[RotaryProphet]

Originally Posted by TitaniumTT

Very nice little system. I lack the electronic knowledge to be able to do this. I wouldn't be using the stock ECU though, I would be using a Motec which has enough inputs/outputs and software to allow me to do this.

Actually, I was hoping to start producing the manifolds, packaged with the control box and the valves. Just pick your turbos, and have a shop make a downpipe.

Originally Posted by TitaniumTT

That's interesting. That's more of a compound sequential system though if I'm reading it properly. That would give very quick spool fom the smaller turbo, but then when the valve re-directs the smaller turbo's boost from the the intack to the larger turbo, boost would rize VERY quickly. Again, this is assuming we are vizualizing the same thing.

I don't think we are. In the situation where that valve would open, the larger turbo is already creating -more- boost than the smaller; the only point here is to allow the smaller turbo to keep spinning and flowing air to somewhere, so that it doesn't stall and stop spinning; it's basically useful to keep the turbo spinning during gear changes and things like that, when you drop back down to the smaller turbo for a short period. Same concept as a blow-off valve; by letting it vent, the turbo doesn't slow down.

Originally Posted by TitaniumTT

I think we're looking for two different goals which is why our systems are slightly different. I'm looking for a total of about 450RWHP and 360ish torque. Not all that much from two turbo's when singles are getting that fairly regularily now. I'm more interested in creating the flattest torque curve possible and extending it as far throughout the rpm's as possible. I BELIEVE you are looking for more power which is why you're using not only bigger turbo's, but slightly different sizes as well. Please correct me if I'm wrong.

No, I think we're looking for basically the same thing. My goal would be to imitate the FD's stock boost curve, except with higher boost levels, and eliminating that transition dip. By bringing the secondary turbo online slowly instead of all at once, I think that's possible.

Originally Posted by TitaniumTT

Regarding my manifold setup - One of the things that concerns me, is as you put it, the smaller turbo acting as a plug in the system. Leaving the second turbo with much less energy to spool up to the same level as the first. I'm worried that the extra distance traveled, the less heat available, is going to lead to a secondary turbo that just cannot keep up with the first. The main reason for thinking about not only the very large traditional WG on the primary turbo's mani, but also an internal gate as well.

The theory of putting one turbine behind another, and having every bit of exhaust flow through both is a sound one... in theory. Once the exhaust leaves the turbo, there's still energy to be extracted, but less so. But here's what I see happening:

To control boost and turbine speed on the primary, you want to put a big wastegate on the manifold, and maybe internally gate the turbo, as well. The problem is that by venting all that pressure past the turbo into the inlet of the secondary, then at higher RPMs, where there's a lot of exhaust, you've eliminated the pressure differential between the inlet and the outlet of the primary; the pressure coming in is the same as the pressure going out, thanks to the big wastegate opening a valve between the two in an effort to keep boost under control. The wastegate will stay open instead of closing, though, because it's linked to system boost, not individual turbo boost. Eventually, because there's very little pressure differential to run it, inlet pressure from the second turbo will begin flowing out of the primary's inlet.

Originally Posted by TitaniumTT

I agree that a different sized setup like the one you are building will net larger gains in the top end. With auto-x and track days and street driving being the primary role of this car, I'm more concerned with the low and midrange performance of the system.

You can get a flat boost curve with a pair of smallish twins, or with a small turbo and a moderately big turbo; either way should work about as well. The small turbo should flow enough air to make up the difference while a bigger turbo spools, it's just a matter of it working alone for longer. As long as the turbos aren't too far apart, it doesn't matter.

The question is, why leave performance on the table when you can get the same results, get the same outstanding low end response and torque when you can -also- get a higher top end? My system would work either way, but it seems silly to leave power when it's there. At very least, you could use a larger turbo, tune for high boost, and use the control box to bring it down when it's unwanted.

And here's something else to consider; in a setup like this, the larger turbo spools much -much- faster, due to the simple fact that the engine is already running under boost while spooling it. A 13b under 15psi of boost is exhaling as much exhaust as a 5.0 liter NA boinger, but with a much more favorable exhaust arrangement, in terms of exhaust pulses, and manifold setup. The primary turbo, being spooled already, is only using at small chunk of that exhaust energy, and the rest is generally wasted via a properly named wastegate.

Originally Posted by TitaniumTT

I live in the SW corner of CT, about 1/2 hr from the city. Honestly though, I would love to come out, see the setup, see the results, and lend my brain to the project. It's probably about a 10 hr drive out which I'd be more than willing to make. I'll check some airfares as well. Please keep me in mind when the time comes, I'd love to see it in action and be a part of it.

I'll let you know, and we'll try some stuff and see what happens.