Linksfahrer

ST-X , You need to make some basic decisions , you are about to climb up an expensive tree of modifications.
even after making lots of choices the WRX 2.0 might leave you on one of the shorter branches.

Ask your self the following questions:

Do I want a car with more than 350-360bhp.

If yes you will need either to go for a 2.0 Sti (could be built and stroked later ) or a 2.5 litre which should be built. ( By built I mean at least with new forged pistons , probably new H rods )
At this point go to a Engine builder and ask what they can give you and for what money. Prepare yourself to answer the expensive question for how much Bhp should the engine be built.
The cost can seem to rise exponentially with Bhp.

If you say No I stay with a 2.0 and 350-360 Bhp is what I need , then you can stay with a 5 Spd box / your R160 rear diff / uprated viscous diff
With the SC36 Turbo Charger / Ported Cast or RCM headers / Harvey Trick up-pipe / sports Panel filter / 550 -565 cc injectors Pinks or Hawk Dark Blues / Sti TMIC / 3 Port BCS / Prodrive 2.5 Sports Cat or Sports Cat 3 inch Exhaust system
Tumbler Delete / you match the spec I have that produces 343 bhp on 8:1 Compression ratio . Go to a Fully decatted system and maybe 8.7:1 CR ( for example with 0.6mm head gaskets ) You should get to 350-360bhp.
adding AVCS / wiring loom is probably worth a + of 20-25bhp at this level of tune. Torque delivery character of 2.0 units is generally inferior without AVCS which are on the Sti's but even the AVCS system cannot compensate with Cam timing for he lack of cubic capacity.
So people don't bother but instead take a full Sti or SH Sti engine and loom and tune that , the reasonable alternative is to bore and stroke the 2.0 , this requires a quote from a engine builder/tuner.

On a 2.0 2.1 A TD04 / Hybrid will give you better Spool and generate considerably more low end torque on this setup , but you may not get over 350bhp top end power. But I wouldn't let that put you off.
As a rule of thumb the TD04 Hybrid will make a better daily car the WRX 2.0 TD05 16G ( SC36) / VF35 on a WRX are more for track days and a blast around in non populated open countrysides.
I say open because in tight lanes and towns the TD04 Hybrid is the better solution. Using a 2.5 and a SC36 /VF35 , will produce a car with really devastating low down torque that is excellent for this application.
I would doubt the SC36 on a 2.5 could reach 400bhp probably 390bhp but I may be proved wrong however that turbo certainly can't exploit the full power potential of the extra cubic capacity block.
But "if" you had built the 2.5 with strong pistons / rods then you can go for a much bigger turbo later , yet still have excellent drivability.

A Harvey trick up-pipe chosen for the power level you require is always a good idea to help spool. Again you need to know the Bhp target to determine
which diameter should be supplied, This you will say / do with AS performance anyway.

Porting of headers is worthwhile if you find yourself not getting any more power gains after push up the boost / timing.
At some point either a header / exhaust / turbo wheel / internal size / air filter / throttle body will be the choke point, the WRX heads I believe can flow for 400bhp
so any modifications are more in line for less turbulence and therefore aimed at better throttle response. I have done some mild smoothing only on mine
and Id say the effect is negligible at 340-350, but perhaps with the ported headers it has helped to extend the length of my power band, I can see this on my graphs

Fuelling, you don't need anything special on 350 bhp but you do need reliable pressure and so while the capability of the pump must be to deliver a stable amount
of fuel for the tune, the Walbro 355lph is a 30 minute DIY job , don't skip this.

Finally reading your Walter Mitty , close , I have to say I think if you currently drive a 335xd then you are going to be terribly disappointed with a 2.0 WRX
An improvement on the flexibility in the 335xd is a tough act to follow , that in my opinion can best be done with a a built 2.5 / 6 speed and a medium sized turbo
for a target 420-450bhp Others on here who have done this on here should guide you with that choice. So its over to the big boys from here.

Linksfahrer

Just want to straighten this out a little ,the SC36 on my 2.04 WRX (TMIC Ver8 Sti ) makes currently 343 bhp is essentially just a slightly better flowing Blouch 7cm housing version of the TD05 16G - I think my old one was lb/min 33.5 CFM 520
on my car the difference was initially worth 15 bhp ( before all modifications as listed in my post above),
I would expect the TD05 18G to make a slighlty laggier 360 370 Bhp with its higher 39-40lb/min flow 18G-CFM 590 Possibly you confuse the Scooby Clinic SC38 offering a 8cm housing version ( renamed 18G XT / XTR Blouch turbo quoted as with 43lbs/min.)

IainMilford

iTrader: (15)

happy to be corrected

tbf the cars I have been in that have had this turbo fitted did have a 2.1 bottom end, that said I’d still expect them to perform well on a stock WRX. Maybe the OP should even consider an SC32 or equivalent for a fast spooling turbo.

ST-X

Ah, the constant internal conflicts of what I want, what I need, and what's practical! I do appreciate the guidance from someone who's been there before and it's why I'm asking the questions now rather than throwing money at a problem based on what a biased business potentially suggests because it'll make them most money.

I think despite any short term plans, this is the long term plan, and I *think* it would be done with a 2.5. Do I need 400bhp? No, but then this car has long stopped being the daily car and is instead basically a toy that I'll keep until the fuel runs out. A built motor, preferably by me, would be the perfect spec. But, and it's a big but, this isn't necessarily something that needs to be done tomorrow. I can gradually amass parts etc as I find them (the same goes for the 6spd gearbox). While I'm not penny pinching by any stretch and have no illusions as to what this will cost to get 400ish bhp, I'm also not the sort of person who would go cheque book racing, I'd rather be sensible and spend money where it needs with some prudence rather than just throw money at someone like ScoobyClinic and say 'build me a fast car'. That's no fun. I guess there are a couple of options; get someone like AS to prep a block/heads etc for me and then assemble all these myself, or get a short block built and go from there myself. I have a few engine builder options for the latter route but they very much won't do anything less than a short block which is absolutely fair enough.

Short term this would seem the prudent option. It's interesting that some old posts by Andy Forrest actually seemed rather disparaging on the AVCS heads but I'll cross this bridge when I go with the longer term plan above. As to the shorter term, I've got the manifolds to port there, an STI intercooler, a straight through decatted 2.5" system (stock STI up pipe) with Prodrive back box, and a K&N panel. Therefore the main thing to go down the upgrade route would be the TGV delete setup, injectors and a turbo of some description, hopefully one that I like the drive of! If we're talking the interim bolt on route I'd not go AVCS etc or head gasket changes as at that point you're into a lot more work than simple bolt ons, and I'm not sure the extra effort would be worth it. Then again, I could be massively wrong on this impression. But the TGV delete seems to be an easy enough thing to do seeing as that whole lot needs to come out to swap out the injectors.

Luckily the driving this car now sees is almost entirely in the Scottish Borders and the NW Highlands. The former is still pretty quiet, the latter unfortunately rather ruined by chavs in financed modified Golf R's doing the NC500. Either way, the driving this car will see is basically now exclusively on fun roads with little traffic. Yes, it's a road car but no, it's no longer a daily driver. That it feels a bit different to a soft daily like the BMW is no bad thing. In real world the roads are fast with not many tight lanes (and where they are tight, I don't drive quickly on them) and so keeping the car on the boil is actually easy enough to do, aside from any driver laziness of course. That said, low down punch is still fun. I always had in mind that the TD04 Hybrid still really maxed out at 310ish bhp? If that is incorrect and say hypothetically could be closer to 330bhp then that would 100% be the preference over a theoretical 350bhp from a Blouche/SC 36.

Given the number of positive words about the Harvey Smith up pipe I'll definitely give AS a shout for one.

The current heat shields are knackered and the gasket to the up pipe seems to be blowing a bit too so I've got a spare manifold there that I've just started to work on by getting rid of all the shield mounting brackets and will follow up with by porting. I'll finish up by getting them cerakoted by a friend and then wrap. Should probably fix the leaking NS rocker cover to stop oil dripping on wrapping though... It seems like a good excuse to do it. Of course it would be easier just to slip a new gasket in place, but where's the fun in that?!

Yeah, for the cost of a new pump it's a no brainer. Easy work too. I did the last pump when I first went for more power and went for a SWRD 290lph one. Indeed in the last 8 years of ownership the car has been worked on and maintained solely by me, so doing the further tweaks doesn't really give me any cause for concern.

You'd think that but they're really not even on the same page for me. Where the BMW is the dare I say 'boring' car that's at home on wide A roads (I bought it as a mile muncher), the Impreza is much sharper handling, massively more engaging and a much faster car point to point because it handles its mass better, and is much, much narrower. I was originally concerned that the BMW would begin to encroach on the Impreza's reason for being in my garage but it doesn't, which is a relief. The BMW is boring, the Impreza still makes me smile whenever I sit in it.

Henrik

iTrader: (5)

Re the TGV deletes, you don't need to touch TGVs when changing the injectors, but in order to "fix" the TGV's, you'll have to take the injectors out, so to speak. Taking the TGVs off are easy enough, but you will probably need new gaskets (genuine subaru ones are not expensive).
If you want to clean them up yourself, you will need something like a die grinder or at a push a dremel. The hole left by the 'arm' that the flaps sits on can be plugged up by threading the left over hole for an m8 bolt, so no welding required in theory.


Regarding hybrids, there are the TD04L based ones, and then there's the TD04HL ones. The L is the exhaust housing you have on now, the HL is the bigger one. The hybrids that make more than 300 are likely the HL ones, but the spool is not quite as good (somewhere between a a td04L and td05). Also, if you haven't got a HL turbine to start off from, it becomes quite an expensive upgrade IMO. The exhaust housing could be modified on a lathe, but it's yet another thing to pay for when building the turbo.
There *are* some Subaru Legacies with a Td04HLA-19T (afaik) turbo. I think these ones use a twin scroll TD04HL housing, and they have been reported (and I think dynoed) at about 350hp.
Cost-wise I only spent about 200 for my hybrid, but I started off with a "hens teeth" td04hl with subaru turbo.

Linksfahrer

Henrik beat me to the TGV / Injector comment,

just wanted to add don't forget to use new seals on them , its a fiddly job to remove and replace all the iron work around the injectors you really don't want this job twice,

Since the rules changed for UK import , I would not recommend using any non UK VAT based supplier at the moment,

ICP ( who are Vat Reg'd Durham) do # ICP10776
4 x Upper O-Rings
4 x Middle O-Rings
4 x Lower Isolator O-Rings

Re, Border Roads, know exactly what you mean , used to drive myself between Peterlee , Livingston and Prestwick in any direction for business.
The yellow bird boxes have ruined the A68 of course, so Bonchester Br -Hawick -Peebles A703 - 701 , B743 Mauchline-Muirkirk-Strathhaven and most of the Ayr road A70 A708 were still good.

adam.pah

I don't have the technical insight that some of the others do on here so I can only go by real world experience. I have 2 blobs, a UK STi running a 2.1 with 460bhp and a standard JDM Spec C running a modest 330-340bhp.
Both cars are set up for early spool and a relatively flat power curve, making them more drivable on the road. There is a weight discrepancy between the cars but the STi still has the higher power to weight ratio.

For road driving in almost every situation, I would choose the Spec C. It doesn't matter if it's a Sunday blast or trip to the shops, it just feels more fun because it's punchy and easier to handle. The 2.1 is too powerful to really exploit on the roads where I live and is a handful, especially in the wet. This actually makes the lesser powered car probably a faster A to B car and therefore more 'fun'.

Someone with a superior driving ability may prefer the more powerful car though...

Linksfahrer

Adam , An interesting 1:1 comparison. What turbo is on the Sti ?

adam.pah

The STi is running an AET built hybrid. It's based on a GTX3071r with 11 blade wheel and 7cm housing. It spools nice and early and holds steady right up to the redline. It's a great road turbo. I did consider going with the larger 3076 version but I wanted a fast spooling road car at the time.

ST-X

Ah, that's good to know. I'd still be tempted to go down the route of TGV removal as it's one less thing to fail when pushed beyond its standard parameter. Again, going back through lots of old posts there were a number of posts from 06-07 suggesting if anything the TGV's left in place seemed to give better drivability, but very little sense. I'm guessing this is down to improvements in mapping and tweaks to suit them but that's me just guessing. Given you're already digging under the skin to get to the injectors it seems worthwhile to do for the extra time involved, especially if I were to pick up some used ones to strip out and port in advance.

More things to investigate on turbos, thanks I do keep coming back to the idea of something like the hybridised TD04, I've always been an area under the curve man. The area under the curve on a big and laggy turbo may well be better if you're keeping it spooled all the time at high rpm but the reality, the more I think about it, is that the bulk of my driving even cross country is still 3.5-5.5k. Going built then a 2.5 built to rev with a decent turbo may well work but I do keep coming back to spool and torque. I guess the balance here is budget; when I go built then I'm not skimping but if I go with the bolt on approach as a stop gap then it's definitely tinted with a view of bang for buck; i.e. no point dropping 2k on an all singing all dancing turbo if I'm missing other key bits, and if that turbo wouldn't then be useable on the later build as I suspect it wouldn't.

In terms of the HL setup, my assumption is that the twin scroll version wouldn't be in any way compatible or modifiable to suit the standard manifold etc (or do you take the exhaust housing from the HL and use it on the L?)? I did see reference to a 19T TD04 conversion elsewhere on Nasioc but the company offering it is/was a) American and b) seems to have ceased trading last year. My question on this (I theorise everything, it's a pain) is, if I could theoretically get one of these 19T conversions for the standard TD04L, is that ultimately still going to be limited by the size of the exhaust housing? And I guess naturally, are there any recommended hybrid conversions available over here? I know Andy used to do them which would have been ideal since he'll be doing the map again, but as he has long since stopped supplying them that's not an option.

Yup, new seals and gaskets etc will always be used! I'm not one for skimping even if I do come across as a tight arsed penny pinching Scottish stereotype on some stuff

ICP are awesome, I've used them loads, and yeah, I'm trying to avoid importing stuff at present (although perversely some stuff seems to be getting through duty free because they've been struggling to keep up with the volumes!).

The A701 used to be my late Sunday night blast back to the city and it was fantastic at that time. No traffic, cool air and very little big wildlife to watch out for (unlike further north). Great roads and relatively camera free - the A68 seems to have got all of them!

Real world 'feel' is just as valid for me as technical, I appreciate your input! What made you go for the GTX turbo over the standard VF? Does it spool better than the VF? I was just looking at the specs of it and it certainly seems to be in the ballpark of what I'm after. Do you have any graphs of it on your Spec C? How similar are the chassis set ups between the two cars too?

460bhp certainly seems in excess of what I'd be after in a build (which is, being brutally honest, partly down to the satisfaction of building an engine for the car as much as it is wanting massively increased performance). Of course costs also increase exponentially with power. If I could build a solid 2.5 motor which gave out 390/400 and spooled well then I'd take that over a peaky track spec'd 460 all day long (not that I'm assuming that's what yours is). Drivability is definitely key in all of this otherwise it ruins what is otherwise a very fun car.

adam.pah

Real world 'feel' is just as valid for me as technical, I appreciate your input! What made you go for the GTX turbo over the standard VF? Does it spool better than the VF? I was just looking at the specs of it and it certainly seems to be in the ballpark of what I'm after. Do you have any graphs of it on your Spec C? How similar are the chassis set ups between the two cars too?

460bhp certainly seems in excess of what I'd be after in a build (which is, being brutally honest, partly down to the satisfaction of building an engine for the car as much as it is wanting massively increased performance). Of course costs also increase exponentially with power. If I could build a solid 2.5 motor which gave out 390/400 and spooled well then I'd take that over a peaky track spec'd 460 all day long (not that I'm assuming that's what yours is). Drivability is definitely key in all of this otherwise it ruins what is otherwise a very fun car.[/QUOTE]

I went for the GTX as it was recommended by AET. The car previously ran 420hp on the standard 2.0 lump and it was laggy as hell so I wanted something that would spool much earlier than my old SR40. I discounted the VF as it wouldn't make the power, iirc a hybrid VF is good for around 380ish. The car runs 460/415 with a very smooth power band. I could probably soften up the coilovers and make it more compliant but essentially it is a very rigid chassis, fully poly bushed and 24mm ARBs, etc.

I don't have any graphs for the spec c unfortunately. The boost on the twin scroll comes on very early though, kicking in at 2k rpm! Chassis wise, it has thicker ARBs and some solid mountings but otherwise is mostly OEM. The suspension is the adjustable pink OEM setup which is standard to the Type RA,

Drivability is ultimately controlled by the driver though. Like I mentioned before, my ability behind the wheel makes the spec c fun because I don't feel like it's trying to kill me at every opportunity; I can't say the same about the black one though....

RetroPug

Once lockdown calms down I'll hopefully be able to post a graph up of a 2.0L on a td04 hybrid. I've gathered all the parts, just need to fit them and get them mapped in. I know specialists are open but I'd rather wait as my chosen one is near my parents so it will be nice to combine it with a visit etc.

It's obviously below the spec you're aiming for but may still be of interest- once I've got the baseline mapped and working well (fingers crossed), I'm then planning on doing as many smaller modifications as possible to help spool and driveability and then going back for a map tweak.

It's my daily WRX so I don't want to go too mad- the goal is a fun, fast daily with great drivability.

Henrik

iTrader: (5)

That would be super interesting. I also need to get my car onto rollers to see how it behaves "actually", rather than just "seat of the pants" feeling

ST-X

Returning this from the dead as the car has covered about 500 miles since this post was written, but it's still in my mind to do something about the power.

The TD04HL is sounding more appealing with a hybrid build. With this, I guess getting an old TD04 (to keep mine in a box of originality) and having it machined to suit the different turbine is a possibility. Is the rest of the HL turbo the same as the L? No bigger volume turbine casing etc? I was curious as Saab's seemed to use the TD04 HL quite regularly, but the exhaust flange is different and thus not much use - would a cold side and centre section from that be useable in a modified exhaust side from the Subaru fitment TD04L?