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Premium Member
1,612 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

908 Posts
Well done. Two points come to mind...
1. Have you considered a metal shroud over the catalytic converter to increase the heated air intake?
2. Having glued the temperature adjustment why did you calibrated it at 65 degrees. Is this the ideal temperatre, or would a warmer temp work better?

Premium Member
1,612 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
2001 5S "Turbo"
12,336 Posts

Idle = 20-21 in. vac. (sea level)
WOT= 0 in. vac.

Premium Member
1,612 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
1,612 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
4,838 Posts
joecvt said:

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

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.


Thanks for your trouble in posting your mod. :)

Two points come to mind in my similar experience with these hot air mods.

1) 110F seems to be the peak for widening the lean burn window.

2) You will need some type of shroud on the CAT to approach achieving the optimal IAT in cold temps.

My version is now in final testing using a converted 86 F150's exhaust manifolds preheat sheet metal. In 40F temps I can achieve a +45F increase in IAT, but it also takes almost 8 miles warm-up distance.

HTH! :)

908 Posts
What did you insulated it with? Whats underneath the duct tape?
Love what your doing, but I worry a little about spilled oil and fire.
Have you considered aircraft scat tubing? It has a smoother bore (easier breathing) and is fire proof. Not insulated though.

Premium Member
1,612 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
4,838 Posts
I use the IAT (intake Air Temperature) sensor read via a scan tool. There are too many other variables in using an add on sensor that would make comparing data here impossible. Its not so much an issue with accuracy but transportability for comparison via this group.

My commute starts with the driveway run, then 1 mile in the neighborhood @20 MPH, 2 more miles on a county road @35 MPH, then the state highway at 45-50 MPH.

Calculating the intake air volume flow is simple:

Engine displacement - 995 cc

1 intake stroke (995cc/3=331.67cc) every 2 revolutions
(one complete cycle of a 4 stroke engine)

RPM/2*(332+-)=166000cc/[email protected]

Since air flow is typically measured in cu/ft per min (USA) converting =

58.6 cu/ft / min @ 1000 RPM

This does not reflect the mass of air nor standardize the volume based on temperature and pressure.

Typically we cruise somewhere closer to 2000 RPM so cfm should be doubled as an "average".

To get a reasonable accurate calculation of the mass of air that would reflect on the amount of heat required to increase its temperature gets very complicated. But we now have a ballpark "idea" of the flow volume. And such a value wouldn't mean much since the amount of heat available at the CAT is even a more complex and variable value to try and pin down.

Its been reliably established by the hyper milers in here that higher IAT's are what opens the lean burn window wider. I can't accurately independently confirm the claim because of too many hills requiring me to frequently drop out of lean burn. But in my modest experience 110F IAT seems to be the peak. 60-70F is better than 15F ambient and you will see an improvement, but your crippling your system if you shoot too low. I've seen my IAT approach 120F without any detrimental effect. And I suspect that Insighter's in the desert SW typically see 120F IAT's in summer too.

Worried about "baking" the engine too much? Coolant temp is regulated to be 180F min and you'll definitely see an MPG improvement with the 6x17" cardboard trick that typically increases ECT (Engine Coolant Temperature) in cool temps to 200F (Fans auto on @205F). Look at your add on sensor after a hot soak, typically 10 min after engine off on a summer day. You'll likely see 150+F temps.

The engine parts can take the heat!

The possible consequence of this mod is increased emissions (NOX) due to increased combustion temps. It's the EGR valve's job is to limit peak combustion chamber temps and it's ability to effect it is much greater than increasing IAT. So our "mod" likely has no effect on NOX.

HTH! :)

and please keep the group updated as your experiment progresses! :)

Hi Insightful Trekker:

___Hopefully you have seen me post on this in the past … Have you considered also installing a fuel filter heater similar to some VW TDI’s and Big-rig’s? I would like you to be the guinea pig so the rest of us can follow with your excellent adaptations ;)

___If coolant temps, AIT’s, and Fuel intake temps can be controlled to those experienced in 80 - 90 degree + temps, you only have the losses due to colder temperatures from friction (tires and wheel bearings come to mind).

___Good Luck

___Wayne R. Gerdes
___Hunt Club Farms Landscaping Ltd.
___[email:27ezfoud][email protected][/email:27ezfoud]


Premium Member
4,838 Posts
xcel said:
Hi Insightful Trekker:

I would like you to be the guinea pig so the rest of us can follow with your excellent adaptations ;)
ME? A guinea pig! NO way! I even delayed my Insight purchase for a couple of years to avoid the possibility! (Seriously! in a light hearted way <g>)

Bought a 2000 Civic HX instead. But being an Insight owner I guess I'm still one of the "herd". Just didn't want the risk of being a leader of the pack! ($)

And more seriously,

The technical challenges, consequences and costs are not justified in my climate. Heating diesel, a heavier hydrocarbon (lower flash point) mix is one thing. Heck, the summer stuff will gel on you down around 0F without an additive. It practically begs to be warmed! Stepping up to gasoline is something very different with potentially dangerous consequences. Flash, crash and burn comes to mind. One technical complexity will be to insure that this heated gasoline does not reach its boiling point else fuel vapor instead of liquid fuel will be injected and a lean misfire will occur. This vapor point is finicky enough that fuel is typically blended differently according to season (not simply for emissions). So I foresee all kinds of technical difficulties with little benefit.

I am thinking that the Prius thermo bottle would be a good mod. Got an idea of cost? How to limit thermo siphoning / circulation?

And a hyper miler gauge package is in the works. May be next Christmas before its fully complete. I'm gonna do the S2000 steering wheel thing first!

1) Adjustable auto radiator fan temp.
(the thermostat isn't fully open till 210F)
(fans are set for 205F. Seems we have some)
(room for increasing ECT and maybe MPG?)
2) Digital ECT Gauge
3) Digital IAT Gauge
4) Digital IMA Temp Gauge
5) Manual override for IMA fan control.
(you may wanna warm'em or chill 'em)

I think the ultimate temp control mod would be that of an adjustable radiator block. It's been discussed in here before, some older models came factory with an adjustable louvered grille. The card board trick works well, but for those that need AC more frequently its too much bother. And its not partiularly good for those of us that intermittently use ours for defogging. In Winter I can't imagine it being a "problem", but late Spring and early Fall is when I "worry" about the increased AC load. Read: wear. And the higher head pressures caused by the radiator block in mild temps are slightly counter productive for MPG.

Still looking for that perfect "something" that will do the job.

Keep an eye on my webpage. :)

Premium Member
4,838 Posts
b1shmu63 said:
Nice web site info. Thanks! Looks like a perfect house roof for solar. :)
Seen the other side have you?

Oriented correctly for the sun with an integrated sunroom (20'x25' glass area). Mainly for "passive" light. I'm just in too cloudy an area for real solar heat.

You can fine me on the terraserver website it you know where to look! <VBG>

John K. Bullock
aka. Insightful Trekker
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