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Old 05-16-2019, 04:30 AM   #1
CHDiesel
 
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Turbine side in depth

To start, I spent hours using the search function, reading some of my old physics and fluid dynamics books, and googling.

I've gotten dozens of recommendations on turbos, with "it's good for this hp and spool" explanations and bro science. I'm looking for real science.

I wan't to know more about how much the choke points of A/Rs effects spool, horsepower, and final flow numbers. How much of a difference the turbine exducer size effects flow and spool compared to A/R. How different exhaust pulse volumes from engines the same size but different cylinder count effect the A/R and wheel size decisions.

I found a great thread I'll quote in a reply that tells some of the science, but leaves a lot of questions specific to engine sizes and hp goals.

I'm hoping more for numbers that help with turbo choice for my 6.7 Cummins, but I think it can help everyone make confident decisions.
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Old 05-16-2019, 05:32 AM   #2
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Apparently I can't quote the post, but I can give a brief explanation. All credit goes to Dizuster at yellow bullet forums.

Peak pulsing pressures are not all the same in 2 engines, one is twice as big as the other but runs at half the RPM.

Engine #1 - 10 pulses of 1lb in 1 second = 10lbs/sec

Engine #2 - 20 pulses of 0.5lb each in 1 second = 10lbs/sec

Both flow 10lbs/sec, but what’s really happening inside the turbine is much different.
The pulses look something like this (not exactly… but you get the idea).
Click the image to open in full size.

Few big pulses from the bigger low RPM engine, and many small pulses for the smaller high RPM engine.
But there is a choke point to every turbine housing/wheel combination. When the big pulse chokes the turbine the flow will kinda look like this.
Click the image to open in full size.

Anything above the choke point shown in grey will not flow as hoped, so drive pressure will continue to go up, but not flow (not counting little extra exhaust density from the pressure)

The Large Engine maxes the turbine on each exhaust stroke. The pulses get choked off, and can't flow through the turbine at the rate the engine expels them.

Thats why a small high RPM engine can get more out of a turbine than a big low RPM engine.

Both have the same flow rate, but in different ways.
The engine is pushing harder (robbing horsepower), but getting no additional flow for the extra work.

It seems like you want the smallest A/R for your engine size and smallest compressor for your hp goal to keep gas velocity as high as possible through the scroll and out the exducer.

Blade design, count, wheel weight, and scroll shape have already been covered by everyone and their grandmother. Also turbine specs in relation to compressor specs is topic for another thread.

So what I want to know is what hot side flow ratings are enough for what horsepower levels. Also what size A/R would be better at each compressor size to accommodate for the larger exhaust pulses of a 6.7 inline 6, and what sizes for the smaller pulses of the other 6+L V8 diesels.

Can we get a list to help all future builders?
Example:
"mm exducer = flow # = hp support" then "this A/R for 6.7 Cummins, this A/R for 5.9 Cummins, this A/R for 6.0 Powerstroke, this A/R for 7.3 Powerstroke"
"mm exducer = flow # = hp support" then "this A/R for 6.7 Cummins, this A/R for 5.9 Cummins, this A/R for 6.0 Powerstroke, this A/R for 7.3 Powerstroke"
"mm exducer = flow # = hp support" then "this A/R for 6.7 Cummins, this A/R for 5.9 Cummins, this A/R for 6.0 Powerstroke, this A/R for 7.3 Powerstroke"
all other engine sizes are between those so people can get a good guess
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Last edited by CHDiesel; 05-16-2019 at 05:44 AM. Reason: more details
 
Old 05-16-2019, 05:51 AM   #3
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I realize my first list example wouldn't work, how about this?
Example:
"this flow # = hp support" then "this A/R for 6.7 Cummins, this A/R for 5.9 Cummins, this A/R for 6.0 Powerstroke, this A/R for 7.3 Powerstroke at this turbine wheel size to not choke"
"this flow # = hp support" then "this A/R for 6.7 Cummins, this A/R for 5.9 Cummins, this A/R for 6.0 Powerstroke, this A/R for 7.3 Powerstroke at this turbine wheel size to not choke"
"this flow # = hp support" then "this A/R for 6.7 Cummins, this A/R for 5.9 Cummins, this A/R for 6.0 Powerstroke, this A/R for 7.3 Powerstroke at this turbine wheel size to not choke"
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93 12v, s366, 5 spd man, cam
98 lifted Ram 5.9 gas
02 Impala, dent in the door

Sold: 02 Duramax
FASS, dual cp3, 60% overs, stock/s475, PPE trans, lowered on NT420S
 
Old 05-17-2019, 01:38 AM   #4
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Turbine is just as HP dependent as the compressor, I talked to the BorgWarner dude a few years ago about making 500rwhp on a 62/65 and he said it was the 65 turbine holding me back....
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Old 05-17-2019, 05:53 AM   #5
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Quote:
Originally Posted by JQmile View Post
Turbine is just as HP dependent as the compressor, I talked to the BorgWarner dude a few years ago about making 500rwhp on a 62/65 and he said it was the 65 turbine holding me back....
Yeah, that's not what I was asking. The question was, what exhaust flow numbers support what levels, and what A/R for each wheel size suits what individual exhaust pulse flow numbers.

The I6 6.7L and V8 6.7L have different pulse sizes even if they are the same power and rpm. So they would require different A/Rs or turbines to keep them as close to the choke points and max velocity as possible.
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93 12v, s366, 5 spd man, cam
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Old 05-17-2019, 06:19 AM   #6
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The guys who know this information aren't going to share it openly on here, you have two options.
1: Choose a turbo guy you can trust and let them steer your towards your goals.
2: Try a bunch of different turbos until you find what you like.

I did both of these, after trying 5 different manifold chargers Weston got it right the first time.
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Old 05-17-2019, 07:14 AM   #7
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That was my experience also.
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puzzy, tune it.

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Old 05-17-2019, 08:36 AM   #8
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I've heard mention the turbine size determines what rpm range peak power is made.
What rpm are you looking to make peak hp?
 
Old 05-17-2019, 08:37 AM   #9
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Quote:
Originally Posted by blackmega3500 View Post
The OP also doesn't take into consideration where they want the power. That's a tiny bit important.
Guess I'm kinda saying the same thing, didnt read.
 
Old 05-17-2019, 10:36 AM   #10
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Quote:
Originally Posted by blackmega3500 View Post
The OP also doesn't take into consideration where they want the power. That's a tiny bit important.
That's irrelevant to the information I'm looking for. If running at peak efficiency (stoichiometric ratio close to perfect not wasting BTUs) then 500 hp will be the same amount of air at 1000rpm or 9000rpm, and exhaust flow will be the exact same. Going bigger just introduces lag and inefficiency.

The only thing that would change turbine requirements is individual cylinder volume. RPM does matter, not for average flow, but for each pulse peak flow to not exceed choke point. That's when you can change how the turbine side makes that average flow to make the engine not work as hard if it does hit choke point.

Quote:
Originally Posted by jasonc View Post
I've heard mention the turbine size determines what rpm range peak power is made.
What rpm are you looking to make peak hp?
Top sled pullers that I know running 6000rpm pick their turbos the same way trailer haulers and OEMs do to run 2000rpm. They find the smallest turbine flow for the power goal so they don't waste any precious exhaust energy. Then pick appropriate A/R and wheel size for exhaust gas velocity.

Wherever the rpms land is where they land. Been told that by CAT engineers and farmers running $200k+ sled pull engines.
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93 12v, s366, 5 spd man, cam
98 lifted Ram 5.9 gas
02 Impala, dent in the door

Sold: 02 Duramax
FASS, dual cp3, 60% overs, stock/s475, PPE trans, lowered on NT420S

Last edited by CHDiesel; 05-17-2019 at 10:46 AM.
 
Old 05-17-2019, 11:03 AM   #11
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Sounds like you got it all figured out.
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Old 05-17-2019, 12:46 PM   #12
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Quote:
Originally Posted by CHDiesel View Post
Top sled pullers that I know running 6000rpm pick their turbos the same way trailer haulers and OEMs do to run 2000rpm. They find the smallest turbine flow for the power goal so they don't waste any precious exhaust energy. Then pick appropriate A/R and wheel size for exhaust gas velocity.

Wherever the rpms land is where they land. Been told that by CAT engineers and farmers running $200k+ sled pull engines.
Have you tried asking them what turbo you should run?
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Old 05-17-2019, 01:45 PM   #13
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Quote:
Originally Posted by fatty View Post
Sounds like you got it all figured out.
I have the fluid dynamics and physics figured out. But not the flow numbers, or choke points, or what makes a bigger difference between the A/R and wheel size in relation to gas velocity at the blades.

Thats why I asked those questions...

Quote:
Originally Posted by zachu812 View Post
Have you tried asking them what turbo you should run?
Yes. Ive asked a dozen people and gotten a dozen answers, and a dozen reasons why each answer was right and wrong. This thread isnt about what turbo is right for me. It's about what exhaust sizes meet what exhaust pusle requirements more efficiently.
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93 12v, s366, 5 spd man, cam
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02 Impala, dent in the door

Sold: 02 Duramax
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Old 05-17-2019, 09:54 PM   #14
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Quote:
Originally Posted by blackmega3500 View Post
U do realize heat is more important than volume though right?
Yeah, everyone knows that, what's your point?

I asked a question about exhaust pulse flow peaks and how they react to similar flow from different turbine combos. And flow numbers in general... if you want to talk about heat, lets start a new thread.

Can someone please just answer the questions asked instead of andwering ones that werent asked or ridiculing the question.

Am I a bad guy for wanting to know something and wanting it public to help others?
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93 12v, s366, 5 spd man, cam
98 lifted Ram 5.9 gas
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Sold: 02 Duramax
FASS, dual cp3, 60% overs, stock/s475, PPE trans, lowered on NT420S

Last edited by CHDiesel; 05-17-2019 at 09:58 PM.
 
Old 05-18-2019, 07:52 AM   #15
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You guys are getting soft.
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Old 05-18-2019, 04:02 PM   #16
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Problem with V8s is pulses are not equally timed, so they will never be as efficient as inline 6.
 
Old 05-18-2019, 05:43 PM   #17
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Quote:
Originally Posted by Leiffi View Post
Problem with V8s is pulses are not equally timed, so they will never be as efficient as inline 6.
Okay... that's a topic for another thread.

I just want an answer to the questions asked.... nothing else.
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Sold: 02 Duramax
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Old 05-18-2019, 08:23 PM   #18
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he doesnt want bro science but thinks sizes are the most important factor rather than design...
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Old 05-18-2019, 09:01 PM   #19
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Quote:
Originally Posted by blackmega3500 View Post
clearly mapped twins will suit that v8 best....
this thread isnt about that. Its about science
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Old 05-18-2019, 10:05 PM   #20
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Quote:
Originally Posted by zfaylor View Post
he doesnt want bro science but thinks sizes are the most important factor rather than design...
I've got physics books, fluid dynamic books, and engineers who pick out turbos for OEMs that all say the exducer opening and volume before the opening effect the max pressure spike and dwel period before exhaust valve close and pressure drop after.

We all know know wheel design and scroll shape matters. That's just as important to me, but why can't I also know about size correlations when it comes to pulse volumes and speeds?

Will it hurt me to know...?
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93 12v, s366, 5 spd man, cam
98 lifted Ram 5.9 gas
02 Impala, dent in the door

Sold: 02 Duramax
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