Oleg

Why do bigger turbos make more hp on the same psi levels?
If you are running b18 , for example, 8 psi on td04-18g you make like....200hp
8 psi on t3t4 supposedly makes 300hp

Why is that if the amount of air entering the engine is the same for the same psi levels.
amount of air = density (according to psi) * Area of your TB * Time

Is it due to the difference in the exaust housing?
Thank you.

Running925

This has definatly been covered before, many times.

It's a volume issue.

Oleg

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Running925 &raquo;</TD></TR><TR><TD CLASS="quote">This has definatly been covered before, many times.

It's a volume issue.</TD></TR></TABLE>

Volume of what?

94whtgsr

volume of air the turbo pushes

Oleg

don't get me wrong, this topic was covered a number of times, but it's a complicated issue and I had a hard time finding the clear and correct responce.
The closest topic that came to getting the answer is here:
http://wzus.ask.com/r?t=p&d=us....html

Civicman86

Its all about how much air the turbos flow, often refered to as CFM.

Best illustration I have heard yet. Say we are talking about 10psi. We take a straw and a water hose. We hook it up so they both are making 10 pounds of pressure. Which will flow more water? This goes the same for a turbo. There are different size turbos that will flow more air than a smaller turbo.

Oleg

Ok......We have two straws(tb) the same diameter with the same amount of pressure(psi) = me get the same waterflow..... ????

stockb18c

let say your eletric fan in your house is 2 inches big and it spins 15 mph..then you have a 2 foot fan that spins 15 mph which one are you goin to feel more??????DUHHHH

adseguy

No No No god damnit!

I saw this post and instead of screaming SEARCH!! I just didn't answer. but now a bunch of misinformation showed up so I have to clear it for the next guy who searches the topic.

2 Things:

1.) Volumetric Efficiency: You were on the right track saying Turbine size makes a difference....it does. The larger the turbine the greater your volumetric efficiency. VE (for short) is how well your engine inhales and exhales. We'll just talk about the exhale part. The smaller the turbine the more reversion of bad gases will stay in the cylinder or get pushed back into the cylinder. Obviously this will loose power. Go too big and you just won't spool up the turbo in time to make boost. Pretty easy concept right?

2.) Efficiency (NOT FLOW!!!!!!) Turbo are bascially pumps. Physics 101 says the more pressure is exerted on a gas the more heat it generates. The larger your "pump" or compressor side and wheel and this and that (all efficiency related) the less heat you will place on the air. Small turbo at the limit of their max CFM really blow out very hot (and dangerous) air. The hotter the air, the less dense, the less oxygen content....you know where I'm going with this.

The whole straw thing is patethic and everyone should stop spreading that around.

tony1

That's all wrong, you guys are making the straws and water hoses your restrictions, in which the restriction is a different size each time. The motor is the restriction, and it's the same with both turbos....

The only way to make more power is to change the mass of air entering the cylinder. Figure out how to do that, and you've figured out how to make more power.

jetlude

Wow!! glad for this topic....While at it answer this. What would happen if I switch my compressor housing from 50a/r to 70 a/r . would I get more flow/hp with greater spool time?

mighty137

Keep in mind as well, just because its a larger turbo doesn't mean it will always flow more CFM. Its also the design of the turbo that makes the diff, like bb as compared to a non-bb. EFFICIENCY is the word!!!

Legion

Why do so many people on h-t think that every discussion can be summed up with a straw analogy?

Q: "Why is a bigger exhaust better?"
A: "Well, let's say you have two straws..."

Nothing on a car is ever simple enough to break down to a simple straw analogy. There should be a "graduate only" forum where only the people who went to college can post

tony1

I didn't go to college.

bmxican

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by tony1 &raquo;</TD></TR><TR><TD CLASS="quote">I didn't go to college. </TD></TR></TABLE>

yeah, that was a horrible analogy he used aswell. Especially for a college grad.

tony413

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by tony1 &raquo;</TD></TR><TR><TD CLASS="quote">I didn't go to college. </TD></TR></TABLE>

way to save money for your car j/k

an to OP: look at a compressor map and see the difference in CFM's at given ratios that should answer your question. or think about density can you poke your finger into a bundle of 1,000 pound block of feathers or a 1,000 pound block of aluminum ? both have the same mass but one is not as dense and can be easily dented

HiProfile

IIRC overall air mass is determined based on the pressure ratio and efficiency of the turbo. A larger turbo makes more power per psi because you usually see them with bigger turbines & AR's for both sides, and that combined with a larger compressor (better high-end flow) means it will hold the torque for much longer.

<U>So we're back to VE</U>. A small turbine ends up being a restriction, bringing down top-end VE, then the decreasing efficiency of a small compressor brings down top-end VE more.

If ever there was a 'silver bullet' in this mess of straws and half-ton bags of fluff, its the word RESTRICION. As the rpm's raise, the amount of required air to hold torque raises, and a restriction of any sort brings top-end torque down.


A T3 and a T3/T04 that are <U>at the same PSI and efficiency </U>[on the compressor map] will make virtually the same <U>TORQUE</U>. The one with the highest average efficiency between the compressor and turbine will make the most <U>HORSEPOWER</U>.

B and B

iTrader: (3)

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by tony1 &raquo;</TD></TR><TR><TD CLASS="quote">I didn't go to college. </TD></TR></TABLE>

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by tony413 &raquo;</TD></TR><TR><TD CLASS="quote">way to make money from cars </TD></TR></TABLE>

fixed ...you are 412 levels down

tony413

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by B and B &raquo;</TD></TR><TR><TD CLASS="quote">

fixed ...you are 412 levels down
</TD></TR></TABLE>

lmao what

Legion

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by bmxican &raquo;</TD></TR><TR><TD CLASS="quote">

yeah, that was a horrible analogy he used aswell. Especially for a college grad. </TD></TR></TABLE>


I didn't use any analogies!

This thread is confusing .

Oleg

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by adseguy &raquo;</TD></TR><TR><TD CLASS="quote">No No No god damnit!

I saw this post and instead of screaming SEARCH!! I just didn't answer. but now a bunch of misinformation showed up so I have to clear it for the next guy who searches the topic.

2 Things:

1.) Volumetric Efficiency: You were on the right track saying Turbine size makes a difference....it does. The larger the turbine the greater your volumetric efficiency. VE (for short) is how well your engine inhales and exhales. We'll just talk about the exhale part. The smaller the turbine the more reversion of bad gases will stay in the cylinder or get pushed back into the cylinder. Obviously this will loose power. Go too big and you just won't spool up the turbo in time to make boost. Pretty easy concept right?

2.) Efficiency (NOT FLOW!!!!!!) Turbo are bascially pumps. Physics 101 says the more pressure is exerted on a gas the more heat it generates. The larger your "pump" or compressor side and wheel and this and that (all efficiency related) the less heat you will place on the air. Small turbo at the limit of their max CFM really blow out very hot (and dangerous) air. The hotter the air, the less dense, the less oxygen content....you know where I'm going with this.

The whole straw thing is patethic and everyone should stop spreading that around.</TD></TR></TABLE>

Thank you for the great explanation....

Civicman86

Isnt that the whole point of using either a super or turbocharger? Your compressing air to make it denser? And same said for using an efficient intercooler that will make the air denser.

I thought the straw comparison was a good one lol. I mean its somewhat about efficiency. The smaller dia hose can only push so much substance through it. lol Im just going to stop now. Listen to them they know better than me Tony1 knows his ****, he could tell me **** could fly and I would beleive him, haha jk.

EDIT I went to search for more information on this. It looks like all these ideas play a role in how it works, flow of the turbo which is pretty much derived from the effciency of the turbo. Anyways just read this. They dont so much talk about two different turbos at different sizes, but same turbo with different hot side AR's (larger vs smaller). So might not be exact whats on topic but a good read none the less. This is from Garrett's website too.

The A/R parameter has different effects on the compressor and turbine performance, as outlined below.

Compressor A/R - Compressor performance is comparatively insensitive to changes in A/R. Larger A/R housings are sometimes used to optimize performance of low boost applications, and smaller A/R are used for high boost applications. However, as this influence of A/R on compressor performance is minor, there are not A/R options available for compressor housings.

Turbine A/R - Turbine performance is greatly affected by changing the A/R of the housing, as it is used to adjust the flow capacity of the turbine. Using a smaller A/R will increase the exhaust gas velocity into the turbine wheel. This provides increased turbine power at lower engine speeds, resulting in a quicker boost rise. However, a small A/R also causes the flow to enter the wheel more tangentially, which reduces the ultimate flow capacity of the turbine wheel. This will tend to increase exhaust backpressure and hence reduce the engine's ability to "breathe" effectively at high RPM, adversely affecting peak engine power.

Conversely, using a larger A/R will lower exhaust gas velocity, and delay boost rise. The flow in a larger A/R housing enters the wheel in a more radial fashion, increasing the wheel's effective flow capacity, resulting in lower backpressure and better power at higher engine speeds.

When deciding between A/R options, be realistic with the intended vehicle use and use the A/R to bias the performance toward the desired powerband characteristic.

Here's a simplistic look at comparing turbine housing geometry with different applications. By comparing different turbine housing A/R, it is often possible to determine the intended use of the system.

Imagine two 3.5L engines both using GT30R turbochargers. The only difference between the two engines is a different turbine housing A/R; otherwise the two engines are identical:
1. Engine #1 has turbine housing with an A/R of 0.63
2. Engine #2 has a turbine housing with an A/R of 1.06.

What can we infer about the intended use and the turbocharger matching for each engine?

Engine#1: This engine is using a smaller A/R turbine housing (0.63) thus biased more towards low-end torque and optimal boost response. Many would describe this as being more "fun" to drive on the street, as normal daily driving habits tend to favor transient response. However, at higher engine speeds, this smaller A/R housing will result in high backpressure, which can result in a loss of top end power. This type of engine performance is desirable for street applications where the low speed boost response and transient conditions are more important than top end power.

Engine #2: This engine is using a larger A/R turbine housing (1.06) and is biased towards peak horsepower, while sacrificing transient response and torque at very low engine speeds. The larger A/R turbine housing will continue to minimize backpressure at high rpm, to the benefit of engine peak power. On the other hand, this will also raise the engine speed at which the turbo can provide boost, increasing time to boost. The performance of Engine #2 is more desirable for racing applications than Engine #1 where the engine will be operating at high engine speeds most of the time.



Modified by Civicman86 at 5:26 AM 5/9/2007

tony413

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Civicman86 &raquo;</TD></TR><TR><TD CLASS="quote">

Turbine A/R - Turbine performance is greatly affected by changing the A/R of the housing, as it is used to adjust the flow capacity of the turbine. Using a smaller A/R will increase the exhaust gas velocity into the turbine wheel. This provides increased turbine power at lower engine speeds, resulting in a quicker boost rise. However, a small A/R also causes the flow to enter the wheel more tangentially, which reduces the ultimate flow capacity of the turbine wheel. This will tend to increase exhaust backpressure and hence reduce the engine's ability to "breathe" effectively at high RPM, adversely affecting peak engine power.

Conversely, using a larger A/R will lower exhaust gas velocity, and delay boost rise. The flow in a larger A/R housing enters the wheel in a more radial fashion, increasing the wheel's effective flow capacity, resulting in lower backpressure and better power at higher engine speeds.

When deciding between A/R options, be realistic with the intended vehicle use and use the A/R to bias the performance toward the desired powerband characteristic.

Here's a simplistic look at comparing turbine housing geometry with different applications. By comparing different turbine housing A/R, it is often possible to determine the intended use of the system.

Modified by Civicman86 at 5:26 AM 5/9/2007</TD></TR></TABLE>

honestly if you wanted to speed up exhaust gas velocities in order to spin a bigger A/R turbine. you could use narrow IN. diameters of your manifold or construct it like a velocity stack where the incomming gas feed into a large dia. then goes through a narrow dia. tube and then exits into a large dia. tube that feed into the turbine. higher speed gases should spin the turbine faster an reduce spool time.

certain people DONT FLAME as this is only a theory that i have.

Civicman86

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by tony413 &raquo;</TD></TR><TR><TD CLASS="quote">

honestly if you wanted to speed up exhaust gas velocities in order to spin a bigger A/R turbine. you could use narrow IN. diameters of your manifold or construct it like a velocity stack where the incomming gas feed into a large dia. then goes through a narrow dia. tube and then exits into a large dia. tube that feed into the turbine. higher speed gases should spin the turbine faster an reduce spool time.

certain people DONT FLAME as this is only a theory that i have. </TD></TR></TABLE>

You mean like an hourglass shape to speed the gas velocity up in the smaller section? It seems like it could work, only thing I would be worried about is flow restriction, and once your worry about that you are pretty much chasing the same problem you were trying to avoid with the turbine side of the turo.

mattcivic

this is exactly why i get away with running 13lbs on my bone stock a6 becasue my turbo is super small people **** a brick when i tell them that but they are dumb and dont understand that the 13lbs my t3 makes isnt crap compared to like an sc61 pushing 13lbs...... silly kids boost is for grown ups.