HondaRacer32

Hey wat does the amount of psi mean when it comes out of the turbo and why the more the better?

Bailhatch

pounds per square inch = psi Well more is better because the more compressed the air is the more oxygen it contains. With more oxygen and more fuel you can make more power if evertything else is setup for it. remember 10 psi form a small turbo pushes just as much oxygen as 5psi from a big one.

stinger

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Bailhatch &raquo;</TD></TR><TR><TD CLASS="quote">pounds per square inch = psi Well more is better because the more compressed the air is the more oxygen it contains. With more oxygen and more fuel you can make more power if evertything else is setup for it. remember 10 psi form a small turbo pushes just as much oxygen as 5psi from a big one. </TD></TR></TABLE>


basically right the theory that a small turbo needs to run 10psi compared to a bigger one running 5psi and making same or more power is because of efficency. The bigger one is more efficent and the air is more dense so it makes same power at lower boost.

Johnyquest

To correct the above post, the reason bigger turbos make more power is mainy (99%) due to the fact that the bigger turbo's have bigger hotsides, which is in essence, a less "restrictive" exhaust, allowing for more power at the same boost level. As was shown in the extrememly long post of a week or so ago, 1psi = 1psi no matter what the compressor size, if the exhaust sides of two turbos are equal. The only time this becomes untrue is when you are overworking a given compressor and superheating the charge.

stinger

to correct you 1psi= 1 psi is incorrect. If you are trying to max out say a stock turbo off a gst or gsx and say run 20psi off of it that air is less dense due to its maximg the turbo out causing that air to be hot. Now lets say you have a t78 and run 20psi off of it. One yes does have a bigger wheel/turbine. But it is also in its efficency range to run 20psi making more power then the stock turbo. That air is also more dense so you can put more into the motor.


Ive talked to Turbonetics many times to get them to explain it to me and thats how they said it to be. they also have math to prove it.

stinger

PS where is this other topic you talked about?

Bailhatch

poor guy just wanted a simple anwser....

stinger

SIMPLE ANSWER!!!!!


PSI=How much air you put into the motor
More then better, The more air you put in the more fuel you can put in creating pony-power!

Mad Cow

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


PSI=How much air you put into the motor
More then better, The more air you put in the more fuel you can put in creating pony-power!</TD></TR></TABLE>

Power is more about flow than pressure.

boosted92

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

Power is more about flow than pressure. </TD></TR></TABLE>

Exactly. Boost is just a measure of restriction your motor places on the turbocharger.

If your theory was correct about 1psi = 1psi if the exhaust housing is the same, then a T4/60-1 with a .81 A/R housing and a Q-trim wheel would make very similar if not the exact same power as a T72 with a .81 A/R housing and a Q-trim wheel.

Johnyquest

pv=nRt

It's physics, and I didn't make it up.
The million page post I'm talking about:

https://honda-tech.com/zerothread?id=710270

Read it all and you'll come to the same conclusion. 1psi=1psi, no matter how you look at it.

If you need an easier way to think about it, how's this:
Forget turbochargers for a minute, lets just say you have a giant tank of air. You pressurize your car's intake @ 10psi. Now lets say you have a tank of air that's half the size. You still pressurize the intake at 10psi. You get the same power.

Now lets say you have one big tank, and you pressureize the intake via a 1" hose at 10psi. Now we have a pressure and a size restriction. You then proceed to pressurize that same car's intake manifold at 10psi via a 2" hose.

Those two scenarios above will make the exact same power right up until the flow of the 1" hose @ 10psi becomes less than that of which the motor requires. You will then experience a pressure drop. This is what happens when your ko3 on your jetta loses boost towards redline: The turbo is too small.

The only thing that would actually make a difference in power in all of the above scenerios that is left is the exhast restriction. For the above examples, we used an air tank instead of a turbo. When the "air tank" is replaced with a turbo, the only change is the exhaust side of the turbo you choose. It's really logical if you think about it, and I don't think it needs too much more anaylisis. A bigger turbine size = more lag + more power for a given boost level due to less exhaust restriction. This is the simple explanation of why (in a given turbos efficiency range) you have to boost higher to acheive the same power (and in essence overcome the self induced restriction the turbo itself induces).

tjbizzo

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by stinger &raquo;</TD></TR><TR><TD CLASS="quote">SIMPLE ANSWER!!!!!
PSI=How much air you put into the motor</TD></TR></TABLE>

Well..almost. Boost pressure is better understood as how much force you have available to push air into the engine. (OK, to be exactly technically correct pressure is force per unit area, but close enough) More psi is better because you can push more air into the engine to make more power with.


<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by MadCow &raquo;</TD></TR><TR><TD CLASS="quote">Power is more about flow than pressure. </TD></TR></TABLE>

True, but this doesn't mean that a higher flowing turbo will make more power. Both too big and too small of a turbo are both bad. Don't forget that the efficiency island has a low side too. Left of that is also very inefficient and heats up the charge air as much at the same pressure ratio as being too far to the right, just at a lower flow rate.


<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by boosted92 &raquo;</TD></TR><TR><TD CLASS="quote">Exactly. Boost is just a measure of restriction your motor places on the turbocharger.</TD></TR></TABLE>

Well...er...um...I guess so!?#% But it is more correct to say that boost is just a measure of the pressure in the intake manifold created by a turbo, and we'll leave it at that.


<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by boosted92 &raquo;</TD></TR><TR><TD CLASS="quote">If your theory was correct about 1psi = 1psi if the exhaust housing is the same, then a T4/60-1 with a .81 A/R housing and a Q-trim wheel would make very similar if not the exact same power as a T72 with a .81 A/R housing and a Q-trim wheel.</TD></TR></TABLE>

Yes, that is correct that 1psi AT A GIVEN TEMP (i.e. efficiency) = 1psi AT THE SAME TEMP if the exhaust housings are the same, although for any two turbos this will probably happen at only one specific flow rate. Below that and the smaller turbo wins. Above that and the larger turbo wins.

OK, now brace yourself. Consider this for a moment. At a low flow rate like 5 lb/min, an IHI RHB5 at 5psi will make more power and be more efficient than a T78 at 8 or 9psi. That's right, you heard me, RHB5 whippin *** on a T78! If you don't believe me, look at the flow chart for a T78. It is terribly inefficient at low flow and low boost, and the RHB5 is in its sweet spot and will totally KICK ITS ***! Except here on H-T where bigger is always better.

stinger

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

OK, now brace yourself. Consider this for a moment. At a low flow rate like 5 lb/min, an IHI RHB5 at 5psi will make more power and be more efficient than a T78 at 8 or 9psi. That's right, you heard me, RHB5 whippin *** on a T78! If you don't believe me, look at the flow chart for a T78. It is terribly inefficient at low flow and low boost, and the RHB5 is in its sweet spot and will totally KICK ITS ***! Except here on H-T where bigger is always better. </TD></TR></TABLE>

I agree with you at the T78 making less power at 5psi. This is true because its out of its efficency rage yes. now if you were using a small turbo maxing out at 25psi and that same t78 at 25psi the t78 would win being closer to its efficency range.

stinger

all he wanted was a simple answer haha

kpt4321

Compressor efficiency doesn't have much to do with flow or power. And I too have the math to prove it.

Hot side flow is what matters.