Sometime back I wrote about my air cleaner experience. At the end of
that air cleaner experience I added a 4" air intake pipe from the grill
to the air cleaner intake. I noticed previously that my GMC could go up
a hill near my home at 63 mph with the air cleaner off but only about 60
mph with it on. I hoped the extension would add back this lost power
which was caused by the air cleaner restriction and it almost did. I now
can go up the hill at almost 63 mph with the air cleaner and extender
pipe in place. I then became curious as to why it helped. Was it the
cooler air to the carberator or a ram air effect? I installed a
temperature probe near where the air would normally enter the air
cleaner and another inside the air cleaner on the inlet surface of the
filter. I also installed a water manometer to measure the vacuum on the
upstream side of the air filter on the opposite side of the air cleaner
air intake. With this apparatus in place I did several tests on the hill
both with and without the extender pipe in place. The results were that
air entering the carberator was about 30 deg. F cooler with the
extension in place. During normal cruise at about 65mph it was about 20
deg. F cooler, about 30 deg. around town and over 40 deg at idle periods
(Temperature in engine compartment was over 160 deg. on extended idles
after the engine had been climbing hills). The manometer peaked at 9" of
vac(water inches not mercury inches) on the hill test with the extender
pipe and 10" when the extension pipe was disconnected. The 1" less
vacuum with the extension suggests to me that the ram air effect (
theortically 1.7" at 60 mph) more than compensated for friction loss in
the extension pipe. However 1" isn't much difference so I supect the
main advantage of the extension pipe is the cooler intake air which is
supposed to give 1% more power for every 10 deg. F drop in air temp.
That seems to be about how much it improved performance on my rig. If I
take the air cleaner completely off I still get a fraction of a MPH
better than with the extension pipe in place. This suggests to me that
the unrestricted atmospheric press. to carb. with the air cleaner
removed causes a slightly more beneficial effect than the cooler air at
a vac. when the air cleaner and extension pipe are in place.
During normal cruise the vac. with extension in place is about 1.5 "
whereas with the normal intake it isabout 2.5 ". Again this slight
difference is probably due to the ram air effect but may be
insignificant.
that air cleaner experience I added a 4" air intake pipe from the grill
to the air cleaner intake. I noticed previously that my GMC could go up
a hill near my home at 63 mph with the air cleaner off but only about 60
mph with it on. I hoped the extension would add back this lost power
which was caused by the air cleaner restriction and it almost did. I now
can go up the hill at almost 63 mph with the air cleaner and extender
pipe in place. I then became curious as to why it helped. Was it the
cooler air to the carberator or a ram air effect? I installed a
temperature probe near where the air would normally enter the air
cleaner and another inside the air cleaner on the inlet surface of the
filter. I also installed a water manometer to measure the vacuum on the
upstream side of the air filter on the opposite side of the air cleaner
air intake. With this apparatus in place I did several tests on the hill
both with and without the extender pipe in place. The results were that
air entering the carberator was about 30 deg. F cooler with the
extension in place. During normal cruise at about 65mph it was about 20
deg. F cooler, about 30 deg. around town and over 40 deg at idle periods
(Temperature in engine compartment was over 160 deg. on extended idles
after the engine had been climbing hills). The manometer peaked at 9" of
vac(water inches not mercury inches) on the hill test with the extender
pipe and 10" when the extension pipe was disconnected. The 1" less
vacuum with the extension suggests to me that the ram air effect (
theortically 1.7" at 60 mph) more than compensated for friction loss in
the extension pipe. However 1" isn't much difference so I supect the
main advantage of the extension pipe is the cooler intake air which is
supposed to give 1% more power for every 10 deg. F drop in air temp.
That seems to be about how much it improved performance on my rig. If I
take the air cleaner completely off I still get a fraction of a MPH
better than with the extension pipe in place. This suggests to me that
the unrestricted atmospheric press. to carb. with the air cleaner
removed causes a slightly more beneficial effect than the cooler air at
a vac. when the air cleaner and extension pipe are in place.
During normal cruise the vac. with extension in place is about 1.5 "
whereas with the normal intake it isabout 2.5 ". Again this slight
difference is probably due to the ram air effect but may be
insignificant.
