Twincharging is using a turbocharger and a supercharger on the same engine.
It is not a twin-turbo system and not a sequential turbo system either. In twincharging, either the output of the TURBOcharger feeds the input of a SUPERcharger (hks) or the output of a SUPERcharger feeds the input of a TURBOcharger. It is sequential and both stages can add boost under different circumstances.
When Twincharging, one of the first things to decide is whether to have air go from the Turbo to the Supercharger, or Supercharger to Turbo. HKS had a kit on the market for a Turbocharger into Supercharger setup. It is no longer available, but was reported to be good for 300 horsepower. Also I beleive that the price of the kit was approx. $6000 US. I work for a living, and I don't think that all three of my cars combined are worth $6000, so I won't be looking for an HK$ twincharging kit for this project.
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When I decided to twincharge my engine, I thought that adding pressurized air to the supercharger would blow the supercharger rotor seals out. Not the lobe seals but the seals on the 'axle' that the rotor spins on. Not wanting to break an expensive supercharger, I elected to have the supercharger blow air into the turbocharger. Also in my favor was the fact that I will be using a turbocharger from a '79 mercury capri (Ford turbo coupe, Mustang SVO) It's turbine (exhaust) inlet and outlet both point down, so it would easily fit on the intake side of the engine with the exhaust pipes crossing under the engine. I have tried to put this turbo on every Toyota I've owned in the last ten years and have never had enough room on the exhaust side of the engine for a 'u' turn in the exhaust pipe to lead back up to the turbo. But, on the 4AGZE, I can route the exhaust under the engine to the intake side, so having the inlet and outlet both pointing down will work. Also, on the 4AGZE, there is a large open area behind the supercharger and underneath the intake manifold to mount the turbo. :) The output of the supercharger blows rearward to where the turbo is mounted. So, Yes with a simple mounting bracket, it will physically fit on the engine, But, will it work?
The turbo came with an 'H' trim compressor with an a/r of .60 and an 'L' trim turbine with an a/r of .48 . I even have a compressor map HERE. All those numbers mean that it has enough airflow for about 300 hp. On the 2.3 liter Ford, it made 8psi of boost at 2000 rpm. Rough calculations suggest that a 1.6 liter engine would have the same airflow at 2900 rpm. Hmmm, 8 psi at 2900 rpm.... Works for me! The turbo was mounted downstream of the carburator on the Ford, this means that the compressor side can tolerate manifold vacuum without leaking oil into the intake manifold.
So about using this Ford-garrett to-3
1: It will make boost by 2900 rpm
2: It has enough airflow for 300hp
3: It can work under manifold vacuum without leaking oil.
4: Most important..I actually HAVE one.
Once the parts placement has been decided, the fabrication begins. The supercharger output pipe was shortened by about 3 inches to blow into a fabricated small black manifold that bolts to the face of the turbo. Also feeding this manifold is a large copper one-way valve from a hardware store... A WHAT? OK, think about this: The supercharger is good for about 8 psi of boost. That's great for low rpm torque and great throttle response, but at high rpm, when the turbo is at full speed, the turbo will be flowing so much air, it will DECREASE the output pressure of the supercharger by sucking air from its output. There will be plenty of air FLOW, but the supercharger will not be able to keep PRESSURE in its output manifold. I think that the turbo will move so much more air than the supercharger that it will create a vacuum at the supercharger's output. What? a vacuum? at the inlet of the turbo? This is obviously NOT a good thing...
Since the supercharger is a positive displacement device (a pump), it puts out a specific amount of air at a specific rpm, no matter if the output is under pressure or a vacuum (of course I'm ignoring leakage because it's small). When the turbo's airflow intake exceeds the supercharger's airflow output, the turbo could be starving for air!
Twincharger under vacuum , - low rpm , - high rpm
To fix this, my options are,
1: Disengage the supercharger's clutch after the turbo spools up and let the turbo over-rev the supercharger by sucking air through it and making it spin faster than engine rpm...(probably a bad thing...)
2: Open the bypass valve to let air around the supercharger ( great idea, except I think it's too small to make a significant difference)
3: Add an auxilliary air intake to the turbo inlet manifold.
I have added an auxilliary air intake system. An auxilliary air intake system can work only if the air that is introduced goes through the AFM (AirFlow Meter) and throttle body, And if air cannot pass from the supercharger back to the throttle body through the auxilliary system otherwise supercharger boost is lost. Thus, the one-way valve is needed. The one-way valve gets its air from a one-inch spacer under the throttle plate.
The engine photo shows the one-way valve. above it (and slightly misaligned) is the spacer under the throttle body, below and to the right is the turbo inlet manifold. You can also see the supercharger output pipe.
That about covers the twincharging part of the project, as for all the other stuff you'll need to do this to your car, click on the Engine swap guide Good Luck!
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