Need Clarification!

[SargeRX8]

Ok I'm in the process of picking parts to upgrade my current turbo. Ive asked for help with some people but someone gave me information which has stumbled me.

I said to him "I'm after a turbo which will comfortably be able to push 19psi". He then replied and said to me "A small turbo pushing 19psi will flow 200hp of air while a big turbo pushing 19psi will flow 400hp(for example) and the bigger turbo will blow your engine".... What the hell? Isn't 19psi of boost just that, 19psi of air going into the engine? If it was anymore, it would be higher. I don't understand.

My current turbo is a rebuilt VL turbo with a Garret 3071 turbine. I'm looking at upgrading to a bigger T3 turbo(going to get something used rather than something new, or get one of those monsta turbos off ebay(I know they're cheap and people say they're crap, but everyone who has bought one hasn't had any issues with them)).

Anyone shed light?

[GTScotT]

check out the dyno thread mate.... ull see people with hiflows running 17 or 18 psi making 230 kw, while ppl running a 3076 will make 300kw on the same.

pressure and flow are not relative, as crazy as it sounds. i wont go into detail, as i think this answers your question.

to your next question: there is a reasonable limit to everything. a small turbo making 200hp at 19psi might not pop your motor while a big one doing the same might, most likely due to the power output.. no matter how much boost you run a standard RB25 isnt going to last forever at 500rwkw, even if its running 10psi of boost (ridiculous arguments sake) theres also the matter of tune state and how hot the charge air is etc etc

this is a BIG can of worms.. so ill let you ask the next question. But beware, your going to be told to search.

[Messiah]

think of it this way, blow air down a pipe at a rate of 1ltr per minute, or you can blow air pressurised to 19psi down a pipe at 1 ltr per minute, or.. you could blow air at 19psi down a pipe at 2ltrs per minute.

make sense now.

[SargeRX8]

It's all coming together now. So the psi rating is the rating of how compressed the air is while the up rating is how much of it is being blow through the turbo! I never thought of the hp measurement. Everywhere I've read is psi psi psi. Ok with this new attained knowledge, at with 18psi of air, how much flow would be suitable to ensure I don't make my motor explode? I'm targetting for about 280rwkw with supporting mods while the engine internal remain intact(I don't want to start changing pistons, valve springs etc).

Now I Donn know what to look for, slot of turbos I see run like 500hp of air. Another factor to consider!

[wolverine]

GT3076 will make the desired power.

[Messiah]

ok... first of all dont worry about making your engine pop, if you manage to do that your doing it wrong.

Your plan is simple, get an turbo big enough that it can flow enough air to make the power you want without being so big that its laggy.

to pad this out, a smaller turbo might need to run more boost to make the power you want.... a big turbo not so much boost as it flows more already, but it will suffer from more lag than a small one.

but this is where my help runs out, i'm not expert at turbo matching. there is a thread dedicated to it tho.

My only advice is, go small enough that you avoid lag, but large enough to give you the power you want plus maybe a little head room for more.

[doo doo]

small turbos running boost outside of their efficiency will heat the air more (becoming less dense=less power- called pressure ratio) as well as requiring retarding ignition to stop pinging at higher temps- no power gain for more boost eventually. Plus you have a smaller exhaust housing which restricts ex gas flow (less power) and piles heat up which keeps cylinder temps up adding to the heat problem etc. Larger turbos can run the same boost at similar flow rates but with much more efficiency- less heat- more power, more ignition timing etc plus a larger ex housing allowing more exhaust gas flow (more power) as well taking out more heat, but at the expense of higher boost threshold (the RPM where you start getting meaningful boost)

Buy Corky Bell's book, 'Maximum Boost' for all the info you need

[SargeRX8]

So you gotta make a sacrifice... This is complicated stuff lol.

I'll see what my uni has for books to gather more info. Ive read alot about the GT3076 and it does look like the turbo I'm after. But they seem more commonly used on 2.0L motors. Reading here and there are a fair few running them on their RB25's with good results but after reading about getting exhaust out of the turbo quicker, I wonder if the extra 2 pistons will produce enough heat and exhaust gases to hinder performance...

Put it simply, if I get a GT3076 with t25 flange + a t25 to t3 flange adapter will I get good results? Any benefits in going externally gated over internally gated? I read that externally gives you better control on boost and helps rid heat from the turbo more effectively.

DAMN THIS IS COMPLICATED!

I also <3 Nazeeee haha

Edited May 20, 2010 by SargeRX8

[That_timothy]

Hey man, basically I'm about to run a 3076 on my car in two or so weeks so I can pass on to you the information I've gathered. BTW what do you do at uni?

PSI, is a pressure reading [pounds per square inch], a measure defined as the average kinetic energy of the gas in a certain volume, or in a more useful description the force that a gas/fluid exerts on the walls of a chamber. Pressure to an extent is irrespective of how much gas there actually is, since if you have REALLY hot gas, it'll have a massive pressure. This is why bottles of coke get really hard if you heat them up without opening the lid. Remember that since gas is easily compressible you're trying to think about the mass of gas that's going through the turbo, since the amount of work, and thus power you'll be able to extract is reliant on the gas releasing it's energy when you ignite it. More gas = more energy => more power. For any given situation you equate this with P*V=m*R*T, where P=pressure, V=volume, m=mass, R=universal gas constant [for mass I think this is 0.287 but you may also see it as 8.315 if you're talking about the number of moles of a gas], and T=temperature [you have to measure this in degrees Kelvin, which are just degrees centegrade + 273.15].

So if you had a turbo at an arbitrary size '1' that was at a certain pressure, it'd have a volume say 'v1'. If you had a turbo at size '2' where the size 2 turbo was twice as big as size 1 [i.e v2=2*v1], and the pressure was the same in both of them, it'd mean that the bigger turbo essentially had twice as much air in it, to maintain the same pressure. Remember that since gas is so compressible

^ ^ This is just year 12 physics stuff really.

For my turbo upgrade I've gotten a 3076 and I've gotten an external gate. I've chosen a Tial 44mm, since Tial have a really good rep, and the one consistent piece of advice is "don't gimp out and buy a cheap gate" since if they go, you can possibly overboost, damage your turbo, and run too high a pressure inside your engine to possibly have a happy time in there.

The upside to external gates is that apparently they control boost a lot better. Downside is that they're expensive [my Tial second hand is $450] and give you more shiney stuff for inspector plod to find in your engine bay. Another downside is that you'll also have to get a new exhaust manifold. For my exhaust manifold I've gone 6Boost, since they're pretty much infallible, come with a lifetime warranty against cracks [these get VERY hot] and it's a serious enough piece of equipment that when you tell people at the pub/cruises they're going to take you seriously and not laugh at you [always bad].

6Boost manifolds cost 1200-1300 though =\ Lots of money.

I'm taking mine to a workshop in about two weeks to have all this go on, and running a china fmic and an ecu tuners tell me I'll hit anywhere up to 370rwhp with everything else stock. From what I hear this is pretty much regarded as the ideal solution for roughly 300rwkw out of an rb25.

YARGHHH I AM A WALL OF TEXT.

Hope that helped =]

[Hanaldo]

Haha good stuff Tim, i actually understood that! Lol.

So by all respects, because a turbo is smaller it requires less volume of air to create say 15psi of pressure? Whereas a larger turbo will pass a higher volume of air, but not create the same pressure

[HtwCHACtkh]

Haha good stuff Tim, i actually understood that! Lol.

So by all respects, because a turbo is smaller it requires less volume of air to create say 15psi of pressure? Whereas a larger turbo passing the same amount of air, will not create the same pressure

fixT...

Another way of looking at this is the conservation of energy. Think of pressure as density energy. The turbo only has so much energy.

Pressure + Kinetic NRG + Gravitational potential NRG = constant

P + 0.5dv^2 + dgh = constant

Where:

P = Pressure

d = density

v = velocity

g = acceleration due to gravity

h = height

Now let's compare two turbo's, one flowing twice as much as the other. _T1 = small turbo _T2 = large turbo.

In both cases the GPE is the same as it follows the same path, so they cancel each other out. Density is the same in both situations, so to simplify it a little further, I'll remove that from both sides too.

This is the law, obey!

P_T1 + 0.5v^2_T1 = P_T2 + 0.5v^2_T2 = Constant

Because we're such law abiding citizens here,

Remembering that the larger turbo flows twice as much as the smaller one, so the velocity of the air inside the larger one is half that of the smaller. (Or the velocity in the smaller is twice that of the larger).

0.5v^2_T2 = 2*(0.5v^2_T1)

0.5v^2_T2 = v^2_T2

If you don't understand this, think about it this way. You want to transport 100 apples through a tube, you have a deadline (no more no less) of 100 seconds to do this. So the flow rate needs to be 100 apples / 100 seconds. If your tube only fits one apple you need to move the apples at 100 apples per second, if your tube fits 2 apples you move your apples at 50 apples per second to achieve the same amount of flow. If you move 2 apples at a time at 100 apples per second like you were doing with your smaller tube, you're doubling your flow rate, moving on!

Lets look at turbo's making 20 psi:

20 psi + v^2_T1 = 20 psi + 0.5v^2_T2 = constant

You can see, to make 20psi the larger turbo has to move the air at twice the velocity (and in turn twice the flow) as the smaller one.

That's twice as much air going into your engine, therefore more power per increase of pressure.

Another thing this law shows you is that if the same amount of air is flowing, the larger turbo will produce half the pressure.

20 psi + 0.5v^2_T1 = 10 psi + 0.5v^2_T1 = constant

You can also easily show that faster moving air is lower pressure generally using the conservation of energy.

P + 0.5v^2 = constant

Double the velocity, in order to keep the constant you must half the pressure.

P + 0.5v^2 = constant = P/2 + v^2

Simple enough isn't it!? =)

[wlspn]

A lot of good info here but I think some of it may be a bit full on for someone just starting to get a grasp on things, especially saying that to move 100 apples in 100 seconds, you need to move 100 apples a second... (haha, it's late dude, I know)

I think one of the easiest ways to explain it is this.

Grab a 600ml coke bottle. Put a hole in it just big enough for the nozzle of a blow-gun (off air compressor) & fill it with air.

Within a few seconds the bottle will be full of air, start to build pressure & will blow off the end or push the gun out.

Now grab a 20L oil drum & do the same thing. it will take a lot longer to build the same pressure...

Once full the pressure will be the same (e.g 5psi) but it takes a larger volume of air to reach that pressure

[KiwiRS4T]

GT3076 will be perfect for 280kw. I'm surprised to see you say they are common on 2L engones - some people think they are too big for an RB25 but at 280kw you will be fine.

You say that people buy ebay turbos don't have any trouble. I am sure that those who buy them and have them blow up in short order don't boast about it. 2nd hand and china copies are a lottery - you may be lucky. I would rather save up a few more dollars and do it once.

[Wheezy]

I didn't bother reading anything after the first post, however the best place to start is here:

http://www.turbobygarrett.com/turbobygarre...bo_tech101.html

http://www.turbobygarrett.com/turbobygarre...bo_tech102.html

This one may be a little above your head at first, but it's worth a read:

http://www.turbobygarrett.com/turbobygarre...bo_tech103.html

[paulr33]

its simple

pressure does not equal volume

volume of air makes power, not pressure

a car tyre at 40psi has lets say 100 units of air

a truck tyre at 40psi has lets say 300 units of air

now we know the truck tyre has more air as its physically larger, but they run the same pressure

moral of the story

how much boost you run means absolutely nothing other than to tell and impress people

id rather make 400HP on 7psi than 400HP on 21psi, but some people prefer it the other way

also be sure to note

boost is pressure above sea level pressure, so actually 19psi is really 19psi + 14 psi for sea level pressure

its know as PSIA so really if your running 19psi boost then the manifold pressure is actually 33psi of absolute pressure (or psia)

go and quote to your mates your running 33psia - i bet that will amaze them

[Dose Pipe Sutututu]

bigger turbo, less restrictions, more airflow

smaller turbo, more restrictions, less airflow

umm how I see it is like a leak in a tyre, the bigger the hole (bigger turbo) the more it leaks, so the more air you need to pump into it to maintain say 19psi.. and say if a smaller leak (smaller turbo) you need less air to maintain that 19psi.. does that make sense????

more air digestion, will require more fuel, which in turn produces more power

[mad082]

a lot of people get a bit confused when it comes to a big turbo and small turbo running the same pressure. they seem to ignore one of the key things that can determine a turbo's performance. the exhaust housing. if you take 2 turbos with the same size compressor housing and alter the size of the exhaust housing you will be able to make different power levels. the one with the larger exhaust housing will make more power, but at higher rpm. the smaller housing turbo will have better response yet make less power at higher revs due to the fact that the smaller housing will become a restriction at higher rpm.

this is lifted straight from the garret website

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 since Engine #2 will be operating at high engine speeds most of the time.

my point is that it isn't just all about how big the compressor is that determines how much power you will get from a turbo. the exhaust housing plays a very big part in it too, because you could have the compressor housing off a truck turbo on your car, but if the exhaust housing is only a small T2 unit off a 1.5L engine then you won't make much power.

[SimonR32]

its simple

pressure does not equal volume

volume of air makes power, not pressure

a car tyre at 40psi has lets say 100 units of air

a truck tyre at 40psi has lets say 300 units of air

now we know the truck tyre has more air as its physically larger, but they run the same pressure

moral of the story

how much boost you run means absolutely nothing other than to tell and impress people

id rather make 400HP on 7psi than 400HP on 21psi, but some people prefer it the other way

also be sure to note

boost is pressure above sea level pressure, so actually 19psi is really 19psi + 14 psi for sea level pressure

its know as PSIA so really if your running 19psi boost then the manifold pressure is actually 33psi of absolute pressure (or psia)

go and quote to your mates your running 33psia - i bet that will amaze them

All correct Except for running 7psi, that's just gay

[SargeRX8]

My brain exploded. Alright, Ive seen to grasp the concept of what were saying here now with pressure and air volume etc. So basically a 400hp turbo will always run 400hp of air regardless of the pressure?

There are so many variations of the GT3076. I found some for $450, some for $700, some for $1000 and some for $2200.... I'm going to keep reading about specific turbos. I know I need a new manifold and a few other parts so I can get them before I get the turbo.

[PM-R33]

My brain exploded. Alright, Ive seen to grasp the concept of what were saying here now with pressure and air volume etc. So basically a 400hp turbo will always run 400hp of air regardless of the pressure?

No.

Have a read of this thread:

http://www.skylinesaustralia.com/forums/Du...+boost+pressure

And this one:

http://www.skylinesaustralia.com/forums/Gt...turbo+boost+add

Heres something I wrote in the other thread which will make you understand it a bit better.

Exactly, boost is a measure of restriction. It means the turbo(s) are pushing that much air, that the engine can't keep up taking it all in so it builds up and increases in pressure. (Think of blowing up a balloon). It is all about volume of airflow! Turbo(s) technically do not create "boost", they create heaps of airflow that as a result of being in an engine environment ends up being pressurised which is what we call "boost". Hence if you pop an intercooler pipe, no restriction, no boost in the intercooler pipes (theres a lot more that comes into play here but in general that's an easy way to think about it).

Edited May 21, 2010 by PM-R33