Turbo high flowing!!

[twin eng, twin turbs]

With the desire for a bit more power i decided to upgrade the current turbo on my mk2 gti but with space a very limiting factor and seeing as i had allready made the manifold, down pipe, induction pipe, intercooler pipe work, oil lines etc etc to suit my current turbo i looked into the different options for high flowing the IHI VF22 turbo i had installed.

This model turbo is the biggest subaru used on the wrx sti models, providing great top end with the sacrifice of a little bottom end drivabilty or lag! Not that i experienced any lag with it as my exhaust manifold is short with 4 into 1pipe work merging together at the turbine housing. It was making boost under 2000rpm in all gears. This turbo flows 325hp with peak efficency at 18psi.

A lot of aftermarket companies supply upgrades for the wrx, sti, forestor gt that this turbo can bolt straight onto but at a big price! So i decided to upgrade the internals using the centre core from a garrett GT 25/40 turbo i had saved for the twin eng mk1 and machining it to suit the IHI exhaust and compressor housings. The garrett GT 25/40 is a awesome ball bearing turbo with great drivability flowing 440hp with a 0.64 air ratio exhaust housing and 480hp with the 0.86 air ratio exhaust housing. The vf22 exhaust housing flows almost as well as the garretts 0.86 unmodified but i have ported and polished it to get the most out of it.

Heres a pic of the vf22 after removing it from the engine. I have modified it a lot from standard.

[twin eng, twin turbs]

You can see the 3" inlet an 2" outlet i have tig welded onto the compressor housing.

[twin eng, twin turbs]

Heres a pic of the standard exhaust wheel before being modified.

[Oneofthegreats]

Nice work.

I had Garrett make me a custom GT25/40 before they were released them along time ago now for my original plan's for my 20VT.

My plan's changed & now have a GT3076R, but I sold it to a mate & fitted it to his CA18 Bluebird & on 20psi made 197rwkw's & was an absolute animal on the street. Could light the tyres up in 3rd way past 100km/h!

Boost build up came on fast & strong & didn't let up. That turbo was designed for fast spool up & high pressure upward's of 26psi.

Look forward to hearing your result's & feedback on this.

[twin eng, twin turbs]

This pic shows half way through machining out the exhaust housing to suit the much larger exhaust wheel of the GT 25/40. I ground an 2.0mm radius on the carbide tipped boring bar to suit.

[twin eng, twin turbs]

Heres the much larger Gt 25/40 exhaust wheel in the VF22 exhaust housing. I gave it 0.40mm clearance to the on each side so when the wheel heats right up it will not scrub the bore. This is the same clearance as garrett housings have. Note the back cutting on the wheel which improves its efficiency at high speed and flow rates.

[twin eng, twin turbs]

After blowing exhaust gaskets numerous times due to the excessive heat i decided to increase the surface sealing area around the exhaust housing and also add another bolt hole where the gaskets were leaking. If you compare with the first pick in the series you can the difference where i have built up the sealing area with weld and added the extra bolt hole. Here i am clocking up the flange for machining.

[twin eng, twin turbs]

milling in progress for a hopefully leak free future!

[twin eng, twin turbs]

Nice work.

I had Garrett make me a custom GT25/40 before they were released them along time ago now for my original plan's for my 20VT.

My plan's changed & now have a GT3076R, but I sold it to a mate & fitted it to his CA18 Bluebird & on 20psi made 197rwkw's & was an absolute animal on the street. Could light the tyres up in 3rd way past 100km/h!

Boost build up came on fast & strong & didn't let up. That turbo was designed for fast spool up & high pressure upward's of 26psi.

Look forward to hearing your result's & feedback on this.

Cheers golfworxs

I am running a GT 25/40 on my Audi A4 aswell and even though its a family car it loves to boost up! I am also building a no expense spared 2.1 litre 16v with a customised GT 35r and an exhaust housing that flares out to a 4" down pipe

[Mischa]

thats great stuff i hope one day i have the knowledge ( or at least some of it ) that you do, very inspirational. we need to hear more about your untold cars though!

[mollins]

unreal mate. thats great work. very thourough.

i have tool envy...

[twin eng, twin turbs]

unreal mate. thats great work. very thourough.

i have tool envy...

Cheers mate, do you remember that alloy cam cover i bought off you? Its in the first pic with the fins machined off and polished up!

[abreut]

Nice work. I like it when people use some ingenuity to get more power instead of just forking out cash for new parts.

[gldgti]

hail the master

nice work mate - couple of questions:

1) is the exhaust housing material easily welded to? is it a simple mig job, or tig? what gas you using?

2) did you increase the turbine size purely for max output advantage? do you envisage a slower spool up now?


cheers

aydan

[twin eng, twin turbs]

nice work mate - couple of questions:

1) is the exhaust housing material easily welded to? is it a simple mig job, or tig? what gas you using?

2) did you increase the turbine size purely for max output advantage? do you envisage a slower spool up now?


cheers

aydan

Yes the exhaust housing is easily welded as it is cast steel, and i simply "v" prepped it and mig welded it with flux cored 1.2mm wire and argo sheild as the sheilding gas. If the housing was cast iron it would still be weldable with eutectic spray welding techniques but this would not be as strong with less penertration into the base metals and the possibility of cracking occuring under the torque of the bolts through the flange. You can weld cast iron with a mig but it will crack! and it is very difficult to machine requiring industrial diamond ceramic cutting tips at around $300 each!

I have increased the turbine and the compressor wheel sizes and flow rate capabilities by a large amount in doing this modification but the size of the wheels is not as important as the design of them! The original vf22 turbo is the highest flowing of the vf range used on the wrx sti's but also the laggiest aswell, this is due to its 10 blade compressor wheel compared to 12 blades on every other vf series turbo. The Garrett GT i used has 14 blades and a more advanced design aswell for improved airflow. The exhaust turbine on the garrett GT is back cut for improved flow in the top end and has a more aggressive rack angle where the exhaust gas hits the wheel but it is a compromise between low rpm response and high rpm power flow. I envisage a little slower spool up but only by a maximum of 500rpm, it spooled up from 1500rpm in each gear with around 5psi at 2000rpm and had usable strong torque across the entire rev range. I am after more top end power for sure and peak boost from 4000rpm up to 7000rpm of around 20psi. This should net 200 plus kw at the wheels, ill post a dyno print out when i get it tuned in coming months.