Well, it looks like I have run into a little bad luck. I made a modification to my one-way valve. The flapper did not always line up perfectly with the sealing surface inside the valve. Sometimes I would get 8psi from the supercharger, sometimes 6psi, sometimes 4psi and then it would jump to 8psi etc... I was losing air thru my 1-way valve. To fix it,I installed a small copper shim to help it line up better. The shim worked fine, boost was consistent at 8psi every time. But the shim, that was soldered to the flap, broke away from the flap, worked its way off of the flapper's pivot shaft (the shaft was about 1/8 inch too short) and found its way into the turbo. It destroyed the compressor wheel, and wedged itself in the compressor housing, thereby stopping the turbo from spinning. I guess it's good that it stopped there... It could have caused damage to a piston and the exhaust turbine if it had gone thru the engine.
So I pulled the engine out to remove the turbo, and took the opportunity to snap some pictures at the same time. I will try to explain the whole setup of how I twincharged this engine.
Refer to this picture and diagram often...
Air enters the big blue air filter and travels to the throttle plate right past the elbow there on top. When the throttle plate closes, everything is in a vacuum, the turbo, the supercharger, the intercooler, everything. The turbocharger came with a special carbon seal installed in the compressor side of the turbine shaft. This allows the turbo shaft to spin, and keep oil out of the compressor housing even when it is in a vacuum. This is a very old turbo (1979 !!) designed to work downstream of a carburator, so it has to be able to work in a vacuum without spilling oil into the intake. Right below the throttle plate there is a hollow spacer plate that is there to add extra air to the turbo... but I'm getting ahead of myself. When the throttle is opened, air goes thru the spacer and continues down into the supercharger. The supercharger blows air into a small manifold that bolts to the front of the turbo. The air is blown thru the turbo (whether it is spinning or not.. doesn't matter) and then forward thru the black pipe to the front mounted intercooler. The intercooler returns the cooled air thru the top metal pipe to the intake manifold, fuel is added at this point, near the intake valves, then air is finally in the the cylinders.
Idle
After the air/fuel mixture has been burned, it exits the engine thru a full sized 4-2-1 or Tri-Y header. After the header's collector, it takes a U-turn under the transmission and heads forward to the turbo. The air spins the turbine, then goes under the transmission again, to the catalytic convertor and muffler.
Now that the turbo is spinning, things change. Let me digress here for a moment. A supercharger is a positive displacement device. Every 1 revolution of the input shaft results in 1200cc of air moving thru the supercharger. This is great if you are pumping air into an engine. Just remember that the volume of air per revolution is fixed, not changeable, constant. The turbo on the other hand, can give a different amount of air per revolution depending on how fast it is spinning, and what the pressure ratio across the compressor is. It is NOT a positive displacement device, and air flows freely thru the turbo even when it is not spinning. I assumed this to be true when I put this engine together and I had the opportunity to prove it when a small piece of copper wedged itself in my compressor wheel and kept it from spinning. The car still performed well despite the turbo not spinning at all. Aside from the complete lack of boost, there was only a small vacuum present in the intake manifold at full throttle and high RPM. (1-2 psi). Let's get back to the setup. The supercharger is pumping a fixed volume of air at any specific engine speed. The turbo is set up for about 14 psi of boost. The supercharger gives me 8 psi. It is clear that the turbo will need to move a higher volume of air to obtain the 14 psi of boost. As the turbo begins to spool up, the turbo will pull air out of the supercharger output pipe. This 'unloads' the supercharger, because it's output is being sucked away by the turbo. Eventually the supercharger is freewheeling, because there is only ambient air pressure in the supercharger's output pipe. At this point, the supercharger is producing almost no drag on the engine and the turbo is supplying all 8 psi of boost. The turbo continues to spool on its way to 14 psi and will create a vacuum at the supercharger's output. The supercharger is unable to flow more air to the turbo because of that whole 'positive displacement','fixed','constant' situation. It works both ways, you get 1200cc/rev no less, no more. So to help this situation, I have outfitted the setup with an auxilliary air supply that I kinda breezer over in the first section. I'll explain it now. There is a 1-inch spacer under the throttle body that connects to that blue silicon hose you see in the pictures. It goes to a hardware store variety 1 1/4 inch one-way flapper valve, then an elbow into the supercharger output/turbo inlet manifold. This way when the turbo needs more air than the supercharger is providing, the air comes from the hollow spacer plate, thru the one-way valve and into the turbo manifold. That way the turbo gets all the air it needs to continue spinning to 14 psi or hopefully even more! The one-way valve is there to keep supercharger-only boost from being blown back to the throttle plate and being lost.
This is the interesting side.... If you look very closely, you'll see the output of the supercharger going rearward to the turbocharger, the large copper one-way valve sucks air from a spacer underneath the throttle plates when the turbo is spooled and requires more air than the supercharger is putting out. (Did you see the diagrams?) Idle , Low rpm and High Rpm.
Photos of the individual pieces of the twincharger setup are on the TWINCHARGING PAGE
Click here for the engine swap guide
So, Do ya think I'm NUTS yet? Twincharger@hotmail.com