IW STi Forum banner
1 - 20 of 22 Posts

· Registered
Joined
·
7 Posts
Discussion Starter · #1 ·
Hello everyone,

I have a 21 STI which am planning to add some mods to give it more reliability.
So far it only has aesthetic mods (18inch wheels, Flowdesign kit, R400 cat back, rear tail lights). Was waiting for a year from the purchase date before I touch anything that would need a tune.

The list I have so far, along with the phases planned:

Phase 1:
  • Oil Temp + Oil Pressure gauge
  • Killer B Elh Header (with Up pipe)
  • Cylinder 4 cooling mod
  • Cob Big SF Intake
  • EGT gauge
  • Protune

Phase 2:

Questions I have so far:
  • Can I go ahead with Phase 1 list without needing to change the stock downpipe?
  • From my research I've read its better to do the fuel upgrade along with the stock downpipe else the EJ25 doesn't like it.
  • Can the Cobb Full Fuel upgrade kit still supports running Flex kit? (I am in Australia)
  • Can I split the Sump upgrade and keep it for Phase 3?
  • Is it worth going for swain coated ELH for street use or can I stick with stainless steel? (How much heat reduction difference have others with similar-ish setup has noticed with the swain coating?
  • I think Killer B ELH have some options for EGT: None, Only cylinder 4, All 4 headers. Is there an option for an EGT at the up pipe? Would that give me an average reading overall? Or should the one on 4th cylinder head be enough?

Thanks in advance!
 

· Registered
2021 WRX STi Sport-Tech
Joined
·
80 Posts
I'll be following this closely as I'm in the same boat and also planning my reliability mods and build.

I'd definitely be doing an AOS and the sump upgrade (just the baffle and pickup) in stage 1 as part of the reliability factor. KillerB themselves have said the pan itself is overkill for street use.

AFAIK there is no flex fuel on Cobb at the moment. You need to go standalone or ECUtek.

I don't have much input on headers yet but this is more of a question - why so focused on EGT? It's not something I've seen done nearly as often as an AFR gauge for example.

Edit: I'm still researching this but a local shop told me that here in Canada they don't even recommend the Cyl4 mod anymore. They've said it empirically hasn't made much of a difference in reliability and you just "freeze your balls off" in the winter because coolant is diverted from the heater core.
 

· Registered
Joined
·
2,147 Posts
Hello everyone,

I have a 21 STI which am planning to add some mods to give it more reliability.
So far it only has aesthetic mods (18inch wheels, Flowdesign kit, R400 cat back, rear tail lights). Was waiting for a year from the purchase date before I touch anything that would need a tune.

The list I have so far, along with the phases planned:

Phase 1:
  • Oil Temp + Oil Pressure gauge
  • Killer B Elh Header (with Up pipe)
  • Cylinder 4 cooling mod
  • Cob Big SF Intake
  • EGT gauge
  • Protune

Phase 2:

Questions I have so far:
  • Can I go ahead with Phase 1 list without needing to change the stock downpipe?
  • From my research I've read its better to do the fuel upgrade along with the stock downpipe else the EJ25 doesn't like it.
  • Can the Cobb Full Fuel upgrade kit still supports running Flex kit? (I am in Australia)
  • Can I split the Sump upgrade and keep it for Phase 3?
  • Is it worth going for swain coated ELH for street use or can I stick with stainless steel? (How much heat reduction difference have others with similar-ish setup has noticed with the swain coating?
  • I think Killer B ELH have some options for EGT: None, Only cylinder 4, All 4 headers. Is there an option for an EGT at the up pipe? Would that give me an average reading overall? Or should the one on 4th cylinder head be enough?

Thanks in advance!
The first set looks good. Egt, especially for street use. Will basically be a waste. If you want it cool, but spend money elsewhere.
To answer the questions:

1 - yes you can do that and protune without a downpipe.
2 - you do not need to upgrade fuel even with a downpipe. Some tuners want that for “safety” but 100% injector duty cycle on these is not a static, many have run over 100%idc without the car leaning out. Yamahasho can explain this better than I.
3 - the Cobb fuel kit can support flex, however the accessport/tuning software can not. You’ll need opensource, standalone. Or maybe ecu tek but the hard parts will work.
4 - if you aren’t tracking the car, you won’t need the oil pan. Just the pickup/baffle combo and use a quality 5w40 oil.
5 - talk to killer b. They are active in here. I personally think yes it’s worth it to keep under hood temps down, I’m sure killer b has actual data.
6 - not sure. Talk to killer b. Again if you aren’t hardcore tracking it egt is really not worth it.

hope this helps.
 

· Registered
Joined
·
207 Posts
What’s the use of the car in the OP?

Is there any actual data that the current oil pickups fail, or there’s something that wrong with the stock baffle, or is this based on ~2005 and that the current versions “look” the same? I can see them making sense if you’re rebuilding or upsizing the pan, but it seems like a heck of a thing to take the oil pan off for on a newer car to be such a universal recommendation on here.

For the gauges if you want to simplify or potentially leave room for more gauges in the future, you can sort of infer temperature from pressure (like I wait until I idle at a certain range before pushing), but it comes down to how much info you want.
 

· Registered
Joined
·
81 Posts
This is for reliability? I'd say leave it stock, maybe just a tune. Change oil at 3k OCI religiously and keep an eye on levels.

You wanna modify? ELH, DP, keep stock airbox, then tune. Maybe throw the cyl-4 cooling mod if you want. If after adding those parts you have fuel problems, then think about fixing it.

Don't need the killerb pickup, fuel upgrade, AOS, etc with those mods on stock turbo.
 

· Registered
2020 Subaru WRX STI
Joined
·
324 Posts
Why get tuned twice when you dont need to? Did you randomly decide what to do in your phases?

Phase 1 (no tune required, these are QoL and preventative measures)):
  • Oil Temp + Oil Pressure gauge
  • Cylinder 4 cooling mod
  • EGT gauge
  • Killer B Sump Upgrade (Pan, Pickup and Tray)
Phase 2 (parts need to be tuned):
  • Killer B Elh Header (with Up pipe)
  • Cob Big SF Intake
  • Cobb Full Fuel Upgrade pack
  • NVIDIA catted Downpipe
  • Protune
 

· Registered
Joined
·
2,965 Posts
Why get tuned twice when you dont need to? Did you randomly decide what to do in your phases?
^^^ Yup I agree! I guess do the reliability mods first if you really want. I like the idea of the oil temp and pressure gauge. Id say add an AFR if you want to as well. Everything else ehhhhhhh, the car is new, I wouldnt say totally needed. To each their own I guess.

Phase 2, yeah do it all at once and bang it out. Protune once and be done. Id throw in a fuel pump, turbo inlet, ECBS, and a fresh set of spark plugs as well. While you're there, replace PCV valve too. I personally dont think you need fuel lines and fuel rails for a stock turbo car.

Speak with your tuner and see what they say.
 

· Registered
Joined
·
7 Posts
Discussion Starter · #13 · (Edited)
Thanks everyone for some great input and feedback :)

I will try and reply to some of the posts

I'd definitely be doing an AOS and the sump upgrade (just the baffle and pickup) in stage 1 as part of the reliability factor. KillerB themselves have said the pan itself is overkill for street use.
I did think of the AOS, but am not sure if its needed on a new car. A regular check of the PCV during the reported intervals should suffice along with oil level checks? If I have too much oil going in, I think I may have bigger problems :) I might put this under Maybe (the Grimspeed one I guess), and either include as part of reliability or put it as a mod when I've gone through the rest of the list. It also doesn't need a tune so can easily squeeze in by myself when my Mrs isn't paying too much attention to my parts bucket :)

If I do go Flex Fuel then my plan is to use the COBB hardware, then ECUTEK for the Flex tune.

you do not need to upgrade fuel even with a downpipe
if you aren’t tracking the car, you won’t need the oil pan
Thanks! Definitely helps. That is interesting, I was not interested in going for Flex kits, but kept reading that downpipe changes needs fuel upgrades, hence thought if I am doing fuel upgrades, why not make sure it supports ethanol setup. I will have a chat with a tuner about this.

What’s the use of the car in the OP?
Spirited road use. I have a daily drive 4wd, so sometimes I use the STI as a daily driver, doing highway/city traffic, sometimes it goes up some windy roads up and down a mountain. I don't intend to track it any time in the near future. (If I were to, then most likely I'll have another car to replace the STI as the weekend fun car, and the STI will get stripped down for rally and I'll do some amateur local stages :) )

Is there any actual data that the current oil pickups fail, or there’s something that wrong with the stock baffle, or is this based on ~2005 and that the current versions “look” the same? I can see them making sense if you’re rebuilding or upsizing the pan, but it seems like a heck of a thing to take the oil pan off for on a newer car to be such a universal recommendation on here.

For the gauges if you want to simplify or potentially leave room for more gauges in the future, you can sort of infer temperature from pressure (like I wait until I idle at a certain range before pushing), but it comes down to how much info you want.
Pretty much based on discussions and information off the older STI threads. I don't have much knowledge about the new gen STI. For the gauges, especially the oil temp/pressure, I was looking at some of the dual read ones. Innovate Motorsports 3913 MTX-D Dual Function Oil Pressure (0-145 PSI, 10 BAR) + Temp Gauge Kit

You wanna modify? ELH, DP, keep stock airbox, then tune. Maybe throw the cyl-4 cooling mod if you want. If after adding those parts you have fuel problems, then think about fixing it.

Don't need the killerb pickup, fuel upgrade, AOS, etc with those mods on stock turbo.
Thanks! This is helpful and most of the comments here are steering me away from a fuel upgrade. I've heard the stock intake holds up well. TBH, I want to do the Intake mod so I can hear the darn intake sound :) Can't put BOV in Australia, BPV maybe, but that is just noise with no performance bump. If the aftermarket intake gets me even 20 ish odd bump, that's bonus :) I have been eyeing the Grimmspeed Stealthbox as well as an option.

Why get tuned twice when you dont need to? Did you randomly decide what to do in your phases?
Thank you! This is a very helpful post. I did randomly put out the two phases based on the purchase plans I had, with the ELH as the first thing on my purchase list.
Reading the posts here, it seems I don't need to do the whole fuel upgrade with a downpipe upgrade and nor do I need to do the oil pan mods. So I can squeeze it all in one go.

get a wideband air/fuel gauge instead of EGT
I would just log those and skip adding gauges for them.

Oil temp&pressure gauges would be nice, but not necessary at this level of modification.
I guess if I am not doing any flex fuel mods, I might just stick with Oil temp and Oil Pressure? Should I still get a wideband EGR? I am using a combination Oil temp/Oil pressure (and if I use the dashboard twin mount around the steering column, I'll have another slot empty) I am not sure if ECUTEK would log EGR by itself without being connected to a laptop if I have the sensors installed when am installing the headers.

^^^ Yup I agree! I guess do the reliability mods first if you really want. I like the idea of the oil temp and pressure gauge. Id say add an AFR if you want to as well. Everything else ehhhhhhh, the car is new, I wouldnt say totally needed. To each their own I guess.

Phase 2, yeah do it all at once and bang it out. Protune once and be done. Id throw in a fuel pump, turbo inlet, ECBS, and a fresh set of spark plugs as well. While you're there, replace PCV valve too. I personally dont think you need fuel lines and fuel rails for a stock turbo car.

Speak with your tuner and see what they say
Thanks!

From the looks of it and after following the comments, my revised list would be:

Phase 1 for reliability and slight performance bump for spirited drive:
Phase 2 [Optional]: at a much later date, if I want to push the car more for performance:
  • KillerB Oil pan upgrade
  • Cobb Fuel Upgrade Kit
  • Flex sensor kit
  • Bigger turbo
  • PCV replacement (I think its part of the service schedule around 25K kms?)
  • Revisit FMIC vs TMIC
  • Retune with ECUTEK
For anyone who uses ECUTEK, is it hard to re-tune if you have new mods added later on (like my Phase 2 list?) The last car (Mitsubishi FTO GPX) I worked on, I used a standalone unit (GREDDY Trust E-manage) and I wasn't limited to tunes. But mostly had to take it to a dyno every time. I've read I can get my tuner tune my car remotely while I datalog off a base map with ECUTEK, which could be pretty handy. I will be booking it for a dyno tune on Phase 1 though.

Thanks again everyone :)
 

· Registered
Joined
·
146 Posts
reliability mod #1: Leave it stock
reliability mod #2: buy a longer warranty from Subaru USA
reliability mod #3: regular oil changes with a high quality synthetic oil of the appropriate viscoscity.
reliability mod #4: regularaly check your oil level

If anything breaks, take it to the dealer to be fixed for free under warranty.

If you want the car to go faster reliably, you bought the wrong motor.
 

· Registered
Joined
·
7 Posts
Discussion Starter · #15 ·
reliability mod #1: Leave it stock
reliability mod #2: buy a longer warranty from Subaru USA
reliability mod #3: regular oil changes with a high quality synthetic oil of the appropriate viscoscity.
reliability mod #4: regularaly check your oil level

If anything breaks, take it to the dealer to be fixed for free under warranty.

If you want the car to go faster reliably, you bought the wrong motor.
#1 - already has a cat back, life is too short to keep stuff stock :) What I want to do is make the car run more efficiently while not chasing 1000hp
#2 - wrong country, similar letters though. :) There's no 'longer warranty' from Subaru Australia.
#3 - already do that, been doing for all the cars and motorbikes I've owned since my first bike 25 years ago :)
#4 - yep, part of my routine.

I may have confused with my choice of words of 'reliability'. I want to ensure the car performs at it's efficient level, by replacing basic restrictive parts while adhering to the local laws of my country for road legal automotive use to the most part.
 

· Registered
Joined
·
826 Posts
Here's my opinion as a fellow 2021 STi owner: Leave it alone. What you are making by doing all those mods is just another modded out STi that will eventually break. All of your "reliability" mods are probably relevant for a pre RA EJ, but much less so post RA. Your hopefully still stock STi will be far more reliable and valuable if you leave it alone and enjoy it as it came from the factory. Just my 2 cents.
 

· Premium Member
See about
Joined
·
6,563 Posts
reliability mod #1: Leave it stock
reliability mod #2: buy a longer warranty from Subaru USA
reliability mod #3: regular oil changes with a high quality synthetic oil of the appropriate viscoscity.
reliability mod #4: regularaly check your oil level

If anything breaks, take it to the dealer to be fixed for free under warranty.

If you want the car to go faster reliably, you bought the wrong motor.
Pretty sure its the only motor they put in an STI :) :) :) :) And . . . the general Subaru design is an expensive design If you like subie, your already bought into that - and it is part of what makes em good cars. But sure, that makes building em relatively expensive . . .

But I agree that in general if you take something apart that ain't broke you aren't enhancing reliability . . .that said, on an EJ it is possible decrease overall reliability by disassembly, and enhance the reliability of a SB.
 

· Registered
Joined
·
5 Posts
I have a 2021 STI and this is what I’ve done to it… ALL RELIABILITY/EFFICIENCY improvements as follows:
1. IAG Air Oil Separator
2. HKS Equal length header
3. Ceramic coat headers
4. Cylinder 4 coolant mod

The following I’ve done to improve performance:

1. Cobb Tuner
2. Cobb Intake
3. Protune by JazTuning
4. HKS Catback Legamax exhaust
5. GrimmSpeed EBCS
That’s it. These mods address under hood heat, cylinder cooling, oil consumption and recirculation, exhaust flow and proper tune for my fuel octane (93).
No issues and lots of fun.
Hope this helps.
 

· Premium Member
See about
Joined
·
6,563 Posts
Deleted
 

· Registered
Joined
·
89 Posts
This is for reliability? I'd say leave it stock, maybe just a tune. Change oil at 3k OCI religiously and keep an eye on levels.

You wanna modify? ELH, DP, keep stock airbox, then tune. Maybe throw the cyl-4 cooling mod if you want. If after adding those parts you have fuel problems, then think about fixing it.

Don't need the killerb pickup, fuel upgrade, AOS, etc with those mods on stock turbo.
Couldn't agree more.
As an original owner of an '04 STI (HPDE and AutoX) and second owner of 21 STI (daily) I highly agree.
If you want reliability leave it alone, check oil levels every 2nd or 3rd refuel, change the oil religiously (especially if you drive the car properly - rev-matching downshifts, etc), DON'T street-race or "track" 1/4 mile events (i.e. dropping the clutch at high RPM's) and follow scheduled maintenance.
Adding all that aftermarket crap may be a fun hobby but adding to reliability is plain B.S. You may have convinced yourself that it will add reliability but to us long-term owners its just B.S.
I've got 195K on the '04 as a daily driver (until I bought the '21 STI) and 18 autoX seasons under her belt with only 1 clutch install at 180k and headgaskets at about 100k. Actaully just last weekend I was told she's blowing puffs of smoke when launching during a car control clinic at Lime Rock Park. So she may need rings which seems about right considering how much I've raced her these last 18 years ( I actually wired the deposit for her to the dealer from the BX trailor in Talil Airbase Iraq in 2003).
If you REALLY want to keep it, leave it alone and drive it the way it was DESIGNED to be driven as a high-performance street/track/rally/autoX car and NOT a clutch-dropping, street racing, 1/4 mile "race" car.
Subaru built their reputation for performance-oriented reliability.
Don't screw up your car by trying to make it something it isn't.
 
1 - 20 of 22 Posts
Top