A new thought for twins - Compound Turbos? Maybe?

[dudemaaan]

Originally Posted by RotaryProphet

The beauty of my setup is that the control box for the turbos is a separate box, and doesn't rely on the stock ECU; you just input your max pressures and allow it to go about it's business.

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.

Originally Posted by RotaryProphet

No, as long as the pressures are equal, both turbo outlets will flow freely; if one produces more pressure than the other, the reed valve on the outlet will close, preventing backflow.

I see. Pressure not flow. Even though one turbo is flowing more air, becuase the pressures are equal at the outlet, they work together and not against each other. Mazda did this with the 20B turbo's actually. One was a Hitachi HT-10 while the other was a Hitachi HT-15.

Originally Posted by RotaryProphet

If you were using a system with more secondary turbo boost than the primary, it would probably be worth using another valve to redirect air from the primary turbo outlet into the turbo inlets, basically making a loop so that the turbo keeps spinning instead of stalling out against a closed valve.

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.

Originally Posted by RotaryProphet

Plumbing the turbos like that isn't likely to gain you anything. The thing to remember is that a turbo is a pressure differentially operated pump. In short, it relies on the difference in pressure between the inlet and the outlet on the hot side to spin the turbine.

So, you have to run your small turbocharger first, or else the exhaust, which can freely flow through the larger turbo, gets backed up against the smaller one, which means there's no pressure differential on the larger one. Because the smaller turbo must come first, the net effect is that once the exhaust runs through the small turbo, you have the difference in pressure between the primary turbo outlet and the secondary turbo outlet to extract useful energy from; far less than there exists in the manifold. Certainly there is energy there, but you'll find your larger turbo takes much longer to spool than it would in a single turbo configuration, which necessitates a larger primary turbo, which raises your boost threshold.

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.

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.

Originally Posted by RotaryProphet

Your concept would certainly work, and I believe your system of wastegates would work perfectly, too, I just don't know what the performance would be like. I would be curious to see it in action, though.

Now, running sequential twins is an option, but it requires two reasonably small turbos. I feel a small and then a somewhat larger turbo will give better top end performance, but again, I'd be very interested to run the dyno numbers on a twin sequential setup with properly sized turbos and a good manifold.

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. I believe that twin GT28's of some trim size will net 450 RWHP if not slightly higher. Jason's setup did 450 or there abouts, and the BNR turbo's are regularily getting close to this mark as well. It's my belief that the restriction in the BNR's lies in the factory manifold. As far as I know, I'm the only one on stock twins that can actually tell you what the EMAP is. Most people just look at it and say it's a nightmare. In reality it's not horrible. It's certainly not on par with a tubular mani and a large A/R turbine housing, but that's not an apples to apples comparision. I believe if we can get the EMAP down in the higher RPM's power and effiecency will increase. Negating the need for a larger pair of turbo's or a larger secondary turbo to get to say 450 rwhp. MOST people would argue that this is a waste of time for such a small power gain, but in terms of NET hp and the intended use, I certainly think it is.

Originally Posted by RotaryProphet

I don't know where you're at in the country, but if you're anywhere near Cincinnati, I've got my engine dyno at the shop setup to test and tune rotaries, and I'm just a bit of fabrication work away from testing my setup. I'll be testing on a stock RE motor, with stock intake and upgraded injectors, and a water to air intercooler for consistency. That way I can test several turbo setups and map them against each other in an apples to apples comparison. It'd always help to have another brain when the time comes to do it.

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.

[TitaniumTT]

Originally Posted by RotaryProphet

The beauty of my setup is that the control box for the turbos is a separate box, and doesn't rely on the stock ECU; you just input your max pressures and allow it to go about it's business.

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.

Originally Posted by RotaryProphet

No, as long as the pressures are equal, both turbo outlets will flow freely; if one produces more pressure than the other, the reed valve on the outlet will close, preventing backflow.

I see. Pressure not flow. Even though one turbo is flowing more air, becuase the pressures are equal at the outlet, they work together and not against each other. Mazda did this with the 20B turbo's actually. One was a Hitachi HT-10 while the other was a Hitachi HT-15.

Originally Posted by RotaryProphet

If you were using a system with more secondary turbo boost than the primary, it would probably be worth using another valve to redirect air from the primary turbo outlet into the turbo inlets, basically making a loop so that the turbo keeps spinning instead of stalling out against a closed valve.

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.

Originally Posted by RotaryProphet

Plumbing the turbos like that isn't likely to gain you anything. The thing to remember is that a turbo is a pressure differentially operated pump. In short, it relies on the difference in pressure between the inlet and the outlet on the hot side to spin the turbine.

So, you have to run your small turbocharger first, or else the exhaust, which can freely flow through the larger turbo, gets backed up against the smaller one, which means there's no pressure differential on the larger one. Because the smaller turbo must come first, the net effect is that once the exhaust runs through the small turbo, you have the difference in pressure between the primary turbo outlet and the secondary turbo outlet to extract useful energy from; far less than there exists in the manifold. Certainly there is energy there, but you'll find your larger turbo takes much longer to spool than it would in a single turbo configuration, which necessitates a larger primary turbo, which raises your boost threshold.

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.

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.

Originally Posted by RotaryProphet

Your concept would certainly work, and I believe your system of wastegates would work perfectly, too, I just don't know what the performance would be like. I would be curious to see it in action, though.

Now, running sequential twins is an option, but it requires two reasonably small turbos. I feel a small and then a somewhat larger turbo will give better top end performance, but again, I'd be very interested to run the dyno numbers on a twin sequential setup with properly sized turbos and a good manifold.

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. I believe that twin GT28's of some trim size will net 450 RWHP if not slightly higher. Jason's setup did 450 or there abouts, and the BNR turbo's are regularily getting close to this mark as well. It's my belief that the restriction in the BNR's lies in the factory manifold. As far as I know, I'm the only one on stock twins that can actually tell you what the EMAP is. Most people just look at it and say it's a nightmare. In reality it's not horrible. It's certainly not on par with a tubular mani and a large A/R turbine housing, but that's not an apples to apples comparision. I believe if we can get the EMAP down in the higher RPM's power and effiecency will increase. Negating the need for a larger pair of turbo's or a larger secondary turbo to get to say 450 rwhp. MOST people would argue that this is a waste of time for such a small power gain, but in terms of NET hp and the intended use, I certainly think it is.

Originally Posted by RotaryProphet

I don't know where you're at in the country, but if you're anywhere near Cincinnati, I've got my engine dyno at the shop setup to test and tune rotaries, and I'm just a bit of fabrication work away from testing my setup. I'll be testing on a stock RE motor, with stock intake and upgraded injectors, and a water to air intercooler for consistency. That way I can test several turbo setups and map them against each other in an apples to apples comparison. It'd always help to have another brain when the time comes to do it.

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.