JThrasher79

why do i hear people say that PSI is irrelivant when discussing turbo setups?

I would assume manifold pressure is manifold pressure no mater how it gets there.

HiProfile

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by JThrasher79 &raquo;</TD></TR><TR><TD CLASS="quote"> manifold pressure is manifold pressure no mater how it gets there.</TD></TR></TABLE>

Correct, but your motor is also effected by exhaust pressure. There's also turbo efficiency that screws up the psi equation, housing sizes, etc. THAT is why a [t4/]T67 will make more power at 5psi than a T25 at 20psi on a 2.0L motor.

Running925

One word.

Volume

JThrasher79

i can only see a difference in the turbos getting the air there at different times and that would cange the power. i dont see how 5psi would make less power than 20psi on the same motor.

JThrasher79

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Running925 &raquo;</TD></TR><TR><TD CLASS="quote">One word.

Volume</TD></TR></TABLE>

volume would explain how fast the air would get there and maintain but if whatever turbos can do that then wouldent 10psi=10psi

RC000E

If you have ever had a motor with a 14b at 10psi, then that same motor with a GT35 at 10psi, you'd believe it.

I went into length on why this is what it is. Basically pressure is the result of restriction, restriction changes at various rpms due to ve, and how different turbo's keep up with the change based on their efficiency and flow capability at the turbine is why there's a big difference.

The reason people don't understand this is because they don't understand how a compressor map relates to their motor or their needs. Go find that other thread and read...it's only like a day old in this same forum.

Schister66

its all about volume...just like everyone else already said. If you learn to read compressor maps, it might help you understand it a little better. Basically though, turbos move a certain amount of air at a given pressure. The real measure of a turbo's output is in lb/min. If you can grasp that concept, you're golden.

I'm sure someone can elaborate a little more on this subject....

fastcrxsi90

mass flow rate...

for example: check compressor maps of two different turbos at a pressure ratio of 1.68 (~ 10psig)

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

RC000E

The reason noone on here understands this concept is because of people and all their one liners...no offense.....

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Running925 &raquo;</TD></TR><TR><TD CLASS="quote">One word.

Volume</TD></TR></TABLE>

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by fastcrxsi90 &raquo;</TD></TR><TR><TD CLASS="quote">mass flow rate...

for example: check compressor maps of two different turbos at a pressure ratio of 1.68 (~ 10psig)

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

</TD></TR></TABLE>

This doesn't tell a guy who knows nothing about this anything.

I went through a big thing about this on a DSM forum, so there are alot of people that know it happens but don't know why. I've been thinking of putting together a write-up on my site pertaining to it to try and get people on the same page.

Once you understand flow maps and your setup, you can approximate when the turbo will spool, how the setup will pull, even an approximate hp output at a given pressure. This is the core way to choose the right turbo.

Honda-Tech has always had their "hype" turbo's....the 60-1's, then the SC61's, then the GT35's, etc. Alot of guys always just relied on posts to tell them what will make what power. There's nothing wrong with that, but I'm just saying there is a better way if you have specific goals.

I think I'm gonna start on the write-up tonight and try and make this all clear.

nowtype

https://honda-tech.com/zerothread?id=1633516

JThrasher79

thank you. i got the answer i wanted.

JaredKaragen

yep, it's pretty simple to think of:

volume vs. pressure

u can have 300psi running in a .25" tube, but 50psi in a .50" tube will yield better flow.

delslo93

Yeah I had it explained like this to me....

You can have a garden hose spraying 10 psi of water and a fire hose spraying 10 psi of water. It's a given the fire hose is pumping a lot more water than the little garden hose.

SOHC_MShue

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by delslo93 &raquo;</TD></TR><TR><TD CLASS="quote">Yeah I had it explained like this to me....

You can have a garden hose spraying 10 psi of water and a fire hose spraying 10 psi of water. It's a given the fire hose is pumping a lot more water than the little garden hose. </TD></TR></TABLE>
Exactly. The more air you flow the more power you will make.

nowtype

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by delslo93 &raquo;</TD></TR><TR><TD CLASS="quote">Yeah I had it explained like this to me....

You can have a garden hose spraying 10 psi of water and a fire hose spraying 10 psi of water. It's a given the fire hose is pumping a lot more water than the little garden hose.

</TD></TR></TABLE>

Not exactly. Read the thread I linked to above. Read specifically my statements on page 2. One thing you will notice between your home hose and a fire hose, the diameter of the thing. Kind of makes your way of thinking not so valid in this case. If you hooked up a garden hose to a fire hydrant, I bet you would get a little higher than the pressure you would see from your house. More pressure = more flow. I bet if you hooked up a fire hose to your house, you would see a drop in pressure. Less pressure = less flow. I bet if you had both circumstances where the pressure was the same, the flow would be the same, big hose or small hose.

sohczcturbo

CFM = Cubic Feet per Minute.

Both turbo's might be pushing 5 lbs of boost, but the larger turbo is going to be pushing more C.F.M.'s than the smaller one. Intercooler piping comes into play for varying psi. If the same amount of air is forced into a 2.5" pipe and a 2" pipe, which will have a greater psi? The smaller one. Dunno if this helps any. Didn't read full topic, just first few posts.

Killa

psi reading = force / area, in this so if you have the same psi reading with different turbos then the area will be greater on the bigger turbo, this means that it's pushing more volume to do so. psi reading isn't too relevant.

Killa

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

Not exactly. Read the thread I linked to above. Read specifically my statements on page 2. One thing you will notice between your home hose and a fire hose, the diameter of the thing. Kind of makes your way of thinking not so valid in this case. If you hooked up a garden hose to a fire hydrant, I bet you would get a little higher than the pressure you would see from your house. More pressure = more flow. I bet if you hooked up a fire hose to your house, you would see a drop in pressure. Less pressure = less flow. I bet if you had both circumstances where the pressure was the same, the flow would be the same, big hose or small hose.</TD></TR></TABLE>

But the fire hose will flow more water at the same pressure as the garden hose, bigger diameter + constant force (pressure) = more flow.

Not here to argue but i'm an application specialist for a company that only deals with pressure, we deal directly with the engineers, not product distributors that only want to sell stuff.
hope this helps

Paul

nowtype

Um, if you flow more air into the same volume, pressure will increase. The only way to flow more air into the same volume and keep pressure constant is to increase volume. The difference in volume because of the compressor and it's housing is relatively minimal. The difference lies on the exhaust side and how much room the turbine can make in the engine. It's all been discussed and written out. There is no reason for half thoughts on this topic any longer.

Killa

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by nowtype &raquo;</TD></TR><TR><TD CLASS="quote"> The difference lies on the exhaust side and how much room the turbine can make in the engine. It's all been discussed and written out. There is no reason for half thoughts on this topic any longer.</TD></TR></TABLE>

I'm afraid that im not following you, what do you mean by " how much room the turbine can make in the engine"? Are you talking about larger turbine = higher VE? Sorry but im not following you here.

nowtype

You have air sitting on both sides of the engine. One is good air, ie the intake. The other is ****, the exhaust. With a turbo'd system, we stick a huge restriction on the exhaust side. The restriction causes reversion. Reversion causes VE to drop. VE is volumetric efficiency. Basically running 90% VE on a 1 L engine is like running 100% VE on a .9L engine. So your theoretical volume is decreasing. If you increase your volume, by decreasing reversion, you're making more room for air to come from your turbo.

tony413

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by nowtype &raquo;</TD></TR><TR><TD CLASS="quote">Um, if you flow more air into the same volume, pressure will increase. The only way to flow more air into the same volume and keep pressure constant is to increase volume. The difference in volume because of the compressor and it's housing is relatively minimal. The difference lies on the exhaust side and how much room the turbine can make in the engine. It's all been discussed and written out. There is no reason for half thoughts on this topic any longer.</TD></TR></TABLE>

i think he messed up the wording and meant to say mass not volume. you can have different masses of air within the same psi. volume is the area and mass is the the amount of air in that volume

Killa

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by nowtype &raquo;</TD></TR><TR><TD CLASS="quote">You have air sitting on both sides of the engine. One is good air, ie the intake. The other is ****, the exhaust. With a turbo'd system, we stick a huge restriction on the exhaust side. The restriction causes reversion. Reversion causes VE to drop. VE is volumetric efficiency. Basically running 90% VE on a 1 L engine is like running 100% VE on a .9L engine. So your theoretical volume is decreasing. If you increase your volume, by decreasing reversion, you're making more room for air to come from your turbo.</TD></TR></TABLE>

I know what VE is, thank you, however, you make no sense. For that you can stick a T25 with a .69 turbine a/r P trim together and make more power than a T3/T4 50 trim with a .48/3 hotside correct? The only thing that would happen would be massive lag on your 1.6 with the T25 compressor matched to the P trim .69 hotside opposed to more power in the 50 trim T3/T4. Exhaust backpressure doesnt exactly mean that you're making less power, it's something that you dont really want but doesnt always translate into that, the compressor is what's pushing masses of air into the motor.

Psi is really just a restriction, turbo will flow mass.
hope you understand.

tony1

Nowtype is right, one of the few that have it right in this post. Read what he wrote, then think about it, then read it again. It's right.

Anybody throwing out volume, cfm, water hoses, etc. needs to research the subject a bit more. I'm not going over it again, it's been covered plenty of times on here and i've written plenty about it.

nowtype

Turbo's flow air. Everything has mass. The mass of the air won't change dramatically unless you're temp changes dramatically. This is where compressor efficiency comes in, but honestly, it doesn't play a huge role. For our purposes we can ignore the temperature changes so basically mass is the same. But if you want to bring in mass, yes the mass of the air will change from one turbo to another based on temperature. If the temps are the same, the masses will be the same.

You are changing too many variables in your thoughts. Ever look at a dyno, two turbos, one smaller and one larger and both make almost the same power? It happens a lot at 5-12psi on our motors. The reason is because the pressure ratio between exhaust and intake are about the same. The differences are when pressure ratios change, you will notice power will change.