Forester STI bhp

[thegraveltrap]

MDMA . said:

I have the Tein springs on mine

currently weighing up a fsti, your only based in wigan are you pal?

[MDMA .]

thegraveltrap said:

currently weighing up a fsti, your only based in wigan are you pal?

Yes. But if you're from St Helens, you're not welcome

Drop me a pm if you want a quick look.

[david1972]

Hello all,

I'm 4 years into Subaru ownership now and have probably lusted after one of these for 3 of those years. Reading this has fuelled that fire again.

So far I've had:

2003 2.0 Forester non-turbo
2005 3.0 Outback auto
and currently have a JDM Blob Impreza WRX auto saloon (v rare in UK)



Just can't get the FSTI out of my head - it will happen, but when.....

[vxr2010]

The Fsti , for me has been the best all round car i have owned , fast practicable 4 wheel drive for snow etc , economical when you want it to be , it benefits from a cat back exhaust and a remap and coilovers , two things one i would like cruise control for a long journey and i would not sports cat it as you want to use the power so mpg gets worse ,there is little difference in sportier driving cat v sports cat yes more power in a sports cat but not much in the performance side of things

[lemmingjames]

What could the fsti engine reliably run, 300, 330, 350?

Yes I know reliable is a long piece of string etc but just wondered.

[vxr2010]

310 to 330 works well , fuel economy reliability not too much strain on it , 20 bhp is not massive in the 0 to 60 stakes

[lemmingjames]

And 350?

[TEKNOPUG]

lemmingjames said:

And 350?

You're on the wrong side of the reliability curve.

[vxr2010]

The Fsti turbo is starting to max out at 330 , change the turbo is straight forward but needs other bits done too injectors etc , downside more lag worse fuel economy , a fsti v and 2.5 sti , fsti is quicker initially as less lag , but over a distance little difference, based on same sort of tune for each car , my fsti destroys my 2 litre jdm sti wagon which has more bhp than the fsti

[MurderousCrow]

TEKNOPUG said:

lemmingjames said:

And 350?

You're on the wrong side of the reliability curve.

That chimes with what I've picked up from various experts - mappers and experienced Subaru engineers / mechanics. Would be genuinely interested to know what they can do, and also what may be required to get one to a reliable 400bhp with say 350-380 ft-lbs on the STi top-mount.

The thought entertains; at around 300-320 bhp my SG9 is already hilarious, but the idea of bigger power is tempting. Perhaps at some point I'll give it a go.

I'd imagine a fully-forged build, 14mm head studs and a very strong HG as a minimum in regards to engine.

Injectors, fuel rails, pressure reg, 255lph pump for fuel?

Intake essential, or get away with a panel filter?

Decent standard-position billet BB turbo almost goes without saying. Certainly not getting anywhere near 400bhp on the standard turbo as VXR says!

Anything I'm missing?

[crispyshark]

vxr2010 said:

The Fsti turbo is starting to max out at 330 , change the turbo is straight forward but needs other bits done too injectors etc , downside more lag worse fuel economy , a fsti v and 2.5 sti , fsti is quicker initially as less lag , but over a distance little difference, based on same sort of tune for each car , my fsti destroys my 2 litre jdm sti wagon which has more bhp than the fsti

2.5 Fsti seems quite happy at 366.4 BHP....

[vxr2010]

The reason i would not do more than 330 was Litchfield were getting a number of engine failures at that level of power , you can always go more but that v reliability , even with forged lumps in both of mine i’m still sticking to the 330 level as they work well at the power plus mpg is sensible if you want it to be

[TartanPaint]

MurderousCrow said:

Anything I'm missing?

3" exhaust. You can't do 400bhp on 2.5"

[vxr2010]

I’m agreeing with above but not lol , cosworth managed 400 ish but i saw one recently on low miles being repaired it was going to be very expensive as the actual piston liner was cracked , that is a cosworth built engine and it still fails , with a bigget turbo a lack of fuel economy a lot of lag , a car i do actually like.... but back to fsti as is i’m still saying around 330 with a forged engine , if engine is not forged then less say 310 or so , a sports cat a sports exhaust and remap make a big difference , i like to lack of lag you get with the Fsti , the bmw m4 was a bit surprised too lol

[MurderousCrow]

vxr2010 said:

I’m agreeing with above but not lol , cosworth managed 400 ish but i saw one recently on low miles being repaired it was going to be very expensive as the actual piston liner was cracked , that is a cosworth built engine and it still fails , with a bigget turbo a lack of fuel economy a lot of lag , a car i do actually like.... but back to fsti as is i’m still saying around 330 with a forged engine , if engine is not forged then less say 310 or so , a sports cat a sports exhaust and remap make a big difference , i like to lack of lag you get with the Fsti , the bmw m4 was a bit surprised too lol

Yep they're very driveable on the torque aren't they.

Yes of course a 3" exhaust would be required. Oh and a decent management system...

I'm wondering what if anything could be done to reinforce the piston liners... I've not seen the inside of an FSTi block (and really hope not to anytime soon hahaha). But, it's probably anatomically very similar to the 2.5 in the UK hawks and later. If so, I believe people such as Alyn at AS Performance can put reinforcing inserts in? Make it a semi-CDB engine in effect?

Edit: CDB engine, not semi

Edited by MurderousCrow on Thursday 7th June 20:36

[vxr2010]

a forged set of pistons , race bearings , a good eg cosworth hg and arp head bolts , do that and it’s pretty sorted that’s why the 330 is a good goal , im sure other things like pinning ? can be done but you don’t need to with sensible power , the turbo maybe fairly small but it works well , im full boost around 2200 revs, my impreza wagon is around 3300 3500 revs , i like driving both but prefer the foz as it’s a lot easier to drive and it’s quicker even with less bhp than the wagon

[MurderousCrow]

vxr2010 said:

a forged set of pistons , race bearings , a good eg cosworth hg and arp head bolts , do that and it’s pretty sorted that’s why the 330 is a good goal , im sure other things like pinning ? can be done but you don’t need to with sensible power , the turbo maybe fairly small but it works well , im full boost around 2200 revs, my impreza wagon is around 3300 3500 revs , i like driving both but prefer the foz as it’s a lot easier to drive and it’s quicker even with less bhp than the wagon

Yes I largely agree. I'm in the same position as you, but my SG9 is running around 300-320 or so on standard internals and a very professional remap by TDR. It was road mapped and hasn't been dyno'd, but the torque is strong and linear which is what matters to me.

However I'm aware of the weaknesses inherent in these engines. If it were to let go I've a good idea of the repair costs i.e. already high!, and like many people yourself included would want to upgrade the engine to ensure it doesn't happen again.

With that in mind, I just want to understand what would be required in addition to make it a reliable 400 (which would be great fun if the turbo and ancillaries weren't working too hard to achieve it).

CDB insert machining would add around £500 to the overall job. 14mm head stud conversion work another £300. If done at the same time as forging the engine it could offer the strength to upgrade later... There's some serious man-maths happening here hahaha