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So after rereading your post a bit on your boost control scheme, I wanted some clarity.

Boost pressure for your small turbo is regulated with two wastegate's referencing total system pressure.

Boost pressure for your large turbo is regulated with one wastegate referencing only the large turbos pressure.

The small turbo will make 3:1 pressure ratio (28psi) on the wastegate spring before the large turbo spools. When the large turbo makes full boost, the small turbo will lower to 2:1 pressure ratio (15psi). This is due to the full system pressure opening the small turbo's wastegates when both turbo's are up on boost.

Did I get this correct?
 

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Discussion Starter #82
So after rereading your post a bit on your boost control scheme, I wanted some clarity.

Boost pressure for your small turbo is regulated with two wastegate's referencing total system pressure.

Boost pressure for your large turbo is regulated with one wastegate referencing only the large turbos pressure.
This is all correct, but I would add that big turbo boost is sent to the top of the two small turbo wastegates. Small turbo pressure rises roughly 1:1 with big turbo pressure. I only say roughly because I'm just beginning to wrap my head around what the big turbo drive pressure is doing to my small turbo boost control, there's some discussion about that somewhere above when it first dawned on me.

The small turbo will make 3:1 pressure ratio (28psi) on the wastegate spring before the large turbo spools. When the large turbo makes full boost, the small turbo will lower to 2:1 pressure ratio (15psi). This is due to the full system pressure opening the small turbo's wastegates when both turbo's are up on boost.

Did I get this correct?
Mostly. The small turbos WG's are open and regulating boost at the 28 psi too. While the small turbo's PR drops to 2:1, the 15 psi is only for reference/illustrative purposes, since the small turbo is still making the same 28 psi when total boost is 45. The PR drops because the inlet pressure goes up, and that's half of the equation. Speaking in absolute terms (assuming 15 psi atmospheric pressure and 30 psi boost pressure for easy math), 15 psi at the inlet and 45 psi at the outlet is 3:1, while 30 psi at the inlet (15 from big turbo) and 60 psi at the outlet (45 psi boost) is 2:1. It's like magic, this shit was just meant to be...

I've been up for almost 24 hrs, hopefully that makes some sense. In other news, I should have the car back together and running on the new motor (with some nice additions to the setup) by the end of the week, so it shouldn't be long before testing continues again finally. :)
 

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I just realized another reason that the system reaches full pressure sooner. Since you are only requesting 15psi from your large turbo rather then 45psi, you are saving 1500 rpms that the turbo would take to go from 15psi to 45psi.

For example, here is a boost response of a S400sx4 (80mm) on a 2jz in a non compound setup. This turbo wouldn't hit 45psi until 6500-7000 rpm on my 2jz. With the added exhaust energy from the small turbo, and lower boost requirement from the large turbo, I bet I could hit 45psi by 4500rpm in a compound configuration. The lower boost output of the large turbo keeps it from surging as well from making too much boost too soon. I'm getting excited about this!

2480/1.24
3031/2.0
3496/3.0
3840/4.0
4090/5.0
4316/6.0
4450/7.0
4621/8.0
4700/9.0
4816/10.0
4907/11.0
5000/12.0
5045/13.0
5150/14.0
5200/15.0
5280/16.0
5311/17.0
5385/18.0
5440/19.0
5499/20.0
5510/21.0
5560/22.0
5600/23.0
5630/24.0
5690/25.0
5750/26.0
5810/27.0
5860/28.0
5910/29.0
5960/30.0
 

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Discussion Starter #84
Alright, I finally swapped in the 5 bar sensor for the back pressure readings. The ratio is 1:1 until 8000 rpm. At 9500 it's only 3 psi more than boost. Not bad for a turbo setup that spools on its own. There was a weird spot in first gear that was 6 psi over but boost dropped until the shift drove it back up. Here's a screen cap. Primary load is back pressure. Switch 5 is the transbrake.

Screen cap

This pass was the first clean pass on the new motor, it went 9.2 at 154 with a lousy 1.52 short time and a lot of wheelspin. I won the round but couldn't restart because I somehow blew the whole tip of the starter off. I'm open to theories on that one...
 

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Discussion Starter #86
My trap speeds are 10-15mph lower than a 5 speed running the same ETs thanks to the hungry auto trans/torque converter, etc. For example, it dynoed 589 to the wheels and then went out and ran 8.9 at 155 on the same tune. :)

Weight is a little over 2400 with me in it.
 

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My trap speeds are 10-15mph lower than a 5 speed running the same ETs thanks to the hungry auto trans/torque converter, etc. For example, it dynoed 589 to the wheels and then went out and ran 8.9 at 155 on the same tune. :)

Weight is a little over 2400 with me in it.
Have you dyno'd this setup yet? Dam I'm 3250Lbs with me in my car that is light. I need to loose some weight off my car :smt077
 

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Discussion Starter #89
Yes, the 589 was on this setup at 40 psi.
 

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Alright, I finally swapped in the 5 bar sensor for the back pressure readings. The ratio is 1:1 until 8000 rpm. At 9500 it's only 3 psi more than boost. Not bad for a turbo setup that spools on its own. There was a weird spot in first gear that was 6 psi over but boost dropped until the shift drove it back up. Here's a screen cap. Primary load is back pressure. Switch 5 is the transbrake.
Excellent information, Kevin. I should probably measure mine too. How did you plumb the sensor?
 

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Discussion Starter #92
Excellent information, Kevin. I should probably measure mine too. How did you plumb the sensor?
This is at the EGR port on the intake manifold. It would be great to see numbers from your setup too for comparison.
 

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This is at the EGR port on the intake manifold. It would be great to see numbers from your setup too for comparison.
Damn, I'd have to come up with something else. I already have that port welded shut on the head. Anti-lag kept causing the manifold gasket to blow on on the previous turbo set-up. Any other ideas?
 

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Discussion Starter #94
You could just tap the cast manifold like people used to do for EGT gauges. Brass fittings will back out all the time but some other more approprriate material would work fine. Run a few feet of copper tubing before converting to plastic or rubber line, depending on how far away you mount the sensor.
 

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Do you have any plans to measure the drive pressure of the large turbine rather than the whole system? i wonder if the 3 psi you see towards the end of the pass has anything to do with the air entering the first compressor stage, maybe ducting air into it diffrently would eliminate some... just a thought.
 

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Discussion Starter #96
The first turbo sticks up through the hood and gets force fed. It may just be that that's how this system runs, but I do know that the big turbo creeps with the current WG config. I could easily put a bung on the turbine side of the big turbo and see what that's seeing for back pressure. With a 1.32 housing and only 70-80 lbs/min airflow I doubt it's even 1:1 though. Only one way to find out! :)
 

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Here's my compound buildup. Hope you don't mind me posting in your thread.

I was trying to get an idea of where I would put the large turbo in my compound arrangement. I think this will be the basic layout. I need to verify that this will all fit with the thermostat housing assembled. The Top turbo is a Borg Warner s300sx3 66mm/91mm compressor & 79mm/73mm turbine with custom 1.10 a/r housing from full-race. On its own is good for ~775whp. The lower turbo is a Borg Warner S400sx4 80mm/110mm compressor & 96mm/88mm turbine w/ 1.32 a/r housing. This turbo is good for about 1175whp currently. I'm looking at 3 or 4 different compressor wheel upgrades. I will likely go with a compressor with the dimensions 88mm/118mm. The goal is to get it to support ~1250-1300whp at a pressure ratio of 2:1.

The engine is being solid mounted to the tube frame. I do have lots sheet metal to cut away to make room for all of the new piping. The down pipe from the small turbo will feed into the turbine housing of the large turbo. The compressor outlet of the large turbo will feed into the compressor inlet of the small turbo. The compressor outlet of the small turbo will go to the intercooler.











Link for more information on the two turbos I'm building this kit around:
http://www.full-race.com/catalog/index.php?cPath=214_1167
 

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Discussion Starter #98
Wow, that big turbo looks crazy stuffed in there! Keep us posted on the progress.
 

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I've decided that this is a better place for the big guy. Should clean up the piping a lot. Not much physical distance to do interstage water injection though...

 

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Discussion Starter #100
Distance shouldnt matter, as long as a nozzle will fit somewhere. The compressor will do all of the work.
 
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