Sr20det Exhaust system question

[Shift_owned]

do you gain hp or lose hp when you remove your exhaust systemand run only turbo outlet pipe

[Nismo_Freak]

do you gain hp or lose hp when you remove your exhaust systemand run only turbo outlet pipe

Depends, but typically you'd gain.

[SR20DETGUY08]

turbo car needs back pressure. dont see why youd gain. you would lose torque i would think.

[slow s13]

haha why would a turbo car need back pressure, the turbo creates tons of backpressure at the exhuast ports, I think you would definatly gain some power but would you melt stuff or gas yourself?

[JDMracer16]

yea the quicker u can get out exhaust gas on a turbo car, the more power you will gain. But you will most likely start to burn up your exhaust valves.

[Nismo_Freak]

turbo car needs back pressure. dont see why youd gain. you would lose torque i would think.

The following is based 100% on thermodynamic law and principles. So for those of you who think I am wrong, I suggest you begin reading up on it.

I will spell it out to you guys.

The Golden Rule of ExhaustYou want zero backpressure, and the greatest mass flow possible.

You want zero backpressure for any car, turbo, n/a or otherwise. Backpressure resists the flow of the gasses.

This is why:

Gas flows because of one very simplistic principle, the pressure differential between point A and point B.

This is called deltaP (the change in pressure) in short.

Now, the turbocharger gets all of it's energy from this simple equilibrium process. You have the following:

Point A - The exhaust manifoldPoint B - The exhaust system

Inbetween A and B you have the turbocharger.

Within the turbocharger you have a nozzled housing, this nozzle reduces the internal volume within the turbocharger which, according to the ideal gas law (PV=nRT), increases pressure. This high amount of pressure is then directed towards the fins of the turbine, creating kinetic energy (result of axial flow). This in turn drives the compressor and produces "boost".

You will notice that the turbine gains it's energy from the speed of which the air is traveling over the fins of the turbine. This speed is dictated in large part by two factors (simplified).

Factor 1 - Pressure Before the TurbineFactor 2 - Pressure After the Turbine

The pressure difference between Factor 1 and Factor 2 shall now be known as deltaP.

As you increase deltaP you will continue to increase the amount of mass flow throughout the system up until a point. This point is invariably considered the Critical Point.

So let's add backpressure to our situation.

Backpressure is pressure within the exhaust that exceeds atmospheric conditions. It can be summerized as trying to run into a headwind. It is a resistance force, and it reduces the efficiency of the motor by decreasing our deltaP, increasing lag, decreasing power.

Another concept that someone raised is that of the exhaust valves burning up as a result of a large exhaust.

This is an old fable that was started long before the adaptation of sodium filled exhaust valves; which are found on the SR20DET engines. It simply derives from the stagnation of the exhaust flow within the head due to either oversized exhaust runners, which reduce the flow velocity, or due to excessive backpressure which again, reduces the flow velocity.

These principles are why everything works the way it does on engines. Even the fuel pump works on the same principle.

The wind you feel on a breezy day is operating on the same exact principle! Next time take a look at the pressure systems near your region when you experience a windy day, odds are you will be between or near a low pressure area.

[Luke]

Yay for the physics lesson! Now if we could get people to read and retain good information like that, stupid posts and misinformation should disappear!

[xekushnr]

Yay for the physics lesson! Now if we could get people to read and retain good information like that, stupid posts and misinformation should disappear!

yeah, good luck with that. i bet half the people on here just read the first sentence then closed the browser.

[ILikeMy240sx]

Great engineering lesson except after a nozzle, pressure would decrease not increase. A diffuser on the other hand would increase pressure.

oh and PV=nRT doesn't apply to steady flow devices like nozzles, in this case you would use energy eqn.

one more; youd want a nozzle before a turbine because it increases the fluid velocity hence increasing KE -> more energy to drive the turbine blade. Not because nozzle increases pressure. (i think you mentioned that in your post)

[Nismo_Freak]

Great engineering lesson except after a nozzle, pressure would decrease not increase. A diffuser on the other hand would increase pressure.

oh and PV=nRT doesn't apply to steady flow devices like nozzles, in this case you would use energy eqn.

one more; youd want a nozzle before a turbine because it increases the fluid velocity hence increasing KE -> more energy to drive the turbine blade. Not because nozzle increases pressure. (i think you mentioned that in your post)

When I said pressure I meant to say velocity, and I don't quite know where PV=nRT came from, I think I was thinking more along the lines of reducing area lol.

I was seeking more of a simplified response, not wanting to dive too far into all the cause and effect.