gt2871r will run okay?

[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.

Originally Posted by codyace

'Runs well' and 'Runs right' are certainly two different things. Kids run 15/16 psi on a t25 without issues, others explode them at 10.

It's not worth the risk, or the minimal gain to push my luck. You're not getting a trophy for running it, and nissan ain't helping you rebuild it if explodes, so why bother pushing it.



What does efficiency islands have to do with total air flow like Justin is trying to explain to you? 70% efficiency on a turbo that doubles the flow of a another turbo in the 80% efficiency is MUCH more air flow and MUCH more power.

7 psi is not 7 psi on anything. t25 to gt35, YSI to F2.

I think what you are trying to say, is that at 7 psi neither the t28 or the gt28xx will blow up the engine...and that's probably true. BUT that's not to say that 7 psi is the same amount of total flow from both. You can NEVER relate BOOST per safe....A t25 car with S3 cams will push everything past the limits, it just flows air like crazy.


So while you may be right about 7 psi not making a difference, your explanation is totally wrong.

Offtopic What I'd like to see is a comparison (albiet it will never happen) of a t25 at 14 psi vs a 28xx at 7 psi to see what has a better average power band....and then measure it across time.