A 5.9 spinning at 4400rpms moves 30lbs/min of air. At 65psi and im assuming 270° iats, compressor flow goes up to 123lbs. So each hx35 is moving ~61lbs/min, and probably not very efficiently, 62%-ish which makes for 560° compressor outlet temp.

That then means the flow out of the lp compressors is now... 43lbs/min, perfectly within range of the hx35 compressor wheel. So the problem is the turbine.

If we back off the lp turbos to the theoretical perfect 50/50 split, the 123lbs/min stays the same, but at a lower pressure ratio, 2.4 instead of the 4.7 they're at now. Looking at the multitude of compressor maps on Google, that might be a problem, stock hx35 compressors don't flow 61lbs/min at 2.4pr. You'll have to either upsize the compressors, bias the flow to the lp turbos some, upgrade to hx40 turbos, or back off on the boost/fuel, for now.

You have alot of wrongs trying to make a right here. My personal opinion, is a "reset" is needed. Back off on the fuel, that will help everything. Go back to a normal hx35 on the manifold, with a dual port actuator. And I would search for 2 hx40s for the lp stage. That will get you a very solid base to start tweaking on. Shouldn't cost very much to do all that. The difference will be immediate and you should have a very smooth system capable of handling what it appears your wanting to throw at it.

 

I am using HE351cw's with 9cm open housings, the Hi pressure is bored for the 67/76 turbine. All have the stock compressor wheels currently. Low pressure pair have stock turbines as well.

 

My intention is to start small (with the 351's) and use the gauges to provide feedback of what is going on. Then try to understand and use what it is telling me to adjust the setup. The HE351 exhaust housings are a little more compact than the HX, and they are easily modified.
Once I outgrow this setup or get to the point the bottom end is on the ragged edge I'm hoping I have enough understanding to put a big combo that is streetable together. I have a Borg S464 that could be a manifold charger, but if data says something else is better I can be flexible. Water/Meth and Nitrous are also on the table if that helps achieve the goal.
For the record, I appreciate your input!

 

Dammit, I missed the he351 part, but that actually works in your favor. All the numbers are the same, but you atleast have some room to back off the lp turbos.

Get lp turbos down to ~22psi. You'll see when you start bringing the hp turbo more online, it'll pull the lp turbos down.

 

I was guessing that might be the case. I'll report back as soon as I swap back to the normal 10 blade. I've also emailed Brian at Savage fab about his turbine, but haven't heard back yet.
I can't help but wonder if 64/76 (HX40) turbines or 67/76 would be better in the atmosphere (oops Low Pressure) pair once I get the Hi pressure unit doing something again, and what compressor wheels might be best. Any opinions on that front?

 

Here's 12 blade hx40 turbine I stuffed in a 351ve. I would do the same as I did where I made it mixed flow, it handles the higher pressure ratios better than a normal turbine. Look at the inducer of the wheel, I trimmed it up and ground the angle in.

Low pressure is where I would stuff the 5+5 turbines, that is where you need flow.
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Maybe I'm thinking of it in incorrect terms. On the exhaust side The hi pressure turbine has to (pass/flow/swallow) all of the exhaust gas that doesn't bypass via the wastegate. The drive pressure drop between the manifold and hot interstage pipe is indicative of the work extracted from the exhaust by the hi pressure turbine. What's left is the drive pressure available to run the low pressure stage (minus exhaust system backpressure).
The Hi pressure compressor is eventually receiving air that is already compressed and will require more torque to turn it.
I would think a hi pressure turbine would work well with a large inducer and an exduder that can flow the target amount of air without creating a restriction. Couple that with a compressor that is small (relative to the turbine inducer) but large enough to get the system moving yet small enough to avoid stalling or surging when the low pressure boost climbs.

Is there a better way of looking at it?

 

Im going to try to answer your questions the best I can without creating a novel or getting too nerdy/ technical.

As boost/ flow rises in an engine, the exhaust flow shrinks. As it passes through the high pressure turbine, it loses energy in the form of a pressure drop and temp drop. How much of each is determined by the efficiency of the compressor, and the temperature of the air the compressor is breathing in.

When it leaves the hp turbine, it is less dense and takes up more space. This is why the low pressure turbine(s) need to be able to flow.

On the compressor side, the wheel doesn't work harder because of the added pressure. Instead, temperature is the dictating factor. The hotter the air it breathes, the harder it has to work.
ALSO, the hotter the air, the faster the turbo has to spin (this is where the work comes from) to make the same pressure ratio. If you've ever driven an engine with a too large turbo, chances are you've noticed that the turbo spools better in cold air than it does when it's hot out. This is why.
The downside to this is that it's possible you can overspeed the hp turbo before it ever Max's out on flow or pressure. To combat that, the hp turbo needs to have a low trim wheel, this brings shaft speed down for the same pressure. Holset usually is already low trim. Interstage cooling the boost also helps, either an a2w intercooler, or water injection.

In short, the hp turbo needs to be setup for pressure, lp turbo(s) setup for flow.

 

I really do enjoy and appreciate your feedback and patience.

When you say low trim are you referring to closer to 1:1?
My 67/76 turbine is .88 trim. A 64/76 turbine is .842 trim.
Is the 67 referred to as the lower trim? (kind-of reminds me of the High and Low rear end gear expressions)
My stock Turbines (60/70) are .86 trim.

I used the cookie cutter S362/S475 compound arrangement as a base reference to compare my setup to.
Hi pressure 62/84 compressor & 68/76 Turbine Low Pressure 75/100 compressor and 88/96 turbine.
On the exhaust side this setup has .89 hp trim and 3631 exducer area / .91 lp trim with 6082 exducer area.
Mine has .88 hp trim with 3525 area / .86 trim lp with 5655 lp total exducer area.
The Holset compressor maps seem to indicate the two could flow more than the 475 but I went with it as a place to start since they are easily modified.
The efficiencies and compressor maps make sense but trying to put numbers to density losses due to heat and then what that does though the Hi pressure side, combined with the reverse on the turbine side, makes my head hurt.
Have a good one!

 

High trim is closer to 1. Your trim numbers are off, but the areas are pretty close. A 64/76 turbine is 64×64/ 76×76= 4096/5776= .71, or 71 trim. Compressor trim is what we're concerned with.

Your he351 exducer combined areas are 5,652mm², the 475 is 6,079mm², so your ~93% of the area of the 475. (Although what REALLY matters is the turbine throat area, or the area between the blades.)
You can make up for that deficiency by using those 5+5 turbines.

When it comes to compounds the part that loses people is "correcting" the airflow after the low pressure turbos so you can size the high pressure compressor.
Then it's calculating the exhaust manifold flow so you can size the turbine and a/r.
Don't ask me to teach either one of those, it's a process, not a formula.

 

I didn't realize the diameters had to be squared to calculate trim... thanks. I had found I got lost in the weeds trying to calculate compound setups (especially with my limited experience with them), so I just built one. After modifying it and experimenting, I built the triples. Now 'm modifying, and experimenting again...lol. Thank you for shedding "technical" light on what seems to be going on and why things are doing what they are doing. Eventually I hope to be able to semi correctly spec a big system that is still streetable. For now, I'll keep tweaking. Thanks again.

 

I'm back. I swapped out the 5+5 for a "normal" 67/76 10 blade. The previous driving characteristics returned. Initial drive pressure increase followed by boost pressure rise (hi pressure stage) and then lower low pressure stage boost follows... (all during normal acceleration from a stop). I haven't done any full fuel wide open pulls yet, but turned down reasonably aggressive accelerations indicate low pressure boost is back to a little less than half of total boost. Egt's are lower, and smoke is a little easier to control. I'm kinda thinking the 191DV's are contributing to that. At som epoint after getting the combination settled in, I'll probably swap the 025DV's I was running in my 160 pump with the 191's and see how it does. According to PDD the 025's fuel like the 191's but with less smoke. The one time I did get on it a bit hard I popped an intercooler boot off. Probably didn't get it aligned and clamped properly when I did the turbine swap.
I also don't think the 5+5 was very well balanced. I only had around 400 miles on it and the radial play was bad enough that the turbine and compressor wheel inducers had touched the housings. I didn't have new bearings so I put the assembly in a rebuilt chra, and used silicone to seal to the compressor housing since I didn't have the O ring groove cut in this cartridge.
On another note, Driving back & forth 10 miles to work a few times, over the Smoky mountains to Pigeon Forge and back, cruising Rod Run, on the dyno, etc. I hand calculated 15.96 mog with the crappy turbine. That's running 3.54 gears and 35x15.5 wide tires. I had anticipated 13mpg.
I'm planning to do some full power testing (wish I had a dyno) before I receive the Savage turbine that he is balancing with a cast compressor wheel like I'm running now. I'm anxious to see if the "butt dyno" can tell a difference.
Top image is 5+5, bottom is 10 blade.
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Now I'm stumped. I found an empty stretch of road on my way home from work, got my phone out and recorded a short 8 second video of a full power pull from around 50mph at 1700 rpm going up a light incline. RMP jumped up to around 2400 as it downshifted main boost was still only a pound or two as drive pressure stepped up to around 20psi. below are the "gauge readings at different points.. can you tell what the system wants for the next modifications / upgrades for improvement?
RPM2700 / EGT 700 / HP Boost 27 / HP Drive 54 / LP Boost 7 / LP Drive 12
RPM 3000 / EGT 850 / HP Boost 55 / HP Drive 91 / LP Boost 17 / LP Drive 29
RPM 3200 / EGT 1020 / HP Boost 65 / HP Drive 92 / LP Boost 37 / LP Drive 46
RPM 3500 / EGT 1250 / HP Boost 68 / HP Drive 98 / LP Boost 44 / LP Drive 53
RPM 3750 / EGT 1550 / HP Boost 72 / HP Drive 105 / LP Boost 52 / LP Drive 58
SHIFT
RPM 2950 / EGT 1700 / HP Boost 65 / HP Drive 78 / LP Boost 45 / LP Drive 47
RPM 3250 / EGT 1820 / HP Boost 69 / HP Drive 92 / LP Boost 48 / LP Drive 51
RPM 3400 / EGT 1900 / HP Boost 69 / HP Drive 80 / LP Boost 48 / LP Drive 52
Let Off

I have the HP wastegate blocked from getting boost until 50 psi.
IF I delay the wastegate to higher pressure won't HP drive go higher?
Would a bigger HP compressor wheel do the same?
Maybe bigger LP Turbines and compressor wheels? (If so how much bigger)

Thanks in advance.

 

Look at your data, in every case lp drive is higher than boost, that's where all your drive pressure is coming from.

For a quick test, lock the lp wastegates open, hell try full open. Drive pressure should drop and the hp turbo should be more responsive.

 

I meant to say, lp drive is higher than lp boost.

Then go back up a couple posts and re read where I talked about the lp stage.

 

I took your advice this weekend and removed the blocks on the LP wastegates. I replaced them with a couple of flimsy throttle return springs just so they wouldn't flop around, but would easily push open.
I tried to duplicate the pull that I provided the data from... same road, same start speed, etc.
There was too much going on with trying to hold my phone and video the gauges watch the road, look at smoke etc. for my "butt Dyno" to tell if it was more responsive, and if it fell off up top, however the numbers improved.
Max Boost was down around 54psi with Max dp around 73. Lo pressure boost was 18 with dp 23. EGT was a tic over 1700. I can't say if that was the peak since my video wasn't stable enough to keep the gauges in full view the whole time.
In light of the latest test I'm planning to bore the atmosphere exhaust housings to accept the 67/76 10 blade turbines and re-test from there. Do you think bigger low pressure compressor wheels will help or hurt? What about Hi Pressure compressor wheel?

You've been a big help, Thank you!

 

Congrats, you have a perfect 50/50 compounded boost ratio. The system isn't perfect, but each turbo is doing exactly half the work.

Your bottleneck is the lp turbines and housings. Your probably running divided housings correct? If so, that hurts flow all around, but really kills it on the top end.
The 67mm turbines will help, but you also really need undivided housings for the lp.

Leave compressors alone for now, installing a temp gauge between each turbo and pre intercooler would help us gauge when to upsize those.

 

Baby steps ! lol.... It doesn't help that you are working with someone that is just learning...
The Turbine housings are 9cm open. The Stock turbine is 60/70 with (I believe) 12 blades.
The stock cast compressor wheels are 60/86 7+7blade.
I have no idea what the a/r is stock nor what it is once the housing is bored to accept the 67/76.
Maybe I'm starting to catch on because I was actually looking into temperature gauge options to add measuring the iat in 4 places: pre air filter (under hood) / After lp stage / after hp stage / and after intercooler or in the intake. If my research was even close, when I had the 5+5 turbine in it on the dyno at 52lbs of boost the temp out of the lo pressure stage was in the 400's and after the hi pressure stage over 500! The factory intercooler could only do so much. Running the numbers back through from my dyno hp, boost etc. Intake temp had to be in the 190 range.
I'm going to leave it with the floppy lp wastegates for now. I'll get a couple housings modified for 67 turbines, and try to be ready for the swap a week or so after I get back from vacation next week.
By the way, what is your first name? Mine is Mike.
You have been a great help! Thank You!.

 

Those are small housings, you really need 12 or 14cm housings, but I don't think they make those undivided.
I guess try the bigger turbines first, then bigger housings. That's why I was recommending just installing hx40 turbos, they're cheap and already bigger with usually bigger housings.

 

I've started to consider a pair of Borg Warner S464's on top. If my turbines are still too restrictive after swapping I may have to finish dialing it in the best I can. The HE351's are so compact and all sorts of modifications are optional. I might just use what I'm learning to build a whole new (bigger) setup... that was the goal of this one anyway.