Im still looking into the details of exactly how to control the transition from supercharger to turbocharger on my nova if I compound charge it like I am planning to do.

I have come up with what a I think is a really simple solution to the problem, and I would like to be shot down in flames if I have missed something obvious as far better to find out now then after having done it.


I am planning on configuring the engine to work like so in terms of where the air goes:

Air filter
Supercharger
Turbo
Intercooler
Intake manifold

Now the supercharger will be setup to flow about 300bhp of Air (hoping to gear it for approx 10psi), but I need the turbo to be able to flow 500bhp of air, so the obvious problem with that setup is that once the turbo spools it will be restricted in flow by the supercharger and worse still what will happen I believe is that the pipework between the turbo and the supercharger will be driven into vacuum by the turbo pulling through more air than the supercharger wants to flow, which means that the pressure ratio the turbo is actually going to be working at could be massive, as if I end up with say 15psi (30 absolute) after the turbo but only 10psi of vacuum (5 absolute) before the turbo, then its a pressure ratio of 6 for example.

So the problem that I need to solve is a way to allow the turbo to breathe more air than the supercharger can flow at high rpm.

Im thinking that the simplest way to do this is to allow a huge airleak between the supercharger and the turbocharger in order to allow the turbo to breathe extra air in that hasnt been through the supercharger.
I realise that while the leak is active it means that the supercharge will no longer be doing anything useful and will just be a parasitic loss on the crank with no benefit, but thats fine as once the turbo is spooled the thing goes like hell anyway.

The idea that I have come up with is to use a twinport wastegate connected to the intake pipework between the supercharger and the turbo, with the connection to the pipework being the opening that is side on to the wastegate piston.

The idea being that when the wastegate is shut the boost from the supercharger will not pass the piston.

Then to control the opening of the wastegate I was going to plumb the top port into the intake pipework between the supercharger and the turbo (so it will measure pre-turbo pressure) and the port that is on the bottom of the wastegate into the pipework between the turbo and the engine (so it will measure post-turbo pressure).

This means that the wastegate will then open when there is a big pressure differential (determined by the spring, probably a bar or so) between the pressure before and after the turbo, ie only when the turbo is spooled.

I realise that a manufacturer would never do it this way, the charger would need de clutching and they'd typically need to recirc the air due to being air mass based mapping rather than speed density etc, so Im well aware that you wouldnt do it this way if you were making 100,000 of the car and hence had a massive development budget for a specific control ECU and electronic valves instead.

Can anyone spot any flaws in my logic there?
As it seems such a simple solution that I cant beleive I havent ever seen anyone else doing it as obviously there are people far cleverer than me who have implemented compound charged solutions!