[SteveR]

Well, the first thing would be that the turbo would be taking hot exhaust gas and forcing it into a supercharger that will be using that hot gas to mix with cold fuel and compressing it. One of the keys to making more power is a cool dense charge. With too much boost on the turbo the first thing would be an uneven a/f ratio. The second would be the fact that you'd have to run two seperate intercoolers, the first for the turbo beeing of massive size and the second for the charger, neither of which would even fit in a Miata and if by some miracle you DID get them to fit, you've just added a ton of weight. The next obsticle would be the fact that a turbo and a charger have way different peak rpms. The turbo can spin much higher than the charger. If my thinking is correct, you'd have to run a small fast spooling turbo to get low end power but the charger will peak out around 5600 anyway. With the size and weight of a Miata you don't need that kind of low end TQ, the car won't be able to put it down effectively so you'd in effect be running a turbo for no reason other than to add weight, increase the intake charge temp, and completely make a mess out of your power curve. A big factor is what type of charger he wants to run. A roots is out of the question, peak rpm is too low. Centrifugal maybe, but the point still remains, why feed a supercharger hot gas that will have a varying temp and density/pressure? Think about it, turbos have a power band that ramps up over time with boost pressure changing. A charger has to be set up for a certain a/f mix and with that kind of air change, you'd probably have to have a computer actively adjusting fuel flow, hence, more weight. Miata's are small, light weight cars. What you probalby don't want is gobs of low-end TQ. I'd say throw a decent turbo on it and be done with it.