Picking an A/R for primary/high pressure turbo...

[Hot COCOAL]

it may be necessary. depending on your setup. tuning a waste gate isn't easy every time. The less wastegate foolery, the better.

Lol

Understood

I'm not "trying" to put a wastegate into a design here, I'm only trying to figure out how to determine how to choose an A/R for a primary turbo and what affect wastegates have on that decision. While I understand they have their place, I believe a well designed system technically shouldn't "need" a wastegate, and I try to implore the K.I.S.S philosophy whenever possible :baby:

 

[cafryer]

Waste gates are necessary in most compound kits without them you would have high drive psi or a slow spooling kit ( loose A/R housings to keep drive psi down) is my understanding.

 

[JoshH]

To be clear, the primary is the atmosphere turbo and the secondary is the "high pressure" or small turbo. It is the second stage of compression hence secondary.

 

[Hot COCOAL]

To be clear, the primary is the atmosphere turbo and the secondary is the "high pressure" or small turbo. It is the second stage of compression hence secondary.

:spit:


NO SHIT I'm not kidding when I say, YOURE KIDDING, RIGHT?

:rofl:

:roflmao:

Wow Josh, thanks man, that actually clears allot up for me...

I wasn't clear on that before :dunce:

...wow...ok

 

[S Phinney]

Yes, I have been around for almost 2 years. Yes, I have started, maybe 3 turbo related threads, and been part of several threads, sure, I've hardly been asking the same question, although I admit to being a bit dense at times, or even most times...

Given that the term "hot pipe" can have more than one meaning/application, and the fact I'm totally lost, clarifying which "hot pipe" you were referring to seemed relevant, I'm only trying to be crystal clear, instead of the norm "clear as mud" descriptions that often get given.
I didn't think that exhaust gasses would be good being introduced into the intake tract, I guess I should have put a bit more thought into my response realizing I was discussing twin turbo systems, but I've always been of the mind set "no question is a bad question" rather than assuming I understand something...and this is the first I've really delved into researching twin/triple turbo set ups since I've become a member, the single turbo stuff is complicated enough, lol

Thank you for clarifying....


:thumb:

So increasing the A/R of the primary turbo isn't really necessary when building a twin set up? I thought that the primary had to flow more on the exhaust side to compensate for the low pressure turbo forcing air into the primary in a multiple turbo configuration?

Drive pressures always seem to be a concern, what do I look for in a turbo that would give an indication as to what drive pressure it will produce? Is there a relationship between the compressor, turbine and A/R that determines drive pressure? Or is there more involved, like the relationship between the turbo and the system it's going into that determines what kind of drive pressure the turbo will run at?

There has to be a known formula/mathematical equation that is used as a guideline, somewhere, isn't there?

In talking to Nathan at MPI I understood him to day that you would want to have close to twice as much compressed flow on the second stage as the first and as much turbine flow on the top charger as you could get in that combination. A/R in the second stage would be used to tune the overall system characteristics. Tighter on the second stage would make for more responsive system . loose would do opposite. Your power is made by the second stage. The first stage is to getting moving in the right direction so to speak. Combination is key for the system to work right.

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[DMAXchris]

To be clear, the primary is the atmosphere turbo and the secondary is the "high pressure" or small turbo. It is the second stage of compression hence secondary.

I always thought it was the other way around. I thought the primary was the high pressure turbo because its the first to receive the exhaust from the engine? Secondary would be atmospheric because its second in line and gets its fresh air from the atmosphere.

 

[LBZ]

I always thought it was the other way around. I thought the primary was the high pressure turbo because its the first to receive the exhaust from the engine? Secondary would be atmospheric because its second in line and gets its fresh air from the atmosphere.

The turbo that has the higher boost pressure on it's outlet is always the second stage.


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[TROJAN366]

I'm glad I spent ten minutes to read this. I feel like I am an expert now lol

 

[chevyburnout1]

Jason I think your stuck in gasoline engine thinking terms again. So for conversations sake forget about blow off/diverter valves. Their main purpose is to vent the pressure surge due to a gasoline engines throttle blades shutting and stopping boost airflow immediately. Diesels don't have that. I have personally installed a BOV on my diesel in the past but it does not relate to this conversation about actually controlling turbochargers..

Now I'm new as well to compound turbos but this is what I have learned so far. The secondary a/r should be tight enough so as to drive the secondary turbo into it's efficiency island as soon as possible in regards to drivability, without maxing out the wastegate. Once spinning in its efficency island the wastegate will start opening up and bypassing exhaust gases around the secondary turbo into the hotpipe that is feeding exhaust into the primary turbo. This will keep the secondary charger spinning at it's most efficient spot regardless of engine rpm/fuel/heat increase. The more exhaust flow, the more the wastegate will open. The primary turbocharger should have an a/r that will put it in its most efficient pressure range when the engine is at it's maximum potential, or more-so where the engine is wanted to be utilized the most.

On my truck due to my lack of fuel, larger than needed turbos, and the want of still driving it on the street I went with the smallest a/r possible on the secondary which was a .58. This gets the secondary turbo up and spinning as fast as possible and into the efficiency islands for the compressor side, which greatly improved the daily driveability habits. To prevent high exhaust drive/backpressure with said small housing the wastegate will open sooner to relieve pressure than lets say a 1.0a/r housing on the same charger. So in theory you would think using the smallest a/r housing would be the best way to go as long as the wastegate can handle the higher exhaust flow. But in reality the turbine housing has it's most 'efficient' a/r setup that matches the turbine wheel. So the smaller you go on the housing the less efficient the turbo is at utilizing every bit of exhaust heat. So it's a balancing act

Like I said I'm still new to compounds as well so anyone correct me where I'm wrong.

 

[Hot COCOAL]

Dustin- :hug:

Nice explanation:thumb:

That actually made allot of sense, thank you for your time

 

[jkholder09]

Dodge guys always say 366 over 480. Where the 480 is the atmoshere and 366 is the second stage. If you say it any other way they actually get offended and angry.
When you put twins on a dodge you flip the manifold and the high pressure is physically right on top of the atmosphere. so that was very logical to them.

On this forum there is not a standard procedure to articulate the setup as far as I can tell.
I always attributed that to the deep technical expertise here (it is usually obvious where the chargers are placed based on size).

I can also see now why the op was confused.

the ford guys use atmospere/highpressue ad a description. I was biased to that.

So on dd what is our official verbage to describe turbo stage and location?

from mobile

 

[juddski88]

as much as we all like a good BJ, your lipstick is the wrong color today, sorry:joker:

 

[jkholder09]

How about a back rub?

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[juddski88]

do you do the hot stone thing?

 

[jkholder09]

And more...........

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[juddski88]

must be a sh!tty feeling when you are held to your word....

 

[jkholder09]

Not at all I am a man of it sir!

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[dmaxbowtie]

good information on this thread, gave me a better understanding of how the compounds are piped in. Would it be safe to say that there are more internally gated high pressure turbos in compound setups or external?

 

[JoshH]

good information on this thread, gave me a better understanding of how the compounds are piped in. Would it be safe to say that there are more internally gated high pressure turbos in compound setups or external?

Depends on the size. Most really big twins and triples are going to use an externally gated secondary because the turbos being used aren't generally available with an internal gate. Up to a 366/4xx setup, the 366 is usually a T3 internally gated style, but I've seen externally gated T4 S366 turbos used also. Stock LB7 turbos are obviously internally gated. Stock LLY/LBZ/LMM turbos are almost always compounded without the use of any gate whatsoever.

 

[Hot COCOAL]

In talking to Nathan at MPI I understood him to day that you would want to have close to twice as much compressed flow on the second stage as the first and as much turbine flow on the top charger as you could get in that combination. A/R in the second stage would be used to tune the overall system characteristics. Tighter on the second stage would make for more responsive system . loose would do opposite. Your power is made by the second stage. The first stage is to getting moving in the right direction so to speak. Combination is key for the system to work right.

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Nice:thumb:

Depends on the size. Most really big twins and triples are going to use an externally gated secondary because the turbos being used aren't generally available with an internal gate. Up to a 366/4xx setup, the 366 is usually a T3 internally gated style, but I've seen externally gated T4 S366 turbos used also. Stock LB7 turbos are obviously internally gated. Stock LLY/LBZ/LMM turbos are almost always compounded without the use of any gate whatsoever.

Is it a safe assumption to say that most T3 flanged turbos are internally gated?