85mm MAF 6.2L and 98 PCM
05-12-2013, 09:04 AM
#1
85mm MAF 6.2L and 98 PCM It appears that I can break the 11khz fail frequency on my 2-3 shift at around 6800 rpm.
My dyno runs always topped off at 6500rpm for power, 7k for the limiter but on a test run during the 1/4 I let it go to almost 7k (logging showed 68xx rpm) and I triggered the code AFTER I went into 3rd gear and had let go of the clutch and the rpms had dropped.
I will do some more logging, but so far it's been repeatable.
My dyno runs always topped off at 6500rpm for power, 7k for the limiter but on a test run during the 1/4 I let it go to almost 7k (logging showed 68xx rpm) and I triggered the code AFTER I went into 3rd gear and had let go of the clutch and the rpms had dropped.
I will do some more logging, but so far it's been repeatable.
05-12-2013, 09:32 AM
#2
LS1Tech Sponsor
You can move the fail frequency up but if it was me I would look at doing the whole tune in speed density anyway.
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05-12-2013, 10:01 AM
#3
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The '98 MAF tables run out to a lower freq than
later years, that's why the fail is set lower. The 85mm
reads a lower air mass at full freq, so kind of a double
whammy there. Even if you get past the fail, what is
the air mass (indicated) saying? Flatlined? Have to
fake it then, for fueling, in the PE vs RPM or something?
later years, that's why the fail is set lower. The 85mm
reads a lower air mass at full freq, so kind of a double
whammy there. Even if you get past the fail, what is
the air mass (indicated) saying? Flatlined? Have to
fake it then, for fueling, in the PE vs RPM or something?
05-12-2013, 10:39 AM
#4
I'll get some datalogging later in the day as I've got a bunch of things to do first and no track day today at near by track or roads empty enough to do some runs.
I thought about the fail frequency going higher and if a)normal dyno says I'm not getting near that high b)its the fact that the 85mm CAN and does report up past 11250 then can I just "ignore" the burst air it pulls in after the shift? I'm thinking its 2-3 shift, its far from being a steady air flow, the MAF reads the "gulp" the engine does, but because of the dynamic state, it doesn't really use the data at that point and it's just the MAF reporting what it does. Is this safe? I mean even after the shift it didn't seem dead or anything and pulled nicely again...
In theory though, is it possible for a LS3 to pull that kind of air? I'm running the truck base 85mm tables which after dyno tuning was fine. I think 2-4% error which was tweaked to as good as it gets.
I'm running 5.3 heads, stage 2.5 which is not even close to the flow levels of the stock LS3 heads. LS6 intake which I think is choked at 6200rpm roughly. Ported stock 98 throttle body (78mm), SLP lid, stock accordion bellows after the MAF and a 4 inch coupler before the MAF (it's sealed well).
This didn't appear on the dyno, its just as stated "after" the 2-3 shift when I've actually heard the 2-3 chirp even which makes no sense as the engine rpm would drop like a rock not pull more air all of a sudden. I can't do a 3-4 shift unless on track so testing along those levels is unrealistic unless I drive a few hours away.
I thought about the fail frequency going higher and if a)normal dyno says I'm not getting near that high b)its the fact that the 85mm CAN and does report up past 11250 then can I just "ignore" the burst air it pulls in after the shift? I'm thinking its 2-3 shift, its far from being a steady air flow, the MAF reads the "gulp" the engine does, but because of the dynamic state, it doesn't really use the data at that point and it's just the MAF reporting what it does. Is this safe? I mean even after the shift it didn't seem dead or anything and pulled nicely again...
In theory though, is it possible for a LS3 to pull that kind of air? I'm running the truck base 85mm tables which after dyno tuning was fine. I think 2-4% error which was tweaked to as good as it gets.
I'm running 5.3 heads, stage 2.5 which is not even close to the flow levels of the stock LS3 heads. LS6 intake which I think is choked at 6200rpm roughly. Ported stock 98 throttle body (78mm), SLP lid, stock accordion bellows after the MAF and a 4 inch coupler before the MAF (it's sealed well).
This didn't appear on the dyno, its just as stated "after" the 2-3 shift when I've actually heard the 2-3 chirp even which makes no sense as the engine rpm would drop like a rock not pull more air all of a sudden. I can't do a 3-4 shift unless on track so testing along those levels is unrealistic unless I drive a few hours away.
Last edited by SladeX; 05-12-2013 at 11:04 AM.
05-12-2013, 05:03 PM
#5
I raised the limit to 12500 hz, no code
Data logged it, got readings as high as 11800 during the upshift. Since it its duing the shift and "hopefully" not trying to use that spike for fueling, I think it will be ok.
Data logged it, got readings as high as 11800 during the upshift. Since it its duing the shift and "hopefully" not trying to use that spike for fueling, I think it will be ok.
