whats a safe PSI to run?

[Carfreak18]

At what PSI for turbos is it safe to run,i was talkin to a kid with a jetta and he runs 24 PSI,also how exactly does a supercharger work?..it runs off the belt right?

[Polygon]

That depends on the turbo, the engine, the fuel system, and quite a few other factors. If you want to know how a super-charger works look at the sticky at the top.

[beyondloadedSE]

like polygon said, it depends on a lot of factors. But in general, small displacement engines can run more psi than larger displacement engines due to the simple fact that smaller engines draw less cfm than bigger engines. It requires more psi to push the same amount of cfm as a larger displacement engine. FWIW, more boost is not always better. There is a limit to every turbo to where it can keep making more boost, but the amount of heat generated actually decreases hp. Believe it or not, I actually know some subura wrx guys that are boosting their turbos beyond its efficiency.

Also, factors such as compression, what size turbo, whether the system is intercooled, altitude, weather conditions, what octane gas, and how well the car has been tuned all play a major role in boost.

[Carfreak18]

thanks taht all helps..what is cfm?..cubic fuel per minute?idk anyway by the way that contour looks pretty crazy.

[KiwiBacon]

Originally Posted by beyondloadedSE

Believe it or not, I actually know some subura wrx guys that are boosting their turbos beyond its efficiency.

Ain't it funny how hard they try.
Even at 15psi (pressure ratio = 2) the efficiency is on the way out. I've heard of clowns trying to run these at 20psi.

Some turbos can efficiently boost to well over 30psi, but they aren't very common in passenger cars.

[UncleBob]

Originally Posted by beyondloadedSE

like polygon said, it depends on a lot of factors. But in general, small displacement engines can run more psi than larger displacement engines due to the simple fact that smaller engines draw less cfm than bigger engines. It requires more psi to push the same amount of cfm as a larger displacement engine.

this is only kinda true. The size of the engine doesn't change how the turbo works. The real issue is with smaller engines, they are more effective due to the smaller combustion chambers.

A properly sized turbo will not be any different on a 1.0L engine, or a 12.0L engine. They both will boost efficiently (reasonable charge temp vs psi). Turbo efficiency doesn't go down just because you are flowing more air...well, I should say, its not that simple anyway.

Anyone that runs 24psi on stock internals without some very carefully thought out engine management system designing and fuel type considerations, is sitting on a very short lived time bomb. But then, you didn't discribe the details of the motor and system. If you spend enough money on a motor, you can make it live through some pretty amazing things. But I assume you're not looking to spend that kind of money

[Carfreak18]

All the info i have on the car is its a 4 door jetta,he mentioned something about a computer chip where he can control the boost,im guessing a boost controller,and other than that I dont think he has any internals done or fuel but I will ask him.

[BeZerK2112]

Another major factor is the compression of the engine. If you have a high compression engine, forcing extra air can be dangerous. Take for instance my Maxima engine. I've read that unless I want to do some major engine work I shouldn't push any more then 6 PSI. Which may not seam like a lot, but in my engine it is. Anything over 6 I chance some major damage to the engine.

I hear about a lot of honda moders that blow their engins very quickly for this very reason.

[Polygon]

Originally Posted by Carfreak18

All the info i have on the car is its a 4 door jetta,he mentioned something about a computer chip where he can control the boost,im guessing a boost controller,and other than that I dont think he has any internals done or fuel but I will ask him.

So, I assume he has a 1.8t? If that is the case then he is full of shit. The stock fuel system can't keep up, and the stock turbo can't provide that much boost without damaging itself.

[BeZerK2112]

Originally Posted by Polygon

So, I assume he has a 1.8t? If that is the case then he is full of shit. The stock fuel system can't keep up, and the stock turbo can't provide that much boost without damaging itself.

Or dammaging whats around it. The wiring harness cant withstand the type of heat that would produce. My brother had the stock turbo maxed out and fried the 1500 dollar harness. You would not only have to mod the engine, but shield all the components in the enginebay if you wanted to run that much boost. Thoes VW's are touchy, anything goes wrong, the whole system shuts down.

[Carfreak18]

Ill find this out from him as soon as i can,also compression ratio I know is measured in the cylinders?..could someone explain this CR to me in details please?

[BeZerK2112]

The compression ratio is between the volume of a combustion chamber and cylinder, when the piston is at the bottom of its stroke and the volume when the piston is at the top of its stroke. The higher the compression ratio, the more mechanical energy an engine can squeeze from its air-fuel mixture. Higher compression ratios, however, also make detination more likely.

You make horsepower by how much air you move through the motor. A high compression 10:1 engine is more efficient than a 7:1 engine, so the 10:1 engine gives you more bang for the buck because the lower compression is not as efficient, it has the ability move more air through it. So, with boost, the 7:1 engine could get a higher compression ratio, which will not cause detonation, and be moving extra air, making more horsepower than the 10:1 engine. The 10:1 engine could be in self-destruct mode and have detonation if you push the same amout of boost through it as you do the 7:1.

It's a touchy process. You have to know what you are doing to make sure you dont blow the engine. Often times mods are required to help handle the higher compression ratio from a turbo or super charger.

[Carfreak18]

Ok,I understand that but I hear detonation alot,is that when the internals go and the motor blows up?

[UncleBob]

detonation is also refered to as pinging, knocking, pre-ignition. Its when something causes the air/fuel mixture in the combustion chamber to ignite before the ignition spark.

What causes it is heat, fuel vapor will ignite at a certain temp, if there is too much heat (a hot spot or what have you) in the chamber, then it will light it off too early. When you increase boost and/or compression ratio, both of those things will add heat. When you ignite it too early, the piston is still traveling upward, and the flame front collides with the piston. This creates extremely high cylinder pressures and things can break....in quite a spectacular fashion.

Detonation is very bad in a boosted engine, because there is so much more force behind the explosion, it can severely damage the motor very quickly. Unlike most naturally asperated engines, which can suffer some occasional detonation with no noticable side effects.

It can break con rods, melt pistons and shatter ring lands. Its the #1 enemy to building a turbo'd engine, and its the limiting factor to what boost you can run.

[Carfreak18]

Well this guy who lives near me always claims that his lifters are "knocking"..is this a different "knocking" from what you just explained?