So... I've been learning about turbos and anti-lag systems recently, and it got me wondering about how to get a big turbo to spin faster without the thermal stresses of conventional anti-lag systems. What if you used a smaller turbo to power the bigger turbo? You connect the engine exhaust to the small turbo, then you connect the boost pressure pipe of the smaller turbo to the bigger turbo, and then you combine both exhaust output and boost pressure pipes from the bigger turbo since they will both contain boost pressure, and feed it back into the engine for the power. I'm guessing it would end up being less powerful than a conventional twin turbo setup, but I am curious whether or not this is the case, and at the very least whether this would work or not.
Would imagine a sequential turbo setup to be more efficient, though the principle is somewhat similar.
Anything involving inline turbos like your little one feeds the big one idea is already an exotic setup and probably unnecessary but cool none the less.
If your smaller turbo was ever making more boost than the larger one (and it would have to at some point) you would experience the same issues as running a turbo with out a blow-off valve/recirc valve, only more severe and at an even less ideal time. The high pressure air re-merging with the low pressure air from the large turbo would experiance less resistance going backwards than into the motor, and it would try to motor the large turbo in the wrong direction. Lag would be magnified on the larger turbo and it could potentially even have an audible flutter on hard acceleration. You would almost certainly have a much higher backpressure at the valves, more exhaust restriction in general, and the inefficiencies of the turbos would be exaggerated. Cool idea, but I don't see it being superior to any other turbo implementation.
Sequential turbos work very well, for example the 6.4 PS diesel came from factory with a sequential turbo setup. The atmosphere turbo is the first turbo and the (biggest) (spools first for low end power) then, air flows to the VGT (high pressure) (variable geometry turbo) (smaller turbo) (top end) air is compressed even further then enters the CAC (charge air cooler, aka intercooler) cools the charge air off then enters the intake manifold. (Simple way to put it) Factory turbo specs Atmosphere (large turbo) 65mm high pressure (VGT) (small turbo) 57mm This helps the 6.4 reach 600-625 RWHP, with a simple tuner, CAI and exhaust. Pros spools quick strong bottom and top end power lower egts Cons High ebp (exhaust back pressure) 52 psi boost/7x ebp psi higher cylinder pressure takes up more room in the engine bay/ harder to work on. etc etc
I could be misreading the OP or you (or both I guess...), but I don't think that is quite what he was talking about. That setup that you described seemed to have both turbos spun by exhaust on the hot side, and the smaller turbo fed its compressed air into the intake inducer of the larger turbo, thus "double compressing the air". I guess you could call it a compound sequential turbo. I think OP was describing a system where the smaller turbo receives all of the exhaust, and its output air is used to spin up the hot side of the bigger turbo. Therefore, the big turbo has boost flowing past both wheels, and both turbos suck in their air right through a pod filter. The output from both wheels of the big turbo is Y'd together and pumped into the engine, while the small turbo functions normally. Here's an extremely crude paint image I threw together of the system described in the OP.
Sorry, once I seen "sequential" I thought of posting, going by your post I know exactly what kind of system you are talking about.
No worries , I clicked on this thread with the same thought and barely stopped myself to fully read the OP. It's an interesting idea, but I think it's one of many ideas that fall victim to the death phrase of ingenuity: "If it worked, we'd be doing it".
...What about if to reduce turbo lag you don't use turbos at all and instead use superchargers driven by a separate engine so the engine doesn't waste power driving the supercharger but still has no turbo lag? Obviously it would be big heavy, terrible for millage, reliability, and would probably be really complex for little to no advantages but otherwise it seems like it could work and probably make more power than a normal turbo or superchargers(assuming that an engine could handle so much air being shoved into it.)
