Which pulley and MAF?
Which pulley and MAF? Looking for a little more power so I was thinking about adding an underdrive pulley and a 85mm MAF. Which pulley works best and gives the best overall results, the SLP or ASP? Is the SLP 85mm MAF worth the money and effort?
In the southland I would not do a pulley, my car has had a marginal
alternator output under load, on hot days, ever since new. Seems
the alt has an overtemp / overcurrent protection that limits its field
current, and at low RPM, A/C on it would drop below 12V output.
Likewise I don't think a MAF will do you any good, at least no more
than popping your screen for free. If it really improves your power
then you were mistuned (like factory) to begin with, and some MAFs
that play with this voodoo-style, give you an initial improvement
that gets learned back out in a little while (fuel trims "fix" the lean
error and then go to ******* you at WOT).
Since you can tune, I would reject the MAF idea or, if you really
-must- do it (like you believe in the Airflow Bunny) get a used 85mm
truck MAF and descreen it, and use a truck table (or the Z06 MAF
table, if you find the truck table gives you a rich error, actual vs
commanded). I found truck MAF and truck table were dead-nuts
until I swapped in the cam, now it's a bit rich. I would not use the
SLP MAF, its calibration is a hoax and it still has a screen. Worst of
all worlds IMO.
If you want to judge whether MAF "airflow capability" is in your way,
it's simple. Log a WOT pull. Look at your MAP reading at (say) 4000RPM
and at 6000RPM or wherever your peak lies prior to upshift. As a
precentage of horsepower "left on the table", calculate
100% x ( MAP_4000 - MAP_6000 ) / MAP_4000
This actually consists of all intake tract pressure drops, slot /
filter / lid / MAF / bellows / TB.
I have been able so see measurable pressure drops across
screened MAFs but a descreened one is indistinguisable from
open 3" pipe, 75mm or 85mm. Down to 1/16" H2O at what a
furnace blower can pull, while a screened one was in the 1/4"
H2O range (both fairly low flow, 65-75g/sec). I did some calcs
for linear and square-law pressure vs flow projecting the drop
up to more interesting levels. See .gif....
By this projection (not proven, but reasonable-appearing)
a screened 85mm MAF only costs you 15" H2O at 500g/sec
airflow. 4" H2O is 1kPa is 1% at sea level. So if you were
drawing 500g/sec (you aren't, without forced induction) a
big 4% left on the table (call it 20HP if it's all MAF drop and
you're making 500HP). Losing the screen makes it < 3" H2O,
less than a percent, way down on the HP/$ list at that point.
alternator output under load, on hot days, ever since new. Seems
the alt has an overtemp / overcurrent protection that limits its field
current, and at low RPM, A/C on it would drop below 12V output.
Likewise I don't think a MAF will do you any good, at least no more
than popping your screen for free. If it really improves your power
then you were mistuned (like factory) to begin with, and some MAFs
that play with this voodoo-style, give you an initial improvement
that gets learned back out in a little while (fuel trims "fix" the lean
error and then go to ******* you at WOT).
Since you can tune, I would reject the MAF idea or, if you really
-must- do it (like you believe in the Airflow Bunny) get a used 85mm
truck MAF and descreen it, and use a truck table (or the Z06 MAF
table, if you find the truck table gives you a rich error, actual vs
commanded). I found truck MAF and truck table were dead-nuts
until I swapped in the cam, now it's a bit rich. I would not use the
SLP MAF, its calibration is a hoax and it still has a screen. Worst of
all worlds IMO.
If you want to judge whether MAF "airflow capability" is in your way,
it's simple. Log a WOT pull. Look at your MAP reading at (say) 4000RPM
and at 6000RPM or wherever your peak lies prior to upshift. As a
precentage of horsepower "left on the table", calculate
100% x ( MAP_4000 - MAP_6000 ) / MAP_4000
This actually consists of all intake tract pressure drops, slot /
filter / lid / MAF / bellows / TB.
I have been able so see measurable pressure drops across
screened MAFs but a descreened one is indistinguisable from
open 3" pipe, 75mm or 85mm. Down to 1/16" H2O at what a
furnace blower can pull, while a screened one was in the 1/4"
H2O range (both fairly low flow, 65-75g/sec). I did some calcs
for linear and square-law pressure vs flow projecting the drop
up to more interesting levels. See .gif....
By this projection (not proven, but reasonable-appearing)
a screened 85mm MAF only costs you 15" H2O at 500g/sec
airflow. 4" H2O is 1kPa is 1% at sea level. So if you were
drawing 500g/sec (you aren't, without forced induction) a
big 4% left on the table (call it 20HP if it's all MAF drop and
you're making 500HP). Losing the screen makes it < 3" H2O,
less than a percent, way down on the HP/$ list at that point.
Last edited by jimmyblue; Aug 9, 2007 at 10:20 AM.
no problems with my ASP in south south florida.
if you want other ideas for mods...how bout a ported TB, electric water pump, or get a little crazy with some 1.8 roller rockers
if you want other ideas for mods...how bout a ported TB, electric water pump, or get a little crazy with some 1.8 roller rockers
Get the March fluid damapened pulley from thunder racing. Best pulley for an ls1. I agree with everyone on the maf thing. Pop the screen, if you want more get the ported ends. Spend the money on porting the tb, or elsewhere.
Chris
Chris
