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Old 06-05-2020, 10:49 PM   #1
Grantmac
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Subaru Stars GM flex fuel coils

There have been a few threads over the years about running GM coils from LS motors. Specifically the flex fuel D585 or IGN1A Super coil.
I decided to buy a set of cheap ones from NP Boosted along with a harness designed for RX8 conversions. I had them swap the plug wires for a generic set but it would be better to get a set of wires from a JDM STI.
I removed the pins from both the stock harness on the car and the female plug of the conversion wiring. I was able to connect them and cover with shrink tubing.

Long story short it runs perfectly using completely stock dwell settings.
By perfectly I mean I'm running 20lbs of boost, water/meth injection and successfully firing copper plugs gapped 0.040!!!!

The most difficult part of the entire process has been finding room for the rather large coils. If I had the JDM plug wires I could mount them on top of the motor. Conversely if I was running an aftermarket intake this would be less of a factor.

Just food for thought.

-Grant
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Old 06-06-2020, 12:06 AM   #2
TDagen
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This sounds pretty cool.

How long have you been running like this? What turbo are you running?
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Old 06-06-2020, 12:40 AM   #3
Grantmac
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Got them in today so hardly exhaustive testing. The mounting is still....temporary.
It's just a EJ205 with K04. Nothing special.

I realize that new stock coils would be totally sufficient for my purposes but I dislike that they are more or less consumable items. All 4 of these cost the same as a single stock coil.
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Old 06-06-2020, 02:22 AM   #4
TDagen
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I think your right, something like the jdm V6 or V5 plug wires would be a nice fit.

So fresh install and it's working, right on.

I've exhausted the stock coils capabilities before, the struggle is real. Kenne bell boost a spark cured it but always looking for new possibilities. Running a 0.040 gap would be great.
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Old 06-06-2020, 10:44 AM   #5
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I actually started with just one coil, then added a second on the same side before doing the other two. I spent probably 10 hours researching wiring so I wasn't surprised, just pleased.

At this point I've done zero soldering or any permanent modifications. I'd like to see if its possible to transfer the stock pins into the GM plug body. I'll pick up a spare to investigate but I'm not hopeful.

The coils are an extremely well known upgrade for a number of other Japanese vehicles, so I was pretty shocked that nobody had tried them for a Subaru.
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Old 06-06-2020, 12:33 PM   #6
TDagen
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I’m really digging this. If you can get a plug figured out for the wiring this will be GOLDEN!

I know Bariga added some holley coils to his sti and mounted them to the sides of the engine bay, used msd spark plug wires. Doesn’t look too shabby. I don’t think his mounting location is possible for most, he must have the battery relocated.


Quote:
Originally Posted by Bariga View Post
nothing fancy, coils are "holley labeled"



Quote:
Originally Posted by Bariga View Post
All wired up and running, total cost of ignition upgrade was about $450


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Old 06-06-2020, 12:59 PM   #7
Grantmac
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It would be extremely simple if I had a battery relocation and ditched the stock airbox. So far I'm into this for $130 and the actual labor was perhaps 5 hours, 3 of which was head scratching about mounting location. Probably 10-15 hours of research, mostly figuring out if the stock dwell would work and seeing if anyone had tried this before.
With the right plug leads I think under the IC or beside the radiator would be possible.

As of right now the drivers side are mounted to an existing hole on the frame rail behind the motor and passenger side to one of the power steering fluid reservoir mounting studs. Neither of which is a long term solution.
Also the universal plug wires I got are a pain to press onto the plugs since the ends are designed for exposed plug tops. I didn't want to invest too much in something that wouldn't work.
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Old 06-08-2020, 01:53 AM   #8
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Another 100km on these. Lots of 20psi pulls and I'm still on track to get above average fuel mileage (for me) despite generally driving with my foot in it.
Looking at where other applications run these in terms of dwell the stock ECU isn't taxing them at all. I may try running the same plug gap as the NA models (0.044) just to see if I can get a misfire although I doubt it. The off boost and cruise performance is excellent.
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Old 06-13-2020, 11:49 AM   #9
nospoolforyou
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I'm really intrigued by this... I was considering Performance Distributors SOS coils https://performancedistributors.com/...aru-sos-coils/ or off the line. But the performance isn't close to GM coils. I thought the dwell time from the ecu was an issue (some Australian on YouTube sti/turbo swapping a SF Forester )
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Old 06-13-2020, 11:36 PM   #10
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SF may have used the short dwell black coils (02-03). I'm running the later model longer dwell grey coils.

Romraider can change dwell settings. From my research I still have some available if I need more spark. D585 dwell charts are easily found online.
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Old 06-14-2020, 01:24 PM   #11
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Considering how many miles you've put on them, I'm impressed. Have you noticed a power increase and/or MPG improvement?
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Old 06-14-2020, 02:03 PM   #12
Grantmac
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It's hard to judge power improvement since I was previously dealing with misfires in boost so my plugs were gapped quite tight.

I would say subjectively it's more responsive off boost. I have gotten a very occasional misfire at high boost so perhaps I'm running just a bit too much gap or I need to get into the dwell table to really maximize the coils performance. The coils likely have some more power available since their heatsinks are barely warm after running at speed.

I have been getting a bit better mileage. But my mileage in general is never great since I've always got a roof box on and I'm frequently in traffic.

Sitting at about 400 miles on them so far.
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Old 06-18-2020, 08:39 PM   #13
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I've had a few minor misfires so I got into the dwell table and there definitely is quite a bit that can be added to the stock setup. I copied the factory settings from a motor running these and subjectively it's better plus absolutely rock solid under boost.
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Old 07-05-2020, 02:06 PM   #14
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Now sitting on 4 tanks if fuel with these. Milage is definitely better. At least 25miles per tank improvement and realistically I'm driving the car harder.

The plug wires I used have not worked very well however. The boots are too short and flexible to get a firm connection, they were designed for the exposed plugs on a SBC. I installed the boots from the stock coils and that has made it work. In the future I'll go with early JDM STI wires and mount the coils under the intercooler on the firewall. That would also tidy up the wiring.

I am not able to run as much timing as I should based on similar builds so I think it's time to play with plug heat range. Good thing these make swapping plugs very easy, getting the stock coils in and out was always a pain before.
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Old 07-05-2020, 03:07 PM   #15
BlueSTI4Me
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I have to ask why? And is there any dyno comparisons? Plus have you pulled and inspected spark plugs? What advantage if any?
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Old 07-08-2020, 02:01 PM   #16
Grantmac
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The "why" is very clearly laid out in the first post.
These are a significantly more powerful coil which allow you to run wider gaps without misfires.

I'm getting approximately 0.75L/100km better milage compared to before. My AF learning views are also a bit more consistent although I can't directly correlate that.
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Old 03-31-2021, 06:17 PM   #17
Grantmac
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+6 month update. Running awesome. Had a tank which was +90% highway and got just slightly better than 10L/100km despite having a full roof rack.
Running plug wires from some GM econobox which the MX5 guys recommended.
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Old 04-02-2021, 10:00 AM   #18
Bud le savoyard
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nice topic
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