Member Profile - Yowie's SH Forester XT

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Re: Member Profile - Yowie's SH Forester XT

Postby Yowie » Sun Mar 01, 2020 10:45 pm

So much thoughtful commentary and so comforting to see the fierce yowie profile pic again!


Cheers very much. Going from 16 or whatever pages of profile on Ozfoz (over 4 years) to not even one page of summarised content here was a bit sobering. Clearly my mods-to-chatter ratio was a bit lean.
Thanks for letting a dirty Forester owner into the gentlemen's forum.

Are you using BtSSM yet?
Its great to have full ssm logging via rear defrost button, and LV, whenever you like!


I've just looked into it and downloaded it to phone now (the Parrot head unit is a pr!ck about connecting to the internet). Plenty to learn by the look of it.


Have you tried facelift Mazda rx8 Tokyo Roki oil filters?


I'm keen to get one and compare with the FB25 filter. They look very similar.


The KAP catch can has a barely sealed plate between left & right sides, from your pic it looks like you might be filtering the heads through this plate (diametrically opposed ports).
Obviously the best way to confirm if your catch can systems are working properly is to put a vacuum/boost gauge on an oil cap modified with a fitting for vacuum hose, or into tees on the inlet returns. (As per FlatIrons again https://www.flatironstuning.com/blog/an ... aru-engine)


Well spotted. Yeah I figured (rightly or wrongly) that sending dirty air around the perimeter of the catch can (past that narrow gap between the separator and the internal wall) might throw a bit of fluid out of aerosol state onto the wall before it comes up through the steel wool and through the "clean" port back to the intake pipe. The Subaru-owner's mass spectrometer perhaps.

That Flatirons video on crank case pressure is a gem - dealing with years of speculation and tall tales in one 55 min video.

I'm a spare oil cap away from trying the crank vacuum test (since I have a redundant-but-functional Turbosmart boost gauge with stuffed LEDs).

Funny you should mention crank vacuum. This weekend I dismantled and checked the crank catch can (Mishimoto) to see why I hadn't collected much lately. Turned out to be the vinyl hoses weren't sealing well on the alloy barbed fittings, despite the use of hose clamps. Rather than switch to rubber hoses or brass barbed fittings (which are a pr!ck at removal time) I used some electrical tape adhesive ethylene race shimming on the alloy barbed fittings to make a snug fit on the vinyl hose.

As it turned out, the clean-return hose on the valve cover (Kapp) catch can also had a loose hose clamp at the intake pipe end. Oops. Nothing like a trickle of unmetered air for to keep target mixtures under load.


I have one of those Perrin inlets to install, I prefer it over the AVO inlet I also have, because it retains the crank case breather return next to the compressor inlet, which according to FlatIrons, provides maximum vaccum on that return port.


The Perrin one was "mechanic's choice" when I first got the car and the OEM pipe was revealed to be chewed at the turbo end. Yeah that's why I picked the Perrin pipe (ahem)
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Re: Member Profile - Yowie's SH Forester XT

Postby bigBADbenny » Mon Mar 02, 2020 6:05 pm

Well one of the Btssm “benefits” has been watching a slow but steady decline in my maf ranges over the last months.

When the figures went under -5% across the board, I pressure tested the inlet post maf, and sure enough my tmic, wastegate and bov ref hoses: all leaking :P

Just need that spare oil cap as well...
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Re: Member Profile - Yowie's SH Forester XT

Postby Yowie » Mon Apr 20, 2020 10:50 pm

A minor update before the better stuff:-

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Some split silicone vacuum hose can be used as trimming for negative wire abrasion relief and to stop inadvertent earthing-out of the 10mm spanner on the battery strap.
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Re: Member Profile - Yowie's SH Forester XT

Postby Yowie » Mon Apr 20, 2020 11:03 pm

Cold Air Intake

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57mm (2 1/4") ID right angle silicone poking out of lower radiator opening (barely visible unless you're really looking).


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...joins a 45 degree alloy mandrel bend (57mm OD), which joins a 45 degree (57mm ID) silicone bend, which joins a 90 degree alloy mandrel bend...


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...which joins a 57mm-to-76mm silicone straight reducing hose held in place with a hose clamp holding the assembly to some alloy angle held in place by two alloy brackets.


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This piece of square profile alloy is held to the chassis rail by two M5 rivnuts inserted into existing chassis rail holes.


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This piece of 60mm x 3mm alloy straight bar hangs off existing threaded holes (one of which holds a horn) and is bent 90 degrees to meet up with the angle (and joins the angle via more rivnuts).


The idea is to have the airbox just as easy to remove and install with the Cold Air Intake (CAI) pipe running to it as it is stock. While a load of bracket fabrication could have been saved by just hose-clamping the reducer straight onto the bottom of the airbox, I didn't want the embuggerance of having to get under the car and remove under-trays just to access the air box & filter.
Last edited by Yowie on Thu Jun 24, 2021 3:52 pm, edited 2 times in total.
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Re: Member Profile - Yowie's SH Forester XT

Postby Yowie » Mon Apr 20, 2020 11:22 pm

Speaking of the airbox, the CAI joins the airbox at the 3" / 76mm OD hole in the bottom (usually the connection point for the "milk bottle" resonator).

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Some plastic needed to be removed from the side of the 3" / 76mm projection in order to make it round. The plastic extra bit used to give the "milk bottle" resonator something to which to attach.

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The 3" / 76mm OD hole in the bottom is shown near the main rectangular air intake hole that is fed by the over-the-radiator snorkel.

My choice of 57mm (2 1/4") pipe diameter was dictated by the narrow points in the front bumper.


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The alloy mandrel bends come with sharp square-cut corners. These clean up easily with a de-burring tool on the inside and a file/sandpaper on the outside.

The system is only ever under very mild pressure or vacuum and is only held together with hose clamps (no rolled bead edges on the alloy).


To make the airbox drop-in easier, I hacked off a large C-shaped clip that was moulded onto the "B" on the centre-right of the image below. The C-clip held a large power steering line snug against the airbox and was always a pr!ck when removing/installing the airbox. Now I just ziptie that power steering line to the airbox "B".

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Also shown in these images is my work-in-progress removing the sound-baffling ribs from the "clean" side of the airbox. I used two different dremel tools, some hobby knives and some sandpaper to take the ribs down.

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I've only had three drives so far to test the new CAI, but early signs are good in terms of airbox temp and response to throttle input.

Airbox temps stay within 5 degrees of dash-stated ambient in cruise conditions, but will still climb in stop-start traffic.

My totally unreliable bum-dyno indicates that the car responds more willingly to sudden throttle inputs, so chalk up some psychological kilowatts there.

It is common to hear feedback about the perils of ingesting water with this sort of setup. I ran the more-or-less the same setup on a 90s Commodore and the worst thing that ever happened was a wet air filter (and reduced performance) after driving through torrential rain at 110km on the freeway. The "clean side" of the air filter had no water droplets after that trip/inspection.

Likewise, I'm not in a great rush to re-tune. The air is still all flowing through the MAF sensor (which can detect amount and temperature of air). Some of the guidance about "re tune after you get a CAI" refers to aftermarket "pod filter in engine bay" intakes that usually have a larger MAF sensor housing.
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Re: Member Profile - Yowie's SH Forester XT

Postby Yowie » Sun May 31, 2020 7:41 pm

I finally finished cutting out the sound-baffling ribs from the clean side of the factory airbox.

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I've managed to borrow a die-grinder, which makes the course grinding much quicker. Shown here with an alloy-eating bit (more open pattern than steel/iron so it doesn't get clogged - it worked fine for plastic). Fine work still needs to be done with a dremel wire brush tool, then a bit of sandpaper.


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The lower restriction should be worth at least 300 killer-wasps.

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Opening up the airbox for the first time since the secondary cold air intake got installed, there was a tiny bit of road grit (sand?) in the airbox on the dirty side of the filter but otherwise no issues or evidence of anything notable.

As a general thing, air filter change intervals will shorten, but I can live with that for the lower intake temps and better flow.
Last edited by Yowie on Mon Jun 01, 2020 10:37 am, edited 1 time in total.
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Re: Member Profile - Yowie's SH Forester XT

Postby bigBADbenny » Sun May 31, 2020 11:38 pm

Love it, have you seen the Prova one piece snorkel/airbox front piece?
Megabux but they claim gains.


How’s the sound with the modded piece?
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Re: Member Profile - Yowie's SH Forester XT

Postby Yowie » Mon Jun 01, 2020 8:58 am

I've only just looked into the Prova thing now - I've found a replacement over-the-radiator duct on one website and that's about it. From the look of it, I think most customers would be paying for the carbon fibre look at the top of the engine bay.

Still, reduced flow restriction is usually a good thing if you can keep the air cold.

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I haven't noticed a difference in sound with the modded piece. There is probably more intake sound on account of the secondary air inlet and the removed ribbing, but hard to tell in the cabin with all the exhaust noise, wind noise, tyre noise, etc.

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My next project in this area is adding a small bellmouth to that awful sharp edge of the MAF sensor housing - probably by running some thick silicone vacuum hose around the outside perimeter and securing it reliably.

That is likely to make the car run leaner (MAF sending x amount of voltage to the ECU, but the housing actually flowing more air). I'm keen to talk to the tuner first to see if the car is likely to self-learn and adjust MAF scaling on its own, or if I should save executing the project until just before the next touch-up tune.

I'm running an outlet from the aftermarket wideband sensor to a PC cable, so the tuner should have the good info on tap if manual re-scaling is needed.

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Apart from that, I'm keeping an eye out for some free weekend time to port the throttle body for better flow.
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Re: Member Profile - Yowie's SH Forester XT

Postby Yowie » Sun Jun 07, 2020 9:42 pm

Throttle Body Porting

With time on my hands, no budget and a desire to reduce pumping losses by 1% here and there, my die grinding project turned to the throttle body this weekend.

The throttle body disconnects from the manifold via undoing the coolant pipes (if you haven't already done the coolant bypass mod), unclipping the 6-pin electrical connection and undoing 4x 10mm bolts.

Intercooler side:-

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(as you can see, the coolant seems to run through a gallery on only one side of the throttle body [left-side of image - passenger side], probably heating the whole casting via conducted heat)


manifold side:-

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The manifold mating surface with orange o-ring:-

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[The back of the throttle body and inside the manifold were all wet with the residue that makes it through my catch cans, but it was very clean and not at all caked in carbon. There may be something to the rumour that E85-fueled cars do not need Upper Engine Cleaner. Eg perhaps ethanol fuel reversion doesn't produce that baked-on oily carbon?]


For time reasons I didn't want to mess with removing the throttle butterfly this time. I also wanted to hold the whole assembly firmly in the vise without damaging anything, so i made this rig out of an offcut of decking hardwood:-

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(ignore the unnecessarily countersunk hole....)

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The slots are to hold the throttle butterfly in the open position. They were made with an angle grinder. There are three slots so the assembly can be bolted on in three orientations.


For a Subaru throttle body it's important to use STI "cherry blossom red" coloured tape to block off the holes where the shaft rotates.

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First I used a dremel-type tool with this bit to smooth down the <1mm lip that separates the machined inner barrel from the cast outer barrel, being careful to note where each side of the butterfly (almost) touches the inner barrel and NOT mess with the flow at those critical points.

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Then it's time to use the electric die grinder with this alloy-cutting "flame" shaped bit to taper the entrance lip some way towards the central lip:-

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From others' work I note that some will use grinding stones then flap-wheels (or similar) at this point. I didn't have a grinding stone suitable to task and flap-wheels are too big with the throttle blade sticking out (yes I could have closed the throttle butterfly, but never mind...). I went straight to hand-sanding with different grades of sandpaper (lubricated with WD40):-

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I wasn't going for an Instagram-quality mirror finish, just smooth enough for the airflow (and smoother than the factory cast alloy texture on the outer section as it turned out). Those marks from the die grinder run in an axial direction, so they do no harm.

[Also - the offset vise is paying for itself here by letting the job hang under it. I didn't need to unbolt and re-attach the throttle body to that timber holder as much as I thought I would.]


Next up was to round off the non-contact side of each end of the throttle butterfly (leaving alone the right angle edge closest to the machined inner barrel). Unlike some examples, I wasn't seeking a knife-edge here, just a "bullnose" on the non-critical side. For this job the dremel-type tool came out again, this time with a small grinding stone.

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Despite putting WD40 on the stone to discourage metal sticking, I ended up with half a stone "brassed". Also, here's a tip: if you have a grinding stone wet with WD40, to save decorating the surrounding area make sure it is within the throttle body before you switch it on.

The timber rig was also useful for getting at the rear of the butterfly. I will need to get some much longer M6 bolts if I want to port the back of the throttle body however. I don't want to port the back (for the time being anyway) because it seems to be much less critical if fast-flowing air exits over a sharp narrow-to-wide step.

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Finished product, for now anyway:-

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Some people grind some flatness into the butterfly shaft and shorten/smooth the screws that hold the butterfly to the shaft. Those might be projects for another time.

At time of posting the ported throttle body is reinstalled but not yet driven.

I did the battery-disconnect thing so the car eases into learning maximum ignition advance etc, so it may be a few drives with poor responsiveness (while ECU learns) before any difference can be felt (if it can be felt).
Last edited by Yowie on Mon Jun 08, 2020 10:10 pm, edited 1 time in total.
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Re: Member Profile - Yowie's SH Forester XT

Postby Yowie » Mon Jun 08, 2020 9:04 pm

Ok, images should work now (including the first one on page 1).

Someone please let me know if the photos are still playing up.
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Re: Member Profile - Yowie's SH Forester XT

Postby Yowie » Sat Jun 27, 2020 8:27 pm

I haven't been happy with the amount of funk that still makes its way through the turbo/intercooler/throttle path, despite having two catch cans and draining them weekly.

The small volume of my Mishimoto "compact" catch can was the likely culprit. The small volume probably fills up with smelly water & oily bits then the intake system probably draws on that fluid.

I discovered that Mishimoto now make an "XL" version of the "Compact" catch can (despite "extra large" and "compact" being an oxymoron) and sell the lower section separately.

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if you draw a line from the lower edge of that internal brass barbed fitting, that is the line of the baffle plate, leaving 10-15mm x the base area (+ drain hose volume) as the collection volume.


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The new main issue is fitting a drain line under the longer catch can base with 45mm to play with before I hit the chassis rail.

The solution is one 3/8" NPT to 10mm barb right angle fitting screwed into the base. Murhpy's Law required that the barb point the wrong way when screwed up tight, so an abundance of thread tape was used to clock the barb correctly with a tight fit.

A second brass fitting (10mm x 10mm 90 degrees) then clears the chassis rail and allows the ball valve (drain tap) to hang near the passenger side lower control arm and ATF lines off the gearbox (to which the hose is zip-tied)

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The whole assembly then goes back up against the passenger-side strut tower under the main wiring loom connection. Shown here with top bracket still loose and a stubby cooler fitted "just because".

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I also replaced the two vinyl hoses and washed out the intercooler (etc.) to get a baseline for the next round of blowby contamination (or reduced amount thereof).

Thanks for reading.
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Re: Member Profile - Yowie's SH Forester XT

Postby Yowie » Sun Jul 05, 2020 3:28 pm

The longer catch can drained about the same amount of fluid after 7 days' driving (and there was still fluid in the intercooler and throttle body hose), so "running out of catch can capacity" doesn't seem to have been the problem with the weekly drain intervals. Having said that, having more catch can capacity is still a good thing.

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The original alloy bracket was made on a limited timeframe at someone else's workshop "back in the day" before I was properly set up at home.

As such, it has way too many holes (to account for different positions that might be needed) and did not take into account the fact that the two M6 mounting bolt holes on the strut tower have an 8mm height difference. This put the catch can on a slant, which was quite noticable with the tall catch can.

Accordingly, a bracket redesign was in order. Another Forester owner is going to run a similar catch can setup, so why not make two brackets at the same time.

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Due to ease of availability of materials, I went for 32mm x 5mm steel bar.


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The bottom one (73 grams) has some sensible mass-reduction applied. The top one (68 grams) is a bit overboard with extra mass-reduction holes. The large central holes were done with a die grinder after drilling some starter holes.


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The original alloy multi-fitment beast is 61 grams, despite being larger in all dimensions.


I'm pretty pleased with the look and function as fitted on the strut tower under the large wiring loom connection:-

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Re: Member Profile - Yowie's SH Forester XT

Postby bigBADbenny » Sun Jul 12, 2020 9:20 am

Love the mods!
Are you still working on the wta with interchiller project?
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Re: Member Profile - Yowie's SH Forester XT

Postby Yowie » Sun Jul 12, 2020 9:29 am

Cheers Ben.

That's Tobyo you're thinking of with the water-to-air intercooler. I think the air-conditioning powered cooling idea has taken a back seat but the WTA project is still going strong (among plenty of other jobs fitting the larger turbo etc.)
Last edited by Yowie on Mon Jul 13, 2020 12:35 pm, edited 1 time in total.
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Re: Member Profile - Yowie's SH Forester XT

Postby bigBADbenny » Mon Jul 13, 2020 8:04 am

Ah silly me, wishful thinking: that we all had wta :P
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