Long vs short ft question
Thread Starter
Burning Brakes
Joined: Nov 2004
Posts: 800
Likes: 3
From: Port Orange FL
Long vs short ft question
I am trying to get my FT as close as possible to 128 in all the cells and am seeing something that is confusing me and leaving me unsure which way to adjust. I thought that LTFT would be determined based upon the average of STFT, so they would both be either rich or lean in a given cell. But I keep seeing areas where my ST may be consistently showing one way and yet the LT shows as correct or the other way. I can even look at the Histogram and see that the overall avg of the LT is different from the average of the ST. Can someone clarify why this is and exactly how to use it to make the correct adjustments?
Thanks
Roy
Thanks
Roy
Race Director
Joined: Mar 1999
Posts: 12,597
Likes: 237
From: Bartlett Illinois
If I understand it right..
STFT is for the short term so you will almost always see adjustments
LTFT is for for the longer period so you could have the LTFT at 128 and the STFT could be moving.. Typically I use the INT and the BLM for tuning on my 89. I have my BLMs set at 128 +-3 and the INT still adjusts for current at that moment conditions..
hope that helps
STFT is for the short term so you will almost always see adjustments
LTFT is for for the longer period so you could have the LTFT at 128 and the STFT could be moving.. Typically I use the INT and the BLM for tuning on my 89. I have my BLMs set at 128 +-3 and the INT still adjusts for current at that moment conditions..
hope that helps
Le Mans Master
Joined: Feb 2005
Posts: 5,146
Likes: 3
From: The Motor City
ltft=blm?
stft=int.?
I am guessing this is what you mean. Then to answer your question, if for example the BLM is 128 and INT. is a low number (108) and if continues in a certain rpm/load arear it will ultimately lower the BLM, you would then want to lower the VE (maf table or map) number in that load/rpm area.
I don't tune using the histogram, after setting injector flow rate and idle, I prefer trying to keep it at certain RPM/LOAD range starting off idle, by building a small load/rpm range gradually up to about 1600 rpm. Then slowly increasing rpm and making adjustments to see where the trend is going and make my adjustments, (this also depends on what I am seeing sometimes tweaks to the AE tables is also needed, if maf also some tweak to the max. af vs rpm under 1600 rpm).
Additionally, if the blm is a bit over 128 say at 135ish, (lean) the int. number will be going lower in an attempt to compensate and trying to attain 128 Sometimes it cannot compensate enough, or fast enough, and therfor the BLM will not change and more fuel is needed. You may also see the INT. showing a similar number to the BLM which again means more fuel is needed. (this is based on lean readings, if rich, reverse the process)
stft=int.?
I am guessing this is what you mean. Then to answer your question, if for example the BLM is 128 and INT. is a low number (108) and if continues in a certain rpm/load arear it will ultimately lower the BLM, you would then want to lower the VE (maf table or map) number in that load/rpm area.
I don't tune using the histogram, after setting injector flow rate and idle, I prefer trying to keep it at certain RPM/LOAD range starting off idle, by building a small load/rpm range gradually up to about 1600 rpm. Then slowly increasing rpm and making adjustments to see where the trend is going and make my adjustments, (this also depends on what I am seeing sometimes tweaks to the AE tables is also needed, if maf also some tweak to the max. af vs rpm under 1600 rpm).
Additionally, if the blm is a bit over 128 say at 135ish, (lean) the int. number will be going lower in an attempt to compensate and trying to attain 128 Sometimes it cannot compensate enough, or fast enough, and therfor the BLM will not change and more fuel is needed. You may also see the INT. showing a similar number to the BLM which again means more fuel is needed. (this is based on lean readings, if rich, reverse the process)
Last edited by mseven; Feb 2, 2008 at 08:49 AM.
Safety Car
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