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Thread: 818S Intercooler Plenum

  1. #1
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    818S Intercooler Plenum

    With the recent talk about intercooler plenum's (mostly for the coupe from what I can tell) I figured I would chime in with my attempt for the S. I have only had the car on the road for a couple of days and don't have a post intercooler temp gauge, but after 20-30 minutes of driving the fins are cool to the touch so I figure it has to be doing something. Planning to get some temperature gauges installed in the near future.

    I made a fiberglass box over the intercooler, scoops for the two upper intakes on the engine cover and a single 5" duct intake from the drivers side intake. The scoop on the passenger side will be plumbed into the air intake. If I end up not getting enough cooling with this set up I will make a plenum on the discharge side of the IC and add a pull through fan. I still need to finish everything up to make it look nice as well.


    20170516_185446.jpg

    20170510_173428.jpg

    20170510_173437.jpg

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    fasterer and furiouser longislandwrx's Avatar
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    looks cool.

    did you drive around with the 5" tube aiming into the passenger compartment to see how much air you were getting out of it?
    A well stocked beverage fridge is the key to any successful project.

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    Awesome work!
    Zero Decibel Motorsports
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    Quote Originally Posted by longislandwrx View Post
    looks cool.

    did you drive around with the 5" tube aiming into the passenger compartment to see how much air you were getting out of it?
    I haven't yet. Just got the plates on the car this last week, so haven't gotten to drive it much. The weather is back to rain this week, so not sure when I will get out again.

  5. #5
    Senior Member AZPete's Avatar
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    As you saw in my post about a plenum on my 818C, the side vents seem to pull in a lot of air once the vent is funneled into a duct, as you have made. It will be interesting to see the air flow from the vents on the top of the side sails now that you made ducts for them. Maybe you can invent a better "flow meter" than the white garbage bags I used, . . . once the weather improves. BTW, nice work.
    818S/C : Chassis #25 with 06 WRX 2.5 turbo, ABS, cruise, PS, A/C, Apple CarPlay, rear camera, power windows & locks, leather & other complexities. Sold 10/19 with 5,800 miles.
    Mk3 Roadster #6228 4.6L, T45, IRS, PS, PB, ABS, Cruise, Koni's, 17" Halibrands, red w/ silver - 9K miles then sold @ Barrett-Jackson Jan 2011 (got back cash spent).

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    How did you make the scoops like what kinda product was the mold made from lookes awesome!
    Last edited by redfogo; 05-30-2017 at 05:58 PM.

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    Quote Originally Posted by redfogo View Post
    How did you make the scoops like what kinda product was the mold made from lookes awesome!
    I have a friend with a laser cutter that sped up the process for how I made the molds, but the same thing could be done by hand. It was easiest for me to make each scoop in two pieces then fiberglass them together. To make the scoop mold I basically traced the curve of the scoop and cut a small wood piece to match, then spaced it off of a flat base by trial and error until it matched up to what is on the car body.20170430_213242.jpg
    Then I stretched a piece of fabric over the wood and soaked it with fiberglass resin. I coated that in mold release and it was half of my mold.
    20170502_162308.jpg
    The other half is where it tapers into the 5" duct. I had my friend cut pieces to form a pyramid of sorts, then used body filler to smooth it out. Covered in mold release and it was ready to go.
    20170430_124308.jpg
    20170430_215712.jpg
    The parts all came off a lot easier then expected and I fiber glassed them together. The installed scoop doesn't show up too well in pictures, but that was kinda the end goal. I still need to fill in the seam where the two pieces come together and paint them black.
    20170507_115816.jpg
    20170514_212854.jpg

    I should also mentioned that they are just held to the body with epoxied studs and tabs.
    Last edited by autostang; 05-30-2017 at 07:33 PM.

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    Now that you have the molds, any interest in making parts for sale to other builders?

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    fasterer and furiouser longislandwrx's Avatar
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    idf just a heads up, FFR is now selling a scoop kit that gives you two 4" outlets to feed the intercooler.
    A well stocked beverage fridge is the key to any successful project.

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    Quote Originally Posted by longislandwrx View Post
    idf just a heads up, FFR is now selling a scoop kit that gives you two 4" outlets to feed the intercooler.
    http://www.factoryfiveparts.com/8114...oop-air-ducts/

    Is that what you were referring to? I really like Autostang's version... can't wait to see some testing, and hopefully he makes some extras to potentially sell! ;-)

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    Nice work. Gonna look GREAT once you paint them!!

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    I did some clean up work on the side scoops and painted them black. At some angles a line shows up where the scoop makes a 90 degree angle. I'll get that straightened out when I do body work on the rest of the car, for now it is good enough for me. 20170610_122957.jpg20170610_122950.jpg

    Unfortunately I am not going to be able to make these for others. I just don't have the time to put into making more. Even with the molds it takes me quite a bit of time to produce a decent looking piece. It probably doesn't help that I don't have much experience working with fiberglass. I could post pdf templets of the shapes I used if it would be helpful.

    I haven't gotten a chance to drive the car again since my first post, so no functional testing completed as of yet. Work and weather are conspiring against me getting to drive the car.

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    IMG_1261.JPGIMG_1263.JPGIMG_1266.JPG
    Here is my experience with the intercooler temperature issue.
    Based on much internet investigation the consensus for intake air temperature leaving the intercooler is 2-5 degrees above the outside air temperature.
    I have placed a small (low thermal mass) temperature sensor at the coupling between the intercooler and the throttle body. This is wired to an industrial digital readout on my dash. Nice large numbers that can be seen at a glance.

    Last weekend I finished the driver side air vent capture. This is fiber glassed in place and has a 3”dia. Air hose fitting. At the intercooler I formed a cover with 2 each 3” inlets. At this time I have completed the driver side vent connection but not the passenger side. See photos.
    I have been driving my car several months with no direct air flow through the intercooler. This has generated air intake numbers from 100 degrees (cool day) to over 150 degrees on a hot day.

    Street driving –I don’t race my car. If I put the pedal down I am through first gear and ready to leave second gear within a very few seconds. At this point I have to slow down to get on the freeway. Point is, any heat generated by the turbo is absorbed by the thermal mass of the intercooler. Actual cooling from air flowing through the intercooler (if there was any) doesn’t have time to do it’s job.

    So I am driving with my new vented intercooler. From my home to Home Depot the intercooler temp is about the same as always. It’s when the car is parked for 30 minutes that the engine compartment begins to heat up. When I start out of the parking lot the IC temp is 130 – 138 degrees. I’m not driving that fast and the IC temp is not moving. I stop at a signal and the temp goes up a few degrees. When I begin to drive and air begins to flow through my air duct the IC temp raises 4-6 degrees before it starts to cool back down. I’m guessing the air inside my duct hose has absorbed heat from the engine compartment. “Cooling back down” is a figure of speech. The entire time I am driving on the street my IC temp is above 130.

    I get to the freeway on ramp and race through first and second gear. I notice the IC temp comes down to the upper 80’s. I’m thinking this is nice but a minute later I see temp is back at 110 degrees. I drive about 70-80MPH and the best my ducted intercooler can do is 110. I pull off at a quiet freeway ramp and wait for a clear path back onto the freeway. IC temp is 125. Again I punch it up to 80MPH and the intercooler temp is back to the upper 80’s. 1 minute later, at freeway speeds, I see the IC temp is back to 110 degrees.
    This entire time the outside air temp is mid to low 70’s.

    I get back home and remove my creative ducting then drive off with the engine cover sitting in the garage. Now the outside air temp is right at 80 degrees. As I drive the IC temp is floating between 90 and 99 degrees.

    My personal conclusion is: The large amount of air flow moving through a front engine Subaru serves 2 important functions. 1. It actively cools the intercooler and 2. It greatly reduces the engine compartment temps. On our 818 cars the air vents work well enough to cool down the engine compartment. Blocking off these vents to duct it through the intercooler allows the engine compartment to heat up. Our air to air intercooler is more prone to absorb the engine compartment heat than it is to cool down from the “too little” air flow provided by the vent openings.

    And when is it you want nice cool pressurized air flowing to your engine? If you are on the street it would be after waiting at a stop signal. It is this point when there is no airflow to cool the engine compartment or the intercooler. I want full power but all I have is hot air. The fact that my IC temps are greatly reduced under full boost indicates that my intercooler is actually raising the intake air temps due to absorbing heat from the engine compartment. Short of mounting a formula 1 air scoop above the roll bar height I’m not seeing how we will ever make effective use of our air to air intercooler.

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    Senior Member FFRSpec72's Avatar
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    Very similar to what I did for the track ...
    Tony Nadalin
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    CNC_Geek,
    Interesting info. Thanks for the detailed post.
    Did you do anything to duct the air out after it passes through the intercooler? Or does it just dump into the engine compartment?
    818R Build date 10/31/15

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    Question/thought, would drawing air from just one side be more beneficial in pressurizing the air box for the TMIC?

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    Top mount intercooler

    Quote Originally Posted by DanielsDM View Post
    CNC_Geek,
    Interesting info. Thanks for the detailed post.
    Did you do anything to duct the air out after it passes through the intercooler? Or does it just dump into the engine compartment?
    My original configuration included the 4 vents cut open and the large opening in the rear plus a couple of smaller vents near the tail lights. This keeps the engine compartment at a reasonable temp but does nothing to lower the intake air temps.818TT Rear View.jpg

  18. #18
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    For what it's worth from what info I can find post intercooler temps on a 2002 wrx hit around 140F. While obviously not ideal, if we reach temperatures close to what the original car sees it should be workable.

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    Ducting air from both sides would produce greater air flow when ducting to a top mounted intercooler AT THE COST of reduced air flow through the engine compartment. The coupe is collecting ram air from in front. This could possibly generate enough air flow/pressure to be useful. Testing would be needed to confirm just how effective it is. Racing is entirely different. I believe those who are racing are all resigned to using air/water systems or large air scoops that would be less attractive for the street. I'm open to hear the ideas and experiences of others. Based on what I have seen in my own testing I'm convinced that an air/water system is the only workable solution for the street roadster version. I was really hoping to avoid the added expense & complexity of an air/water installation.
    Last edited by CNC_Geek; 07-05-2017 at 11:58 PM.

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    Quote Originally Posted by autostang View Post
    For what it's worth from what info I can find post intercooler temps on a 2002 wrx hit around 140F. While obviously not ideal, if we reach temperatures close to what the original car sees it should be workable.
    Is that while racing or daily driving? The ECM will compensate for some variation above the intake temperature sensor (near the mass airflow sensor) but 40 -60 degrees above OAT is probably beyond its design limits.

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    From what I can tell it's hard accelleration during daily driving, but I've had a hard time finding a lot of good info. That is just the best I have been able to piece together from a few wrx forums.

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    My TMIC temps at or close to ambient on my R (track use only) so not apples to apples (my air box draws from the RH hump). In talking to Jim at FFR and recall what was posted about the wind tunnel testing that opening up the lower portion of the rear fascia proved more beneficial than opening both the lower area and around the taillights.
    818 racecar rear.jpg

  23. #23
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    Mitch,
    Just curious, where is your intake air temp sensor?
    818R Build date 10/31/15

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    3.5 inches from the throttle body in the bottom tank of the IC.
    Last edited by Mitch Wright; 07-07-2017 at 09:29 AM.

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    Finally got to do a little bit of testing. I tapped an Auber instruments RTD into the IC, just ahead of where the air exits to the throttle body. Ambient air temps were in the 75-80 range. My air intake is not ducted to outside air yet. The passenger side scoop, directs air toward it, but there is a 4-6 inch gap. I am guessing this results in air a little bit warmer then ambient being drawn in. Once the engine was up to temp. I was seeing intake temperatures around 90 with normal driving 45-55 mph. During hard acceleration temps got up to 106ish, but dropped back into the 90s pretty quickly. The only exceedingly high temps I saw were after parking the car for 20 minutes. When I started it back up, they were in the 140's, but cooled back down to around 90 fairly quickly.

    There are some tweaks I want to do to try and improve things a bit more, just have to find time!

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    FYI, ducting from side vents with factory fives new side scoop ducts to my centered 08+ STI intercooler works great. I have the glowshift inlet and outlet temp gauge and it is typically always show a 30 degree difference between in and out

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    This is a pretty old thread, but I did a little bit different test today. Stuffed an old shirt in the side scoop feed to the intercooler and blocked off the two upper vents. Post intercooler temps climbed up to ~120F with intake temp of about 80F. I pulled the shirt out (able to reach back and grab it while driving) and the post intercooler temperatures almost immediately dropped back down to ~85F. It may not be quite as efficient as an air to water intercooler, but it definitely shows that the system is doing some cooling.

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    Quote Originally Posted by autostang View Post
    This is a pretty old thread, but I did a little bit different test today. Stuffed an old shirt in the side scoop feed to the intercooler and blocked off the two upper vents. Post intercooler temps climbed up to ~120F with intake temp of about 80F. I pulled the shirt out (able to reach back and grab it while driving) and the post intercooler temperatures almost immediately dropped back down to ~85F. It may not be quite as efficient as an air to water intercooler, but it definitely shows that the system is doing some cooling.
    I have been noticing similar. I actually put a fine water mist system on mine. Just an aftermarket windshield washer fluid pump and reservoir. I use distilled water to prevent buildup. Drops temps even faster and stays cooler for a long time.

  30. #29
    Senior Member Frank818's Avatar
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    Quote Originally Posted by CNC_Geek View Post
    Just noticed this awesome plexiglass window under the rollbar. Do you have a thread somewhere which explains all the details of the entire solution?
    Frank
    818 chassis #181 powered by a '93 VW VR6 Turbo GT3582R
    Go-karted Aug 5, 2016 - Then May 19+21, 2017
    Tracked May 27/July 26, 2017
    Build time before being driveable on Sep 27, 2019: over 6000h
    Build Completed Winter 2021

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