RexNuts Subaru Forums

Hey guys,

OK, i'll try and keep this as simple as i can, whilst providing some background info.

Car is a 98 WRX, and has existing mods:
- 3" APS TBE
- APS Cold Air Induction (pipe from front bar to factory airbox)
- TMIC Waterspray Kit
- UNICHIP-A
- 18psi tune and 131.3kW ATW
- STi 4.11 Gearbox and LSD rear diff
- Exedy Standard Replacement clutch

Planned mods are as follows:
- Apexi PowerFC (already bought)
- ProcessWest TMIC (already bought)
- PSR Silicon Intake and SFB (already bought)
- V4 STi 440cc injectors (already bought)
- Walbro Fuel Pump (already bought and installed)

Now for the questions;
1. What turbo should i be looking at? This is what i want from it. Currently the turbo is still the stock turbo (TD04?) and i love the low end spool and pull from about 2.8k which makes it a very fun car to drive. I do not want to lose that (if possible?). With that in mind, people have recommended me anything from a VF24/P18 and VF34/P18, to a VF35/P15 and VF29/P18. Honestly, i just dont want to be disappointed when i plant my foot and have to wait til like 4k for the turbo to kick in. Im guessing that ANY bigger turbo is going to spool up a bit later than what i have now, but is there any compromise i can go with?
2. Any other mods i should be looking at doing in addition to the above? I was thinking of maybe adding a set of aftermarket headers aswell (UEL of course! ). Can anyone recommend ones i should look for specifically for my car? Or are the factory ones good enough? I figure that everything else on the induction side will be upgraded (i.e. CAI > Silicon Intake > Turbo), i should probably also upgrade the exhaust side too yeah (in addition to the current TBE). Thoughts welcome.
3. I know this is probably not an easy question to answer and that theres a HEAP of variables involved, but how much power would i expect to gain from all of these mods?

Anyone that knows me will know that i like to 'do things once, and do them right'. This isnt something i'm prepared to skimp on or do half arsed, and i dont mind paying for good work. So with that said, if theres anything about the above that anyone thinks i should change or do differently etc, please let me know, and suggest an alternative!

Thanks guys, just doing my homework on this for the next couple of months, but looks as though the turbo is the next thing on the list to buy!

Cheers,
Rick.

Just a suggestion .. 99rex has a vf34 for sale real cheap... maybe u could look into it as its very cheap.. get it tested maybe.
vf34-turbo-for-sale-t1893.html

Yeah i spotted that the other day Frank, thanks, but i dont want to rush into buying the turbo just for the sake of theres one available here and now. I want to research etc to make sure im getting the right one for the job.

Go the VF34 mate, you will not look back, you think it goes okay now! wait till you put a VF on along with the other bits & a custom tune..

The TD04 is quite dissapionting once you step up a level

What are the spool characteristics of the VF34 like though? As in when does it kick in?

I have had a ride in, and a drive of SaViOr's Bugeye WRX that has a VF34 (and ~210kW ATW) and was impressed. The main difference between his and mine though is in mine, the turbo just kicks in and pins you to the back of the seat at around 2.8k, whereas his, the boost seemed to come on really smoothly and barely noticibly (i mean that with regards to suddenly kicking in).

Though i think thats more to do with the tune, than the turbo, yes?

Vf34 will come on later then the td04. It's a bigger turbo with more mass to resist spooling. A good tune will keep it quite responsive but realistically a bigger turbo cant/won't spool as fast.

The mid and top end will be where you appreciate it

Yeah definitely consider all your options first.
3 inch into 2.5 different back is supposed to improve bottom end.
2.0 litre engines seem to have more kick than 2.5 which are smoother but fast as well.
I think the more torque down low the less kick you get.
But its true the bigger the turbo the more lag and front mount ic also cause a bit extra lag I think.

V35 is supposed to kick on sooner than a vf34 but with less peak.

I had a GTPS01 on my old 04 rexy ad it made near 200kws with tbe, bigger top mount, fuel pump, injectors, cai and tune. Kicked in at around 3k and really threw you, more so than my current car if that helps Rick.

Thanks guys, this is the sort of info i'm after.

Yeah i have read about the whole 3" > 2.5" diff back thing. I dont think mine has that, BUT there is a small section where the piping gets smaller before it enters the rear muffler, i'll try get a pic of it tomorrow to see what people think. I doubt it was done with 'performance' in mind, but rather to actually fit that particular muffler with a smaller inlet. You guys will probably know better than me (give me a stereo to wire up any day! ).

I wont be going FMIC Frank, i already bought my nice ProcessWest TMIC, although i'm yet to fit it because i want to try and figure out a way to put a head shield under it. More on that later though.

As for the last part, the direct comparison between the VF34 and VF35 is again the sort of info i'm chasing. I figured that with the smaller exhaust housing the VF35 wouldn't have as much top end/peak as the VF34, but exactly how noticeable would the difference be between the two, when the main thing i want is the low-midrange kick and pull? If that makes sense?

Thanks Nick, i'm really hoping to go for something from the VF range though, purely because of their bolt on/ease of installation. May be something to consider though!

Keep the comments and suggestions coming, any more info about headers etc? Should i add these to my to do list?

Mate, i know where you can get a brand spanking new VF43 (yes VF43 from an 06-07sti i think) for about 1 - 1.1k

do your research on specs tho, i have no idea about that yet

Put it this way, my old setup was a 11 second car which i considered fairly responsive & WRX's with VF34's were beating me out of corners through the hills at Kangaroo valley
You are doing ECU too, so with tuning, bottom end will probably feel better than it did with the TD04 & mid/top will completely eclipse what you had before

Best two turbos to go for on the 2L without changing too much, would be either the vf35p15 or vf34p18.

The VF35 will hit boost around 3300rpm, and net around 190-200kw.
The VF34 will hit boost around 3600rpm, and net around 195-210kw.

Second hand prices, the 35 is around $550, the 34 is around $800

VF35 between 195-200kw ???????? Who has that... My vf35 hits boost well before 3300rpm as well...and mine only ever had 181kw...thats before the MSR tune

Wrxsti02 - 203
Sanjeet - 200
Johnnyfamous - 190
wrexy_87 - 205
twinscrollsti - 198
BL35ED - 200

All with a VF35p15. Im not pulling these number out of my bum. 181kw is pretty low for a vf35, considering a td04 can reach 170kw atw. Are you running really low boost?

Which ones are NOT sti's...?

What does it matter? If anything, a wrx should get more power, and sooner. Better compression and better heads.

Eg, im getting 210kw with 21psi. Joel is getting 211kw at 20psi. All thanks to the wrx heads.

In my opinion it matters alot...

A STI has forged internals dont they...compared to the cast ones i have...

And how can you compare your car (turbo) to the vf35's that we are talking about....

You have the twin scroll which i thought would have been good for at least 220kw ?

Arent the dyno runs done in 5th gear with the 6 speed box as well ? (is this better or worse)

Mine is only a 5 speed therefore the dyno run was done in 4th ?

Yes, the sti engine has forged internals, so it can handle more boost and more power.. Doesnt mean the turbo is going to make any extraa power from it.

I never compared my vf36 to a vf35. I compared mine to joels, who is running an identical set up. Turbo, headers, uppipe, sump, pump, dump pipe, midpipe - all identical in every way.

A vf36 wont get 220kw unless its a happy dyno. twin scroll is for torque. Chances are, if you compared you dyno to mine, id have close to 2x the torque, even if power was identical.

99% of 6 speed dynos are run on 4th gear. it seems to be the standard for both wrx and sti. If anything, an sti run on 4th gear will show a higher figure than what it actually is - again proving my point.

Anyway ... back on topic.. you bought STI 440 injectors ... I wonder if you would benefit from even bigger ones... how big are the stock injectors?
Are you able to have dual maps with that computer?
if so, look into E85 tunes ... I believe you could gain around 20% more power and would have cleaner emissions and no detonation ...
I know E85 is not readily available everywhere but it will be soon I hope..
Then you could swap from 98 to E85
Just something else to think about.

Wow, who knew my thread would turn out like this? lol

Frank, thanks for the recommendation. I bought the STi 440's after MSR recommended them in his 'what goes good with what' thread, and i posted up what my plans were. As far as im aware, the stock ones are 380cc, which makes the 440's about a 15% increase in capacity. I dont know if thats enough, hence why i asked the questions, i'm kinda going off recommendations here, and what tuners are telling me. In this case, MSR.

I'm not sure about the PowerFC and its multi map capabilities, but regardless, the car is a daily driver, so i dont think i'd be looking at E85 just yet. I have a mate with Supra thats tuned for E85 and he has to drive to Heathcote to get it (around 50min from us) lol. Maybe something to rethink in the future when its more readily available, but not yet.

Still waiting for someone to chime in with some headers discussion! Maybe i'll start another thread just for that, this ones gone WAY off topic now anyway...

Topic has been cleaned up.

Just get any GT spec UEL type, will make more power everywhere over stock.

New you can pick up for about $550, used $200-$400

Don't worry about the headers. IMO bad bang for buck value. Keep the standard ones.

I'll put up another vote for the GTPS01. I had one on my rex and it was pretty impressive. Not quite as much top end as a vf34 but considering the price difference I think it was a good turbo. You just have to remember that in going to a bigger turbo you ARE going to have more lag.

They are a great bang for buck, they completely transform the power/torque delivery. There was a built 2l on w3xn3t that picked up 30kw peak power. From my experience on a stock 2l running VF34, they made it come on boost much stronger & more power everywhere at same boost.

From memory it was 10kw increase atw peak power, but heaps more torque everywhere

Thanks for the info - now where will i find a set of those so i can suss them out? lol.

search the online vendors & for sale ads on wrexnet. If you really stuck, go see old mate Jason at SMW (which is who you should be speaking to seeing you live in Illawarra)