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Hi,
At the drags Sunday, some of you noticed that I had a heat shield on top of
the radiator core to attempt to keep heated air out of the intake ducts. Last
evening I did some temp tests with an accurate, digital, multi-channel temp
gauge to see what was really going on with the intake air temps and to see if
the shield helped.

I found out some interesting stuff. First the heat shield doesn't help at
all. Second the air intake system is bad for keeping the intake air cool. I
measured ambient air temp, the temp about 2" inside the front of the air
duct, and also in the air box on top of the air cleaner element. The temp
sensors were all in free air, not touching anything. I had the air intake
louvers open (louver motor power plug disconnected) for the test. At speeds
above 20 mph the air temp at the inlet was 2 degrees F warmer than ambient
both with and without the heat shield. The air picked up another 8 to 10
degrees between the inlet and the air box. With the louvers operating
normally (louver motor power plug connected) add 10 degrees to each reading.
I tested at speeds between 20 and 65 mph with results within a degree or 2
regardless of speed. Below 20 the air inlet temp gets progressively hotter so
that idling for 5 minutes will have both the inlet air temp and the air box
temp at 130 degrees F. From a 5 minute idle, a fast acceleration to 100 mph
(lots of air going in) only lowered the air box temps down to about 118 F and
after continuing at 70 - 80 for about a mile brought it down to 105 F. The
hot air heat soaking the air box at idle is coming from the hot radiator.
After running with the air temps stable, and stopping to idle, I could see
the air inlet temp rise within a minute or so to 130 with the air box temp
lagging. Another 2 or 3 minutes had the air box temp equal to the inlet temp.
Start driving at 35 mph or so and the air inlet temp drops soon, but the air
box temp remains high for several minutes.

The ambient temp was between 77 and 75 after sunset so no influence of sun
hitting the hood or in shade.

Insulated air duct tubes like GTS have would probably help some at speed, but
the rapid heat soaking at idle comes from the air intake being in close
proximity to the radiator.

Just thought I'd throw this out to y'all to confirm once again that these
cars weren't made for hot climates, and if you have intake louvers, keep them
locked open in the summer.

Louie Ott
'90GT

Hi Louie,

I was hopeful that your shield would work :-( . I know my car gets
way too hot under the hood, can't even touch the strut bar after a
run on a hot day. I always figured it was my black hood contributing
to the heat, but after your results maybe not. Given that your car
is white it would be less affected by the sun. Maybe if you check
the temps on a black (or darker color) they will be even hotter?


I suppose the only way to get around it is to construct those ducts
in
the hood ( or the Devek route--cowl induction ).

Anyway, thanks for the info and keep up the good work.


Later,
Tom

P.S. Pats pics are up on the web site, check them out.

In the bracket drags section.

Hey Louie,

Thanks much for the info. I guess this raises the simple question of why
not use the cowl induction method? It would seem machining some tall shims
on the rear mounts of the hood and modifying the air box cover is all that
it would take. I don't think having an expanding hood seam would be too
unsightly on the 928.

If this isn't a direction you'd be interested in pursuing, let me know and
when I get my shark back together I'll go for it. It definitely poses an
interesting question.


-Adam



----------

From: LouisOtt@...
To: PacNW928@...
Subject: [PacNW928] Heat shield
Date: Tuesday, June 27, 2000 9:21 AM

Hi,
At the drags Sunday, some of you noticed that I had a heat shield on top

of

the radiator core to attempt to keep heated air out of the intake ducts.

Last

evening I did some temp tests with an accurate, digital, multi-channel

temp

gauge to see what was really going on with the intake air temps and to

see if

the shield helped.

I found out some interesting stuff. First the heat shield doesn't help at

all. Second the air intake system is bad for keeping the intake air cool.

I

measured ambient air temp, the temp about 2" inside the front of the air
duct, and also in the air box on top of the air cleaner element. The temp

sensors were all in free air, not touching anything. I had the air intake

louvers open (louver motor power plug disconnected) for the test. At

speeds

above 20 mph the air temp at the inlet was 2 degrees F warmer than

ambient

both with and without the heat shield. The air picked up another 8 to 10
degrees between the inlet and the air box. With the louvers operating
normally (louver motor power plug connected) add 10 degrees to each

reading.

I tested at speeds between 20 and 65 mph with results within a degree or

2

regardless of speed. Below 20 the air inlet temp gets progressively

hotter so

that idling for 5 minutes will have both the inlet air temp and the air

box

temp at 130 degrees F. From a 5 minute idle, a fast acceleration to 100

mph

(lots of air going in) only lowered the air box temps down to about 118 F

and

after continuing at 70 - 80 for about a mile brought it down to 105 F.

The

hot air heat soaking the air box at idle is coming from the hot radiator.

After running with the air temps stable, and stopping to idle, I could

see

the air inlet temp rise within a minute or so to 130 with the air box

temp

lagging. Another 2 or 3 minutes had the air box temp equal to the inlet

temp.

Start driving at 35 mph or so and the air inlet temp drops soon, but the

air

box temp remains high for several minutes.

The ambient temp was between 77 and 75 after sunset so no influence of

sun

hitting the hood or in shade.

Insulated air duct tubes like GTS have would probably help some at speed,

but

the rapid heat soaking at idle comes from the air intake being in close
proximity to the radiator.

Just thought I'd throw this out to y'all to confirm once again that these

cars weren't made for hot climates, and if you have intake louvers, keep

them

locked open in the summer.

Louie Ott
'90GT



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In a message dated 6/27/00 1:10:37 PM Pacific Daylight Time,
midlman@... writes:

I was hopeful that your shield would work :-( . I know my car gets
way too hot under the hood, can't even touch the strut bar after a
run on a hot day. I always figured it was my black hood contributing
to the heat, but after your results maybe not. Given that your car
is white it would be less affected by the sun. Maybe if you check
the temps on a black (or darker color) they will be even hotter?


I suppose the only way to get around it is to construct those ducts
in
the hood ( or the Devek route--cowl induction ).

Anyway, thanks for the info and keep up the good work.

Hi Tom,
I bet a black car would be even worse. That's why I did the test after
sundown so the sun wouldn't be a factor.

Get out the sawzall and whack out a big hole in the back of the hood for a
scoop.

Louie

In a message dated 6/27/00 5:16:18 PM Pacific Daylight Time,
adamb777@... writes:

Thanks much for the info. I guess this raises the simple question of why
not use the cowl induction method? It would seem machining some tall shims
on the rear mounts of the hood and modifying the air box cover is all that
it would take. I don't think having an expanding hood seam would be too
unsightly on the 928.

If this isn't a direction you'd be interested in pursuing, let me know and
when I get my shark back together I'll go for it. It definitely poses an
interesting question.

Hi Adam,
I'm still pondering what to do. What you suggest would work. Also a couple of
flush NACA ducts at the rear of the hood on each side of the air box would
work and not change the appearance much. I hate to cut anything though. I
better get an old "test" hood from somewhere. Anyone make a fiberglass
replacement?
Louie

Louie wrote:

Hi Adam,
I'm still pondering what to do. What you suggest would work. Also a

couple of

flush NACA ducts at the rear of the hood on each side of the air box

would

work and not change the appearance much.

I'm wondering about the pressure dynamics of a rear hood inlet. It's my
understanding that a cowl induction hood gets air from the high pressure
front that forms at the windshield. Propping the back of the hood like I'm
proposing raises some questions (that I'm sure would require testing):

1) How high would the rear of the hood have to be propped. A cowl
induction scoop raises about two inches off the hood, is this enough to get
out of the boundary layer?

2) Would propping the rear of the hood have any affect on ground adhesion?
It's seems that it would release a lot of under hood pressure (if there is
any), as well as increase the face area of the hood into the oncoming air.
This would seem to be beneficial.

3) Would NACA ducts mounted at the rear be efficient? It seems that they
would be almost horizontal at that point. I always kind of pictured the
ducts to rely on the ram effect of incoming air.

I hate to cut anything though. I
better get an old "test" hood from somewhere. Anyone make a fiberglass
replacement?

I don't know of any 'glass hoods, but I think I may have a line on a
slightly crunched GT hood. It's Barney Purple, ( Hi Bobby! :0 ) but might
be a nice fashion statement for the Great White Hope (your GT).

-Adam "Does head and shoulders work on aluminum shavings?" Birnbaum

Louie

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