a question about spooling...(more)
07-22-2002, 05:52 AM
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a question about spooling...(more)
i've asked this before, but didn't get a definitive answer.
does a larger exhaust help the turbo spool faster or slower? i'm not asking about boost or amount of boost, but more about lag.
for instance, would a chipped k03 with the stock exhaust spool faster than a chipped k03 with freeflow cat, downpipes, and 3" piping? (just to compare extremes)
//jason
does a larger exhaust help the turbo spool faster or slower? i'm not asking about boost or amount of boost, but more about lag.
for instance, would a chipped k03 with the stock exhaust spool faster than a chipped k03 with freeflow cat, downpipes, and 3" piping? (just to compare extremes)
//jason
07-22-2002, 07:06 AM
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differential lag for identical turbines is due to the pressure ratio...
The ratio is 2:1 or thereabouts. So, the goal is an exhaust that has enough cross-section to flow the max air volume with the lowest drop in velocity (since we don't have an accurate exhaust pulse correction for exhaust length).
So the greater the exhaust restriction, the greater the lag.
So the greater the exhaust restriction, the greater the lag.
07-23-2002, 08:22 AM
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A larger exhaust lets the turbo spool quicker....
Turbos work on a pressure differential, so there are two ways to increase spool-up.
1. Increase exhaust manifold pressure (before turbo)
2. Decrease exhaust pressure (after turbo)
Which one do you think is easier to do?
1. Increase exhaust manifold pressure (before turbo)
2. Decrease exhaust pressure (after turbo)
Which one do you think is easier to do?
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07-24-2002, 06:16 AM
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no, we would have a soda straw. There must be a balance between the backpressure from the engine to
the turbine wheel and turbine wheel to exhaust system. Too much exhaust manifold pressure and your engine will not be able to expel all the exhaust gas and you will lose power. Too little and your turbine wheel will flop around like a limp d--k. It will move a little ,but it won't really accomplish anything. If you have a restrictive exhaust system. It will increase the pressure on the backside of the turbine wheel, and reduce turbine speed. It also will allow the turbo to absorb more heat and lose additional efficiency. The slower the exhaust gas moves the more energy is wasted in the form of heat in the turbine housing.
07-24-2002, 10:35 AM
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and then the motor would stall, because the exhaust isn't leaving the combustion chamber.....
Then you'd have zero pressure on the turbo if the motor wasn't running. Not very effective, huh?
There's always a compromise. You want something that will keep exhaust pressure up (and velocity), but not be a bottle neck at higher RPMs, and not affect combustion chamber filling.
There's always a compromise. You want something that will keep exhaust pressure up (and velocity), but not be a bottle neck at higher RPMs, and not affect combustion chamber filling.