| How do you know that he wasn't exceeding the limits of his compressor? Wouldn't this support my position that higher VE will see lower max boost because the superior flow through the engine will exceed what is capable of the compressor? He wasn't exceeding the limits of the compressor given the boost plot data that we have on his car. The "new" compressor map overlay I put together in this post [ http://twinturbo.net/net/viewmsg.aspx?forum=general&msg_id=1839972 ] shows that he isn't even reaching the compressor's maximum capability. The black lines showing airflow at given RPM's is reflecting 100% volumetric efficiency, so the overlay plots I have added are likely in reality, slightly shifted to the left (100% VE in all cases is impossible to achieve), so we can clearly see that we are not beyond the capabilities of the compressor - his turbine section simply isn't providing the energy to the turbine to bring the compressor into its higher pressure ratio operating range. This refutes the claim that a higher VE is the source of the lower maximum boost; in actuality, it is the boost characteristic that is affecting the VE(massflow; explained below how these two basically have to be viewed as one in the same with FI setups) - Seb's car, Dee's car, and my car are all making the same peak power at the same RPM, which suggests that we are all operating at identical massflow rates at that peak. If it were the VE at fault, one would expect there to be a difference in power output at this peak we are looking at. Also, it is clear that the massflow is much lower in Seb's car from 2500RPM to 6000RPM where it is making considerably less power and torque: given this information, would you still say that his car has higher VE? What is happening here is pretty simple to understand: it isn't about volumetric efficiency, it is all about how the compressor is functioning, which is solely dependent on the ability of the turbine to generate shaft speed. But, Dee can't make any more than he already is - that was the limit. Of what? his compressor or hot section? Dee's setup cannot produce more than 26psi. It simply will not do it. Again, this is because his balance of parts is not allowing the compressor to achieve the necessary rotational speed to generate a higher PR, rather than him outflowing the compressor (see boost plot overlay to comp map). Don't confuse VE and mass flow...VE is a unitless measurement that is not dependent on mass, but rather volume. mass flow is what it is...kg/sec, or whatever units are appropriate I'm not trying to confuse the two, apologies if it seems that way. I understand the difference between the two, however, when you are speaking of VE in a forced induction system, pressure has to be accounted for. This introduces the requirement to analyze it in terms of massflow. I think this may be where some of the fuel for the debate may be coming from. Volumetric efficiency and massflow are the same thing so long as you are taking the pressure difference into account. Lets consider this for a moment: IF you want to look at the VE of the engine, one would normally look at the actual airflow rate vs. the theoretical airflow rate: Theoretical Airflow:
EngineRPM * Displacement / 3456 VE = (Actual Airflow * 100) / Theoretical Airflow The only problem with looking at a forced induction setup is that the additional manifold pressure will make these numbers appear ridiculously high, so, the boost pressure must be factored in to get a more accurate depiction of VE. The correct equation would be: Theoretical airflow psicorr:
(EngineRPM * Displacement / 3456) / absolute manifold pressure VE = (Actual airflow/absolute manifold pressure) * 100) / Theoretical airflow psicorr In this case VE would be manifold pressure corrected and will offer a more accurate depiction of the VE of the engine under these boosted scenarios. We also wouldn't have to look at it component-seperated, as in, just looking at the engine without the turbos, or the turbos, etc etc.. Given that we ARE discussing a FI setup and do not have the luxury of knowing what the actual VE of the systems are, we only have the dyno results to indicate the status of the system's breathing capability. The data reveals an insight into VE, massflowrate, etc, which makes that datum really one in the same. I know the original statement was that higher VE means lower peak boost and I am trying to keep my pose in that context, but my attempts to show how that is not the case ultimately is showing how the two are completely unrelated, which brings me back around to the point of how the boost response is affecting the massflow. The bottom line is that nothing is really affecting the boost response other than the selection of hardware. Saying that it is the VE affecting the boost response is a completely illogical statement.
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