Why you can't just chuck a bigger turbo on !!

Posts specific to the 2.5 litre turbo engine

Why you can't just chuck a bigger turbo on !!

Postby Stifull » Wed Jun 16, 2021 2:16 pm

So as you may know I am in the process of installing a bigger turbo on my Liberty. I was offered a bigger one cheaply that had been rebuilt but after a short period of time that turbo was having issues, when it wa taken out there was a lot of end play but without any side play. This seemed like a bit of a mystery to me and i know some of you may know why thus had occurred but I didn't and I am sure some of you aren't aware of the reason either.. I spoke at length with a well known turbo builder who has workshops in Sydney and melbourne areas and he explained that the turbo received all this end play because it had been put onto a car that didn't have the supporting mods... It probably didn't have...a HIGH FLOW air filter, nice big silicone inlet hoses, a free flowing IC and a silicone IC to inlet manifold hose... Without these free flowing hoses etc that allow the turbo to easily get the amount of air it was capable of supplying the fan (can't think of correct name atm) was actually pulling itself and the shaft out of the cartridge in the direction of the air flow like a planes propellor pulls the plane forward.. Similarly the exhaust fan van also push the shaft and both fans forward if it can get rid of the exhaust gases fast enough because the downpipe is unable to cope because it may have still had a stock downpipe. Once explained this all made sense as to why this newly built turbo is wasting away on a workshop shelf because it has basically tried to pull itself apart starving for air ..
So.. onto my completed list of goodies already either on my bench or in the mail, I just added a K&N high flow air filter.. Part number is 33-2304-3 ... the last -3 is the HIGH FLOW one.. it is different to the normal 33-2304 .. It's just another thing I have learnt today.. So.. now I have all the hardware.. I think I have done well so far as I have only spent $1850 in total for all 3 KOBE Japan Silicone hoses (2 biggest ones brand new and one 2nd hand IC to intake manifold), an AVO style intercooler in excellent condition, a Megan Racing S/Steel bellmouth downpipe and a fully rebuilt with Genuine IHI parts but never installed VF 52 with 6 months warranty, and a High Flow K&N air filter.

Now all I need is some patients and a tuner that can bring all these together after I install it all. Can't wait to hear and drive it. I have been wanting to do this for 2 years but the time just wasn't right. The way it has all come together now with the awesome prices and helpful people in the Subi community have shown me that when the time is right things just start falling into place. I am suspecting that these mods will take it from 130(+-) to 180+ on a 15-16lb boost. May need fuel pump and Injs but we'll wait and see..

Any recommendations for a good tuner in or around Brisbane please let me know..Will need the auto tuned as well..
Current Subarus
07 Liberty GT (mine) 180kwt on 16lb
98 WRX Club Spes 2 with 2.5ltr upgrade(mine) sub 14 sec
99 Ver 6 Sti also with 2.5ltr upgrade (son) sub 14 sec
02 WRX Bugeye Hatch lots of goodies(wife)
09 Non Turbo Impreza(daughter#4)
Previous
98 GC8 WRX Hatch(daughter#1)
02 Bugeye WRX (daughter#2)
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Re: Why you can't just chuck a bigger turbo on !!

Postby Yowie » Wed Jun 16, 2021 2:58 pm

Interesting comments. Low restriction in the exhaust and in the intake (in that order) is certainly a good thing.

However, I find it hard to believe that a VF52 (a stock turbo on many Subarus) "pulls itself apart" due to the compressor wheel acting like a propeller towards the air filter and the turbine wheel doing similar on the hot side due to stock intake/exhaust restrictions. Indeed if the exhaust is restrictive, the pressure differential on either side of the turbine will be less and the turbine won't spin-up as fast.

Sure restrictions can cause issues/damage in extremis (look into turbocharging challenges for the thin air on top of Pikes Peak) but a Japanese car manufacturer is not going to build millions of power units that are prematurely destroying turbos.

Rally cars have standard-size restrictors in front of their turbos in certain classes, yet the turbos somehow survive.

Also, as a rule, the air filter itself is the least restrictive point in a stock (or sensibly modified) intake system - see the numerous Autospeed articles where they take manometer readings to demonstrate this on several cars.

I'm all for minimising restrictions (see my build thread), but we need to take with a grain of salt some of the "accepted wisdom" that gets shared by otherwise good & knowledgeable people. Including from people on the internet, including from me. There are plenty of reasons that certain "accepted facts" lose touch with reality, including the expense/difficulty of actually testing mods scientifically and confirmation bias. I bought a Peter Brock Energy Polarizer so, yeah, it's essential that everyone else on this forum does too.

---

In terms of Brisbane (ish) tuners, consider:
- Tony Young of Coyote Tuning (the website says Slacks Creek now and doesn't mention Tony - interesting)
- Matt Spry of PITS tuning (Molendinar)
- That Sunshine Coast bloke The Skid Factory are using lately (would need to watch the video and look up)
- Cleveland Exhaust & Towbars (& tuning)
- Chiptorque (Yatala)
- Matt / Kido if his travel schedule can work with your mod schedule

I only have experience of Coyote (Subi), Kido (Subi) and Chiptorque (Commodore) but the rest seem ok too based on things I've heard.

The good news is that a VF52 on an EJ25 (auto) shouldn't be too exotic a job for those that do Japanese engines. Obviously do your homework to select the tuner with the right combination of factors for you.

--

Consider also whether you want/need a 3-port boost controller. The main benefit seems to be more tuner control over how boost kicks in. Opinions of different tuners vary, so talk to your tuner and work out if $150 is better kept in your wallet.
Last edited by Yowie on Wed Jun 16, 2021 5:33 pm, edited 1 time in total.
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Re: Why you can't just chuck a bigger turbo on !!

Postby bigBADbenny » Wed Jun 16, 2021 4:29 pm

Turbo shaft elongation was mentioned in the link I posted, in your other other post intriguingly..
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Re: Why you can't just chuck a bigger turbo on !!

Postby Stifull » Wed Jun 16, 2021 5:21 pm

Hhhmm.. Ok.. The fellow who I had been talking to said things like high boost levels using a stock air filter and pipes and stock downpipe could be the reason this particular turbo had got forward and back movement. He said that was the most logical reason apart from whoever built it stuffed up the build. He said it was unusual case. I can edit or remove the post if you think it is bad info.. I just thought it sounded like a logical conclusion given the info we have about this failed turbo. Matt Spry is the fellow who tuned the previous Apexi Power FC that was in the Sti until it's recent conversion to a Link ECU. Coyote keeps getting mentioned and i think they are on my side of Brisbane. Thanks Ben for the input. Always good to hear a voice of reason. Let me know if i should delete this thread.. Cheers.. The fellow that supplied and fitted the Link unit did a great job and the Sti is now running like a dream better than ever and is making 204 atw on 15lb with lots of torque (it has a 2.5lt with some forged internals). Could wind it up more but it is very quick and should last for ages ..
Current Subarus
07 Liberty GT (mine) 180kwt on 16lb
98 WRX Club Spes 2 with 2.5ltr upgrade(mine) sub 14 sec
99 Ver 6 Sti also with 2.5ltr upgrade (son) sub 14 sec
02 WRX Bugeye Hatch lots of goodies(wife)
09 Non Turbo Impreza(daughter#4)
Previous
98 GC8 WRX Hatch(daughter#1)
02 Bugeye WRX (daughter#2)
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Stifull
 
Posts: 412
Joined: Sun Nov 18, 2018 11:30 pm
Location: Brisbane
Car: '07 Liberty GT '98 WRX CS2 2.5ltr

Re: Why you can't just chuck a bigger turbo on !!

Postby Yowie » Wed Jun 16, 2021 5:31 pm

For what it's worth, these ideas are worth discussing, so I don't think any threads or posts should be deleted.

"High boost" causing turbo damage is possible. In my observation most people go to a strengthened engine and bigger-than-VF52 turbo when they want to run boost in excess of 16-18psi (and they presumably run aftermarket hot & cold breathing), but there are plenty of idiots in the world, and bleed-valves are cheap, so you wouldn't rule anything out. I doubt a VF52 in more regular service would suffer damage from that cause.

"...apart from whoever built it stuffed up the build." Confirmation bias here, but I've had direct experience of that. There are Turbo Builders with high-speed balancing machines and "turbo builders" with home garages.
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Re: Why you can't just chuck a bigger turbo on !!

Postby bigBADbenny » Wed Jun 16, 2021 5:43 pm

Never delete, we’re all for debate, new ideas.

Personally I think boosting a vf to over 20psi is not advisable but plenty do.
If a compressor map existed for them it would be well out of the sane efficiency level.

The elongation thing, possibly related to way too high egt’s.
Iirc the vf36 has a titanium shaft, potentially to combat this, plus less rotational mass.
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Re: Why you can't just chuck a bigger turbo on !!

Postby subyroo » Wed Jun 16, 2021 8:34 pm

Stifull wrote:Without these free flowing hoses etc that allow the turbo to easily get the amount of air it was capable of supplying the fan (can't think of correct name atm) was actually pulling itself and the shaft out of the cartridge in the direction of the air flow like a planes propellor pulls the plane forward.


On one end you have the turbine fan and on the other is the compressor fan.
I know that much about turbo's from my Airport days and hanging around Qantas - TAA and Ansett aviation engineers. :D
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