http://forums.stlmustangs.com/index.php?showtopic=39904 look at this. crazy......

 

The current trend of twin turbo diesel V8s is actually compound turbo charging. The smaller turbos actually feed the bigger turbos, so if one turbo makes 15psi, and it feeds it into the second turbo, then the result is somewhere around 40-50 psi. at the manifold. The new 6.4 Ford diesel is actually pushing 70psi at full boost, and Banks Engineeringhas tested a roadrace diesel truck with over 150psi!!! I've never heard of a Duramax with 6 turbos, but I have seen pics of a dual compound setup (4 turbos total) that made 100psi at the manifold and over 1500lb ft. of torque!!!

Compound turbocharging a gas motor would be almost pointless though. You'd get to the point that there is not enough ignition retard to prevent detonation (I'm not talking about just pinging either).

In order to sequentially turbocharge a "V" motor, you would have to collect ALL of the exhaust and then feed it from one turbo to the next, AND come up with a way to prevent backflowing into the smaller turbo under boost. I don't think there is that much room under the hood of an S4.

 

It looks like the turbos feed the supercharger, The Subie motors can only hold about 25psi max, so I think that is EXTREME OVERKILL, as the turbos probably make that at 2000rpms so the BV's would be going crazy before 3k rev's.

 

no they aren't feeding the sc at all. I did some more research into it. this does seem like over kill to me. but they have a kit with a sc and turbo together that is suppose to put up really good numbers. the sc is for low end boost and the turbo for for high end boost to keep it from flattening out.

 

due to the fact of advancing dual ball bearing turbo technology that reduces lag signifigantly since the old journal bearing turbos were the norm. that's just one reason..

but k04's take a long time to boost for you? that is one of the dumbest things i've heard about turbo lag to date. have you ever even been in a k04'dcar?

a sequetial setup will not get you what you are looking for. what you are looking for is a 6.0L V12 out of a ferrari. no lag, and pulls til redline. but i doubt you'll fit that in the B5 engine bay

anyways, why are you trying to reinvent the already perfect wheel? there are plenty of options out there for a variety of power out of your S4. from 500hp k04 setup, to a 900hp GT28RS setup.. k04 cars have no lag and pull till redine. and with a fully built head and block, you can have a dual GT28RS car pull from 3000rpms to 9000rpms, put down 650Awhp, and run 10s full weight.. that'll cost ya about $20,000

but if you wanted to do a sequential setup, it's going to cost you probably $25,000 minimum, including internals... and it's going to be a long project with results that wont be worth it.. or you can spend $6,000 for a stg3 setup and you'll have more power than you'll ever need for the streets