Compound Charging

[derekf]

There was a Lancia rally car in the late 80s that was both super- and turbo-charged. If memory serves, there was an RPM where the intake changed over from the SC to the TC.

A google search found some info:
(from http://www.carsfromitaly.com/lancia/deltas4.html - you'll have to click the "Delta S4" link, their page redirects if it's outside its frames)

The unusual route of using a supercharger and turbocharger together was to avoid the poor performance of the large turbochargers at low engine speeds. On the S4 the order, from the air intake was turbocharger, intercooler, supercharger, intercooler, inlet manifold. Once the supercharger became less efficient, at higher engine speeds where the turbo performed better, a bypass allowed the turbo to feed the engine directly.

http://www.lanciaaustralia.com.au/pa...es/rallyhq.htm says

A special bypass valve cut out the supercharger after 5000 rpm. On gravel the two forced induction systems worked together up to those revs when the turbo took over. The benefit was the low rev torque by the supercharger assisted in removing the turbo lag which had made some developing turbo cars difficult to drive.

[Blown353]

well I know some diesels use the compound charging, and u might be able to get more boost into the engine from it, and part of it is because I would like the challenge to do it

The diesels you are referring to are likely 2-stroke diesels (probably the detroit "V" series, they're quite common) and they NEED the positive displacement supercharger to function; they don't have a "normal" intake stroke to suck in the air and need to have the air shoved in-- thus they need boost all the time and that's where the positive displacement supercharger comes in.

The new Euro-market VW TDI's are using twincharging to help with the low end power and emissions. Some MR2's also used twincharging around '87. I remember Koenig offered a twincharged engine package for Ferrari Testarossa's back in the late 80's too. Lots of piston aircraft engines from the 30's/40's/50's used twincharging with intercoolers between each stage and also turbocompounding, but that's another thing entirely.

You could probably make your own by piecing together factory parts; use an electromagnetic supercharger clutch from a new 'Benz and run a servomotor or have a diaphram type actuator trigged by manifold pressure and controlled via a solenoid valve to actuate a bypass valve to transfer from the supercharger to the turbocharger based on engine speed/load.

Honestly, I think you would better spend your efforts adapting a VNT (variable nozzle turbine) turbo than spend time to make your own twincharged setup. VNT turbos if done right can have very good low end performanace will still having good top end. Unfortunately I don't know of any "aftermarket" VNT setup; you need a way to monitor engine load/speed and a backpressure sensor to control the VNT vanes, which are usually controlled via oil pressure and an electronic regulator. They're becoming quite common lately from OEMs; mainly on diesels but on gassers now too.

Troy