Please help me critique this twin setup. ("Aurora" 7500 over an He351VE)

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me2

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I am trying to get my head around how a twin turbocharger setup works, mathematically, especially when there is a big mismatch between the two turbochargers.

A certain company is promoting the use of an Aurora 7500 (apparently capable of 135 pounds/minute) over top of a stock HE351VE on a Cummins 6.7 as a super all round turbo charger setup. Suitable for every day driving, towing, pulling, etc.

I'm looking for factual, technical information to prove or disprove these claims.

First of all, what model of turbocharger is an Aurora 7500 turbo based on ? Is a compressor map available ?

How do surge limits work with twin turbos ? One of the problems with a big single turbo is that it will surge at low mass flows (read low RPMs) and high boost pressure. How does this work with twins ?

In the case of the A7500, it supposedly has a maximum flow rate of 130 lbs/minute. A Cummins 6.7 at 1600 RPM and 30 PSI of boost is flowing about 30 pounds per minute. Wouldn't the A7500 be pretty much stalled or freewheeling at that flow rate ?

Then we get to spool ups. How does spool up work with twins ?

Something I don't understand is how someone can claim that a twin setup can spool as fast as a stock single turbo. The same engine exhaust flow is now split between (over) two turbines, so each turbine is only getting half the exhaust energy. And the compressor on the A7500 is massive. How does a twins setup overcome this ?

Then we get to airflow matching. The HE351 has a maximum airflow within its map of less than 60 lbs per minute. The A7500 has an air flow of 130 pounds per minute. How can a turbocharger rated at 60 pounds per minute efficiently feed a turbocharger moving 130 pounds per minute ?

I'm not saying that all these claims are wrong, only that I am not understanding the principles at play.

Thanks in advance for the help.
 
If its a real compound the exhaust flow won't be split, it'll go from manifold to the small Turbo to the big Turbo. The spoolup will be slightly slower than stock. The big Turbo feeds the small Turbo, not the other way around.

Sent from my DROID X2 using Tapatalk
 
Ya like said above the a7500 goes on the manifold the exhaust exits that charger then goes into your other then through the exhaust. Same with the intake it gets sucked through the filter then compressed through the first turbo. That air travels into the intake of the second turbo. That air is a positive pressure instead of a neutral pressure so it is going to force the air through that turbo and get even more compressed then goes to your intercooler. That is a compound turbo set up.
Your OP was asking about a twin setup which would involve two identical turbos. And they would not be connected exhaust to exhaust intake to intake.
Most people run compounds and they tend to run the coolest. Hope this helps.
 
lorendiesel5.9 said:
This thread is so full of fail I'm not sure where to start.
Click to expand...
Please educate me. I'm listening.

I obviously meant compound, not twins, although I think a lot of people use twins when they mean compound.

I knew that the exhaust went through both turbos, one after another. When I meant the exhaust was split, I meant that the exhaust energy was split, versus what it would be if it was just powering one turbo.
 
Here is an S480 map.
gryphon68
 
BD used to have a nice map for all of there turbos up, I saved it so I wouldn't lose it:
BDdieselcompressormap.jpg


You can see that twins really widen the map quite a bit and extend it up into higher pressure ratios thanks to the compounding effect. What the map doesn't show is that you do lose spool quickness that the secondary would have as a single and you lose some of the flow that the primary would have if it didn't have to push into a secondary. So despite what people may think it is in fact a compromise in performance, but in the right application the benefits can greatly outweigh them.
You also have to the mindful that when talking about flow that density of a gas is greatly affected by pressure.

You have to be careful saying that the turbos split anything. They do in some ways and they don't in others.



:soap: Sorry for the rant but this has been bugging me lately: I'm not sure why some members get upset about something that may have been discussed before or they don't think is good enough for them to give their opinion on. This isn't a social media site, we don't care if you don't like the subject, so if you don't want to help someone you don't have to post saying it. Don't feed the trolls and they will go away on their own. :soap:
 
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Thanks for the reply. That is a very interesting graph.

I hope you have some energy left for discussion.

The HE351 is a sub 60 pound/minute turbo. The S480 is a 120 lb/minute turbo.

Typically which turbo would be the primary and which would be the secondary in a setup like this ?

How does one get 120 pounds of air through the HE351 without over speeding the compressor ? If you look at an HE351 compressor map, even at zero boost it doesn't go to 120 pounds.

Thanks again.
 
I'll bite...
Your HE351 is your secondary, it "compounds" the the air from the primary (big turbo). This is the whole reason behind putting a high pressure turbo over a high volume turbo.

The whole idea when looking at a turbo map (specifically lbs/minute) is how efficiently you can use (or need) that volume at a certain pressure ratio for where you operate.
 
The larger turbo is the primary. Do you understand pressure ratios? I don't get paid enough at work to explain this from my phone, I'll let someone else have fun.

Garrett

Probably getting paid at work to post this from my D1
 
Do I understand PRs ? Of course !

I found my own answer here.
Compound Turbocharging for Dummies

The mass flow rate through the second turbo gets increased because its being fed compressed air, not ambient air. Makes sense. The turbo at a certain RPM has a specific CFM, but if you increase the density of the CFM, you get greater MASS flow.

The equation is m2=m1*sqrt((T/Tmap)/(P/Pmap))

where
m1 is the original mass flow
T is the inter stage pressure
P is the inter stage pressure
Tmap is the original temp
Pmap is the original pressure

I can figure out the rest from here.


1 other question. What makes an Aurora 7500 different from an S480 ?
 
Quote: The mass flow rate through the second turbo gets increased because its being fed compressed air, not ambient air. Makes sense. The turbo at a certain RPM has a specific CFM, but if you increase the density of the CFM, you get greater MASS flow. Ain't that what I said just more gooder worded?
 
me2 said:
Thanks for the reply. That is a very interesting graph.

I hope you have some energy left for discussion.

The HE351 is a sub 60 pound/minute turbo. The S480 is a 120 lb/minute turbo.

Typically which turbo would be the primary and which would be the secondary in a setup like this ?

How does one get 120 pounds of air through the HE351 without over speeding the compressor ? If you look at an HE351 compressor map, even at zero boost it doesn't go to 120 pounds.

Thanks again.
Click to expand...



That HE351 is working like a bastard compressing that new dense atmosphere, in fact if you plotted compressor rpm, it is in fact slowing down as primary pressure is coming up.
 
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