[TitaniumTT]

Originally Posted by RotaryProphet

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.

That would make it VERY easy to sell, I like that idea. I generally don't like piggy-back systems, mainly for aux injection type situations it scares me. Your idea though controls everything related to ONE part of the system which I don't see a problem with.

Originally Posted by RotaryProphet

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.

I agree, especially in a situation where we're looking for the best response from a turbo, keeping as much energy in the system is critical. I also believe that the EMAP plays a huge role in the torque curve as well. So in a situation where the EMAP is on the rise, the torque will fall off. Eliminating a spike in EMAP by keeping the turbo spinning would further increase low end torque.

Originally Posted by RotaryProphet

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.

I think with standard valves and what not, it'll be difficult. That's the problem that we ran into on the dyno on Tuesday. We would either see a dip, or a surge. We were logging the boost that the secondary was creating in the space between the compressor outlet and the Charge Control Valve so we knew what the turbo was producing. I adjusted the RPM resoltion down to 50 rpm increments around the transition and it was still difficult to get a smooth transition. I think your REED valve idea is going to be the only way to bring the secondary online smoothly. Looking at the datalogs we were able to get the transition dip down to .15s. Its VERY slight, but it's still there. I'm still working on the transition on the street and it's definately getting better.

Originally Posted by RotaryProphet

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.

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.

That's the reason that I'm thinking that two turbos of close to the same size would be a better choice than one small and one large unless the larger one is run first - to take advantage of the pressure differential. It's my belief that the smaller turbo would need less of a pressure differential to create some CFM to add to the larger turbo.

What I would like to try is a pair of very similarly sized turbo's collecting both runners exhaust right at the point where they would split off in a Y - one going to the primary turbo, the other to a LARGE WG. I would like to take advantage of the energy post WG-before being sucked up by a turbine. This would be routed directly to the bottom of the flange on the secondary.
Going back to your point of the lack of a pressure differential on the primary, I'm not sure if the exhaust of the primary should be routed around the secondaries turbine, or to it. I think there is response lost if it's routed around it. However, maybe the thing to do is use a slightly larger A/R on the primary to let it breath a little better.

Originally Posted by RotaryProphet

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.

I agree it's silly to leave performance when it's there. But I am more focused on a flat torque/boost curve than higher HP. This is just based on my experience with my FC. Over 300ft/lbs, the suspension/tires really can't handle it. I may feel differently when I get a set of A6's, or get on a track where my RA1's can get up to temp. But right now, the higher end performance is wasted becuase I simply can't put it down. Now with the ability to put a 10.5" wheel and bigger tires behind an FD, and given the better suspension geometry associated with the FD, I may feel differently. That's why my goals are 450RWHP, and 360ish ft/lbs.

Originally Posted by RotaryProphet

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.

Agreed, which is why I'm torn between routing the exhaust of the primary to the bumper, or to the secondary turbo

Originally Posted by RotaryProphet

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

Please do. I'd love to get a first hand look at what's going on, what works and what doesn't