Surging/Bucking Related: How much does timing affect airflow requirements? (rambling)
11-20-2004, 09:00 PM
#1
TECH Addict
Thread Starter
Join Date: Feb 2004
Posts: 2,826
Likes: 0
Received 0 Likes
on
0 Posts
Surging/Bucking Related: How much does timing affect airflow requirements? (rambling) I ask, because I would think increased timing would require additional airflow, right? I have just been kicking around options for eliminating surge, and the one that I keep wondering about is airflow related. Don't mind me while I ramble here...
As soon as you touch the throttle you go into the main spark tables, which at light throttle will usually put you in the 30s or 40s degrees. Now I have noticed at cruise that cylinder air dumps to .09 g/cyl and less. On a stock vehicle with a stock TB you have that lip to restrict air at low rpms, and I would guess that normally the IAC would compensate for any additional airflow that you need. On cammed cars we need more air at idle, so I would think that we need more air at light cruise too. Unfortunately the throttle cracker is not specific enough to give us the air we need only at light throttle. So I have started toying with the Airflow vs. TPS table. I think that may be where we need to start adding some airflow at. Additionally, I think a throttle body with the lip removed will help because it will do the exact same thing; gradually add slightly more air as the throttle is cracked.
As soon as you touch the throttle you go into the main spark tables, which at light throttle will usually put you in the 30s or 40s degrees. Now I have noticed at cruise that cylinder air dumps to .09 g/cyl and less. On a stock vehicle with a stock TB you have that lip to restrict air at low rpms, and I would guess that normally the IAC would compensate for any additional airflow that you need. On cammed cars we need more air at idle, so I would think that we need more air at light cruise too. Unfortunately the throttle cracker is not specific enough to give us the air we need only at light throttle. So I have started toying with the Airflow vs. TPS table. I think that may be where we need to start adding some airflow at. Additionally, I think a throttle body with the lip removed will help because it will do the exact same thing; gradually add slightly more air as the throttle is cracked.
11-20-2004, 09:39 PM
#2
I believe the TB lip is there to increase the airspeed at low blade angles - neccessary to maintain airflow in the intake tract at low TPS%.
Running AirFlow is very important for part throttle response and idle transitioning - at least with "fly by wire" it is. FWIW.
gojo knows alot about this ....maybe he'll chime in???
-joel
Running AirFlow is very important for part throttle response and idle transitioning - at least with "fly by wire" it is. FWIW.
gojo knows alot about this ....maybe he'll chime in???
-joel
11-22-2004, 11:34 AM
#4
TECH Enthusiast
iTrader: (12)
Join Date: Mar 2002
Location: w.s.n.c.
Posts: 539
Likes: 0
Received 0 Likes
on
0 Posts
As was pointed out in your thread "LS2 TB...is it 90mm all the way? No lip or anything?"
The "lip" is there to provide for smoother transition from cruise to idle. It's really not a lip. If you look at the TBlade as it opens you will see the blade follows a curve in the TBody to about 10% open. Without it you will not get a smooth transition. The adjustments to airflow are made in the RAF table by temp. to control the TBlades transition to idle position and affect cruise speed when your off the gas. After that the TBody is really like a hole and the adjustments are made by VE's, IFR's, PE, Timing. etc. Your trims will show you what's happening and add or subtract fuel. As for timing, I only know to use the bi directional controls in EFI and find what works. Whenever I've seen bucking it's been when you're off the gas and the RAF is set too low. When the car starts to move the RAF should be set to create a slight amount of cruise. I think that just as a cammed car needs a higher idle it needs more RAF to keep from bucking and surging. Note that I'm talking about YBodies. I have not tuned any FBodies, but my C5 idle and limiter tables are all stock except for idle and RAF.
The "lip" is there to provide for smoother transition from cruise to idle. It's really not a lip. If you look at the TBlade as it opens you will see the blade follows a curve in the TBody to about 10% open. Without it you will not get a smooth transition. The adjustments to airflow are made in the RAF table by temp. to control the TBlades transition to idle position and affect cruise speed when your off the gas. After that the TBody is really like a hole and the adjustments are made by VE's, IFR's, PE, Timing. etc. Your trims will show you what's happening and add or subtract fuel. As for timing, I only know to use the bi directional controls in EFI and find what works. Whenever I've seen bucking it's been when you're off the gas and the RAF is set too low. When the car starts to move the RAF should be set to create a slight amount of cruise. I think that just as a cammed car needs a higher idle it needs more RAF to keep from bucking and surging. Note that I'm talking about YBodies. I have not tuned any FBodies, but my C5 idle and limiter tables are all stock except for idle and RAF.
11-22-2004, 03:52 PM
#5
TECH Addict
Thread Starter
Join Date: Feb 2004
Posts: 2,826
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by gojo
As was pointed out in your thread "LS2 TB...is it 90mm all the way? No lip or anything?"
The "lip" is there to provide for smoother transition from cruise to idle. It's really not a lip. If you look at the TBlade as it opens you will see the blade follows a curve in the TBody to about 10% open. Without it you will not get a smooth transition. The adjustments to airflow are made in the RAF table by temp. to control the TBlades transition to idle position and affect cruise speed when your off the gas. After that the TBody is really like a hole and the adjustments are made by VE's, IFR's, PE, Timing. etc. Your trims will show you what's happening and add or subtract fuel. As for timing, I only know to use the bi directional controls in EFI and find what works. Whenever I've seen bucking it's been when you're off the gas and the RAF is set too low. When the car starts to move the RAF should be set to create a slight amount of cruise. I think that just as a cammed car needs a higher idle it needs more RAF to keep from bucking and surging. Note that I'm talking about YBodies. I have not tuned any FBodies, but my C5 idle and limiter tables are all stock except for idle and RAF.
The "lip" is there to provide for smoother transition from cruise to idle. It's really not a lip. If you look at the TBlade as it opens you will see the blade follows a curve in the TBody to about 10% open. Without it you will not get a smooth transition. The adjustments to airflow are made in the RAF table by temp. to control the TBlades transition to idle position and affect cruise speed when your off the gas. After that the TBody is really like a hole and the adjustments are made by VE's, IFR's, PE, Timing. etc. Your trims will show you what's happening and add or subtract fuel. As for timing, I only know to use the bi directional controls in EFI and find what works. Whenever I've seen bucking it's been when you're off the gas and the RAF is set too low. When the car starts to move the RAF should be set to create a slight amount of cruise. I think that just as a cammed car needs a higher idle it needs more RAF to keep from bucking and surging. Note that I'm talking about YBodies. I have not tuned any FBodies, but my C5 idle and limiter tables are all stock except for idle and RAF.
11-22-2004, 04:31 PM
#7
TECH Enthusiast
iTrader: (12)
Join Date: Mar 2002
Location: w.s.n.c.
Posts: 539
Likes: 0
Received 0 Likes
on
0 Posts
Send me your e-mail and I'll send you my RAF Numbers as an example.
They are in the 10's also.
I would put all the files back to stock. Particularly the IAC Park. Work on the RAF tables so that you can feel RAFs take over as you slowly move up from idle. If you have a scanner with bidirectional controls, try moving the timing in, the problem area, a degree at a time. I added timing to mine up to 1200 rpms and it did help smooth idle and slow moving.
They are in the 10's also.
I would put all the files back to stock. Particularly the IAC Park. Work on the RAF tables so that you can feel RAFs take over as you slowly move up from idle. If you have a scanner with bidirectional controls, try moving the timing in, the problem area, a degree at a time. I added timing to mine up to 1200 rpms and it did help smooth idle and slow moving.
Trending Topics
11-22-2004, 09:20 PM
#8
TECH Addict
Thread Starter
Join Date: Feb 2004
Posts: 2,826
Likes: 0
Received 0 Likes
on
0 Posts
Oh well. Our running airflow tables are almost the exact same. The normal operating temperature airflow is within .1 of each other. I am sure .1 isn't going to cause this problem.
11-23-2004, 07:15 AM
#10
Originally Posted by gojo
When I'm close to right .01 makes a difference. Try raising RAFs at the temps where you have bucking. It can't hurt.
joel
11-23-2004, 05:14 PM
#11
TECH Addict
Thread Starter
Join Date: Feb 2004
Posts: 2,826
Likes: 0
Received 0 Likes
on
0 Posts
Really? Well anyways, I did some testing today. I think it is fuel related. I forced the car into open loop while I drove home. Open loop=smooth driving any rpm. Closed loop=crappy bucking. It was pretty smothered with gas too though. I am thinking that the problem is related to the O2 switching. I noticed I was not running as rich after my cam install. Any possibility that the reversion is diluting the cylinders enough to cool the mixture and cause it to pull too much fuel?
Side note: WTF is up with the HPTuners a/f ratio adjuster on the scanner tools? I moved it up and down and it didn't do anything. (Probably a 98 thing I bet.)
Side note: WTF is up with the HPTuners a/f ratio adjuster on the scanner tools? I moved it up and down and it didn't do anything. (Probably a 98 thing I bet.)
11-23-2004, 11:00 PM
#13
TECH Addict
Thread Starter
Join Date: Feb 2004
Posts: 2,826
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by Bink
By undriveable I mean driving in traffic.......throttle response at low rpm and idle transition turns to **** when the RAF is off. Stop and Go traffic 
- I'd just as soon park it.
- I'd just as soon park it.
