8/12/2023 0 Comments Total engine airflow![]() The cooling air is expelled overboard via a vent system or into the engine main gas stream, at the highest possible pressure, where a small performance recovery is achieved.ĬOOLING 3. Therefore, to reduce engine performance losses, the air is taken as early as possible from the compressor commensurate with the requirement of each particular function. An increasing amount of work is done on the air, as it progresses through the compressor, to raise its pressure and temperature. Up to one fifth of the total engine core mass airflow may be used for these various functions.Ģ. The system also supplies air for the aircraft services. These functions include internal engine and accessory unit cooling, bearing chamber sealing prevention of hot gas ingestion into the turbine disc cavities, control of bearing axial loads, control of turbine blade tip clearances (Part 5) and engine anti-icing (Part 13). The system has several important functions to perform for the safe and efficient operation of the engine. The engine internal air system is defined as those airflows which do not directly contribute to the engine thrust. Once again, the lower-compression motor would allow higher boost levels given an octane-induced detonation threshold.Fig. Remember, we ran the same pulley ratios on the two motors, so the compression was the only variable responsible for the loss in power and boost pressure. The peak boost registered on the low-compression motor was 9.3 psi at 3,800 rpm, while the boost finalized at 8.7 psi at 6,300 rpm. It is interesting to note that the boost pressure was slightly lower on the low-compression motor than the high-compression version. Note that the change in compression (see Kenne Bell Effect of Compression graph) reduced the power output across the board from 3,000 rpm to 6,300 rpm. Compared to the high-compression supercharged motor, the peak power was off by 67 hp while peak torque suffered just 39 lb-ft. The peak torque jumped from 368 lb-ft to 500 at 4,400. The blower upped the power output of the low-compression short-block from 365 hp (in normally aspirated/low-compression form) to 533 hp at 6,300 rpm. The Kenne Bell 1.7L blower assembly was then applied to the low-compression 4.6 with equally impressive results. Obviously the power would drop as we decreased the compression ratio, but to what extent? This is an important issue, as many engine builders currently offer low-compression 4.6s designed for blower and turbo applications. While considering the new short-block configuration, we began to wonder about the effect of the change in compression ratio. Knowing this, we decided to take a closer look at lowering the compression ratio to facilitate running elevated boost pressures. ![]() ![]() While the 10.1:1 hybrid motor ran well in all of our testing, we knew that the high compression was not the ideal choice for forced induction, especially for street use. The difference in chamber volume meant that the installation of the TEA PI heads raised the compression ratio of our early short-block by nearly 1 full point (from 9.2:1 to 10.1:1). The chambers on the '98 non-PI heads checked in at 52 cc. The chambers on the TEA-modified PI heads checked in at 45 cc, slightly higher than the stock PI measurement of 42 cc. The installation of the PI heads on our early (non-PI) GT motor naturally upped the compression ratio. ![]()
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