Quote:
Originally Posted by mct3351
Let's run a little thought experiment. Imagine a majic box capable of unlimited mass flow rate at ambient temperature. Imagine we connected this to the throttle body of an sr20 and asked it to pressurize the intake manifold to 7psi, then took measurements of the mass flow rate as the engine rev'd from 4k rpm to 7k rpm. The mass flow rates measured are measurements of the mass flow rate demand/required to pressurize an sr20 manifold as it rev'd through the rpm range with air at ambient temperature. Remove things like cams, intake manifold and ve from the experiment because we arent changing those things. This majic box experiment is the most ideal/upper limit flow rate required to pressurize the intake manifold, becasue regardless of how effieint a real world compressor is it will heat the air because of the idea gas laws. The power output by the sr20, connected to the majic box, at its peak engine speed will be the peak/absolute maximum power possible, because this is the ideal case. The torque curve will be flat through the rpm range because the cylinders are filling with the mass quantity of air regardless of engine speed. When an intake valve opens the most amount of air mass it can take in is equal to 2.0 liters divided by four cylinders that is pressurized to 7psi. Increasing engine speed will increase the mass flow rate required to maintain 7psi in the intake manifold because there are more intake events in a given amount of time. So the difference is turbos will lie somewhere in terms of flow rate underneath this maximum/ideal case.
Assuming we are using air there are only so many parameters that can affect mass flow rate. Pressure, Volume, Temperature and engine speed. If we are talking about 7 psi manifold pressure and the volume of the engine is fixed as well as engine speed rangre the only remaining parameter that can change is temperature. When a small turbo like a t25 is asked to pressurize the intake manifold of an sr20 to 20 psi it will do so reasonably efficiently up to the mass flow rate limit of its compressor wheel. If the intake manfold pressure does not at some point drop after the mass flow rate limit has been reach that means that it has begun heating the air. Usually what happens when the mass flow rate limit has been reached is a combination of unnecessarily heated air and the intake manifold pressure will drop.
So when comparing the two turbos a t28 and a 2871 as installed on an sr20, they are both capable of producing adequate mass flow rate to pressuize the intake manifold of an sr20 to 7 psi without adding excessive amounts of heat or droping the intake manifold pressure near redline. Yes there will a slight neglible difference in the neighborhood of < 3-5% percent probably (I hope thats not what you are arguing for). But, at 7psi the engine's "pumping" ability will be the mass flow rate limitation. Between the two turbos this is not true at 14 psi. That is when your absolute rule that Xpsi is not equal to X psi becomes true when comparing these two turbos or any other turbo at least as big as a t28 upto and including a t88 on a 2.0 liter.
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How much horsepower does a SR20 with a T25 make at 15 psi?
The same stock SR20 with a 3071R at 15psi?