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Old 04-15-2017, 05:55 PM   #1
dahoseman
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Default Supercharged STI?

I'm curious if any one has seen a purely supercharged STI? Specifically, using the TVS2 chargers? It seems like it would be an interesting and fun build, if nothing else.

Given that the latest generation TVS2 chargers are practically like magic for efficiency and power, I'm curious to see how a supercharged EJ257/255 would perform. I've been looking around and haven't seen one yet. Has anyone seen one?

I'm mulling over my next project and considering what sort of "tinkering project" I might get into for an older STI. After seeing the magic of TVS2 chargers on other vehicles and how they have essentially resolved all of the previous negatives associated with older (and other) supercharger designs, I'm considering deleting the turbo aspect altogether and simply running one of these chargers.

For anyone not familiar with the TVS2 chargers, the rotors were designed by Eaton and licensed out to a variety of manufacturers to insert into proprietary housings from each company. The summary of the improvement is that they have an internal and external compression effect, hold consistent boost at much higher rpm, consume less parasitic crank power at a given rpm, increase total power (outside of decreased parasitism) at a given rpm, produce significantly less heat on boost, flow significantly higher lbs/min per revolution, have a much wider efficiency range than previous designs, have higher rpm capabilities, weight less, and are fairly quiet.

Bullet Points:
-Series lineup averages >70% thermal efficiency (up to 76% in some applications)
-20% higher engine power compared to “roots” type
-12% less parasitic loss at same flow
-10 - 16% improvement in isentropic efficiency
-25% lighter (reduced inertia) compared to the previous generation
-High pressure seals that can withstand pressurized environments and reduce pumping loss
-Low speed airflow has been improved by >30% and enables increased torque at low engine speed
-New ball bearing system that enables temporary speeds up to 30,000rpm
-Compression is cool/efficient enough that an intercooler is not completely necessary
-Decreased noise and vibration characteristics
-And .... what I care about most, no lag and no spool .... power on tap at all RPM from idle to redline.

Obviously, I'm pretty enamored with these things. I'm also a bit of an 'old man' in that I couldn't stand the whine of superchargers on street cars (the scream of lost energy).
These are pretty slick, but I'd like to see if anyone else has volunteered as mechanical guinea pig.
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Old 04-15-2017, 06:11 PM   #2
GlarryHoodDIT
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I think most people prefer making power with lots of boost, I would think by 15lbs that SC is out of efficiency on a 2-2.5l motor.
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Old 04-16-2017, 09:18 AM   #3
industrial
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Super chargers can push serious CFM. Just pressure alone doesn't mean anything. It's like the difference between a td04 @20psi vs a GT35 @20psi...vastly different.

OP: Nope, never seen one. Not for the EJ or FA20F. It's one of those things someone might do just to do it but I really don't see the point. I had a supercharged FA20 which I think had a much better power band than my turbocharged FA20. It was a rotrex so not super high tech but it pulled from 4000-7300rpm like nobodies business. Made [email protected] (350whp). It was sweet when everything was working but with any car that custom, I spent just as much time chasing down demons as I did just driving it. I like my protuned FBO wrx better, I just get in and drive.
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Old 04-16-2017, 09:56 AM   #4
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^^Good to know thank you.
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Old 04-16-2017, 07:00 PM   #5
dahoseman
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Quote:
Originally Posted by GlarryHoodDIT View Post
I think most people prefer making power with lots of boost, I would think by 15lbs that SC is out of efficiency on a 2-2.5l motor.
That is exactly why the TVS2's are so awesome. 30PSI ..... No problem.
You're thinking of other designs and older designs. They're even significantly better than the original TVS1 design, which is better in nearly every way than other chargers.
They also are available in various sizes .... and are used on LS2 engines.


Quote:
Originally Posted by industrial View Post
Super chargers can push serious CFM. Just pressure alone doesn't mean anything. It's like the difference between a td04 @20psi vs a GT35 @20psi...vastly different.

OP: Nope, never seen one. Not for the EJ or FA20F. It's one of those things someone might do just to do it but I really don't see the point. I had a supercharged FA20 which I think had a much better power band than my turbocharged FA20. It was a rotrex so not super high tech but it pulled from 4000-7300rpm like nobodies business. Made [email protected] (350whp). It was sweet when everything was working but with any car that custom, I spent just as much time chasing down demons as I did just driving it. I like my protuned FBO wrx better, I just get in and drive.
To be fair, the FA20, by itself, wasn't designed as a boosted engine (The WRX and BRZ engines are not the same). They hold power well, but the engine and management wasn't designed to deal with it. The EJ25X's are designed from the factory for boost and management. I'm sure tuning would be a bit unusual, but not insurmountable.

The Rotex is a very different design from these .... and heavily parasitic. The TVS2's are practically like magic. Check them out. Seriously. They're WAY more efficent than nearly all the other supercharger designs and can actually beat the efficiency of a turbo in some applications, and without lag/spool issues, which is pretty awesome. Despite what everyone loves to regurgitate about turbos , they are not "free energy" (not even in theory). They're great for increasing specific power output, though, which is why we all love them.
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Old 04-17-2017, 12:11 AM   #6
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There was a member here years back that was building old supercharged legacy wagons. I think his board name was reddevil.
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Old 04-17-2017, 12:45 PM   #7
Techie Will
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I've seen some twin-charged set ups in the past laying down a ton of power. Also looks like there's a red 2015+ STi running around with a supercharger as well.

Not sure how much efficiency they're getting going off the beaten path like that, as I'm assuming that is a lot of custom fab work.
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Old 04-17-2017, 02:01 PM   #8
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Quote:
Originally Posted by Techie Will View Post
I've seen some twin-charged set ups in the past laying down a ton of power. Also looks like there's a red 2015+ STi running around with a supercharger as well.

Not sure how much efficiency they're getting going off the beaten path like that, as I'm assuming that is a lot of custom fab work.
I've seen a few of the twin-charged cars also. It seems like all the Subarus that I've seen use the old school "roots type" blowers on twin-charge. Cool setups and lots of area under the curve. The roots blowers are OK, but they have some downsides.

The twin-charge was my original project that I was shooting for, to get the torque curve to look more like a coffee table than a rock climbing project. After doing more research on the various charging options, I started to reconsider. The various types of superchargers are surprisingly different and have wildly differing efficiencies. The TVS2 design is relatively new and just better all around.

I will definitely be doing some fab work. That's part of the fun of a mechanical project for me, within reason. I was going to have a larger turbo force-feeding a supercharger for compounding re-compression. However, considering how efficient the TVS2's are, I'm thinking of just going purely supercharged and leaving most of the stock secondary control systems in their place to simplify tuning.
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Old 04-17-2017, 07:16 PM   #9
industrial
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Quote:
Originally Posted by dahoseman View Post
To be fair, the FA20, by itself, wasn't designed as a boosted engine (The WRX and BRZ engines are not the same). They hold power well, but the engine and management wasn't designed to deal with it. The EJ25X's are designed from the factory for boost and management. I'm sure tuning would be a bit unusual, but not insurmountable.

The Rotex is a very different design from these .... and heavily parasitic. The TVS2's are practically like magic. Check them out. Seriously. They're WAY more efficent than nearly all the other supercharger designs and can actually beat the efficiency of a turbo in some applications, and without lag/spool issues, which is pretty awesome. Despite what everyone loves to regurgitate about turbos , they are not "free energy" (not even in theory). They're great for increasing specific power output, though, which is why we all love them.
Eh you don't have to tell me that the FA20 wasn't designed for boost. It still takes it extremely well and the dual injection setup and heads are better than the FA20F. The demons I was chasing down were mostly from aftermarket fuel components not working as advertised and the supercharger kit not working as advertised. The engine itself was fine taking boost and the ecutek development on the platform was pretty comprehensive. Any car you more than double the horsepower is going to have its issues. That's more of what I'm getting at.

TVS2 sounds great but are you really going to take a STI with a EJ2xx, remove the turbo and design a custom TVS intake manifold, fuel delivery, and tuning to make pretty much stock power? I personally think the future is in electric turbos. There was some development in the BRZ/FRS world and it looked promising. It would probably be great in a sequential charge setup. Either way, that's a whole lot of custom work.
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Old 04-17-2017, 10:54 PM   #10
dahoseman
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Quote:
Originally Posted by industrial View Post
Eh you don't have to tell me that the FA20 wasn't designed for boost. It still takes it extremely well and the dual injection setup and heads are better than the FA20F. The demons I was chasing down were mostly from aftermarket fuel components not working as advertised and the supercharger kit not working as advertised. The engine itself was fine taking boost and the ecutek development on the platform was pretty comprehensive. Any car you more than double the horsepower is going to have its issues. That's more of what I'm getting at.

TVS2 sounds great but are you really going to take a STI with a EJ2xx, remove the turbo and design a custom TVS intake manifold, fuel delivery, and tuning to make pretty much stock power? I personally think the future is in electric turbos. There was some development in the BRZ/FRS world and it looked promising. It would probably be great in a sequential charge setup. Either way, that's a whole lot of custom work.
Yeah, the FA20, in either form, is a much more solid design than the EJ. I'm still crossing fingers for a FA25 for an STI in the future. If they had DIT and port fuelling, that would be icing on the cake.

My project would be on a wrecked car or one with a grenaded motor. I wasn't planning on doing a "complete" fab for the supercharger setup, which is why I'm considering that option now. That's one of the reasons why I would go with it. All of the necessary hardware is already in place, to some degree. If I did the twin-charge, then I would need to design a custom manifold and heavier intercooling ..... or be lazy and buy/modify one of the pricey BRZ charger manifolds (preferably Harrop) ..... which are obnoxiously expensive. Those kits also use the "older" style TVS1's, which significantly decreases the benefit. On a side note, I've built and welded a number of other projects before and I can never understand why those kits are so damn expensive, considering I have made my own kits and accomplished essentially the same thing at 1/5 the cost. The last supercharger (M62) I got was actually a giveaway.

http://www.moto-east.com/store/harro...6-brz-frs.html

I did some measurements and I would "potentially" do the alternator relocation kit, and extend then pulley-snout so that the supercharger sits under-and-recessed below/behind a WRX/LGT-style manifold. The extruded nylon manifolds have a surprising amount of room underneath and the TVS2's are suprisingly compact. I would just route the intake around the manifold (like a rotated setup) to the supercharger, then a short piping setup through either a stock-location TMIC or FMIC. Nothing terribly fancy. No fancy fuel systems needed in either case. Even if I fabbed up a custom manifold, I would use a stock-ish manifold as a base and weld everything up to stock-type runner pedestals to avoid making it more complicated.

I'm not sure where I gave the impression I was looking for stock power because I would definitely bump it up. I figure I can calculate some flow and, if need be, "titrate" the rotor speed (pulley) to a power/PSI/Boost level of around ~350 WHP. Nothing terribly crazy. I mostly want a more even torque curve ..... for a variety of reasons. The compound setup is still a consideration, but we'll see. It would be really cool to have multiplied boost, though that pretty much automatically requires meth-injection, a custom manifold, FMIC, and a "fully" built motor.

I agree on the electric turbos or just electric-assist. I think that electric-assisted turbos are going to become more common at some point. They use an electric motor/charger to maintain boost pressure at low RPM (essentially driving it like a centrifugal supercharger) and then draw/recharge at higher speeds. They have been around for quite a while, but there just wasn't money or any incentive to develop them until more recently.
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Old 04-18-2017, 09:54 AM   #11
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Quote:
Originally Posted by dahoseman View Post
-And .... what I care about most, no lag and no spool .... power on tap at all RPM from idle to redline.
That's the beauty of a compressor
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Old 07-28-2020, 10:34 AM   #12
Loki6
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Default Compound Supercharger

There is a company Forced Air Tech (FAT) in Phoenix, Arizona. The owner made a 2007 compound supercharger/turbo set up. https://dsportmag.com/the-cars/super...ubaru-wrx-sti/ It has been my dream to do this to my 07 STi
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