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Premium Member
1,631 Posts
Discussion Starter · #1 · (Edited)
Hello all,

This modification takes outside air from the front of the car (sort of a RAM
AIR intake) when the temperature is above 65F. When temps are below
60F (approx) the air is taken from the catalytic converter. When the
temp is in between there is a mixture of air. Some of the parts I needed
came from a 1984 Honda CRX...I still had the air cleaner assembly and
some vacuum hoses. Here is what the air cleaner assembly looks like from the 1984 Honda CRX:

Honda Automotive Parts

The parts that I used are:
1. Cut off portion of the air cleaner assembly itself
2. Air intake sensor - number 16 in the link above.
3. Vacuum check valve - purchased at Autozone (need 2 "T" as well)
4. Vacuum tubing - already had from the CRX
5. 3" to 2" PVC adapter - from Home Depot
6. 2" 90 degree elbow - from Home Depot
7. 2" extension with one side female threaded - from Home Depot
8. 1.5" Preheater hose - from JC Whitney online
9. 2" Preheater hose - from JC Whitney online
10. 2" 90 degree rubber elbow with clamp - from Home Depot

Take the 3" to 2" adapter and the inserted elbow and place it in the oven
until both are plyable. Quickly, take it out and using hand protection push
down on the end of the 3" opening to elongate it as well as the portion
were the two pieces meet. When done the 3" opening should be 1.5" x
5" (Approx - It will take a couple of heatings).

Take the air cleaner assembly and cut the air intake portion off where
it meets the circular part of the air cleaner. This portion has the vacuum
valve (missing in the link but it operates the gate.) Take the rubber
elbow and cut it to fit and glue it onto the wide side of the air intake.
The other end of the elbow will be put directly into the air cleaner on
the Insight. I did not take pictures during assembly but the air intake
with the gate will be mounted up-side-down and should look like this.

Remove the four bolts that hold the air cleaner plastic and lift the bottom
enough to route the 1.5" hose from the front to the rear by the catalytic
converter. It should look like this.

I put wrap insullation on mine and covered with duct tape. You can not
cover the whole hose with insulation until you know the final shaping.

Take the plastic cover out above the radiator on the left hand side. (I cut
a hole in mine where the molded PVC will go through). Put the PVC in
the hole with the elbow facing towards the air cleaner. Put the threaded
adapter on and the 2" preheater hose and connect the other end to the
air intake. The opening should look like this. and the back end side
should look like this. This is what it looks like from the top.

Take the air intake sensor and cut the glue holding the adjustment screw
in place. You want to modify it by turning the screw so the metal opens
up at about 77F (you can use the freezer for this) then glue the screw in
place again. Take the vacuum line that comes up from the intake
manifold and "T" it over to the air intake. Along the way you will need
to put a vacuum check valve in to keep the gate constant during vacuum

Drill two holes into the bottom plastic (towards the front) to accept the
sensor. The sensor must be placed inside the air cleaner because it
creates a small vacuum leak so it must have filtered air.

Connect another "T" from the check valve and put one hose on the gate
motor (really vacuum controlled gate) and the other one on the sensor.

Finally you are done. There was one day when it was 55F degrees and
the gate shut off the cold air intake and by the time I drove into work
it switched over to the RAM air intake. I put a remote thermometer in
the air cleaner to monitor the air temp but I have to wait until winter
again. I also put a screen in the RAM air intake portion just to stop
some bugs and leaves in the fall from entering the hose.

JoeCVT - Just your average CVT owner

Premium Member
1,631 Posts
Discussion Starter · #4 ·
The air temp sensor is a bi-metal piece that bends with a change in
temperature bleeding vacuum or closing shut. There is a time when
the valve is partially open so there is about a ten degree range in the
setup. I know that at 55F it is closed allowing heated air to enter. The
OEM setup of this valve closes at 100F...I thought that it was too long
to wait so I wanted to get it down to about 60F - 70F ...Did you ever
notice that in the spring as the days get warmer all of a sudden your
car gets better mileage?...I'm talking any car, not just the Insight.
I would guess that charted out, there is a point where the gas mileage
increases the most. From driving different cars, it seems like the change
is somewhere between 60F - 70F so that is why I choose that setting.
Just to remind you that this is only a guess from my driving experience.

I did notice the heat shroud on other setups...I left the hose flexible so
that I could hook one up later if I found something that would fit. That
may be a modification later on but thanks for mentioning it.


Premium Member
1,631 Posts
Discussion Starter · #7 ·
Here is a portion of my original description of the warm air intake:

"Take the vacuum line that comes up from the intake manifold and "T"
it over to the air intake. Along the way you will need to put a vacuum
check valve in to keep the gate constant during vacuum changes. "

The vacuum check valve will only allow vacuum to go in one direction.
Putting the check valve before the vacuum air sensor and the vacuum
motor operating the gate will keep vacuum in the line until the bleed
valve opens on the air temp sensor. This part of the setup is really the
same design from the 1984 CRX (as well as many other cars).


Premium Member
1,631 Posts
Discussion Starter · #8 ·
An update to the automatic warm air intake. In the last two months it
has been pretty cold in New Hampshire (the lowest temp so far is 16F)
and I have a Radio Shack remote temp sensor in the air cleaner to check
the temps inside. On the highway I'm able to get to 70F still but I noticed
on back roads the temp only goes up to 60F-63F. My guess is that the
throttle is opening a smaller amount on the back roads resulting in not
much warm air flow through the heated pipe causing the pipe to cool off
more than the highway speeds. So I took it all apart and insulated the
piping more and routed the pipe a different way. I also took off the heat
shield and made a hole and screwed in an opening for the warm air pipe.
This should be a better setup than my last attempt but time will tell. The
average mileage has gone down from 62-64 to 58-59 ...Still not to bad.
Here are some pics of the new setup.
From the vacuum valve to the battery and behind the engine.
From behind the engine to the cat.
A closeup of the connection to the cat.

JoeCVT - Just your average CVT owner

Premium Member
1,631 Posts
Discussion Starter · #11 ·
I used Pipe Wrap Insulation Tape Self-Adhesive 1/8" thick Foil and Foam
from Frost King purchased at Home Depot. The Preheater hose is made
from metal but it looks like there is some clear plastic around it. It is
designed for the exhaust so it can handle the heat. I did leave about 6
inches exposed from the insulation and duct tape because of the high
heat area. The reason why I used duct tape on the outside is even
though the insulation tape has adhesive, it would unwind around the hose,
and around the curves there would be some air gaps. Plus the tape made
it alot stronger as well. The six inches exposed also helps for flexability
for engine vibration. The picture of behind the engine to the cat shows
the exhaust tubing and the oil fill but they are really pretty far apart
because the tubing is really gowing downward and away from the oil fill.
The picture does not show the depth correctly although I could see your
concern of oil spill. I took another picture from a different angle to show
how close (or far) it really is. From this angle you can barely see the hose.

Insightful Trekker,
I could bump the temp sensor up a little more but in the summer time
I want the cool air to come in as well. I'm actually using the heat shield
as the shroud that you mentioned. I took off the shield, cut a 1.5 inch hole,
screwed in a pipe inlet so now the air going into the tubing must pass in
between the cat and heat shield. How do you measure your temps? My
method may not be as accurate as yours if you are scanning the air intake
temp sensor. Are you driving on the highway or back roads for those 8
miles?...The reason why I'm asking is because I'm curious how much air
passes through the throttle opening during warm-up.

Thanks for your comments,

JoeCVT - Just your average CVT owner

Premium Member
1,631 Posts
Discussion Starter · #22 ·
An update to the automatic warm air intake mod:

I moved some parts around so they are much different compared to the original posting at the beginning of this thread.

I took more pictures and replaced them using the same name so older links will still work but will contain the newest pics.

To make it easy for viewing, here are just the pics of the update.

The tube that goes from the cat to the air mixer is now all one piece that goes under the battery. It is wrapped with tons of duct tape for stength and some insulating value. After the initial duct tape wrapping of several layers, there are two layers of insulation tape (R2 value for each layer), then another wrapping of duct tape as a final layer. So I know that it is at least R5 value or more with all of the wrappings.

I was able to shorten the length of the insulated tube by repositioning the angle of the warm air inlet 180 degress from the stock part so now the inlet faces the rear of the car.

Also, the metal air mixer is double layered insulated as well.

We will see how next winter goes :smile:

JoeCVT = Just your average CVT owner
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