400+whp from a Subaru WRX/STI VF series turbo and 500$.

[@Pavel_Engines]

PRE upgrade for the Subaru WRX and STI IHI turbos is based on the modern Garrett G25-550 turbo. BACKSTORY OF GARRETT: Garrett started offering ball-bearing turbos for production vehicles around 30 years ago in the early 1990’s and one of the cars using it was a JDM 1994+ S14 Nissan Silvia. The S14 used a ball-bearing Garrett T28 variant which is basically a GT2560R as called by the more modern Garrett nomenclature. Since then, Garrett went from the GT-series turbos (GT28, GT30, GT35, etc.) to the GTX-series with the GTX28, GTX30, GTX35 turbos. The only difference was a more efficient billet compressor wheel which was able to flow more air as measured in pounds per minute. After the GTX Gen1, came the GTX Gen2 turbos which had an even more efficient compressor wheel which typically can flow 10% more than the GTX Gen1 turbos. The turbines stayed the same for GT, GTX Gen 1, and GTX Gen 2. It’s all great at this point, but it became the end of the line for the GTX turbos. No matter how efficient the compressor wheel was at supplying air, you also need to get it out of the turbo and you need to get it out efficiently. This is the key to all this. The 25-year old Garrett turbine blade rotor technology worked great for two-plus decades, but has become the restriction. Exhaust restriction will increase exhaust back pressure, commonly known as EMAP (exhaust manifold absolute pressure) or EBP (exhaust back pressure), increase EGT (exhaust gas temperature), and can even lead to cylinder misfires and knock. Garrett did a complete redesign of their turbos and called them the new G-series. The GTX28 has been replaced by the G25, the GTX30 has been replaced by the G30, and the GTX35 has been replaced by the G35. There are a few larger GTX->G turbos that follow this nomenclature evolution as well. G-series compressor wheel design has been greatly improved even compared to the GTX Gen2 turbos, but most importantly, the turbine blade rotor design has been completely changed. The extra mass air flow that can be supplied by the comp wheel, can more-efficiently exit the turbine with less back-pressure. This combination of a highly-efficient compressor wheel is matched by a highly-efficient turbine for a 'balance-flow turbo'. An inefficient, old-tech, turbine cannot get the extra exhaust volume out and creates excessive exhaust back pressure (EBP), higher EGTs, and even additional knock will occur. Most common solution to lowering the exhaust back pressure is a larger turbine rotor (larger inducer and exducer) or an archaic clipping of the turbine exducer blades on the stock turbine. A larger turbine rotor will usually help reduce back-pressure and EGT, but usually at the expense of extra weight, higher moment of inertia, and more lag. Clipping turbine blades means you literally set up the shaft in the lathe or a surface grinder and machine off the tips of the turbine exducer blades to reduce their area, open up the area between the blades, and allow the exhaust gasses to get out of the turbo with less flow restriction. Reduction of blade area can also cause added lag. PRE TURBO UPGRADE HISTORY DEVELOPMENT I started rebuilding Subaru IHI turbos in 2010 and did my first upgrade on a VF39 back in 2014. The 11-blade compressor wheel you see most IHI turbo rebuilders use is based on the Garrett GTX2860R Gen1 and I worked with a company back in 2014 to develop it. This was a drop-in billet compressor wheel which required no compressor housing machining or modification and flowed 10% more than a stock IHI and typically picked up 30whp. Where a stock STI IHI turbo made +/-300whp on a Dynojet on pump gas, this upgrade made +/-330whp, while having same spool characteristics and better top end. The compressor wheel costs $100 and while 'already in there' for a turbo rebuild, makes perfect sense as the HP per dollar can't be beat and there is no other part you can bolt onto your car that will make 30whp for $100, PERIOD! After maxing out the capabilities of the drop-in comp wheel, I started machining compressor housings and fitting slightly larger comp wheels with great success. Eventually, you can’t go bigger than a 20G compressor wheel in stock housing so you have to start designing more efficient parts. The stock turbine shaft becomes a flow restriction with the 20G-sized compressor wheel anyway. Going back to the whole ‘crapping out what you take in’ theory. This is how the ‘G25 turbine blade rotor design on an IHI shaft’ came about. There are ‘high flow’ and larger turbines available online for the IHI, but all they literally do is keep the same blade profile as stock and remove one or two blades to increase volume between the blades and reduce back-pressure. This is nothing innovative compared to what Garrett did when they designed the G-series line of turbos. IHI has used the same turbine shaft on Subaru-production cars since late 90’s when the Impreza 22B came with a VF22 turbo. This turbine technology was great at one time, but now, can be considered 'ancient' and needs modernization. The goal of my upgrade project was to have a new comp wheel and turbine to work as a matched set rather than a stock turbine with high-flowing, bigger compressor wheels. PRE G25-500 UPGRADE FOR THE IHI TURBOS The Garrett G25-550 compressor wheel and turbine rotor sizes is very close in physical size to what’s in the stock Subaru WRX/STI IHI turbos. All these IHI turbos use the same cartridge with the same compressor wheel and turbine shaft dimensions and aero profiles. My solution is a custom hybrid turbine shaft and a custom compressor wheel based on the Garrett G25-550 turbo. The dimensions of the G25-550 compressor wheel had to be manipulated to make it fit the stock IHI compressor housing and be as close to original form as possible. Compressor wheel development went in the similar footsteps of the GTX->IHI from 2014. The G25-550 comp wheel is very similar in size to the IHI. Making minimal changes to the G25-550 allows it to fit the stock IHI compressor housing without modification. Since my product is not related to the Garrett corporation, I cannot use their G25-550 name, and don't need a 'cease and desist' for violation their likeness. Thus, the name of my upgrade is G25-500. The turbine shaft is a hybrid design using the blade rotor from the Garrett G25, but made with the IHI journal bearing shaft dimension and the blades are profiled to fit the stock turbine housings without any modification or machining required. The hybrid turbine shaft project was a fairly large financial investment, order of 100 pieces, and a 6 months manufacturing lead time. The first G25 turbine test ran on the dyno in October 2020 and by August 2021, I ran through all 100 turbine shafts from the original batch. After that, I had a second batch of 200 pieces of the G25 hybrid turbine shafts made. Attached is a picture of the stock IHI turbine shaft and my G25 hybrid turbine shaft. Blade shape is completely different and that’s what gives it the efficiency to match to high-flow compressor wheels. The compressor wheel and turbine shaft are both machined to fit the stock compressor and turbine housings without any modifications. For the DIY customer: buy the parts, drop them in, and go for a tune or buy a complete CHRA and swap it into your compressor and turbine housings. PERFORMANCE RESULTS AND COMPARISON TO STOCK A stock STI from factory is rated at 300hp at the crank. On a Mustang dyno, a stock STI on pump gas makes right around 220-225whp. On a Dynojet, which reads 10% higher than a Mustang dyno, a stock STI makes right around 250whp. An FBO STI on pump gas on a Mustang dyno makes right around 270-280whp. That’s right around 300-310whp on a Dynojet. An FBO STI on ethanol on a Mustang dyno makes right around 300-310whp. That’s right around 340-350whp on a Dynojet My G25-500 upgrade consistently makes 340-360whp on a Mustang dyno on pump gas. The lowest I have seen was 338whp and that was a 2019 STI at 19psi on pump with stock TMIC, stock turbo inlet pipe, and 100% stock header/up-pipe. Just basically my upgraded VF48, AEM340 fuel pump, ID1050x injectors, and a tune. The highest I have seen was 362whp at 20psi on pump gas on a 2012 WRX with a new OEM RA shortblock, stock D25 heads, HKS header, no-name up-pipe, full exhaust, and Perrin FMIC kit. On e85, my G25-500 upgrade consistently makes 390-400whp on a Mustang dyno. Lowest I have seen was 389whp on a 2006 STI with a new RA shortblock, stock heads, 100% stock header/up-pipe, stock TMIC, and turbo-back exhaust. Due to the restrictive stock header, it took 23psi to make that power. The highest I have seen so far was that same 2012 WRX that made 362whp on pump. That car made 404whp and 421 lb-ft on e50 at just 20psi while still being internally gated AND using an OEM wastegate actuator. I have a few people using my G25-500 upgrade on track day cars with great success and this summer, my upgrade was allowed to be used in SCCA Rallycross.

[@shiloh5199]

Good topic and good video.

[@traviscea]

Thanks for watching!

[@IcySTi]

I cannot wait to see the results of this. The results after your tune is updated will determine whether or not I go to single scroll/ewg or not.

[@traviscea]

@@IcySTi Hopefully will have the results next weekend. Will be installing this weekend and have to run out the E85 and work with the tuner

[@WRBWRXWGN]

Very interesting. Keep us posted on your results. I have a Ver 8 motor and VF36 that might need this.

[@traviscea]

Vf36 is like a ball bearing vf37 right? Pretty rare and only came on the spec c IIRC

[@josephhicks1091]

I loved my twin scroll vf37 ej20x. Made 380 hp and 320 torque on e85. I now have a 2.5l sti with a large old garrett and the driving experience is different. I am slow as all hell until i hit 3500 - 4000. Made 360 on 91 and it feels arguably faster because of the crazy jolt of power istead of linear power band. Small twin was better driving experience but bigger single on 2.5 is more fun :)

[@traviscea]

@@josephhicks1091 Now imagine the vf37 on 91 with the same power as the Garrett but none of the lag...that's this mod. I'll be installing it hopefully in the next week or so, then get it tuned and post a video on the results.

[@josephhicks1091]

@traviscea if you have a 2l it's great. Usdm cars its just not worth the money when you can get a blouche 1.5g2r and perform better for less

[@josephhicks1091]

@traviscea BTW I also get anc 91 fuel so you kind of have to go e for power here. I'm excited to see how it performs

[@traviscea]

@@josephhicks1091 I was looking at the blouch for the past couple years. It's 2k$ and I don't plan on going over 400whp. This is 500$, and works on any VF series turbo, vf39, 48, 52, etc and will net you over 400, or at or just below conservatively on E.

[@josephhicks1091]

@traviscea yeah that will be a really fun car! And you're absolutely right it gets way more expensive when you want to go for higher. I have to redo my whole fuel system and will probably be 4k into upgrades including tune. I got lucky and picked up a 2.5xtr for $800

[@bigo3902000]

I have a 03 wrx on flex and im running 22psi all the way to redline. Engine is ej205. Its been 15k since i tuned my car and its been solid. Now i want more power 😂. But going to keep as is for longevity

[@traviscea]

@@bigo3902000 What turbo is holding 22 to redline?

[@orlandovillela3029]

Yes , on a 2021 vf48. @traviscea

[@traviscea]

Granted Im reving out to 8k in my ej207, but how the hell is your vf48 holding 22psi to redline? It would be working so hard and just be extremely hot air at that point.

[@orlandovillela3029]

@traviscea not sure honestly, could be the 18+ sti i believe have a bigger hot side.

[@Imprezach]

Same I’m on a stock usdm 205 on E with a vf48 in my gc pushing 360 whp at 20ish psi. Ethanol makes a huge difference

[@IcySTi]

Also, please do an install video anyways❤😂

[@traviscea]

I may show a little of the install. Showing the turbos side by side, how to prime, etc.

[@carnagefpv8256]

Ive been talking to PRE a little bit. Kind of torn. I have a Dom 1.5 in hand right now, and am trying to decide which way to go. I have 3 options. Run the dom 1.5 as is, send my stock turbo to him for the g25 combo, or send the Dom to him for a g series upgrade that he hasnt tested yet. So tough to decide what to do! I really just want ~375whp on pump.

[@traviscea]

@@carnagefpv8256 375 on pump will be easiest probably with the 1.5. The G25 VF will get around 360 on pump. G25'ing the blouch would be the most expensive option and I don't think it would be worth it. Personally, I think 350 on pump and 400 on E is the most you should really shoot for.

[@worstleesinplays4379]

From what I have heard the blouche turbos are already essentially the g line of garrett turbos.... this would mean changing the blouche would be pointless

[@traviscea]

@worstleesinplays4379 Correct. This mod is in lieu of, not in addition to. You save 2k$ and get close to the same power.

[@Pavel_Engines]

@@worstleesinplays4379 There is nothing about Blouch turbos that is remotely similar to the Garrett G-series. Blouch turbos are based on the Garrett GT/GTX-series of ball-bearing turbos. Blouch used to buy genuine Garrett cartridges and install theur billet compressor wheel. I don't know when this changed, but rebuild Blouch turbos going back to 2017, they were already Garrett-copies using all aftermarket parts. This does not mean it is better or worse than genuine Garrett, but rather, an observation. For the Dom1.5, Blouch has a custom 71mm billet compressor wheel made in Malaysia and the turbine shaft is an Asian copy of the Garrett GT29 that is readily available on eBay from a lot of vendors. The Dom1.5 is equivalent size-wise to a GT2971R. The GT29 turbine from Garrett was never great. Garrett took a very efficient GT30 NS111 turbine and cut it down from 60mm inducer/55 exducer size to 56.5mm inducer.52mm exducer. This reduction in size also killed turbine efficiency. There is a reason Garrett discontinued the GT2971R and GTX2971R line of turbos. What I proposed as an upgrade for the Dom1.5 is a custom compressor wheel which is based on the G30-660 and fits as a direct replacement into the compressor housing without modification. To complement the compressor wheel which will flow just about 60lbs/min, use a custom 'hybrid turbine shaft' that has the straight shaft portion like the GT/GTX turbos, but the blade rotor design and shape like the G30. This effectively would make it a cartridge similar to a G30-600 stuffed inside the Dom1.5 housings. I already have there custom comp wheels as I use them to upgrade the GT2871R turbos for the Nissan community as this is still a very popular turbo on the SR20DET and KA24DE engines.

[@michaelfreeman9275]

What kind of dyno are you using? It's just the compressor wheel swap?

[@traviscea]

@michaelfreeman9275 I am tuned opensource via ShinjiTuning. Using virtualDyno for HP and a dragy for 1/4 mile times. For this mod specifically, I will dragy 40-70 and 40-80 to show the actual real world gains as well. It makes around 345-350hp right now on E85. Pavel Racing engines does the compressor wheel AND the turbine from a G25 550. Plus cleaning, balancing, and ceramic coating for 500. A compressor wheel alone will not give you much in the way of power.

[@miguellopez7694]

Well Well Well...

[@traviscea]

@@miguellopez7694 Watch the video...I have my reasons lol

[@anthonyvazquez5366]

What turbo should i buy for this. I am currently running vf39. Im going to build a 2.1 stroker with 4032 piston, forged rods, springs, valves, shimless buckets. Just trying to build a oem+ Ej205

[@traviscea]

@@anthonyvazquez5366 Any VF will work. The vf39 will make 400 on E85 with this upgrade

[@anthonyvazquez5366]

​@traviscea So all I need than is a g25 550 compressor wheel and have it custom fit at a machine shop.

[@traviscea]

@@anthonyvazquez5366 I would just ship the entire turbo to Pavel. That's what I did.

[@Pavel_Engines]

@@anthonyvazquez5366 My upgrade service consists of a custom billet compressor wheel AND a custom turbine shaft with the G25 blade rotor profile. Just doing the compressor wheel is not effective. The stock turbine shaft is the restriction in the system. My G25-500 upgrade service is compatible wth all journal-bearing STI IHI turbos: VF30, VF35, VF37, VF39, VF41, VF43, VF48, VF49, VF52

[@jeff666p]

how much power you got now?

[@traviscea]

@@jeff666p I say in the video. About 350 on E85 and 310 on pump