dyno tuners who didn't even actually FIT the fucking chip, they just had a brew and moved the air probe and gave them a car back. (Sadly, I KNOW FOR A FACT that this goes on. )

If you want some food for thought... think about this.
How does that intake correction work on a Turbocharged car at all since the air the engine actually ingests has had its composition changed by a compressor?


We go one further than that actually... We show it graphed live with the dyno run.

Here are some examples of the graphs you would get from us.

 

The fact that the ambient air temp may have been 15 C is irrelevant IMO if the charge air was 60 scooby

 

I understanhd what your saying tony but the thing is the dyno wont correct for the charge air temp it will just reduce the power output, the acts wouldn't of been 60 on either of them runs im 100% confident of that looking at there set up, heck I ran my old t4 saph at 2.2 bar on a shit dyno with a pathetic fan and it never got to 50d.

what im getting at is the difference it makes with just the temperature sensor location, im not comparing the measured powers, im compareing the difference between the two corrected power figures to there respective measured power readings.

theres a 50 hp discrepancy in the correction to din standards going from 23d upto 58d.

 

it is crazy stu how many people no doubt get shafted daily

that's some comprehensive data you've got there.

if it wasn't such a travel id come and pay a couple of hours dyno and we could do it with my car and a cuppa tea

id love to see your yard now its many years ago when I last came down and you mapped my white saph for me.

 

I know what your getting at but the charge air temp is critical you should log your charge air with your power runs and use ATW power only for your tuning

 

all those figures are at all four hubs mate, no tcf but they all show din correction as its industry standard, but I thought mmmmm whats the true uncorrected figures then and here we are.

I think they will have act data I just didn't ask for it tbh mate.
they would have said though if the intercooler wasn't coping but all was well
tbh I don't even mean this thread to be about my car as such its just a comparison as its shocked me the differences these settings make to a power output.

 

This is a topic I have a vested interested as I work with engine dynos in my job. Just to give you some info in each test cell ( similar to stus) we have a fully independent weather station. This measures temperature pressure and humidity values. This information is fed into the automation system so we can have engine power corrected to the the sae standard.
We can also tweak these but we aren't chasing numbers like some chassis dyno operators (and their customers) are

 

We have a weather station on our system too, we do not ever have to manually input the figures, and it updates on every run

 

.


Ditto

 

where I had my car mapped has everything monitored, I just didn't get a graph with all the data on it, but I do have an old one of theres.

it watches just reading off the read out columns
rpm, torque, map, temp, airdens, baro, relhum, lambda, afr, speed, t.effort, accel, distance, theres a few more but I don't think there relevant like hub rpm, pcratio etc.

its not controlled afaik but it is monitored.

 

stu when you have a suitable car on the dyno would you be able to do one extra run with the temp sensor having a cuppa ?

 

Just for info, not being a smart ass , 29.92 in/hg is actually 1013mb.

This is the standard atmosphere to ISO:

1013mb / 29.91 in/hg at 15 degC at sea level.

That is used worldwide to calculate aircraft performance & has modifiers for temp/ density etc, and it makes a HUGE difference, so fooling a dyno with a dodgy ambient temp would be easy peasy.

Interesting topic

 

And the 2 c.f's are exactly why 2 identical cars can make different power in the summer when one is in England and the other's in California

It would be near-impossible for a dyno to calculate the effect of IAT's on power on a forced induction engine (imo)

That's a separate sheet which you can get from the Dynapack software

 

crazy isn't it both industry standard corrections can be so far apart with a little temp change and as far as im aware the higher reading sae is the most common.


I do have a sheet from 2008 from a dyno pack it shows a lot of data amb temp, humidity, baro pressure etc.

 

when we gonna get an ambient vs cuppa tea run then stu ?
with a din, sae and dds own cfs aswell if possible

 

Will try and do one this week mate.

 

top man thanks stu, I look forward to seeing the results

 

yes they a great idea james,but then DD gave you option of turning it off and manual tweaking readings!

for me the weather station sits to one side of dyno cell and intake air temp probe too.

this for me is way for most consistant results.

 

i dont like corrected figures, (they are only good for comparison sake)
What the car produces on that day is what its doing! there is no telling if the car will ever produce the corrected figure! (maybe the car has never been mapped at 20 degrees inlet temp but this is the corrected figure.)

gareth