[Subscribe to Daily Digest] |
The following is specific to the T7. For a T5, there would be some differencs, so this does not fully apply to a T5.
With the T7, the ECU is controlling the mass air flow. So reduction of flow resistance with filter, pipe and IC changes should lead to the turbo compressor working less hard to move the same amount of air. The reduction in shaft HP delivered from the turbine to the compressor will allow the wastgate to be a bit more open. This reduces the turbine back pressure, EGTs and residual gas in the combusion chamber. The last item increases volumetic efficiency and the compessor again has less work to do to force a target air mass flow into the cylinders (does not have to fight against residual gas in the chambers). The reduction in turbine effort and backpressure results in a direct increase of engine torque/HP. The reduction of compressor effort reduces the compressor discharge temps. The discharge pressure is reduced as less pressure is required to overcome IC and other intake system resistances. The compressor's operating point then also moves to a location on the map which may be a bit more efficient (less heat).
Less heat going into the IC also means that the IC then has less of a temperature drop to achieve. The cooling is a compression of sorts, as the volume of the gas is dropping (V rate in does not equal V rate out). This delta V at pressure represents work. Reduction of this delta T (and resulting delta V) that is obtained with a better IC (reduced compressor discharge temps) reduces the work that the compressor has to do. Another secondary, but synergistic effect.
So torque will increase when the ECU is controlling/achieving the target air mass flow. At high RPMs or CFMs, the turbo may not be able to maintain the target mass air flows and there will be 'boost droop' or 'torque droop' effects. In these situations, a better IC and other changes may allow for the setup to meet the target mass air flows that could not be achieved before. This can increase torque at the higher RPMs. This does increase the CFMs over the prior setup, and one needs to be concerned with the fuel keeping up with the mass air flow rates. As one approaches the limits of controlled fuel delivery, a small change can take one over the edge. Detonation that occurs at these RPMs can make bad things happen very quickly.
Summary: The change to a beter IC will decrease intake temps, and does create a secondary but direct effect of increasing torque. But the improvement at high RPMs that reduces boost droop will demand higher fuel flows which might take one over the edge.
I know that this is all very general, but it is an interesting thought process. One still has to measure AF ratios and make the same changes with or without these considerations.
One thing that concerns me is the stock FPR. It does increase fuel pressures with the effect of the boost pressure being applied to the FPR's diaphagm. So with hot intake temperatures, the system has to deliver at higher pressures to achieve a target air mass flow. That is a reference point and lets pretend that we have a situation where the fuel delivery is getting marginal. Now we have a very efficient intake and IC setup. The intake air is cooler and denser. So the boost pressure to achieve a target mass air flow is reduced. So the operation at lower temperatures and boost pressures now reduces the pressure applied to the FPR and the fuel pressure is reduced. The effect may not be large, but is something that is working against you as you make such changes. If the AF was getting marginal, such a change would make it worse. Couple that with increased fuel demand by reduction in boost droop, and there are two steps in the wrong direction that could take a marginal AF and create a serious problem.
There are many gas flow synergies that occur with reduction of flow resistances. There may be increase fuel demands. Fuel pressures may drop slightly.
No Site Registration is Required to Post - Site Membership is optional (Member Features List), but helps to keep the site online
for all Saabers. If the site helps you, please consider helping the site by becoming a member.
 |
 |
 |
 |
 |
