Legacy GT:Fourth generation (2003–2009) – BL, BP/What Turbo?

From Legacy GT

Every day there are new threads asking for help choosing a turbo. Most of the time they start out either with no power targets or targets that are unrealistic. Then the questions come up on what mods are needed to support a given turbo, and a lot of turbo choices are made and then abandoned when the person realizes the extent of supported mods needed to run said turbo and the targets are revised or abandoned when the parts bill is added up. Most of us now realize that buying a bigger turbo is not the only expense in a project and that the parts list needed gets longer the bigger the blower we bought, and that's before anything goes pop.

A lot of discussions on which turbo to buy for which power level and so on end up in disarray because of differing supporting mods applied. You can’t easily compare two turbos if they are supported differently.

Here I want to try a different approach and explore some of the limits of the stock systems in our cars, and how they should affect our purchasing decisions. Call it a turbo chooser matrix if you like but it’s more about entire systems. Any of the knowledgeable members will tell you it's not individual parts that make a strong car, but parts that work well together.

I’m going to pick some points which may seem arbitrary but I think many people shop system setups in this way. A lot of people have some kind of deal-breaker that sets a threshold that they won’t cross, or won’t cross until that part has failed or worn out already.

Laid out below are some scenarios which to me represent the limit of some fairly important or hard to replace part which represents a threshold of complexity or expense. From this would-be builders can hopefully plan their setups more easily / realistically. Note that power and torque figures are going to fall into a wide range because of varying factors like supporting mods, atmospheric conditions, fuel quality used, dyno correction factors, heartbreaker dynos, the time of the month and phase of the moon. Please use your discretion and by all means look for plots which support the numbers you think are reasonable. I suggest we level the playing field here by assuming we are using pump gas of 93MON, reasonable temps and pressure as per sea level.

Of course tuning is a big factor in final output so I will again assume that timing is within a degree or two of knock, and AFRs are in the 11:1 range since this is what the vast majority of us are doing

For purpose of comparison I’m using the following factors:

  • 1lb/min = 14.27cfm
  • 1liter air = 1.0914g
  • 1ft3 air = 0.0682lb
  • 1cfm = 30.90g/s
  • 1lb/min = 7.35g/s

Since the best way to get good information around here is not by searching or asking, but by posting wrong or incomplete info and then waiting for those who know to come out of the woodwork, I'll start with a few scenarios for you guys to critique / fix.

What I'd like to happen is for the mistakes to get corrected, more turbos to be suggested (along with data to support their categorization). Unique turbos can be added to the scenarios which best describe the mods required to support them. More scenarios can be added to expand into the bigger setups. Hopefully like this people can get a ballpark idea of what is going to be required to reach a given power range beyond an actual turbo.

Scenario 1: Stock turbo maxed out

Expectations

Airflow range: up to 230g/s (31lb/min) (442cfm) Typical power outputs: 200 ~ 270whp This is typical Stage II country for LGT / FXT / WRX models with the small stock turbos VF-40, VF-46 or TD04L-13T.

Limits

Shortblock: OK assuming healthy tune. Pistons within limits. Rods are good to 7k0rpm or so and that's not necessary or even desirable with turbos this size. Torque will be limited by boost, which on stock head bolts should be limited to 18psi.

Clutch: LGT models may see clutch slip at these figures

Intake: Stock intake ok

Intercooler: Stock TMIC may leak at or around 18psi boost

Injectors: Stock injectors should be running at more than 90%

Pump: Stock pump within safety limits if in good condition

EGBP turbine: Choke point

EGBP exhaust: High-flow catted or catless downpipe mandatory

Scenario 2: Turbo upgraded, stock injectors / TMIC / clutch maxed out

Expectations

Airflow range: 270 ~ 290g/s (36 ~ 39lb/min) (513 ~ 556cfm) Typical power outputs: 270 ~ 320whp This is the typical range for EJ255s with moderate turbo upgrades such as the following, listed in rough order of potential. There is very little to choose between some of them: VF-39 / VF-43 / VF-48* VF-52 TD05H-Evo16G (BNR and Kinugawa offer direct bolt-on fitments for '05~'09 LGT models)

Limits

Shortblock: OK assuming healthy tune. Pistons within limits. Rods are good to 7k0rpm or so and that's not necessary or even desirable with turbos this size. Torque will be limited by boost, which on stock head bolts should be limited to 18psi.

Clutch: LGT models will most likely have clutch slip at these figures. WRX models should hold.

Intake: Stock intake ok

Intercooler: Stock TMIC may leak at or around 18psi boost and these turbos could produce higher peak torque if run up to higher PRs, even on pump gas. Evidence suggests the stock intercooler will see 2 to 3psi pressure drop over the core at high boost / high rpm states and an aftermarket TMIC or FMIC will be of benefit, if not strictly necessary.

Injectors: Stock injectors should be running at around 95% so this could be said to be the critical limiting factor. These turbos do run out of breath at high rpm and high boost, and in most cases more power and reliability can be had by tapering boost off and running more ignition timing. Therefore adding larger injectors to this range of turbos will not usually improve power potential on pump gas.

Pump: Stock pump may limit AFR available even if in good condition. Expect stock pump life span to be shortened considerably by being pushed this hard. Recommend upgraded aftermarket pump or stock GRB item (which flows 20l/hr more than LGT/FXT/WRX unit).

EGBP turbine: Good.

EGBP exhaust: High-flow catted or catless downpipe mandatory. Headers will add power and torque to this set-up but will almost always slow spool and response to some degree. Catback exhausts will add something at this point but still optional.

Other: Some stock BPVs may leak at these pressures. 3-port EBCS will add control authority and help smooth boost response. Stage III tune required at this point, pro-tune, dyno-tune or e-tune, they all cost $ unless you have the chops.

Scenario 3: Sensible limit for stock block?

Expectations

Airflow range: 290 ~ 320g/s (39 ~ 44lb/min) (556 ~ 627cfm) Typical power outputs: 300 ~ 340whp This is the typical range for EJ255s with turbo upgrades like the following, listed in rough order of potential:

  • TD05H-18G
  • TD05H-68HTA on pump gas (this turbo really meant for E85)
  • Blouch Dom 0.5R*
  • Blouch 380XT
  • TD05H-20G
  • ATP GT28RS*
  • ATP GT2871R*
  • TD06SL2-18G
  • TD06SL2-20G

Limits

Shortblock: Marginal, reliability only possible on a healthy tune, expect shorter life. Note that most billet turbos have good efficiency at higher boost pressures, ie. over 18psi, which will stretch stock head bolts and lead to gasket failure. Stock rods are good for over 400whp but don't like being spun over 7k0rpm. Note that it doesn't take more than a couple of knock events at these power levels to destroy the ring lands on the stock pistons. Clutch: All models require a clutch upgrade at this point, but disk-type WRX clutches with streetable spring pressures are fine. 6MT cars with stock clutches will be fine. Intake: Stock MAF tube close to being maxed out. Consider aftermarket intake / big MAF etc. Intercooler: Stock TMIC is well past its choke point now and would be a serious restriction. Aftermarket TMIC is minimum requirement and FMIC will be of benefit. Injectors: Recommend 740cc or larger. Pump: Aftermarket pump mandatory. EGBP turbine: TD05H-20G will be held back by the small turbine. 18G compressor can use TD05H turbine for quicker spool or TD06SL2 turbine for better top-end. Recommend 8cm2 housing at minimum for turbos in this class running on gasoline. EGBP exhaust: High-flow catted or catless downpipe mandatory. Headers may not be necessary on the smaller TD05H-18G setup but will add solid gains, at the expense of slightly slower spool / response. Catback exhaust also helpful at this point.

Other: Some stock BPVs may leak at these pressures. 3-port EBCS will add control authority and help smooth boost response. Stage III tune required at this point, pro-tune, dyno-tune or e-tune, with injector and / or MAF scaling to do they all cost $ unless you have the chops.

Notes

  • Stock-location STi fitment turbo, doesn’t fit the stock TMIC, the typical AVO / Perrin aftermarket TMICs or straight bolt-on FMIC kits. Check fitment.

Scenario 4: Time to go built shortblock?

Expectations

Airflow range: 320 ~ 360g/s (44 ~ 49lb/min) (627 ~ 700cfm) Typical power outputs: 340 ~ 400whp This is the typical range for EJ255s with the following turbos, listed roughly in order of potential:

  • Blouch 440XT
  • MD321T*
  • Blouch Dom 1.0XT
  • Blouch Dom 1.5XT
  • EFR6758**
  • ATP GT3071R*
  • ATP GT3076R*
  • GTX3071R**
  • GTX3076R**

Limits

Shortblock: This is really well beyond what the stock pistons are going to deal with. A healthy stock bottom-end should be okay at this point but the pistons are really out of their depth. It would be very difficult to crack 400whp without exceeding 18psi boost, which is all the stock head bolts and thus gaskets will withstand. Even on a perfectly clean tune you are pushing the pistons very hard (like 100whp each) and you can expect them to fail at any time. Stock rods and rod bolts are okay to 7k0rpm but some of these turbos will leave with quite a narrow usable power band with that rev limit.

Heads: Stock ports and cams are not yet the choke point but you would gain with a TGV-delete.

Clutch: All models require a clutch upgrade at this point, but disk-type clutches with streetable spring pressures are fine.

Transmission: Subaru 5MT is a question here. Many fail, some don't. If you're careful how you drive you may get away with this. If you're the launch-control kind of driver you may break things.

Intake: Stock MAF tube critical at this point as it can read up to about 380g/s with typical scaling. While there are turbos in this size range that can fit the stock intake it's probably the time to go aftermarket intake and big MAF.

Intercooler: Most people running in this power bracket have a FMIC fitted. While it's possible to run a very good TMIC like the Process West item you will probably do better with a FMIC. Note there are very few flange outlet turbos in this size range.

Injectors: Recommend 850cc or larger.

Pump: Aftermarket pump mandatory.

EGBP turbine: MHI-based turbos need an 8cm2 housing minimum, and consider 10cm2. With the Garretts stick with the .70 A/R housings and all will be well.

EGBP exhaust: High-flow catted or catless downpipe mandatory. Headers will add solid gains on these larger turbos, and the stock manifolds would probably be a serious choke point. Catback exhaust also really needed at this point unless you want to leave significant power on the table.

Other: 3-port EBCS will add control authority and help smooth boost response. You may even consider a hybrid system with both an EBCS and MBC. Stage III tune required at this point, pro-tune, dyno-tune or e-tune, with injector and / or MAF scaling to do they all cost $ unless you have the chops. This is also the point where many people will choose to go to a rotated setup to avoid stuffing a big intake under the intake manifold, fouling the TGVs etc. There are still good choices in the stock-location sector however.

A lot of people are fitting catch cans or air-oil separators along with mods like these as blow-by can and does become an issue.

Scenario 5: I just got divorced and I want to go crazy

Expectations

400 ~ 450whp range.

  • MD321V
  • Dom 1.5R
  • Dom 2.0XT
  • EFR7163**
  • ATP GT3576R*
  • ATP GT3582R*

Limits

Shortblock: Upgrade pistons are mandatory, forged rods are too because you will not be happy having to shift at 7k0rpm when the turbo is telling you to keep going. Head studs mandatory. Larger bearing clearances advised.

Heads: Stock ports are not yet the choke point but you would gain with a TGV-delete. It's now time to consider which cams to buy because the stock ones are definitely holding top-end power down.

Clutch: Shop 6MT clutches to match your new...

Transmission: This is really 6MT territory now unless you like the sound of straight-cut gears and insist the 5MT has better ratios for drag racing.

Injectors: Just get the ID1000s, you will need them.

Pump: Available drop-in pump? Think booster pump, surge tank, parallel pump set-up etc.

Other: 3-port EBCS mandatory. You may even consider a hybrid system with both an EBCS and MBC. Stage III tune required at this point, pro-tune, dyno-tune or e-tune, with injector and / or MAF scaling to do they all cost $ unless you have the chops. This is also the point where many people will choose to go to a rotated setup to avoid stuffing a big intake under the intake manifold, fouling the TGVs etc. There are still good choices in the stock-location sector but you're being stubborn now.

Catch cans or air-oil separators are probably a must-have as blow-by can and does become an issue.

Notes

  • STi fitment turbo, doesn’t fit the stock TMIC, the typical AVO / Perrin aftermarket TMICs or straight bolt-on FMIC kits. Check fitment.
    • Non-standard uppipe and discharge fittings. You will need exhaust components to match the turbo, might be available as a kit, might not. Quite likely that the turbo does not fit into the stock location and/or the intake pipe cannot be fitted under the intake manifold.

Modmatrix

Caption text
Turbo Header Downpipe Full Exhaust Fuel Pump Injectors Clutch 6MT Custom Tune 3-port TMIC FMIC Intake TGV Delete Forged Short Block Cams
Stock Stage 1 ❌ ❌ ❌ ❌ ❌ ❌ ❌ ❌ ❌ ❌ ❌ ❌ ❌ ❌ ❌
Stock Stage 2 ❌ ✅ ❌ 🟨 ❌ 🟨 ❌ 🟨 🟨 ❌ ❌ ❌ ❌ ❌ ❌
TD05H-E16G / VF52 🟨 ✅ ❌ ✅ 🟨 🟨 ❌ ✅ ✅ 🟨 ❌ ❌ ❌ ❌ ❌
TD05H-18G 🟨 ✅ ❌ ✅ ✅ ✅ ❌ ✅ ✅ ✅ ❌ ❌ ❌ ❌ ❌
TD05H-20G ✅ ✅ 🟨 ✅ ✅ ✅ ❌ ✅ ✅ ✅ 🟨 ❌ ❌ ❌ ❌
TD06SL2-20G ✅ ✅ 🟨 ✅ ✅ ✅ 🟨 ✅ ✅ ✅ 🟨 🟨 🟨 🟨 ❌
Blouch 440XT ✅ ✅ ✅ ✅ ✅ ✅ ✅ ✅ ✅ ✅ 🟨 ✅ ✅ 🟨 ❌
GTX3076R ✅ ✅ ✅ ✅ ✅ ✅ ✅ ✅ ✅ ✅ ✅ ✅ ✅ ✅ 🟨

❌ = No, unnecessary, perhaps even counterproductive.

🟨 = Maybe. Might help, might be a good investment for the future, might give negligible gains, might even hurt.

✅ = Yes. Will most likely be worth doing, maybe essential.

Replacement / upgrade oil line solutions.

Oil lines do nothing for performance so are not included in the mod matrix. These will fit stock or usual MHI-based upgrade turbos. Individual turbo vendors may require you fit their oil line kit or specify one you must use if you want your warranty. The very popular BNR is one such MHI-based turbo builder that requires an oil line upgrade, and there are probably others. Any turbo will probably benefit from such an upgrade as the factory lines are skinny, easily kinked or clogged and have built-in restrictors. As a general rule, IHI non-ball bearing turbos will survive on stock oil lines as long as the lines and banjo filters are clean and clear. MHI turbos seem to need a bit more oil volume to succeed and may require an aftermarket oiling solution. Turbos based on Garrett ball-bearing guts usually have a restrictor built-in, or need one in the line, and have more particular requirements in general than others. Consult the vendor to be sure.

You may want to read the turbo failure wiki to see how and why the factory VF-40 and VF-46 turbos die so easily.

FP oil line. This can be ordered with an inline filter which is easier to get to than the stock banjo filter. Caution: Buy extra crush washers for this project if fitting the line to MHI turbos. I had to fit three washers under the banjo at the turbo end to avoid the fitting fouling the bearing housing. Some have needed four. A smaller number of owners report problems with the new banjo fouling the turbo inlet tube. The inline filter kit may need additional -4AN hardware to install it.

Infamous Performance oil line kit with inline filter, fireproofing etc. This is a very well thought-out kit that's been on the market now and is well-received. There's one review here, if you know of another please mention it so I can add a link.

Not quite an oil line kit, more like a filtration system revamp. Amsoil remote 2-micron filtration kits.

Source

Original Source https://www.legacygt.com/topic/86761-what-turbo-wiki-with-a-twist/

thanks to fahr_side

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