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supercharged m90 impreza gx
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Old 10 Jul 2013, 07:39 PM   #1 (permalink)
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supercharged m90 impreza gx

hi,
Its been a while since I was last here. about two years and there's no excuse.
Ive decided to do a project on my impreza gx ive given it plenty of thought and its not gonna be cheap. I could of just bought a turbo in the first place but I like to do projects.
Im expecting this to take a month to complete but just have to wait and see what crops up.
so this weekend I going to fit a new excedy clutch and change both valve cover gaskets and seals as 1 side has a leaking plug seal and give her a full service.
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Old 11 Jul 2013, 12:41 PM   #2 (permalink)
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Re: supercharged m90 impreza gx

sounds interesting
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Old 11 Jul 2013, 04:34 PM   #3 (permalink)
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Re: supercharged m90 impreza gx

Thanks tidgy

My idea came when I saw a picture Subaru published of a concept supercharged classic impreza but they never took it further which is a shame.
Then the gears started to turn in my head.
There are some supercharged m90 impreza in America but they never can manage to keep it all under the bonnet so they hack a dirty great big hole in their bonnet !! which to me aint that cool.
Rest assured tidgy im gonna do it right and the only hole in my bonnet is the standard turbo scoop
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Old 11 Jul 2013, 04:56 PM   #4 (permalink)
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Re: supercharged m90 impreza gx

hehe cool, ost folks just stay with theturbo, its all set up for it, but fair play for giving it a go
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Old 12 Jul 2013, 09:25 PM   #5 (permalink)
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Re: supercharged m90 impreza gx

ok guys lets get started with some specs and numbers

eaton 3rd gen m90 supercharger (90 cubic inch displacement per revolution)

impreza gx 2.0 na
comp ratio 10:1
specific torque 92.28 nm/litre or 1.12 ft lb cu
max torque 184 nm/litre or 136 ft lb at 3600 rpm
specific output 61.7 bhp/litre (101 bhp/cu2)
max power output 124.7ps (123 bhp) (91.7 kw) at5600 rpm
(cid) cubic inch displacement (121)
crank pulley 5.25"

atmospheric pressure at sea level 14.7 psi

so we now have some vital stats to do some maths, you cant just fit this and hope for the best we get this wrong and the boxer engine will throw them pistons right out of the block like a heavy weight champ.


lets be sensible and only aim to achieve 5psi of boost
so intercooled or not ?
no intercooler no pressure drop
intercooled pressure drop of 1-2 psi depending on efficiency

so Im going intercooled so we will do the calcs on 7psi with a pressure drop of 1-2 psi giving a total of 5ish psi

pressure ratio
14.7 +7/14.7 = 1.47 to achieve 7psi

volume efficiency (ve)

ve = hp x 75213/ap x cr x bhp x rpm
ap =14.7
cr = 10.1
bhp = 123 at 5600

123 x 75213 / 14.7 x 10.1 x 123 x 5600

9251199/102266136 = 90.4%

so we now know gx is 90% ve

air flow rate

can be calculated in two ways both should be same answer
cid x rpm/3456
121 x 5600/3456 = 218.8 cfm
or
cid x rpm x 0.5/1728
121 x 6250 x 0.5/1728 = 218.8 cfm

so
218cfm x .90 = 196.1 cfm = 100% ve

now calculate boost (pr)x air flow
air flow x pr
196 x 1.47 =288.12 cfm
218 x 1.47 = 320.46 cfm max ve 100%

so now we know how much air we need and the pressure ratio required
all we have to do now is finding a way of getting that out of the m90

7000 rpm on the m90 performance map generates around 320 cfm not taking in account any delta calcs for heat or wear in the rotors

pulley ratio

so at last we can transfer calcs to the gx crank pulley to achieve 7000rpm from supercharger to red line of 6250 rpm engine to establish a pulley
so
7000/6250= 1.12 pr
5.25/1.14 = 4.68"

its all done !!!

we need a pulley 4.6" to spin supercharger at 7000rpm at engine max of 6250rpm to produce 7psi with a parasetic loss of 1-2 psi through the intercooler resulting in 5psi to the cylinders

so now comes the fun ive got to get this lump under the bonnet
when I work out how to get pics on the site il keep you all up to date

Last edited by mikeblackett; 30 Jul 2013 at 08:29 PM.
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Old 30 Jul 2013, 08:32 PM   #6 (permalink)
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Re: supercharged m90 impreza gx

ok guys im 50% into the build and I have pictures but ive ground to a halt I don't have the option to create an albumn in my cp so hopefully soon I can show you hows its going anyone know how I can sort this out

Last edited by mikeblackett; 30 Jul 2013 at 10:20 PM.
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Old 31 Jul 2013, 07:11 PM   #7 (permalink)
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Re: supercharged m90 impreza gx

ok I think ive got this picture thing sorted lol
lets start with a bog standard impreza gx engine

http://www.subaru-impreza.org/forum/...1&d=1375297703
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File Type: jpg $T2eC16ZHJHsFGlmvqgwtBRzFWrw0!g~~60_3.jpg (64.5 KB, 21 views)
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Old 31 Jul 2013, 10:02 PM   #8 (permalink)
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Re: supercharged m90 impreza gx

lets start with a bog standard impreza gx engine bay

remove all the filter assemblies to open up some space but this still isn't gonna be enough so I extended the factory cut outs in the inner wing to move the abs pump and pipework back 4" (100mm)
IMG_0107.jpg

next I had to move the power steering reservoir from the chassis leg next to the abs pump and mount it on the front slam panel and re-pipe it

IMG_0109.jpg

I did some some more measurements and decided that the crash frame around the injectors had to go along with a total re-work of the main power steering hoses from the steering rack to keep them over the intake manifold.
I re-adjusted the position they came out of the rack then the main feed one from the pump was lengthened and the 90 degree was shortened which allowed me to move the pipes up 3" and towards the intake manifold by 6"

IMG_0111.jpg
IMG_0110.jpg

ive opened up enough space now to get this monster in and its still gonna be tight I did the mock up which was a total nightmare starting with the supercharger pulley connected making sure that it is in perfect alignment with the alternator pulley then fabricating an upper and lower mounting brackets bearing in mind that the angle of the supercharger must match precisely the alternator pulley so now it is correct on both axis or the supercharger will destroy the belts and chew up the bearings.
ive now painted the brackets and temporally fitted them

IMG_0113.jpg
IMG_0114.jpg

Next was to clean up the supercharger and give it a full service stripping it right down cleaning and polishing the rotors change both rear and front bearings then replace the coupler with a upgraded version reseal it all up and change the oil.

Next I had to deal with boost side of the charger fabricating from scratch and finding a way of getting such a tight turn to get it to come up and over the charger and keep it as tight as I can so that the bonnet closes without hitting the supercharger or the pipework I also had to make sure I also incorporate a way of piping the control bypass valve into the boost pipe before it came over the charger
IMG_0088.jpg

you can see the control bypass valve under the main boost pipe we will come back to this as this is critical to how a super charger works because you cannot use a dump valve with superchargers it just doesn't work.
another thing that does'nt work on superchargers is the throttle body after the supercharger air must be controlled going into the supercharger so that's the next thing is making a flange adapter to go from the bypass valve to another throttle body which during the mock was a big headache avoiding the master brake cylinder and the power steering hoses and making sure I did hit the brake servo but still give me enough room to fabricate a way to filter the air going into the new throttle body which had to be shortened by taking out the cruise control lever and removing the coolant pre-warm pipe and part of throttle body.

IMG_0087.jpg

now strip it all down make new gaskets from scratch
clean it all and degrease
polish aluminium
weld in bypass valve pipe into main boost pipe and fit silicone hose
spray all cast parts with vht silver spray
fit mounting brackets ready to install supercharger

IMG_0116.jpg
IMG_0117.jpg

Last edited by mikeblackett; 31 Jul 2013 at 10:13 PM. Reason: picture error
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Old 31 Jul 2013, 11:42 PM   #9 (permalink)
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Re: supercharged m90 impreza gx

okay so tomorrow we will fit the intercooler and make the final piece of joining pipework.
so lets talk about the reason why I decided to install full solid pipework yes its more expensive than silicone hosing and more difficult to work with but this eliminates hoses collapsing under high vacuum on idle/cruising and flexing under boost so the only silicone hose I will use is to join two hard pipes together with a maximum of 3mm gap between pipes.
I also have to consider that we obviously can only operate one throttle body so I will have to source some muliti plugs to extend the loom from the original throttle body to the new location so the ecu still gives and receive signals from the second throttle body for the idle speed motor and throttle potentiometer.
the original throttle body to inlet manifold will still remain in place but will have the multi plugs disconnected and plugged into the loom extension to second throttle body we also remove original tb butterfly as its not required as the accelerator cable operates tb in front of supercharger now so it now controls air flow and il have to replace all vacuum pipes to incorporate new tb location, the air assist valve,boost gauge and the control bypass valve actuator for the supercharger.
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Old 01 Aug 2013, 05:16 PM   #10 (permalink)
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Re: supercharged m90 impreza gx

have you figured out what engine management your gonna use yet?
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Old 01 Aug 2013, 08:48 PM   #11 (permalink)
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Re: supercharged m90 impreza gx

not yet, but im getting to the point of adding management to the list now that the fabrication all done and its under the bonnet now.so many types out there any suggestions ?
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Old 01 Aug 2013, 09:32 PM   #12 (permalink)
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Re: supercharged m90 impreza gx

I managed to get the supercharger fitted under the bonnet tonight I didn't fit the pulley il do that once I sort out the idler and bracket so I can kick the supercharger belt under the radiator hose to the alternator.
IMG_0120.jpg
IMG_0118.jpg
IMG_0119.jpg

I went with the Subaru forester xt intercooler basically its not as deep but wider than the new age turbo intercooler and by the dimensions I got I don't think it would of fitted as I only have 20 mm of clearance from the bulkhead so I think I made the right choice ive finished the pipework from the supercharger to the intercooler but I didn't take any pics as I was in a rush to leave workshop so threw on the hks filter so I can run car properly but I did take a pic of intercooler with its vht paint
IMG_0127.jpg
IMG_0128.jpg


you will notice that where the bov/recirculating valve would normally be ive made a blanking plate as this wont be required due to they don't work on superchargers as they use a bypass control valve between the tb and the charger

next issue is wiring loom extension to new tb now these are a tyco/amp multi plug. the bugeye potentiometer connector is a 3 pin but requires a 4 pin econoseal receptacle with only 3 pins in it which you cannot get as they don't make them because the existing loom has a female econoseal they are designed to only plug into potentiometers and nothing else so il have to make one as I don't want to cut into my existing loom unless it absolutely necessary
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Old 05 Aug 2013, 07:40 PM   #13 (permalink)
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Re: supercharged m90 impreza gx

ok managed to make the loom extensions over the weekend, the plug that I was going to have a problem sourcing was solved I got a 4 pin to match my potentiometer out of a Nissan micra alternator of all places, I drilled out all the pins and cut it down reinstalled correct pins with wires and sealed them with atex putty which sets like stone it is 100% water proof and fully insulates the connections.
potentiometer loom extension
IMG_0135.jpg
IMG_0136.jpg
idle speed control motor
IMG_0133.jpg
IMG_0134.jpg

tonight after work I fabricated the idler bracket for kicking the supercharger belt under the radiator hose. I mounted it behind the power steering pulley its snug to say the least between the pulley and its housing.

IMG_0129.jpg
IMG_0130.jpg
IMG_0132.jpg

this took a while as I had to be precise to pick up all the hole centres mounting to pump in one go, then drill everything which was not easy due to the face of pump not being flat as you can see from picture
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Old 05 Aug 2013, 10:24 PM   #14 (permalink)
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Re: supercharged m90 impreza gx

gauges next so ive ordered a dash mounted 3 gauge pod from hta but apparently its gotta be screwed or glued into the opening left by removing the clock facia which is gonna look naff with screws and useless if glued down and you need to try and remove it later.
ive got a second clock facia to modify and try and fit one inside the other so I can utilise the original clips.
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Old 06 Aug 2013, 08:44 AM   #15 (permalink)
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Re: supercharged m90 impreza gx

interesting little read,keep it up fella
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