DIY Subaru Forester STI conversion advice

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gecko242
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DIY Subaru Forester STI conversion advice

#1 Post by gecko242 » Sun Mar 15, 2020 12:08 pm

Hey all,
I have been lurking for a while, but finally decided to create an account and ask for some advice.

I previously owned a UK spec Forester XT. Awesome car, I loved it to bits, and swore never to change it.
Until a well priced import Forester STI came up ;)

So long story short, I sold my project car (MK2 golf) and I am in the process of selling my old XT (anyone interested?) And I bought the STI.

I had always entertained the idea of an LPG conversion on the XT, but it was a little high milage for me to consider it a good plan. Now I intend on keeping the FSTI for a few years ahead, and some quick maths shows the conversion would pay me back in less than a year.

Some useful info:
EJ255 4 cylinder, 2.5l flat four
330 bhp
Possibly non standard OBD interface, having come from Japan.
Somewhat soft valve seats

Tinley Tech are relatively local to me, and I have contacted them about the conversion. Firstly, they have been super helpful, so if they are lurking on here, thanks for your advice so far :)
They have recommended the following kit, paired with Hana injectors:
https://tinleytech.co.uk/shop/lpg-kits/ ... it-34-cyl/

They have said this kit will reach 280bhp or thereabouts, and then add some additional petrol to meet the full 330hp demand if required.

They have also recommended an electronic valve lube system, than will inject the fluid into the common gas rail before the injectors, and therefore dosed into the individual nozzles accordingly.

Firstly, I have no problem with system only reaching 280hp. I rarely hoon it to that extent, (and when I do, fuel economy isn't my top concern) and the addition of the petrol should only help reduce VSR.

My only concern with this is the valve lube injection into the common rail - I have heard bad things about this, but I may be wrong. Any advice here would be appreciated.

Ideally, I would like something along the lines of the Prins valveCare system, with a fully sequential dosing unit. But maybe I am being too anal about this?

Also, thoughts on that kit and the components?

Appologise in advance if I seem to be being picky, this car is my baby and I want to take good care of it :)

Thanks in advance for any advice you guys might have.

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Re: DIY Subaru Forester STI conversion advice

#2 Post by LPGC » Sun Mar 15, 2020 12:48 pm

The first thing to know before starting a Subaru conversion is whether or not the inlet manifold has flaps (that divert all intake air through a narrow section), the petrol injectors are below the air diversion area so at idle incoming air goes right past petrol injectors and at medium/high loads petrol still squirts into the wider main air intake area. If flaps are present it's even more important than it usually is to make sure gas enters at the same point as petrol. Even if flaps are removed (swirl flap deletion), if the manifold was designed for flaps you still don't want gas to be injected into the narrow diversion section.
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gecko242
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Re: DIY Subaru Forester STI conversion advice

#3 Post by gecko242 » Sun Mar 15, 2020 1:24 pm

Good point - yes this manifold has TGVs, however they are the earlier style that are not active, I.E they are only closed for a few seconds on a cold start, and are then permanently open for the rest of the drive.

I plan on deleting the flaps, and grinding out the narrow section, in order to reduce intake restriction, and also to make LPG nozzle placement easier.

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Re: DIY Subaru Forester STI conversion advice

#4 Post by Brian_H » Sun Mar 15, 2020 8:12 pm

You can get an electronic version of the flashlube dispenser - Doesn't need an interface to set it up, you simply set a dose rate using a small dial on the front of the unit. That combined with a spider type arrangement with the valve lube is a better solution than putting it through the gas injectors. Some Prins hardware (and I don't know if the valve system includes this) can be difficult to get access to the software to set it up, so if you decide to go down that route, then check you can actually get hold of the required software if your intending to install it yourself, or that you have access to someone who can do.

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Re: DIY Subaru Forester STI conversion advice

#5 Post by LPGC » Mon Mar 16, 2020 10:18 am

Prins electronic lubes inject fluid into the pipes between injectors and manifold, so at least don't see lube fluid going through injectors.. but they're expensive and the refill process crazily involves the full lube bottle (sealed with foil) being stuck onto a spike upside down (foil at the bottom...), with any luck you then turn the full bottle on the spike to lock it on and make the seal before all the fluid from the bottle leaks into the engine bay. The (add-on) splitter / multi-cylinder distribution units are supposed to ensure each cylinder gets the same dose of fluid but they're dumb units so it's difficult to see how they accomplish 'ensure'. Only ever seen on Prins installs.
Another type often fitted on BRC installs (though iirc BRC don't make these units) injects lube fluid into the gas line between reducer and injectors. The problem with this type is that fluid pools in the pressurised gas pipe between reducer and injectors, reaches injectors and simply pours through the first open injector it reaches. Doesn't do the injectors or accuracy of fuelling any good. This type has to feed into the pressurised gas pipe (you couldn't for example plumb it to the vacuum side of injectors in a similar way to the above Prins type), if the lube outlet is under vacuum the vacuum simply sucks the fluid out of the BRC bottle at very high (un-metered) rate. Not only seen on BRC installs but this type needs it's own specific interface cable and software to adjust flow rate.
Out of the electronic lube systems I prefer the Flashlube setup, with or without a dumb splitter depending on engine manifold design. If the manifold has any low areas in which fluid could pool I'd fit a lube spider (a dumb splitter but far cheaper than Prins dumb splitter), it not I'd fit the single lube outlet in airflow just on the vacuum side of the throttle body. Most Subaru manifolds have the throttle body high and no low areas in the manifold for lube fluid to pool in.
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Re: DIY Subaru Forester STI conversion advice

#6 Post by gecko242 » Mon Mar 16, 2020 6:30 pm

Interesting to know about the Prins system - I had noticed the strange refill instructions in the manual, but thought that I must be getting it wrong!
It seems too closed down for what I like, so I think that rules one system out!

I have the same reservations as you with the BRC unit (that is what tinley had recomended), it seems it would not provide a very even distribution of fluid. Also good to know that it has no limiting if attached to the vacuum side of the injectors.

Still not sure what I think about a single point of lube injection - Maybe I am over thinking this, especially seeing as I will get some occasional petrol injection!

What are peoples thoughts on the rest of the system they have recomended?

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Re: DIY Subaru Forester STI conversion advice

#7 Post by Brian_H » Mon Mar 16, 2020 7:01 pm

As Simon's said above, if you can get a good point to inject it at, it shouldn't matter. after all the air that goes through the throttle has to get to each cylinder, and the dosing really isn't that precise at the best of times, its more a case of make sure it gets some, rather than being precise about splitting it between all cylinders. Really depends on the manifold design, a lot of Ford ones have a low loop hence you have to use them, sounds like you may not have that issue.

The spiders are needed in some cases, but if you can get away without one its preferable to do so. 3 less holes to drill, and much easier to hide it away out of sight that way.

I've used the flashlube electronic dispenser on a Ford Zetec for around 70k miles and its still running without major VSR issues, and they are known for having soft valve seats. I did start off with the manual one and really found it problematic to keep it dosing consistantly. The electronic one is just a case of set it up and top it up every so often.

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Re: DIY Subaru Forester STI conversion advice

#8 Post by 3sGTE » Mon Apr 13, 2020 12:17 pm

Hi OP, I have a Forester STI too - a 2004 pre-facelift :D
I was all set to convert it to LPG but haven't bothered yet as my mileage & the fuel price differential doesn't currently make it urgent.

In terms of components, I previously successfully converted my Celica ST205 which had similar'ish demands to the Subaru engine - 2L turbo, 280hp, big mid range torque, full time 4wd.
I'd prioritise good injectors (I used HANA Blue & would likely go with them again on 2x 2-injector rails), 8mm multivalve & feed pipe from tank to the front, & lots of vaporiser - I went through a few & ended up using 2x KME Gold reducers, each supposedly rated for 300hp, in order to keep the gas pressure completely stable.
This was however without petrol substitution at the top end - doing it again I think i'd use a different ECU that had this feature, & have it blend in early.

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Re: DIY Subaru Forester STI conversion advice

#9 Post by gecko242 » Fri Apr 24, 2020 10:16 pm

@3sGTE

Sorry I missed your post initially!

Sweet, mines an 04 as well, with some mild mods so far :)
Whereabouts are you based?

Similar situation here at the moment, although looking to convert once this is all over.
Sounds good, do you think I would get away with a single vapouriser up to 200hp ish?

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Re: DIY Subaru Forester STI conversion advice

#10 Post by LPGC » Sat Apr 25, 2020 5:03 pm

gecko242 wrote:
Fri Apr 24, 2020 10:16 pm
do you think I would get away with a single vapouriser up to 200hp ish?
You can get away with a single vaporiser up to 400bhp ish
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gecko242
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Re: DIY Subaru Forester STI conversion advice

#11 Post by gecko242 » Mon Apr 27, 2020 11:09 am

LPGC wrote:
Sat Apr 25, 2020 5:03 pm

You can get away with a single vaporiser up to 400bhp ish

Sounds good... What brand would you recommend?

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Re: DIY Subaru Forester STI conversion advice

#12 Post by LPGC » Mon Apr 27, 2020 2:50 pm

Emer Palladio, MJExtra or RomanoHD.

The Palladio is bulkier than the MJExtra and RomanoHD but has a slight edge on the others in terms of flow. I'd rate the MJExtra and RomanoHD very similar in terms of flow but reckon the MJExtra usually has the slight edge and is a bit more pressure stable (especially at higher pressure settings) . If I were converting the Subaru I'd go for the MJExtra unless it was over 350bhp-ish because it will make for the tidiest results and is narrow enough (and flexible enough with piping arrangements etc) to be sited low down for good water flow.

There is a make/model of reducer (AMR) supposedly rated at 575bhp.. but I've tried them, they're not good for 500bhp and not very pressure stable.
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