Okay i dont quite get this hp with the psi thing!? Could you guys put it to more detail for me because i dont get how they work.? if you make high hp and have it at low or high psi, why is that? why do you adjust it higher or lower? more hp the higher or lower psi? some people i've read has 2 to 300 hp and has high psi and some have lower, why is that? i dont know how it works so im asking the professionals, which are you guys. Thanks

 

There is a good thread in the single turbo section on this.

 

http://auto.howstuffworks.com/turbo.htm

 

ok this the watered down version.

We will assume that you have the correct amount of fuel for any given psi

It's rather easy: the higher the psi the more oxygen molecules you are squeezing into the combustion chamber. More oxygen + more fuel = bigger explosion (for a lack of a better term) = more power.

two settings are good. Why be at your cars maximum all of the time?

higher psi = more power

not all setups are the same. Single turbos can squeeze more air at the same psi level as the twin, others run better IC's (cooler air), some have tired turbos, others may have a hiflow cat vs a midpipe, some guys engines have better compression. All this are factors when it comes to HP at the same level of psi.

 

Larger turbo compressors will spin slower producing less heat so the air/PSI produced is more dense with more oxygen, nitrogen and everything else air is made of than the air from the smaller harder working higher air temp producing turbo.

Think Nitrous which is basically a shot of cold air

 

Its not the psi, but rather the CFM's that flow into the engine. Psi is only relative to the turbo that is using it.

 

Generically, the higher the boost pressure (psi), the more hp because you are adding more compressed air into the combustion chamber. You need to add fuel accordingly so you do no detonate.

Here's an example:

10 psi with a small turbo is significantly different than 10 psi with a turbo (i.e. 10 psi with a T04E is different than 10 psi with a T04Z)

 

So every turbo run its psi differently because of the size, blades? So that means that any turbo could put out only so much psi?

for example:
stock engine/turbo with intake and intercooler makes more hp which means psi will go up, right? but with a cat-back added on makes it go drop? because i remember reading this somewhere and then thats when you end up with an aftermarket ecu (PFC) and tune it so it can _________?

 

Like stated above psi is just the pressure of the air you are pushing into the engine. Depending on the turbo the amount/density of that air at the same psi could be more/less.

By changing the intake/IC/exhaust you COULD affect the psi (boost creep - do a search to know that this is), but by changing just hardware mentioned you are not increasing the psi. The engine can make more hp b/c it is getting a cooler charge of air at the SAME psi as before. With a catback you are also positively effecting the exhuast flow allowing the engine to breathe better increasing the hp.

BUT you must be careful b/c not necessarily will you affect psi but you WILL affect the air/fuel ratio and this is VERY important. Too lean and you WILL DEFINATELY blow the motor. This is where the PFC comes in. It allows your tuner to adjust the A/F ratio as well as other engine parameters to keep the engine in good working order.

Do lots of reading on here (stickies are you friend) before you begin to modify your car. Right now it does not sound like you have much automotive knowledge so please don't modify anything anytime soon.

 

Turbo A makes 250hp at 12psi. Turbo B makes 300hp at 12psi. The efficiency of the turbo is what describes this difference. The difference is the temperature of the air.

What's physically happening is that a turbo both compresses and heats the air. It's all goverened by thermodynamics; it's enough to know you can't compress air without heating it. Hot air at 12psi has less molecules (less oxygen) than cooler air at 12psi. So turbo B heats the air less, meaning more molecules and more HP.

Wait, intercoolers are supposed to cool the air, right? Well everything is relative. So a bigger intercooler may make turbo A work better, all things being equal it's still a less efficient system.

Dave

 

an engine is like any other form of fire, give it more fuel and more air and it goes better.
a turbo is a way of giving the engine more air then it could usually breath by itself. Psi is just the pressure of air that the turbo is forcing into the engine.

so what a turbo does is forces pressurised air into the combustion chambers. this pressurised air is in turn mixed with increased amounts of fuel to compensate for the extra air. in turn making more power.

psi is only a measure of the pressure of air that is being forced into the motor.
so the more air you have, the more fuel you can give it, in turn making more power. this is why engines make more power at higher psi because the engine is able to burn more fuel/air.
more psi = more air into engine, mixed with more fuel = more power.

remember that psi is only a measure of pressure not VOLUME.
If we have two engines the same both set to 10psi. it is possible that they make different power. Imagine you have a drinking straw and a water pipe. if you were to pressurise both to 10psi the water pipe would be holding a far greater VOLUME of air in turn being able to supply the engine with a greater VOLUME of air at the same pressure level (psi).

 

What reallly matters is how much air you put in the cylinder for your combustion (there is no explosion in combustion enines appart from knock). This is directly dependant on MAP, Manifold Air Pressure, which is in turn depending on the turbo, the intercooler and ambiant air pressure (and of others like throttle but let's keep that simple).

As per attachment, a turbo (well compressor) characterisitic will be a compression ratio (pressure out of the compressor divided by pressure going in the compressor. Or Pout/Pin). It will compress intake air as a function of the air flow and turbine speed. That is basically the psi mentioned above.
FD turbos have fixed blade geometry but two different turbines. Some newer engines get variable geometry turbos to have similar advantage to the twin turbo but with one turbine only.

As mentioned (by Dave above), compressing the air will get it hotter therefore you have an intercooler that will make it cool down. The colder the air, the more dense. It is a fine compromise and design effort to size the turbo and IC.

If you remember the "perfect gas" law (not sure exactly how it's called):
PV/RT=Mair
P: air pressure
V: volume
R: constant
T: temperature
Mair: Air mass

Which means the higher the compression ratio the more air, but the higher air temperature the less air=> turbo design certainly goes with IC design.

 

It's the "ideal gas law."

 

I can't believe you're 20 years old, own an FD and don't know how an internal combustion engine and turbo work.

-J

 

the most important thing to know about PSI, hp, and flow, with all three being relative to each other, is the turbo's efficiency.

which is why im surprised not everyone who upgrades doesn't read turbo compressor maps.
they indicate at what pressure, rpm, and cfm it is best efficient at, with a given boost pressure. there are points in that map that tell you where the turbo will not make any more power, since you can only go so far above that "ideal efficiency range" where the turbo is just heating the intake charge unnecessarily.

generally speaking, a bigger and more efficient turbo will always make more power with less boost, than a small twin setup that is not very efficient at the same relative psi and tune.

 

actually i do know how the rotary works. i've been reading my stuffs. its just the fact that i just wanted to know how psi and hp works together. plus people dont have automatic knowledge like you here. thats why there's people called beginners. and for people like you bringing them down like that isnt something to be proud about because your smart. im the person of people who dont ask for too much just little things to understand. so if you want to put me down go right ahead i dont mind. and for the others who are helping me out thanks for the information.

 

Well said.

 

In a sense, yes. Theoritically, you can have the turbos spin as much as you want, but this is the real world. The more boost you run (i.e. more the turbo has to spin), the more heat you create. Then this excess warm air is pushed back into the motor which is not optimal.

Turbos have an efficiency range because there is only so much oil and coolant that you can deliver to it to keep it working properly. Once you get over a certain boost pressure, it's pretty much useless. On the stock twins, it's safe to goto 14 psi (with the supporting mods so you don't lean out and blow the motor). There are some guys that run 17 psi and these turbos don't last very long.

If you still don't understand boost pressure...here's an example (I'm not an engineer and don't know the real workings of it but it's my best guess):

You have a 3" pipe and the air running through travels at a velocity of 10 mph (for example sakes). Now, you also have a 3' pipe and the air is traveling at 10 mph as well. Which one is pushing more volume of air?

Here's the bottom line. The more air and fuel you have, the more hp you can generate. So, all a turbo does is increase the amount of air you force into the combustion chamber. The intercooler just compresses the air so that you can get more air into the combustion chamber. Now, the more air you have, the more fuel you need i.e. bigger injectors, fuel pump, rails, etc... to make more hp.

The exhaust side just allows the turbo to spool and generate the air flow. With a less restrictive exhaust, this allows the exhaust to flow more freely and increase the spool time and the amount of air flow. Now, the turbo does not know when to stop making boost (i.e. increased air flow), so you need a wastegate to manage that. When the boost pressure reaches a certain point, the excess air needs to be expelled somewhere and that's the purpose of the wastegate. Boost controllers control the wastegate. I can go on forever about what each item does and give simple examples if you really want, but that's it in a nutshell.