I've been musing about draw-thru turbo carb setups...one of the biggest obstacles seems to be the following issue: Under a full boost/ WOT situation, when the throttle plates (on the carb) are closed, you end up with a vacuum between the carburetor and the turbo. This vacuum can suck the oil out of the turbo, turning your hot turboed creation into a mosquito killing smoke machine. The solution everyone on teh webs seems to agree on is carbon seals in the turbo, to prevent oil sucking into the intake charge stream.
However, carbon seals can fail, and not every turbo has them. So, I had an idea: what if you were to move the throttle plate from the carburetor to between the turbo and the engine? Or, possibly, run two synchronized throttle plates- one at the carb, one between the turbo and the engine? Thoughts on such a setup?
When the blades are between the engine and the turbo, they ARE in the carb, do you mean upstream of the turbo? It works with superchargers, they have carbs on top. Maybe the easy solution is to put the whole carb upstream of the turbo.
On a draw-through setup, you have, in this order: Air cleaner, carb (with throttle blades), turbo, intake manifold, engine. So the throttle blades would be between the carb and the turbo. This creates a vacuum when the blades are shut at W.O.T/ full boost, which sucks oil out of the turbo. I'm trying to figure out, basically, how to eliminate this potential vacuum, rather than simply trying to seal against it.
On a blow-through system, the blades are between the carb and the engine, but the turbo is upstream. A fuel injected setup would typically use this sort of setup, too.
Why not just switch to blow-through instead? Draw-through w/ carb is the worst possible turbo configuration IMO.
I would keep it simple. A carb wouldn't work right with the throttle body part separate from the main body. Not sure if two throttle bodies like you said would be a good idea. When the engine is at idle the turbo see vacuum as well. As long as the turbo seals are in good shape, you shouldn't have any leaking problems. Especially if you consider how much oil pressure is on the other side, a bit of vacuum shouldn't make a difference.
Maybe consider going with a blow-thru setup instead of a draw-thru.
There is absolutely no reason to have a draw-through turbo setup at all.
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