Why is the factory PE table set up so RICH?
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Staging Lane
Joined: Aug 2005
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Why is the factory PE table set up so RICH? I noticed looking at my '98 stock PE/RPM table (b3618-PE modifier based on RPM), AFR starts out at 12.6:1 at low RPM, then rises to 11.7 at 2400 RPM on up.
That seem awfully rich!
Why did GM make the PE WOT so Rich? Is this just over cautious, so as to make sure you never go lean?
I have not touched this table yet, as I don't have a WB yet.
But I'm tempted to change it at least some, then log and check for KR.
Right now I have no WOT KR, and my narrowband O2's are giving around 930 t0 945mV when WOT so I probably am rich?
That seem awfully rich!
Why did GM make the PE WOT so Rich? Is this just over cautious, so as to make sure you never go lean?
I have not touched this table yet, as I don't have a WB yet.
But I'm tempted to change it at least some, then log and check for KR.
Right now I have no WOT KR, and my narrowband O2's are giving around 930 t0 945mV when WOT so I probably am rich?
Because the VE and MAF are off so damn much anyway that you still wont ever actually run that rich. With a few bolt ons my actual AFR was like 14.8 with a commanded 11.7.
alot of tuners such as redhardsupra and Foff have told me i could modify my PE anywhere from 1.2-1.15 on a bolt-on car without a wideband...is this the best way to do it? no, but it seems safe for now...
Originally Posted by brad8266
Because the VE and MAF are off so damn much anyway that you still wont ever actually run that rich. With a few bolt ons my actual AFR was like 14.8 with a commanded 11.7.
My WOT AFR with just a lid, pulley, longtubes and ORY was 13.7-9. 
here's an example why even an obnoxiously rich stock tune will make you go very lean on boltons only:
stock car eats X air to make ~300rwhp, at 11.7AFR.
since airflow is directly proportional to hp, let's say it's 300 Unidentified Airflow Units
With this data, that means we'll need 300UAU/11.7AFR=25.64UnidentifiedFuelflowUnits
i'm really amusing myself with this...
if you dont change the tune but add boltons, that means you're gonna be running now about 350rwhp (or in this example 350UAU) yet still dumping the same 25.64UFU of fuel.
so now we calculate AFR for this setup: AFR=UAU/UFU, so 350/25.64=13.65AFR amazing how the numbers work out, isn't it?
on top of this, LT's and other boltons usually work the most at midrange, or for our cars, the peak torque, which is already knock prone. add another 7-10% airflow at the peak tq, combine it with 2 extra AFR points, and you're knocking so bad that all the extra airflow from the boltons is going to be null and void on behalf of the computer freaking out and pulling so much timing it's going to be as weak as before.
short version: tune your boltons or knock forever!
stock car eats X air to make ~300rwhp, at 11.7AFR.
since airflow is directly proportional to hp, let's say it's 300 Unidentified Airflow Units
With this data, that means we'll need 300UAU/11.7AFR=25.64UnidentifiedFuelflowUnits
i'm really amusing myself with this...if you dont change the tune but add boltons, that means you're gonna be running now about 350rwhp (or in this example 350UAU) yet still dumping the same 25.64UFU of fuel.
so now we calculate AFR for this setup: AFR=UAU/UFU, so 350/25.64=13.65AFR amazing how the numbers work out, isn't it?
on top of this, LT's and other boltons usually work the most at midrange, or for our cars, the peak torque, which is already knock prone. add another 7-10% airflow at the peak tq, combine it with 2 extra AFR points, and you're knocking so bad that all the extra airflow from the boltons is going to be null and void on behalf of the computer freaking out and pulling so much timing it's going to be as weak as before.
short version: tune your boltons or knock forever!
^^^^^^ That sums it up. Well written! After learning the basics, I can truely understand and admire the logic behind tuning. As RedHardSupra posted in the thread, if you throw some numbers around you can clearly see where you stand. Its not rocket science!
Andy
After learning the basics, I can truely understand and admire the logic behind tuning. As RedHardSupra posted in the thread, if you throw some numbers around you can clearly see where you stand. Its not rocket science!Andy
Last edited by White.Lightning; Feb 17, 2007 at 10:46 AM.
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I see it as, GM wanting to not have to do warranty service
on every steenkin' F-body out there for customer "my car
pings" complaints, so they made it fat, safe and dumb.
Lean, mean and edgy, that's on you.
on every steenkin' F-body out there for customer "my car
pings" complaints, so they made it fat, safe and dumb.
Lean, mean and edgy, that's on you.
Originally Posted by RedHardSupra
here's an example why even an obnoxiously rich stock tune will make you go very lean on boltons only:
...
if you dont change the tune but add boltons, that means you're gonna be running now about 350rwhp (or in this example 350UAU) yet still dumping the same 25.64UFU of fuel.
so now we calculate AFR for this setup: AFR=UAU/UFU, so 350/25.64=13.65AFR amazing how the numbers work out, isn't it?
...
if you dont change the tune but add boltons, that means you're gonna be running now about 350rwhp (or in this example 350UAU) yet still dumping the same 25.64UFU of fuel.
so now we calculate AFR for this setup: AFR=UAU/UFU, so 350/25.64=13.65AFR amazing how the numbers work out, isn't it?
