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.

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).


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.


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

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"

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....

JQmile said:

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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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.

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.

That was my experience also.

zachu812 said:

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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The OP also doesn't take into consideration where they want the power. That's a tiny bit important.

I've heard mention the turbine size determines what rpm range peak power is made.
What rpm are you looking to make peak hp?

blackmega3500 said:

The OP also doesn't take into consideration where they want the power. That's a tiny bit important.

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Guess I'm kinda saying the same thing, didnt read.

blackmega3500 said:

The OP also doesn't take into consideration where they want the power. That's a tiny bit important.

Click to expand...

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.

jasonc said:

I've heard mention the turbine size determines what rpm range peak power is made.
What rpm are you looking to make peak hp?

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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.

Sounds like you got it all figured out.:clap:

CHDiesel said:

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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Have you tried asking them what turbo you should run?

fatty said:

Sounds like you got it all figured out.:clap:

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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...

zachu812 said:

Have you tried asking them what turbo you should run?

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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.

CHDiesel said:

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.



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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Are you one of those tubular header lovers?

I'll agree with Fatty..... but for all of us dummies this is what you'd need to use.

http://www.turbos.bwauto.com/aftermarket/matchbot.aspx

U do realize heat is more important than volume though right?

blackmega3500 said:

U do realize heat is more important than volume though right?

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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?

CHDiesel said:

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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Use matchbot.

You guys are getting soft.

Problem with V8s is pulses are not equally timed, so they will never be as efficient as inline 6.