Some facts you might not know about our resident tech guru:
- Eric Hsu can play Xbox Live on a Motec M800.
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Every time Eric Hsu answers a stupid question, a kitten spontaneously combusts.
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When cops pull Eric Hsu over, he laughs as they try to talk their way out of it. It never works.
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Eric Hsu eats cereal bowls for breakfast. Not bowls of cereal.
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City governments pay Eric Hsu to park wherever the hell he wants.
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If Charlie Sheen is winning, it’s because Eric Hsu isn’t playing.
Wanna know what’s up?
questionit@importtuner.com
This Month’s Winning Letter
Compressor Surge
I’m trying to understand compressor surge. My basic understanding is that when the pressure behind the compressor drops to below the outside pressure, it will cause air to travel the opposite direction. Most examples involve airplanes dropping out of the sky, but other than engine performance dropping off, can either the engine or the turbo be damaged by this phenomenon? I want to ensure I don’t cause damage to my 300ZX TT's GT-675RS turbos.
-John Tacchi
via importtuner.com
I’m not quite sure what you mean by “behind the compressor”, but compressor surge occurs when it is beyond the compressor’s ability to deliver airflow stably. Flow becomes unstable when a compressor is run to the left or above the surge line on a compressor map. When flow becomes unstable, you can hear the audible flutter or “barking” from the inlet of the turbo. Surge can occur in one of two situations: 1) under load, when the compressor is being run at a high shaft speed and the compressor cannot deliver stable flow to the engine because that point is to the left or above the surge line, and; 2) when the throttle is quickly closed in boost which momentarily drives the compressor way to the left of the surge line. The first situation can also vary significantly depending on how efficiently your engine breathes, so it isn’t going to be the same point from car to car. Atmospheric pressure at the inlet of the compressor affects when a compressor surges. With more pressure, the surge line moves to the left and vice versa. In other words, your compressor will work much better in lower elevations, such as Santa Monica, CA, versus the Rocky Mountains in Denver.
Wheel/blade shape and housing design are factors that can affect where a surge line is on a compressor. A compressor section that is optimized for flow at high shaft speeds might have the surge line toward the right of the map. A compressor section optimized for a wide operating range may have its surge line moved over to the left, but it might also have lower overall airflow at any shaft speed. Compressor housings with ported shrouds can help to move the surge line to the left, but do so at the sacrifice of peak compressor efficiency. As with anything else, it’s difficult to have your cake and eat it too. Newer turbo models like the BorgWarner EFR and Garrett GTX offer “wider” compressor maps that give you the best of both worlds.
Monster Machine
Due to some unforeseen spending, I was unable to afford the Nismo Z I was saving for. I recently purchased an ’11 Scion tC as a more affordable daily driver. I want to modify it, but am not sure which parts menu will equal the 300 hp I want out of it. I have looked online for parts, but I would hate to spend money on components that won't play nice with each other. Is the tC capable of 300 horses without nitrous, turbo, or other engine mods?
-Yonierikz
Fort Drum, NY