lid and descreened maf = hp loss ???!?
05-13-2007, 01:22 PM
#1
lid and descreened maf = hp loss ???!? i knew the title would get your attention. someone please chime in here.
i was looking through some old HPTuner logs and came about two that were a day apart. the thing that caught my attention is that the delivered engine torque (was using it as more of a novelty) was lower after putting on a lid and descreening the maf..
both logs have the same tune (sorry i don't have the tune anymore).
below are two screenshots of the log in very similar conditions in terms of engine speed, gear, maf lb/min.
after the lid, the iat drops a few degrees and the map is starting to show a little ram air effect! you'd think that would give more air and more power, right??
instead, you'll notice that after the lid, the dynamic cylinder airmass has dropped and so has the injector pulse (less air/fuel to the cylinders).
what's goin on here??
i was looking through some old HPTuner logs and came about two that were a day apart. the thing that caught my attention is that the delivered engine torque (was using it as more of a novelty) was lower after putting on a lid and descreening the maf..
both logs have the same tune (sorry i don't have the tune anymore).
below are two screenshots of the log in very similar conditions in terms of engine speed, gear, maf lb/min.
after the lid, the iat drops a few degrees and the map is starting to show a little ram air effect! you'd think that would give more air and more power, right??
instead, you'll notice that after the lid, the dynamic cylinder airmass has dropped and so has the injector pulse (less air/fuel to the cylinders).
what's goin on here??
Last edited by BobDoLe; 11-15-2009 at 04:42 PM.
05-13-2007, 02:18 PM
#2
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Torque is figured off airflow/air mass and spark. If you
fool the airflow the torque follows. With a descreened MAF
any airflow bias induced by the lid (like a lot of curvature
in the neck, making centrifugal crowding to the top side
etc.) can skew the MAF reading.
If it's a "good kind of lean" then you might leave it be; if
it's a problem and inaccurate then the MAF table may need
a few percent tweakage.
fool the airflow the torque follows. With a descreened MAF
any airflow bias induced by the lid (like a lot of curvature
in the neck, making centrifugal crowding to the top side
etc.) can skew the MAF reading.
If it's a "good kind of lean" then you might leave it be; if
it's a problem and inaccurate then the MAF table may need
a few percent tweakage.
05-14-2007, 04:47 AM
#3
thanks for the input.
i took a look at the maf and decided the wires were filthy. i took to correcting that with a little rubbing alcohol, q-tip, and 10 minutes.
now i'm back to seeing .70 g/cyl and an extra 30+ lb registering in "delivered engine torque." a great sotp difference.
i still need to get the maf dialed in though.
thank you
i took a look at the maf and decided the wires were filthy. i took to correcting that with a little rubbing alcohol, q-tip, and 10 minutes.
now i'm back to seeing .70 g/cyl and an extra 30+ lb registering in "delivered engine torque." a great sotp difference.
i still need to get the maf dialed in though.
thank you
05-14-2007, 10:38 AM
#4
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Nice car. Looks just like mine except yours says SS on it and mine says Z28. ;-) Same year/color though.
My experience has been that reducing intake air flow restrictions generally richens the WOT mixture. When I tuned both my 1999 Z28 and my buddy's 2000 Corvette I noticed the same thing on the dyno - putting a high flow air filter richened the fuel mixture at WOT, which was actually very surprising. Maybe it's because the MAF calibration tables are suddenly operating in a range the factory didn't tune as well? For whatever reason, this is the case, and I was able to gain an extra 5-6HP at the wheels by getting the mixture dialed in, for a total of about 15HP RWHP gain on the Corvette.
I never thought about tuning to the reported torque from the PCM. That's an interesting concept, and a valuable tip if the number is accurate.
My experience has been that reducing intake air flow restrictions generally richens the WOT mixture. When I tuned both my 1999 Z28 and my buddy's 2000 Corvette I noticed the same thing on the dyno - putting a high flow air filter richened the fuel mixture at WOT, which was actually very surprising. Maybe it's because the MAF calibration tables are suddenly operating in a range the factory didn't tune as well? For whatever reason, this is the case, and I was able to gain an extra 5-6HP at the wheels by getting the mixture dialed in, for a total of about 15HP RWHP gain on the Corvette.
I never thought about tuning to the reported torque from the PCM. That's an interesting concept, and a valuable tip if the number is accurate.
