I noticed the other day when dynoing in here in FL with humidity around 90% and temps around 90 degrees that the SAE correction factor was nill. SAE and actual HP were like 554 and 555 respectively. I then looked up my old dyno from 3 months ago with the 385 motor and looked at conditions. It was 70 degrees and about 40% humidity. But the correction factor was basically the same. HP and actual were again within 1 or 2 hp. It was like 520 and 522.

ANyone have problems with weather stations on thier dynojets? Anyone ever follow trends with weather and corrections?

 

http://dynojet.com/gmhtpmag3.shtml

In the United States this is usually Society of Automotive Engineers (SAF) standard J1349 Rev JUN90. Correcting to SAE J1349 alters the data to make it seem as if it was taken when the atmospheric pressure was 29.23 in/hg., the temperature 77°F and the humidity zero.

the correction software has trouble getting humidity correct. but, atmospheric pressure is the biggy.

 

also, i've been on a dyno 25feet inside a building doors up. it rain about 1 minute before my run and it say humidity was 23% hmmmmmm..........

 

I have never felt the correction faction was that accurate.
We had the same problem Sat in Ft. Myers.
It was 90+ easy outside with 90+ humity and when we ran the correction we were loosing big power.
One car went from 361 down to 345. That is bullshit in my oponion.
The correction should have added power with the weather the way it was.
Another car went 411 down to 399. Again bullshit. How is that correcting?
To me correction factors should be more accurate.
If you on a dyno with very little or no humity, and 55 degree weather when you power is corrected you should loose power. When you dyno in muggy, hot, sticky, nasty weather you should gain power when correcting.
I am willing to bet that the cars on our dyno will make between 15-25 more Horsepower in January.

 

Around here it seems pretty accurate. I know of at least one high hp car that dyno'd within 6hp at another dyno at sea level (6hp/1200+ isn't really anything).

Of course, we're at a mile above sea level (5300+ft), so my correction factor was 1.19. So everyone's dyno numbers after correction goes up by like 18-20%. I've never really paid attention to the variation on the same car on a different day, or on a different dyno.

 

I've never felt they are accurate, atleast not in Florida! That is why I just use it for a tuning tool and go for numbers in the winter. Only option we have in Florida, the humidity state!

 

That is my theory as well John.
I have never been able to proove it but soon I will.
I am gonna take some customer's cars that I am 99% sure they are done moding them and dyno tune them in a couple weeks.
I am then gonna pay to have them redynoed on the same dyno 4-5 months later and see how unaccurate the correcting factor is.
One is a 6 speed Z06 and the other a A4 Z28 so we can see the difference in the A4 and M6.

BTW not to get off topic but where are you out of John and what do you specialize in?
I have not seen you as a sponsor before and dont see a webpage of any kind.

 

I agree with you about the tuning tool.

But it just seems like it is more of a problem here in FL.
The humidity according to the dynojet weatherstation said 40% humidity when i dynoed. But the local forecast was in the 90 % humidity range. I wonder if that the problem we have in FL?

I have seen many cars get work done up north and dyno 5-15% when they cam back to florida.

I think im gonna go dyno in Jersey so I can jack my numbers up..lol.

I mean hell...if the dynojet here is jusy gonna spit out ACTUAL HP #s the same as SAE...I may as well just wait to dyno in 45 degree weather with high barometer and 0 humidity. Id probably gain 45 hp..lol.

The more I think about it I am pretty plaese with the 555 ACTUAL rwhp in these conditions. Should be enough to run low low 10s even in this heat.

 

I don't have any hard numbers, and I've never really paid attention to the specific temp and humidity readings. I should go back and check my records.

But we're pretty much at sea level where I am, and every dyno I have used (two dynojets) has always had about the same CF of .96 or 0.97, regardless of whether it was raining, sunny, it was spring, summer, or it was winter. So, I've never seen much change across the board.

 

I agree. Another possiblity to consider is the location of the weatherstation in the dyno room and how well ventilated the room is. This can have an effect on the weatherstation readings and the dyno numbers.

 

And this is why a properly designed dyno room and a repeatable engine dyno are almost impossible to beat.

 

anyone have any dynos that show the CF on a very hot hunid day...and then on a very good day? I would like to see actual and SAE corrected.

 

Don't feel bad. I dynoed about a weel ago in Chicago, Il. It was 90 plus out side and the dyno said it was 5% humidity ! Chicago has NEVER seen 5% humidity. Oh well, I know when I use to use a superflow, the dyno operator was very careful in entering all weather data. Also he kept rechecking through out the day. The corrected HP would change alot! The 23% humidity while raining outside is a good one!

 

You guys that are serious about getting the straight skinny when you hit a chassis dyno (or engine dyno for that matter) should purchase a weather station and bring it with you to compare to the conditions the dyno weather station is using to establish the correction factor. A good one isn't that expensive any more and its a great tool to have when you hit the track as well. Whether your car is faster or slower based on your recent changes (or driving technique) versus weather conditions (D/A) from your last outting is extemely important information.

Also, keep in mind that the biggest factor in correction factor is the barometer which is something you really can't feel....humidity and temperature play a much smaller role in correction factor (and D/A).

Tony M.

 

actually tnoy a good weather startion is VERY expensive.

 

OK....a "decent" weather station....LOL
($300-$500)