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Re: Compound tubo charging

I'm actually in a thermodynamics class, and was last semester and we talked about this. The best way to optimize what you have is to reheat the exhaust gases after the first turbo to supply more drive power for the second one. On the compressor side, intercool the air between the two compressors and again after the second compressor. The relationships can be shown on a pressure vs. volume graph, work(power) is shown as area under a curve on this type of graph.
 

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Discussion Starter #22
Re: Compound tubo charging

LMAO, my luck it would. It should be fine though, it's still independantly boost regulated to only 27 psi. :) This is one reason I'm a fan of this boost control scheme, as opposed to setting the small turbo for total boost.
 

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Re: Compound tubo charging

I'm actually in a thermodynamics class, and was last semester and we talked about this. The best way to optimize what you have is to reheat the exhaust gases after the first turbo to supply more drive power for the second one.
No real need for that practically speaking. On big HP engines there is still plenty of energy left in the exhaust stream.
 

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Discussion Starter #24
Re: Compound tubo charging

And the fact that there is plenty of exhaust gas energy left is evidenced by my setup's ability to spool that big 1.32 t6 turbo at such a low rpm. Heating it would help of course, but it only loses a couple hundred degrees which doesn't seem too hurt much.
 

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Re: Compound tubo charging

Somebody may have already said this, but didn't the 93-95 RX-7's have compound turbos? I think they were only rated at 265hp, but from the driver's seat it felt like a TON more than that. I would think a rotary engine would be the ultimate application for compound turbos. They have basically NO torque, but they can RPM to the MOON! I would think compounds would cure all their ills.
 

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Re: Compound tubo charging

thanks for that explanation Kjewer1. putting it in idiot terms helped me, lol.

Somebody may have already said this, but didn't the 93-95 RX-7's have compound turbos? I think they were only rated at 265hp, but from the driver's seat it felt like a TON more than that. I would think a rotary engine would be the ultimate application for compound turbos. They have basically NO torque, but they can RPM to the MOON! I would think compounds would cure all their ills.
nooo there are enough of them at my local track already... beeeemp beeeeemp beeeemp beeeeemp beeeemp beeeeemp beeeemp beeeeemp beeeemp beeeeemp beeeemp beeeeemp weeeeeeeeeeeeeeeeeeeeeeeeeeeen BaCkFirE sputtter sputtter.
 

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Re: Compound tubo charging

thanks for that explanation Kjewer1. putting it in idiot terms helped me, lol.



nooo there are enough of them at my local track already... beeeemp beeeeemp beeeemp beeeeemp beeeemp beeeeemp beeeemp beeeeemp beeeemp beeeeemp beeeemp beeeeemp weeeeeeeeeeeeeeeeeeeeeeeeeeeen BaCkFirE sputtter sputtter.
lolololololololol!
 

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Re: Compound tubo charging

Very cool Kevin! You have me half tempted to try and build something for my beater. :) You need to get the hot side redone in stainless!
 

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Re: Compound tubo charging

Somebody may have already said this, but didn't the 93-95 RX-7's have compound turbos? I think they were only rated at 265hp, but from the driver's seat it felt like a TON more than that. I would think a rotary engine would be the ultimate application for compound turbos. They have basically NO torque, but they can RPM to the MOON! I would think compounds would cure all their ills.

Scott no.....the RX7 and the Supra were both sequential setups. I own both cars and can tell you its a pain. Most convert the systems to true twin mode.....eliminating the sequential aspect.
 

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Discussion Starter #31
Re: Compound tubo charging

Very cool Kevin! You have me half tempted to try and build something for my beater. :) You need to get the hot side redone in stainless!
Do it! I would have already redone this in stainless if I wasn't so lazy about it, and lacking in welding skills and equipment. :)


The power band on this setup is pretty sweet too. I can make 45 psi from ~5,000-10,000 rpm, which I definitely wouldn't be able to do with a 2 liter and a single big turbo. I hit ~10 psi at 3000 rpm. What's interesting is that leaving at 5800 rpm on a fuel cut 2 step the big turbo actually makes zero boost. Any time fuel cut engages the big turbo shuts off. Most likely due to losing the exhaust gas energy that comes with that fuel. The small turbo stays up at 30 psi. As soon as I release the trans brake/2 step, the big turbo shoots straight up to full boost. It looks pretty funny in the logs.
 

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Re: Compound tubo charging

Maybe, we'll see. I am pretty sure I'm going to put an EVO motor and tranny first though, just need to find the time. One of PTE's 5857's feeding a billet 76mm sounds freaking sweet though. :)
 

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Re: Compound tubo charging

What if a guy wanted a 1000-1200 hp 400 inch V8 and only needed 15-18 psi but wanted
it feel like a roots blower could it be possible with a compound setup?

It seems to me that this done for high boost pressure applications,
can it be done for fast spool and lower boost?
 

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Re: Compound tubo charging

I believe 1000-1200hp with a 400incher at 18psi is possible with a single turbo provided a decent head/cam setup, but compounding will allow an earlier spool and could be made more efficient.
 

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Discussion Starter #35
Re: Compound tubo charging

What if a guy wanted a 1000-1200 hp 400 inch V8 and only needed 15-18 psi but wanted
it feel like a roots blower could it be possible with a compound setup?
Sure, size the big turbo for the 1200 hp and size the small turbo based on what rpm you want it to spool. Then divy up the PRs accordingly.

It seems to me that this done for high boost pressure applications,
can it be done for fast spool and lower boost?
On diesels it's done for high boost, but even at 45 psi I'm only at medium boost for a gas motor. I do it for the exact reason you mention, fast spool. Or more accurately, low rpm spool.
 

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Re: Compound tubo charging

Great! I have 2 T3/T4’s 60-1 x stage 5 with .82 AR.
They worked good on my mild 355 but I fear they’re a bit on the small
side for the new motor.

But a 91-101 would more in line for it.

It would be a blast to drive with the spool of the T3/T4’s and the top end flow
of 101.

Do you control your manifold psi with the gate controlling the big turbo
or is it a combination of the two gates?
 

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Discussion Starter #37
Re: Compound tubo charging

There are a few ways you can control boost. What I think is working well is running the big turbo just regulating it's output pressure. The small turbo has manifold pressure to the side port, and add it's inlet pressure (=big turbo outlet pressure) to the top port. For example, I've got a 13 psi spring in the big turbo's gate, and a 28 psi spring in the small turbo's gate. The small turbo comes up and makes 28 psi, and then the big turbo starts to make boost and as it comes up it's output pressure is added to the small turbo's spring rate via the top port. Total boost ends up at 41 psi. It's additive in this configuration. What's nice is that the small turbo is never really asked to make more than 28 psi. As manifold pressure comes up to 41 psi, the small turbo's pressure ratio actually goes down. :) Then I just put an MBC on the big turbo and add say 4 psi to it to get up to 45 psi, etc. The trick is all in getting the pressure ratios where you want them.
 

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Re: Compound tubo charging

you have stolen my consept :)! (not 100% reddy yeat, in the dyno)

fun to se you try this system to.

sorry my spelling is bad (from sweden;))

if you like i can show som pic on my engine?

have you run the engine onley on the smal turbo ? dos it spool faster or slower?
 

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Discussion Starter #39
Re: Compound tubo charging

Nice! I would definitely like to see some pics of your setup. I ran it on the small turbo with the big turbo not install, and installed. Doing time to rpm tests there was no change, showing no measureable decrease in small turbo spool due to the big turbo.



I should also clarify something from my last post. I mentioned a 28 lb spring in the secondary WG. Of course, with the Tial V44, there is no such spring. I actually have 2 wastegates on the small turbo, each with a 19 lb spring. For some reason I've yet to determine, it provides 26-28 psi boost. It's not boost creep, since it's flat across the whole pull and does not increase with rpm. I made up a graph to show this, and it includes boost from both turbos, pressure ratios, etc. The vertical yellow line on the left is where I released the transbrake, the vertical white line is the marker/cursor.

http://www.posracing.net/files/Compound_Turbo_graph.JPG

The image conversion hosed the quality, but it's still readable. Hopefully that helps to illustrate some points about how the setup works. Keep in mind the primary turbo is the big one and the secondary turbo is the small one. Some points of interest on the graph:

-Total boost and the two individual boost pressures add up (if they're off slightly it's due to filtering).
-Pressure ratios are multiplied to equal total PR.
-You can see that the big turbo makes no boost until I release the transbrake and the 2 step that goes with it. It ramps in over about a second.
-As the big turbo comes up, the small tubo stays flat (I needed to add a second WG to avoid creep here), but it's PR goes down. :) Its PR is highest when it's doing all of the work.
 

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Re: Compound tubo charging

Thanks for your time.

If your where to turn the boost up or down witch
gate would you do this with?
 
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