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GT Forester performance mods

Subarino

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Nov 23, 2008
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I have posted a similar question on another forum so i appologise to anyone who has read it there and now here.

I have an 01 GT Forester (ej20 turbo). If possible i want a simple, cheap and effective power increase mainly in the lower rev range. Everything is stock and i have heard changing turbos may increase turbo lag and require a few things swapped over.

Please stop me if im wrong cos im no Forester guru and im going off my research with the google machine. I have read a lot about manual boost controllers. Could this be an option for what im after?

I read that the factory boost level is 6PSI and increasing it to 10PSI should be able to be acheived without problems.

Any ideas? Anyone done this is anything else? Can the factory ECU be simply re-tuned for higher boost?

Thanks in advance
Dave
 
I understand the 01 GT has a very small turbo, which will limit it. Thing is, whatever you do will cost some $$$, because you will need to re-tune the car (ECU). The basic things would be a better exhaust, but even that will require a re-tune. The WRX of the time runs a TD04 turbo, which itself I consider too small for a 2 litre engine, so I swapped for a VF24. Lag is hardly any different to TD04, but it is stronger in the mid and high rev reange. So either of those turbos, with a decent exhaust and a re-tune will provide good performance for you- PROVIDING the injectors and fuel pump are up to it. I do not know if they are.

Costs? 2nd hand TD04 you could get for $200 for a good one. VF24/28/29 good one for maybe $500?
Exhaust- stainless over $2000, but mild are much cheaper.
Re-tune- Ecutek about $1500? Otherwise piggy back and re-tune for the same or less

Another thing you could do is remove the resonnator. Cost is free, but it brings issues with water crossings and dust.
 
You could also go to a different gearing either in the transmission or the diffs... if its like the US WRX, the diffs are 3.90's... You could install the diffs from a non turbo model, which are i believe 4.11's (or something around there)... which would allow your engine to rev easier bringing the power on sooner... but would also lower the km/h you shift at also... the other option is a 2.5rs 5 speed transmission... almost the same gearing as the JDM STi Type RA track transmission, just a lot cheaper...

Those are the best ways iv heard to get rid of or at least significantly reduce the turbo lag on the ej20 turbos.
 
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Changing gearing will certainly improve response- the downsides being cost- you need to change the rear diff as well- and cruising ability. The engine is revving about 500 RPM more and you do notice that. A 6 speed fixes that for a lot of $$$.

Things to watch are changes with the drop down ratio in the gear box and ensuring overall gearing front and rear is the same. You need to do your maths, and if maths is not your strong suit, find someone who is a maths guru.

As for WRX diff ratios, they changed from 3.9 to 4.1 with the MY02. All WRX's prior to that (MY94-01- but not STI's) ran 3.9. At least in Oz AFAIK
 
Not a huge lot you can do in the low revs with a turbo.
Most answers will improve performance once the turbo is on boost, but do little below that. Some may make boost come on a bit later.
Boost controllers etc will be similar - they will improve top end (ie on boost) performance.

The downside to turbos is that they run lower compression ratio to make up for the boost. But this means low revs will be poor.

To really improve low revs you probably need to go with a smaller turbo and increase compression ratio - move towards the SAAB style turbo. But you could lose a bit of top end in doing this.

To make you weep a bit - ever driven an XT?
The bigger engine does help a fair bit at low revs (but is still far from ideal)
 
A 3" turbo back exhaust will have the stock turbo spooling up virtually from idle. I've done some research on how to get a good setup for towing and have been told that although a TD-04 is larger and spools up a tad later, the lag is offset by adding a free flowing 3" exhaust which effectively allows for the TD-04 to spool up almost like the stock turbo with stock exhaust.

I was told NOT to bother using the stock turbo with a 3" exhaust as it spools up so quickly that stop/start driving in traffic was said to be annoying to the driver - however, I wouldn't take their advice as gospel because I feel that this would be a nice torquey low revving engine with great bottom end response similar to a supercharger.

I'm quite curious as to how this would go as I'm not a great fan of winding an engine out to 6000rpm - even when I'm driving hard I rarely rev my GT out to much more than 5000rpm.
 
Nice suggestion... thanks for that... anyone else have any thoughts on this.

Dave
 
Whereas I think of that song, "Take it, to the (rev) limit, one more time" :)


A
I'm quite curious as to how this would go as I'm not a great fan of winding an engine out to 6000rpm - even when I'm driving hard I rarely rev my GT out to much more than 5000rpm.
 
which are i believe 4.11.

4.44 I believe

Not a huge lot you can do in the low revs with a turbo.
Most answers will improve performance once the turbo is on boost, but do little below that. Some may make boost come on a bit later.
Boost controllers etc will be similar - they will improve top end (ie on boost) performance.

Turbo charged engines aren't made for a lot of low end power. Intake, exhaust, cams, and retune will help, but I'd maybe look into a 3.0 H6 swap... why not, eh?
 
They've got plenty of it. They've got 240 hp on premium fuel, iirc. A lot of power comes on at low rpm. If I do any motor work, a 3.0 swap is what I'll do. The only problem with the 3.0 is that there aren't nearly as many aftermarket components for them like the ej25 has, so 240 hp is about all you can get out of them without spending a lot of money.
 
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