Question about logging air mass in different temps.
11-27-2003, 08:20 PM
#1
Junior Member
Thread Starter
Join Date: Oct 2003
Posts: 538
Likes: 0
Received 0 Likes
on
0 Posts
Question about logging air mass in different temps.
I dont have alot of experience with audis so Im not sure how this works. I have notticed that when its cold 50F or cooler, the car will hit about 3 psi less than when it is warm out.
I have heard stories that this is because the computer sees the air temp and adjusts boost to keep the air mass the same.
Can anyone confirm that in the winter and in the summer your air mas was the same.
I have heard stories that this is because the computer sees the air temp and adjusts boost to keep the air mass the same.
Can anyone confirm that in the winter and in the summer your air mas was the same.
11-27-2003, 09:46 PM
#2
AudiWorld Super User
Join Date: Nov 2000
Posts: 6,270
Likes: 0
Received 0 Likes
on
0 Posts
Lower temperature air has more density...
therefore more mass.
Theoretically, a 30F drop in air temp will result in an airflow increase equavilent to a 1.5psi boost increase on a 1.8T motor.
This is post-IC, so outside temps of 50F vs. 80F may actually be more like 105F vs. 145F post-IC (I'm making these numbers up)
way back when I had a stock turbo, I would notice ~2psi more boost when going through the mountains. Since higher altitudes have less dense air, the boost had to be increased to maintain the same MAF readings compared to sea-level.
Theoretically, a 30F drop in air temp will result in an airflow increase equavilent to a 1.5psi boost increase on a 1.8T motor.
This is post-IC, so outside temps of 50F vs. 80F may actually be more like 105F vs. 145F post-IC (I'm making these numbers up)
way back when I had a stock turbo, I would notice ~2psi more boost when going through the mountains. Since higher altitudes have less dense air, the boost had to be increased to maintain the same MAF readings compared to sea-level.
11-27-2003, 10:52 PM
#3
Rest In Peace
Join Date: Mar 2000
Location: Chicago
Posts: 37,562
Likes: 0
Received 0 Likes
on
0 Posts
Lemme get this straight - first you claim yourself an "expert" but now you're saying you're...
"not sure why" the cars make less boost when it is cold out?
I love the fact that you've adopted that Bozo Bop Bag as your sig. So fitting...<ul><li><a href="http://www.audizine.com/forum/topic.asp?TOPIC_ID=37219&FORUM_ID=6&CAT_ID =3&Topic_Title=Duh+Engineering+FMIC+installed+ BWW&Forum_Title=1%2E+B5+A4">"if you dont consider me an expert, you obviously dont read my threads.
I love the fact that you've adopted that Bozo Bop Bag as your sig. So fitting...<ul><li><a href="http://www.audizine.com/forum/topic.asp?TOPIC_ID=37219&FORUM_ID=6&CAT_ID =3&Topic_Title=Duh+Engineering+FMIC+installed+ BWW&Forum_Title=1%2E+B5+A4">"if you dont consider me an expert, you obviously dont read my threads.
11-28-2003, 06:27 AM
#5
Elder Member
Join Date: Sep 2002
Posts: 14,366
Likes: 0
Received 0 Likes
on
0 Posts
You also saw a increase of boost because the motor was making less vacuum
Easy way to see that is to look at a vacuum gauge at idle in different conditions like air temps and altutude changes.
11-28-2003, 06:55 AM
#6
Junior Member
Thread Starter
Join Date: Oct 2003
Posts: 538
Likes: 0
Received 0 Likes
on
0 Posts
I understand this
I know about the air density vs temp. My question is...being that the computer pulls back 2 psi in lower temps, when you have the EXACT same set up all year round.
Do you log the same air mass values in both scenarios:
40 degrees F, 15psi
or
85 degrees F, 18 psi
Do your air mass values match becaue of the lack of air density in the warmer weather, but more pressure and then the abundance of air density in the colder weather, but lack of requested pressure?
Do you log the same air mass values in both scenarios:
40 degrees F, 15psi
or
85 degrees F, 18 psi
Do your air mass values match becaue of the lack of air density in the warmer weather, but more pressure and then the abundance of air density in the colder weather, but lack of requested pressure?
Trending Topics
11-28-2003, 06:58 AM
#8
Junior Member
Thread Starter
Join Date: Oct 2003
Posts: 538
Likes: 0
Received 0 Likes
on
0 Posts
...
I put that there for you.
Nw can you answer this question? Or does your knowledge not go any further than intercoolers?
I understand how this system works, I just want to know some air mass data..do you have any?
I am suer why Audis make less boost in the cooler weather dick, thats why I was asking for air mass values.
See, in the DSM, when the temp gets cooler, the air density increases, as does the air mass, the computer has no control over the boost pressure, I do, so I do not lower the boost pressure when the temps drop, hence, I put boost into the motor at 26 psi, yst the air quanity has increased because of the density.
When you lower the boost, you are equalizing the boost with the air temp to allow the car to ingest the same qwuanity of air irregardless of weather. Which means, these cars see no real benifit of lower intake temps.
Nw can you answer this question? Or does your knowledge not go any further than intercoolers?
I understand how this system works, I just want to know some air mass data..do you have any?
I am suer why Audis make less boost in the cooler weather dick, thats why I was asking for air mass values.
See, in the DSM, when the temp gets cooler, the air density increases, as does the air mass, the computer has no control over the boost pressure, I do, so I do not lower the boost pressure when the temps drop, hence, I put boost into the motor at 26 psi, yst the air quanity has increased because of the density.
When you lower the boost, you are equalizing the boost with the air temp to allow the car to ingest the same qwuanity of air irregardless of weather. Which means, these cars see no real benifit of lower intake temps.
