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Has stiffer springs
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Discussion Starter #1
First up, thanks svede1212 for all his work on this. I pinched some of his ideas.

There are a large number of posts here about intake temperatures, and this is
justified. Holden really screwed this up, both in the quality of the air intake and in
the measurement of the intake temperature.

A big problem which we have in fixing Holden's mistakes is in not knowing
whether the intake temperatures are really as bad as the sensor says they are,
or whether it is a false reading due to the crappy design of the sensor.

The first thing I did was to fix the sensor. Once that is done, it becomes
possible to understand what is really going on in there, and to fix it.

So. First, the sensor.

You can tell just by looking at it that there is a lot of thermal coupling
between the stock sensor and the surrounding plastic and metal. This
introduces thermal inertia and incorrect temperature measurement.

I relocated the sensor into the crown of the Volant CAI's filter:



and used the Omega thermistor. Let's call this the shorty IAT sensor:



No dice. It is very slow to react to changes and I just don't believe what it
is telling me. So I bought another Omega thermistor and built a new sensor.
Let's call this the long tube IAT sensor:



With the long-tube sensor the thermistor is floating right in the center of the Volant filter cone.

The long-tube IAT sensor is much better than the shorty sensor. Much, much
faster to react. Basically the shorty sensor is reading the temperature of
the lump of plastic which it is connected to, rather than the temperature of
the air. So we still have a lot of thermal inertia with the shorty.

The long-tube sensor tells us interesting things. When sitting at the lights
the IAT rises maybe 15F to 30F above ambient. When the car starts moving
again the IAT skyrockets 15-20F within five seconds and then falls away
rapidly (this was not observeable with the shorty sensor). I don't know why this
happens. Perhaps there was a buildup of hot air in the engine bay and
when forward motion commences, that air is shoved into the Volant intake.

But whatever. I now have a sensor which I can actually believe. And it tells
me terrible things. The worst case is when the car is at full temperature and it is
parked for ten minutes and then you drive away. The IAT reached 145F:
70F above ambient. It falls reasonably quickly: down to 100F after a couple
of miles, maybe. But it's still really bad.

Conclusion: yeah, sucking intake air out of the engine bay is hurting a lot.


So having fixed the sensor, the next step is to fix the air intake itself.
 

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Has stiffer springs
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Discussion Starter #2
I cut a 4 inch hole through the fender and through the Volant case:





And blocked off the Volant's engine bay intakes:



(Believe it or not, that white plastic was a "Beware of the dog" sign which I
bought from Home Depot. It's maybe a millimetre thick and does the job
nicely).

The intake air flows around the coolant overflow bottle. There are quite a
few gaps around that bottle and I expect that there isn't much air resistance
happening there. But it is so simple to lower the bottle half an inch (ie:
drill four holes) that I did this just to be sure. You do need to remove the
front bumper to do this.

 

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Has stiffer springs
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4,875 Posts
Discussion Starter #3
Took it for a test drive and I now think that both problems (inaccurate sensor
and high intake temperatures) are sufficiently fixed. But there is still some
room for improvement:

First test:

Get car fully up to temperature, fans running. Park for three minutes
with engine off. Drive away again. The IAT had risen 5F (to 15F above
ambient) and rose another 10F as the car got underway. It fell back to 15F
above ambient within 30 seconds.

So the worst case here was a few seconds at 25F above ambient, which is
heaps better than several minutes at 70F above ambient.

Second test:

Get car fully up to temperature, fans running. Park and leave engine
idling for three minutes, drive away.

It's pretty similar to the first test. 5F IAT rise during idling, another
10F as the car started to move, fell back to normal 10F above ambient within
20 seconds.

Took a couple of pics of the flinkmobile while performing the
does-it-get-hot-during-idling test:





Notes:

- when cutting that 4" hole a lot of steel shavings get tossed out at high
speed. Unless this is the sort of stuff which you like having strewn
through your engine bay, cut the hole from underneath.

- I don't believe I need the long-tube sensor any more. Now that the
temperatures no longer wildly swing around I could put the shorty back in.

- I don't believe there is any point in shielding the intake tube, or in
shielding the air box, or in stressing out about the intake tube
temperature.

At 3000 RPM and full throttle, these cars swallow 150 litres of air per
second. So air transits the filter box and the tube in around a tenth of a
second. There is just no way in which the air will be significantly heated
in such a short time, in such a large tube, which such a small temperature
difference (less than 100F).

- There is a risk with this setup that there might be a low-pressure zone
around the intake. There might be venturi effects from air scooting past
underneath the coolant bottle. Or there might not be - I just don't know.

It would be interesting to put a pressure sensor inside the filter box to
find out whether this is happening. Fabbing up one of svede1212's trashcan
scoops seems like a good idea to me, but I'd like to have a reading of the
pressure in there first to find out if there is a problem and whether the
scoop fixed it.

- If I had my time again, I wouldn't relocate the IAT sensor.

The middle of the intake tube (near the MAF) is a good place for it: the
air velocity will be higher there than in the filter cone.

So I think the best sensor would be to place an Omega thermistor in the
center of the intake tube, away from the walls. Hang it in the middle of
the airflow, like those sensors in the MAF.

Holden could have done this quite easily if thay had cared.
 

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Registered
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Nice job. I like what you've done.


In my personal opinion, the only true solution to this 'problem' is to put the IAT sensor directly behind the TB - ala FAST relocations by drilling the EGR port on the FAST intakes. What better place to take the air temp going into the engine than the air temp in the engine?

Aside from that, I agree that having the sensor in the intake tube is probably good enough... relatively high velocity, good turbulence, etc. However, there is the closed TB decel situation to look at. In my data logging, I have noticed that the IAT's will rise as much as 10*F depending on how long the decel period is. This results in whacky IAT's and resulting fueling for a few minutes - right, minutes - until the temperature stabilizes again.
 

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CAUTION!!!!
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9,883 Posts
very interesting. I am planning on re-locating my IAT sensor with my K&N and I was debating on if I should do it at the end of the filter or by the neck. With what you're saying about getting the IAT where there is more air flow, I guess I should put mine at the neck.
 

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Has stiffer springs
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4,875 Posts
Discussion Starter #7
Thanks guys.

It would be pretty simple to get a little bit of ram effect down there with some 4"
pipe and some form of scoop. If that bottle wasn't there.

Does anyone know what that overflow bottle actually does? Is it just to stop nasty chemicals
from dropping on the road, or does it try to act as a reservior? And what would happen if it joined
the ever-growing pile of OE parts in the back shed? ;) And why is it so damn big??

I do want to get a pressure sensor into that box to find out what's going on. The
car already appears to have one - the dashhawk talks about "Barom kPa" (the car's
a mobile weather station, afaict). Does anyone know where that pressure sensor
is postioned, what it is, etc?
 

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Has stiffer springs
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4,875 Posts
Discussion Starter #8
I have noticed that the IAT's will rise as much as 10*F depending on how long the decel period is. This results in whacky IAT's and resulting fueling for a few minutes - right, minutes - until the temperature stabilizes again.
Interesting, I haven't noticed (or looked for) that.

Which measurements are you looking at here to see the whacky fuelling? STFT's?
 

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1LE
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13,384 Posts
FWIW I've been doing some testing and insulating/shielding does help a great deal with heat soak.

Before insulating the stock airbox I would get a 10~15* temp rise at a light in hot weather, after a few lights the IAT's would be 145~150*. After insulating, driving the same lights only raise IAT's 18~20* instead of 50~55*. Cool down while cruising use to take quite a while, now I cool down rather quickly.
I took a infrared temp gage and checked the airbox temp after a test loop. The side of the airbox next to the exhaust was 155*:eek: even though the IAT's were a high 120*. After insulating the same test loop the airbox was ambient +2*:D and the IAT's were 97*. All this on a 92* day.
Just a thought.
 

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1LE
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On a recent 4 hour trip, I pulled over and checked the temps, it was in the mid 80's that day:


The Predator tune has the fans on earlier, keeping the engine running around 200*:


Hood scoop plug mod does blow cool air onto the intake tube:


Insulation keeps intake and MAF cooler:


This is all done with the stock airbox and IAT, I just got my Volant which should isolate the MAF from the radiator heat better and easier to insulate/shield.
Work in progress....
:wall:
 

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Interesting, I haven't noticed (or looked for) that.

Which measurements are you looking at here to see the whacky fuelling? STFT's?
Yup, I'm watching STFT's and IAT temperature.
 

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Registered
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Nice write up. You are also correct in that your original sensor placement was not in the main air stream. It is better to place it a few inches in front of the filter cone in the tube. Then insulate the tube and the box, if you have a box, and carefully wrap enough material around the sensor to prevent heat soak from the radiator. Wrap the tube completely back to the TB.

I use a tube type with a hole in the wheel housing like you, put without the box. Instead, the filter is attached to the tube after it passes through the wheel housing in the cool outside air above the street and out of the engine compartment. In addition, the left fog lamp was removed which allows cold air to stream over the filter when the car is moving. A chrome mess was placed over the fog lamp opening and siliconed in to prevent debris from entering the airway and to improve the appearance.

You may want to try an expensive Australian mod I viewed here on the net, where the air flowed through the front above the radiator similar to the air lid on a Vette or Trans Am. On our cars of course, this mod requires a low profile racing-type radiator to provide clearance for the intake. The radiator supposedly costs about $700 USD, plus the cost of the intake. Yikes!!

Also, you can tweak around somemore after making the mods I suggested above, but you are at the point of diminishing returns. In otherwords, hours worth of work and trial and err, might yield only one addition HP. This is a good as it gets with our cars, so your time in the quest for more power would be better utilized elsewhere.
 

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2004 GTO Owner
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I did something similar. I have a CAI. I cut the whole bottom of it out and a corresponding cut on the car body. It comes with insulation inside so I bought more insulation and attached it on the outside too. Next, I managed to Locate the MAF inside the CAI away from the engine compartment and put the IAT in the plastic neck between the filter and the MAF. Lastly, I added insulation on all the intake tubing leading to the CAI. I thin it works very nicely. I am still messing with it to see if anything can be sealed off to improve. it. I am usually within 10 degrees ambient but climb about 15 - 20 degrees while sitting at lights.
 

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Pandas eat Bamboo!
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Which of the other choices of sensors do you suggest, the 3000 ohm is back ordered 3 weeks, any suggestions? Thanks,

Scott
 

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Gearhead Daddy
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Nice work and great writeup and effort.
 

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Growing up is an option
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Which of the other choices of sensors do you suggest, the 3000 ohm is back ordered 3 weeks, any suggestions? Thanks,

Scott
the only choices that i've found are the Vector kit at ~$100 or the Omega at $15. this is a great writeup in that for ONCE somebody actually measured what's going on and didn't rely on SOTP, dynos and whoosing sounds. nice work.
 

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*will work for mod $*
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Nice write up! I have a k&n for now so I won't be able to do much insulating but does anyone know where I could find some of that insulation material as used above in 87lc2's post?
 

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Beer Geek
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Onew other really cheap thing you can do on highway trips:

When you stop for gas, open the hood. Pump your gas. Check the oil. Close the hood. Drive away. "lower" IAT for when you hit the freeway on ramp. My Interceptor data is in my other pants.
 

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1LE
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