My compound turbo set-up

[94awdcoupe]

No I can make 500whp or 700whp at various backpressures above or below 50psi. It's called turbine matching. An evo3 16g turbine itself flows enough mass for 500whp. A 44mm gate even with a 90* turn added to that is plenty. I've already explained how the 16g 44mm gate will be wide open for anything after the desired boost is reached, you know later in the rpms, when the motor is developing 550whp.

When the 60-1 (2nd gate) opens, that doesn't mean the first one closes. It's set to open at 10-11psi, whatever resulting volume flow is neccesary to get the 60-1 spooling faster. When the 2nd gate opens, backpressure in both turbine housings go down. Yep, the 16g slows in rpms, but who cares the 60-1 is maintaining the boost. Afterall, it's already spooled enough to open the 2nd gate. As well, the 16g doesn't increase in spool speed or take any more energy from the exhaust once its wastegate opens (1st gate). It looses energy transfer very quickly, since the state of the gases upstream of the 16g turbine equalize to the state of the gases down stream of the 16g turbine. Where there is no temp change there's no work done. Eventually the 16g compressor/turbine/shaft is free wheeling. It's done it's job. The 60-1 is on boost.

This is incorrect. here are some pictures to clear it up for you. as I said earlier wastegates do not work to control back pressure. These are pictures of how a 11psi actuator works. I hope we can all agree that external wastegates function the same as internal actuator. 10 psi yields closed wastegate. 11psi wastegate starts to open. but barely. at 14psi it is clearly open but still not by much. it takes a full 20psi before its fully open.

This is because wastegates have a spring in them. as the spring is compressed with boost it takes more boost to open it farther and farther.

so your statemnet that the wastegate will be wide open at boost is not correct. it only goes wide open during momentary over boost.

Lets say you have a 15psi gate. at 14psi the gate will not be open. at 15psi it will be barely open. just enough really to bleed enough exhaust to control the boost at 15psi. the wastegate isnt fully open for max flow till you see 25psi at the cannister. problem is you are trying to run 15psi boost. so it will never be open that far except for momentary boost spikes.

mow what happens when you run 30psi on a 15psi spring? same thing really at 29psi the wastegate will not be open. doesnt open till 30psi. and it wont be fully open till the boost is at 45psi since the wastegate is now being "fooled" by bleeding pressure off.

This is the same reason a larger 60mm gate wont flow more than a 44mm gate. The valve on 60mm will simply be closer to its seat than with the 44mm gate. This is why larger better flowing waste gates control spikes better. they flow better only during spikes when the valve flys open during over boost.

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[dsm-onster]

Wow that was a big waste of electrons. Nevermind the energy you spent to set that up. You could have helped a poor ricer recirculate his BOV. The 44mm 16g gate will be wide open because it is tied into the manifold pressure that will be over 30psi. The 16g gate spring is set to control boost at 11psi when fed volume flow under no more pressure than ambient (it begins to open long before that BTW). It will keep exhaust flow moving to the 16g turbine until that threshold is seen. After that, it is opening enough to maintain that. As the 60-1 is taking over, the pressure from the increasing boost that the 60-1 compressor is doing the work to accomplish is pushing the 16g gate open more and more. . . I've already explained this.

The 16g gate is only set for 11psi. At what pressure did your little experiment yield a wide open gate when said gate was set at 15psi?

BTW, I think the 90* internal gate on that diesel compound kit professionally designed and proven in the very first picture Paul posted in this thread must be a big epic fail. Never gonna flow enough

 

[99gst_racer]

So all the bickering aside, any news on the progress?

Nope. Upon mock up with the compressor cross-pipe, I found that my stock lower radiator hose will also be in the way. So I pulled it all out and it's getting more -16 bungs welded on tonight. And I can't fully install the turbos until the radiator is in place.

And I'm taking a day off from the garage today.

I should have more progress to share this coming weekend.

 

[99gst_racer]

BTW, I think the 90* internal gate on that diesel compound kit professionally designed and proven in the very first picture Paul posted in this thread must be a big epic fail. Never gonna flow enough

I was thinking the same thing. They really should re-design internal and external wastegate design across the board. These things are never going to work with any 90* directional flow passages...

 

[talon187]

dead sexy! nice fab skills hope it works out good for you

 

[bling5tatus]

DSM-Onster, did you consider that the compound setups in the diesel trucks are using VGTs and extremely large turbos that aren't going to choke because one is not significantly larger than the other? I would say Paul's major problem is going to be the a/r of the smaller turbo choking the flow of the larger one, wastegate open or not. I am fairly certain that's what 94awd was trying to tell you.

 

[TofastForU_99]

I saw this car in person along with the build... great setup and I can't wait to see it done ....

 

[dsm-onster]

DSM-Onster, did you consider that the compound setups in the diesel trucks are using VGTs and extremely large turbos that aren't going to choke because one is not significantly larger than the other? I would say Paul's major problem is going to be the a/r of the smaller turbo choking the flow of the larger one, wastegate open or not. I am fairly certain that's what 94awd was trying to tell you.

Btw, don't bother insulting me because i'll flag your posts. Be a man and an adult when replying since you have that "wiseman" status under your name, set the good example.

Thanx for the lecture. But I've already explained why I got on this gentleman's case. Actually, unlike the rest of the crowd of which he's initially, directly insulted and called names; I think he's bright enough to catch on and has a good mind to contribute. But I'll not stand by and let the ones with the bad attitudes and closed minds deficate their negativity in these forums. I'm proud to display the example of one who takes offense to direct name calling and assanine, condescending, "you fail" attitiudes that are rampant everywhere else. And I'll stand up every time. There's a difference in using an accurate adjective to describe someone's actions vs. direct name calling and otherwise smartass closemindedness that went no where. Insulting someone because they disagree with you begets a similar response.

We all know what 94awdcoupe was trying to tell US. And we all know how he initially insulted. You've contributed positively here in the past; it won't bother me at all standing up to you if you act the same as he. Flag that

Now moving on. . .

The original setup Paul gave a picture of has noticeable difference in a/r of the turbine housing. As well, so do the setups commonly used. I.E., the cummins diesel guys commonly use the internally gated hx35 (52lb/min turbo at common ambient conditions) with the hx60 or hx80 frame sizes (126lb/min-200lb/min at common ambient conditions) as the primary. BTW, the hx35 has a tiny turbine housing for a twinscroll setup. Each pulse is seeing about the same critical area as a 6cm^2 14b turbine housing.

Further, housing size can be deceiving. What wheels are used in that first picture shown? A td04 6cm^2 starquest turbine flows much less than a td05h 14b 6cm^2 T/E/L turbine. Just food for thought.

 

[bling5tatus]

Ok, I guess I'd be interested in knowing what is the limiting factor, is it the hot or the cold side of the smaller turbo... and why? How can this be over come?

It seems to me that once there's an assload of exhaust being pushed by the motor because of the large turbo creating boost... it still has to go through the small turbo's hot side/wg setup before it can even get to the large turbo's hot side....
so the small turbo's hot side and wg would theoretically have to flow enough exhaust to "outflow" the large turbo's turbine housing for the wg to even be needed on the larger turbo
otherwise the small housing on the small turbo is going to limit the boost strictly on the size of it not allowing enough exhuast through to properly keep the larger turbo spooled.

Or is that all jacked up somehow that I'm not realizing? I've talked to quite a few people about this and they all seem to be on the same page about that. I'm not looking for a debate, just enlightenment.

 

[SpeedAddict62]

I think the first one in that pictures DOES have a wastegate. Correct me if I'm wrong, but it looks like the turbine housing sticks out quite a bit on the outlet side, and you can see a "box" where the wastegate should be, and it would exhausting into the side of the pipe, not exactly like we are used to. Also, the top of the wastegate actuator on the compressor side is another clue.

I would think the small turbo would be placed first, because it also spools the fastest. Once it starts flowing more air, that would also start spooling the second turbo up. An interesting concept, I want to see what happens in practice though.

 

[RipperXX]

I think everyone is waiting to see what happens once it is fired up. I know I sure am!

 

[99gst_racer]

Ok, I guess I'd be interested in knowing what is the limiting factor, is it the hot or the cold side of the smaller turbo... and why? How can this be over come?

In a perfectly designed and constructed compound turbo set-up, the compressors are the limiting factor. They are limited to their peak PR's. This basically applies to any turbo set-up.

On my particular set-up, my exhaust would probably pose a restriction before I could ever max out both compressors (not that my engine would take that abuse anyway). But that's just my theory. I don't, however, feel that the exhaust sections will pose a restriction for my goal of flowing 60 lbs/min. But I won't know for sure until the car is drivable.

It seems to me that once there's an assload of exhaust being pushed by the motor because of the large turbo creating boost... it still has to go through the small turbo's hot side/wg setup before it can even get to the large turbo's hot side.... So the small turbo's hot side and wg would theoretically have to flow enough exhaust to "outflow" the large turbo's turbine housing for the wg to even be needed on the larger turbo

Yes, this is true.

otherwise the small housing on the small turbo is going to limit the boost strictly on the size of it not allowing enough exhuast through to properly keep the larger turbo spooled.

On my set-up, I wouldn't doubt that the exhaust will be it's limiting factor to how much boost can be created. But I honestly don't think that restriction will show it's face until after 50+ psi. Then again, that's just my theory.

 

[dsm-onster]

Here's what I was taught. . .

Once the gate of the first turbo opens (set to a lower boost that the gate for the second turbo), the exhaust gases bypass the turbine of the first turbo. It will open all the way since only 10-15psi is required by the first turbo to get the second turbo seeing enough volume draw to spool it faster than with just the motor alone. As I mentioned, the gate of the first opens more and more as the second turbo starts to take over. The boost is maintained because as the first gate is opening more mass flow is entering the exhaust stream to counter it, massflow from the higher flowing larger turbo.

There is plenty of energy to power the larger turbine. Run an externally gated turbo with the gate flopping open and you get zero boost. The turbo is taking very little energy from the exhaust evident from zero boost. SOME energy is being taken, yes. With a compound setup, the backpressure of each turbine is about equal once the first gate is wide open. The turbines then take energy from the exhaust in proportion to their size. The second gate is there to keep in check the amount of energy BOTH turbines convert.

Now, as the motor demands more from the compressors, there is more exhaust mass to keep the boost up, just like in a single turbo configuration. Why? The second compressor compresses the air again to fit more in the motor; this draws more air from the first, larger compressor. The larger compressor draws more air from atmosphere. More flow into the larger compressor means that more mass will be in the exhaust to spin both turbos. The higher the compounding effect, the earlier there is more exhaust mass to spin both turbines. The 16g compressor requires no more energy to recompress the air, increase volume flow, than the exhaust gas mass increase that results from the increased volume flow. Thus, every compressor stage, as long as it has a turbine stage that can extract energy from the exhaust, will increase enough flow to sustain itself and more to do other work like increase the thrust load or compress the air for a gas motor or click.

This is called jet turbine staging. The stages all have 'wide open wastegates' since axial flow turbines take less energy from flow at lower flows. Gases flow around the blades until pressure is built up sufficiently. Since radial flow turbines take more energy at lower flows (keeps the flow in the turbine wheel longer to do work), there has to be gating.

. . .So the 16g compressor multiplying the pressure further causes the volume flow demand from the 60-1 compressor to increase, just like if the stroke of the motor were increased. This causes there to be much more mass flow in the exhaust gases, just like an increase in stroke. More gases to work with means more gases to power both turbines and a compressor always inputs much more mass than a turbine needs to do work to the compressor (assuming decent compressor efficiency), so the rest of that energy makes the compressors spool faster until gates open. Feedback is feedback, no matter how many stages. The compressor always nets a flow increase (as long as it's in it's efficiency range) that will yield far more energy than required to keep it spinning. Meanwhile you see a a higher manifold pressure (denser aircharge) earlier for the gas motor to do work with.

 

[99gst_racer]

I have some real honest to God questions about this picture.

Wouldn't that over rev the first turbo since there is no gate? It would seem to me that in order for #2 turbo to do work, it would need exhaust, and it would have to go through #1 ... so that is a really disturbing picture for me ?

I'm not sure how "complete" that set-up is in that picture. The smaller turbo looks like it has an internal wastegate (or at least parts of one), but I don't see a gate on the larger turbo. For total boost control, each turbo will need a wastegate.

That picture is really only good for displaying the routing of exhaust gases and the compressed air charge.

Is there really anymore useable exhaust to drive a second turbine when the 1st turbo's turbine absorbs the brunt of the kinetic energy ?

Yes, definitely. Especially knowing that one 44mm wastegate is re-directing a large amount of that energy around the first turbine. And the unused energy from the 16g's turbine will be used in the 60-1's turbine as well.

If so, is there some kind of minimum distance required for the exhaust to reshape itself back into a steady stream ?

I cannot answer this. I'm far from being a fluid dynamics genius, so I wouldn't even know where to begin to calculate an answer to that question. I'd be interested to learn more about this though.

Why is it always smaller to larger ? Wouldn't you want the larger turbo absorbing the strongest exhaust first and letting the smaller have 'left-overs' ?

The smaller turbo is the primary. It is what helps build boost sooner (because it it's small size), so it's placed first in the exhaust stream. If the larger turbo was first in the exhaust stream, it would defeat the purpose of trying to build boost quicker than the larger turbo is capable of on it's own.

 

[bling5tatus]

Well I am interested to see how it all works out when it's complete, just as many others are.

I think the first one in that pictures DOES have a wastegate. Correct me if I'm wrong, but it looks like the turbine housing sticks out quite a bit on the outlet side, and you can see a "box" where the wastegate should be, and it would exhausting into the side of the pipe, not exactly like we are used to. Also, the top of the wastegate actuator on the compressor side is another clue.

I would think the small turbo would be placed first, because it also spools the fastest. Once it starts flowing more air, that would also start spooling the second turbo up. An interesting concept, I want to see what happens in practice though.

It looks like that first turbo on the exhaust route is a VGT to be honest, I'm thinking that's what that box is... and if that's the case then it wouldn't need a wastegate....

 

[dsm-onster]

Well that is an understandable assumption. But, Aero Salle proved that a VGT is not enough to control the boost when running on a gasoline application. At least in the range that his operated in (I think about 6cm^2 to 22cm^2 ). There's just too much heat that can do too much work. He had to gate his he351VGT, even though it was hanging off his 2.0L 4g63. He has a build thread on here if you're interested. We gassers have much more energy in the exhaust to work with than the diesel guys who run this form of charging.

 

[99gst_racer]

So I guess my next question is, where do you believe turbo #2 will get most of its energy from, post exducer from #1 or from unused exhaust from #1 wastegate? Just from pictures of your piping I'm going to assume you think it is from exducer since you have some decent piping size in comparison to the gates themselves?

I'm not sure which path will yield the most usable energy for the 60-1's turbine. I'm just relying on the sum of the two to be enough.

 

[94awdcoupe]

I talked to a turbo shop friend of mine to confirm some thoughts I had on why this compound might not work. The problem still surrounds the first turbo. If the first waste gate doesnt work to control boost of first turbo, then you have no turbine speed control of the 16g. Since the 44mm gate on the 16g is wide open under boost you might get too much flow through the waste gate or not enough . you have no way to adjust flow between the turbine and the waste gate flow. . The only boost control you have is with the second waste gate. When that gate opens it controls the flow of entire system. The amount of flow over each turbine will be a ratio. The two turbines will be spinning up simultaneously with no way to adjust flow bias between the two.

It seems to me a third waste gate will be needed to control the turbine speed of 16g independent of the second turbine. Do you think maybe you should have left internal waste gate on the 16g since the first 44mm gate is not actually functioning as a waste gate?

I am pretty much drawing same conclusion hakcenter is hitting on.

 

[RipperXX]

99, are you going to take detailed air temp logs at multiple points?

 

[spoonman]

Why is there no one running this type of set up in import (even domestic) drag racing, Le Mans, Indy? Class restrictions? The only motor sport that I think of is tractor pulling.

I have been talking to a few engineers that I work with on my second job, who have a tractor pulling team, they racing in unlimited tractor with dual Allison v-12 engines with four pairs of compound turbochargers on each engine. They have calculated that by using the four sets of compound turbo that they are flowing 37% more air than when they were only running the four larger turbos. The pressure in the exhaust manifold was higher due to more restriction from the smaller turbo and elaborate new exhaust system but the difference was not exceptionally bad. The boost pressure was kept at the same level they were running before but the turbos where still flowing more air, then they raised the boost pressure intill both turbos were in a good efficency islands, which resulted in the 37% more flow and slightly lower IAT. The larger turbos are Borge Warner that where from semi engines and the smaller turbos are Garret GT35R's. They have over $175,000 in two tractors, just to pull a sled a couple hundred feet.

 

[99gst_racer]

Well in an event good luck with the setup.

With your fab skills you may end up revising that manifold setup, you probably have enough space to add another wastegate infront of the 16g incase you find out that is where your trafficing the most energy to the 60-1.

Thanks. There's actually no more room for another large wastegate. It's pretty tight for space as it is. I would need to redesign everything to get another gate in the mix. Not that I'm apposed to the idea of building a tubular manifold and improving the overall design a bit.

Last question here for awhile, how will you be able to measure the performance/load/work either turbo is doing ? Combined is pretty obvious, just wondering how to measure one of them singly.

The only thing I plan to measure is their respective outputs in PSI. I just want to make sure neither turbo is creeping.

99, are you going to take detailed air temp logs at multiple points?

Not right away. Right now the car has an air temp probe a few inches before the TB, but that's it. Eventually, when I'm ready to entertain the idea of an air-to-water intercooler or meth injection, I'll have to spend some time figuring air temps at different points.

A few of the guys on the Link boards did the math to figure efficiencies and charge temps at different points, but it would be nice to have real world data to back up their math.

 

[99gst_racer]

Why is there no one running this type of set up in import (even domestic) drag racing, Le Mans, Indy? Class restrictions? The only motor sport that I think of is tractor pulling.

Yup, class restrictions. Kiggly designed a nice compound set-up on paper about 8 years ago, but never was able to build and run it due to the class restrictions for the sanctioned body he was racing with back then.

When I was at SEMA 5 years ago, there was a rear-engine dragster on display. It hosted a cummins deisel engine and a sick looking pair of compounded turbos. They said it was the first of it's kind for a dragster. I can't remember what they said it ran though.

Another member on this site is currently building a late 80's Thunderbird with a 2.3L engine and they are going to be running two very large two in a compound set-up. Shooting for 8's, IIRC.

Like I said, it's not a mainstream idea yet, but it's popularity will grow as soon as the word spreads about the success of running something like this on a gasoline engine.

 

[aero_sallee]

Can't wait to see how this works. It would be very interesting to see the primary turbo in a setup like this as a VGT/VNT turbo. It seems like it would be an ideal marriage.

 

[evileclipse909]

I wanna see update pics! And quit arguing. He'll find out if it works by trial and error. No need to bicker over a posible future error. Just try it and find out.

 

[99gst_racer]

Paul does that mean, there isn't really a way to measure individual work each turbo is doing ?

Would it be possible to tap a map sensor/boost gauge between #1 and #2, to see what #1 is doing, then subtract the total from that to see individual ?

No, I'll be able to measure the work of each turbo my using two boost gauges (already mentioned this somewhere in this thread). I already have them in the dash. One will measure at the outlet of the 60-1 and the other will measure manifold pressure. And yes, I will have to do a bit of math to figure the 16g's individual output, but it's pretty simple stuff.


94awdcoupe - Quit posting about how things WILL work and problems that WILL occur. You're passing your theory off as fact and it's rather annoying. Unless you can show me how YOU'VE done this before and how it worked out for YOU.