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'07 OB, '92 Miata, '91 Dakota 3.9
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Discussion Starter · #1 ·
Installation and temperature recording of a Hybrid Intake

For the Hybrid Intake build on a 2G Subaru Legacy Outback EJ22/EJ25, Impreza EJ22/EJ25, 1G Forester EJ22/EJ25, you'll need an intake for a natural aspirated 1999-2004 3G Legacy or Impreza. These are usually around the $40 mark on eBay. Most name-brand intakes run around $100+ and will accomplish the same goal; get air into the intake faster than OEM.

The picture shows plumbing heat wrap and aluminum heat tape. Unlike DEI's gold heat tape, this heat tape is 1/5 the cost. Essentially, it all does the same thing; reflects heat away from whatever it is adhered to. The plumbing heat wrap was not used as the outside temperature did not warrant it being put into effect.

The test that is being demonstrated to give an idea about the varying temperatures we will see based upon OEM and aftermarket intake will be as follows:

First, the temperature of each intake will be taken with engine off, at Normal Operating Temperature (NOT) while idling, and after 5 minutes of NOT at 2,000 +-100 RPM. Temperatures using Meat Thermometer were recorded with hood closed. Temperatures using Infrared Thermometer were taken after opening hood.

The blue masking tape is to ensure that the intake's reflective surface will not skew the results of the Infrared Thermometer. The Meat Thermometer's probe was put inside the intakes near the middle to get an average result of beginning temperature air from the air filter and end temperature air at the throttle body.
The Meat Thermometer could not read below 32*F. The Infrared Thermometer was +5*F.

Ambient temperature at time of OEM intake: 30*F.
Ambient temperature at time of aftermarket intake: 34*F

Temperature's using the Infrared Thermometer (IT) were gathered in three spots: Filter Box (1), Middle of Intake (2), at Throttle Body/Silicone Coupler (3).
Temperature using the Meat Thermometer (MT) were gather in the middle of the intake (2).

The engine was allowed to cool fully between tests.

OEM Intake OEM Intake Results IT Cold Engine
1: 20.2*F
2: 18.7*F
3: 15.8*F
Average: 18.2*F

OEM Intake Results MT Cold Engine
2: N/A

OEM Intake Results IT Normal Operating Temperature (NOT) Engine Idle
1: 69.6*F
2: 70.2*F
3: 69.7*F
Average: 69.8*F

OEM Intake Results MT NOT Engine
2: 50.0*F

OEM Intake Results IT NOT After 5 minutes at 2,000 (+- 100) RPM
1: 97.6*F
2: 94.9*F
3: 93.8*F
Average: 95.4*F

OEM Intake Results MT NOT After 5 minutes at 2,000 (+- 100) RPM
2: 72.0*F

Aluminum Intake without Heat Wrap Aluminum Intake Results IT Cold Engine
1: 40.3*F
2: 37.7*F
3: 40.3*F
Average: 39.4*F (Increase of 21.2*F)

Aluminum Intake Results MT Cold Engine
2: N/A

Aluminum Intake Results IT NOT Engine Idle
1: N/A
2: N/A
3: N/A
Average: N/A
(Results will be obtained soon enough)

Aluminum Intake Results MT NOT Engine Idle
2: 55.0*F

Aluminum Intake Results IT NOT After 5 minutes at 2,000 (+-100) RPM
1: 71.4*F
2: 68.9*F
3: 78.3*F
Average: 72.9*F

Aluminum Intake Results MT NOT After 5 minutes at 2,000 (+- 100) RPM
2: 65.0*F

The results are honestly surprising. Not only does the aluminum intake remain colder overall, but by an astounding amount. Rubber apparently heat soaks much more quickly, and by a large variation. If you want to retain your fuel mileage; use the OEM intake design; the hotter the air, the better the mileage. If you want to get slightly more power (~2HP) utilize a hybrid intake design; cold air is more dense thus the engine needs more fuel.

To properly fit this intake in place of the OEM rubber intake, part of it needed to be trimmed to fit. Depending on the 45* silicone coupler, you may or may not need to trim more. I allowed myself some wiggle room while making the cuts with an angle grinder with a cutting wheel attached. Certainly makes quick work of aluminum.

The picture shown is the longest distance ("top") of the intake's curve. Add approximately 1/8" to measurement for how much material the cutting disc removes.

The picture shown is the shortest distance ("bottom") of the intake's curve. Add approximately 1/8" to measurement to adjust for amount of material the cutting disc removes.

Remove the bottom vacuum hose port on the intake.

The material which is removed is closest to the filter box, NOT closest to the throttle body.

With the intake installed loosely, it is a large change in the amount of room that is under hood.

The OEM vacuum hoses are approximately 1/2" while the intake's vacuum ports are 3/8". Unfortunately, it's rather difficult at this moment to find 1/2" to 3/8" vacuum hose adapters to properly route the vacuum hoses. For the time being a 1/4" ID hose will be put inside the OEM vacuum hoses, tee'd together, and then stretched to fit over the vacuum hose port on the intake. The picture below of the "finished" product shows a 3/8" ID fuel vapor hose stuffed into the vacuum hose leading to the OEM PCV vacuum hose. Certainly not a professional way to do it, but 34*F makes for some cold work. (Excuses excuses.)

The finished product.

Tools used: Flathead screwdriver
Philips screwdriver
Angle grinder with cutting wheel (or hack saw)
Socket wrench
10MM socket (removal of OEM torque box support)
12MM socket (removal of OEM torque box support)
File/Deburring tool
Brake Clean
Lint Free rag
Silicone Spray
3x90MM worm screw clamps
1x83MM worm screw clamps
Subaru Forester/Impreza/Legacy Intake (Link in Imgur Album)
2.75" to 3.0" 45* silicone coupler (Link in Imgur Album)
3" straight silicone coupler (Link in Imgur Album)
2x Foam Insulation Tape for water pipes (Link in Imgur Album)
1x Aluminum Heat Tape for duct work (Link in Imgur Album)
3' 1/4" ID vacuum hose
1x 1/4" vacuum tee 6"
3/8" ID fuel vapor hose (substitute 6" 1/4" ID vacuum hose)
2x 1" worm screw clamps

Installing any intake is normally simple. This one is only slightly more complex in that you must trim to fit the intake that is going on your EJ22. Remove your old intake by loosening the throttle body worm screw clamp and the air filter housing worm screw clamp. Remove the three vacuum hoses from the 'torque box.'

Remove the bolt on the upper portion of the torque box support (10MM), then remove the intake and torque box assembly. Remove the lower bolt (12MM) for the torque box support. Spray silicone onto the throttle body side of the intake and install the 45* silicone elbow. Adjust as necessary to accurately find where to mark on the airbox side of the intake where you must cut. MEASURE TWICE CUT ONCE. It is far better to make multiple trips cutting than to cut once and remove too much material. After test fitting, make sure you thoroughly clean the intake and silicone couplers of aluminum debris using brake clean and a lint free towel. Install intake and vacuum hoses.


Installing this intake onto the car obviously does nothing for power. Let me make that absolutely clear. Putting an intake on any N/A car, without heavy supporting modifications to intake manifold, heads, headers, and exhaust, will most likely net you 2 HP, certainly nothing to be happy about. However, if your plan is to add a header, exhaust, and supporting modifications, this is a nice modification to do that costs around $50 for intake and couplers and will help in the long run.

The purpose of this installation was to find out the difference between temperatures of an OEM intake, aftermarket intake, and an aftermarket wrapped intake (again, the ambient temperature is too cold out right now to gain any knowledge from wrapping the aluminum intake itself, but it will be done in warmer weather and this post will be edited to reflect the new data).

There are four types of intakes available on the market today; OEM, Short Ram Intake with open filter, Cold Air Intake with open filter, and Hybrid Intake (utilizing stock air box). The hybrid intake bridges the gap between an open element filter (which draws in more under hood temperatures if not properly sealed from them) and the OEM intake (which is smaller in volume, has sharp bends, and 'tumbles' the air within). Wrapping a hybrid intake, I will assume given the data, will be the best outcome of all the intakes; negating any increase in air temperature from under hood by reflecting the heat away and insulating the pipe itself from the already cold air coming in from the OEM air box, and holding a smooth interior surface for air to flow.

What we can extrapolate from the data provided is that the OEM Subaru intake hose holds onto the heat from the engine rather than shedding it off (heat soak). Although the idle temperature is 5*F hotter with the hybrid (55*F compared to 50*F at idle), it does not increase in temperature nearly as much as the OEM intake does (65*F hybrid compared to 72*F OEM), nor does the outside pipe temperature become as hot (average 72.9*F Hybrid vs 95.4*F OEM).


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