Chips and their effect on turbos. Humor me here.
08-13-2002, 01:37 PM
#11
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The wastegate is between the exhaust and turbine...
Holding the wastegate closed results in maximum pressure from the exhaust manifold so the turbine speed will increase as the exhaust flow increases. The turbine speed (charge pressure) is regulated by opening the wastegate based on input from the charge pressure control unit. Change the programming of this guy and you change the amount of exhust flow directed to the turbine.
Another tidbit. The 2.7Tengine also has a barometric sensor to prevent turine overspeed at high altitudes. Without this, the ECM will try to deliver the same requested charge pressure at high altitudes as it would at sea level. Since the air is thinner at high altitudes the turbine has to spin faster to deliver the same pressure. Allowing this to happen could exceed the max design RPM for the turbo.<ul><li><a href="http://www.rs4.org/quattro/technical/s4-engine/engine17.jpg">Turbo Flow Diagram</a></li></ul>
Another tidbit. The 2.7Tengine also has a barometric sensor to prevent turine overspeed at high altitudes. Without this, the ECM will try to deliver the same requested charge pressure at high altitudes as it would at sea level. Since the air is thinner at high altitudes the turbine has to spin faster to deliver the same pressure. Allowing this to happen could exceed the max design RPM for the turbo.<ul><li><a href="http://www.rs4.org/quattro/technical/s4-engine/engine17.jpg">Turbo Flow Diagram</a></li></ul>
08-13-2002, 02:02 PM
#12
A stock car bleeds off boost at a certain point, thus
preventing the turbo from spinning any faster. By allowing more pressure to build, you cause the turbo to spin faster. In turbo failures, the bearings are often the first thing to go. Too many rpms and too much heat.
Also, there comes a point when the turbo size ( especially smaller turbos ) when pumping efficiency has been exceeded.
In addition, if the fuel mixture is messed up ( too lean most often ), the turbine blades can get very hot - so hot they break or melt. These can be found embedded in the cats sometimes.
Each type of turbo has its own prime operating range to produce peak boost as well as lag characteristics. Generally smaller turbos have little lag, but limited boost capability - especially at higher rpms. Larger turbos have lag, but make more power but at higher rpms.
You need to consider if you have an oversquare or undersquare engine design, and what turbo best compliments the engine as well as its intended application. VAG prefers torque at low rpms over high rpm power. Thus we see long stroke engines with small turbos.
Here is a good overview link:
http://autozine.kyul.net/technical_school/engine/tech_engine_3.htm#Overview<ul><li><a href="http://www.thedodgegarage.com/turbo_fun.html">Some very good turbo 101</a></li></ul>
Also, there comes a point when the turbo size ( especially smaller turbos ) when pumping efficiency has been exceeded.
In addition, if the fuel mixture is messed up ( too lean most often ), the turbine blades can get very hot - so hot they break or melt. These can be found embedded in the cats sometimes.
Each type of turbo has its own prime operating range to produce peak boost as well as lag characteristics. Generally smaller turbos have little lag, but limited boost capability - especially at higher rpms. Larger turbos have lag, but make more power but at higher rpms.
You need to consider if you have an oversquare or undersquare engine design, and what turbo best compliments the engine as well as its intended application. VAG prefers torque at low rpms over high rpm power. Thus we see long stroke engines with small turbos.
Here is a good overview link:
http://autozine.kyul.net/technical_school/engine/tech_engine_3.htm#Overview<ul><li><a href="http://www.thedodgegarage.com/turbo_fun.html">Some very good turbo 101</a></li></ul>
08-13-2002, 02:05 PM
#13
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It spins faster at most rpms, from what I can tell, due to altered wastegate operation.
This is the only way to get more pressure going into the engine. More air is gulped by the engine because the turbo supplies it at higher pressure, thanks to a wastegate that is more closed than stock most of the time.<ul><li><a href="http://www.rs4.org/quattro/technical/s4-engine/engine17.jpg">See http://www.rs4.org/quattro/technical/s4-engine/engine17.jpg</a></li></ul>
08-13-2002, 02:18 PM
#14
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Sorry, but it a) spins faster...
...due to more exhaust flow on the input side and thus generates greater pressure (boost) from the faster spinning impeller, and
b) generates a lot more heat, from hotter and faster flowing exhaust on the input side.
Like a high-rpm engine, the only 'natural' restrictions on RPM and hp are fuel/oxygen/exhaust flow and mechanical limits of the various spinning and reciprocating parts. So we have rev. limiters, inlet restrictors (racing), and wastegates to spoil the fun before someone (or something) gets hurt.
Aside from increasing the size of the turbo (and its various plumbing) an easy way to make more power is to let a smaller turbo keep spinning faster. The risks are that it will fly appart or burn up its lubricant and sieze (as well as blowing something in the engine from the effectively higher compression).
b) generates a lot more heat, from hotter and faster flowing exhaust on the input side.
Like a high-rpm engine, the only 'natural' restrictions on RPM and hp are fuel/oxygen/exhaust flow and mechanical limits of the various spinning and reciprocating parts. So we have rev. limiters, inlet restrictors (racing), and wastegates to spoil the fun before someone (or something) gets hurt.
Aside from increasing the size of the turbo (and its various plumbing) an easy way to make more power is to let a smaller turbo keep spinning faster. The risks are that it will fly appart or burn up its lubricant and sieze (as well as blowing something in the engine from the effectively higher compression).
08-13-2002, 05:47 PM
#15
Just some more info to add...
If you look at the S4 failures, quite a few of the ones I've seen have impeller blades missing.
Quite a few programs have boost levels outside the efficiency range - with the K03s, pretty much anything over 16PSI from what I understand. Most people have boost spikes (we do even running stock), but some people have reported running sustained boost levels above 16PSI, somewhere in the area of 18 to 20, with K03 programs - kind of scary IMO. Taner from the S4 forum is one that comes to mind. His turbos are now failing also, although they did last quite a while, and I think he is going to upgrade to K04s.
-st
Quite a few programs have boost levels outside the efficiency range - with the K03s, pretty much anything over 16PSI from what I understand. Most people have boost spikes (we do even running stock), but some people have reported running sustained boost levels above 16PSI, somewhere in the area of 18 to 20, with K03 programs - kind of scary IMO. Taner from the S4 forum is one that comes to mind. His turbos are now failing also, although they did last quite a while, and I think he is going to upgrade to K04s.
-st
08-13-2002, 05:50 PM
#16
Turbos are more than the turbine....
they are a system. Good chips not only allow for more pressure to be generated (at greater turbine speeds), but they do it within the limits of lubrication, cooling and the cars ability to deliver the right amount of fuel. Generally turbos fail as a result of heat or lack of lubrication. One can cause the other. Usually it is the center section that fails. Blades don't usually come apart unless foreign material is introduced in to the air stream. Even a fine mist of water introduced prior to the turbo on the intake side will work like rough sandpaper on the blades. Pieces of a motor (valve, piston) on the exhaust side. Boost when controlled within the limits of all the systems generally does not lead to turbo failure. When boost is uncontrolled and you create very lean conditions, you create super heat and things melt and things fail. Chipping as done by GIAC or AMS or others are carefully designed to stay within certain limits. As long as all the systems stay intact, cooling, lubrication, fuel, longevity "should" be fine. Will things wear out sooner, maybe. This is my 3rd turbo charged car, I have raised the boost on all 3 and have not suffered any major failures as a result. Audi,Volvo,Syclone. It is a relatively safe way to get power. Things can go very wrong, chipped or not if lubrication, cooling, fueling or the system that controls boost has a failure.
My .02
My .02
08-14-2002, 05:56 AM
#20
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The answer is... (so you do not have to read the string):
Stoney, GIACUser, April and FtWorth (and others) came through.
It's really all in the wastegate. The WG is upstream of the turbine, and it allows the engine exhaust to bypass the turbo when boost hits a certain level (computer determined). Chips change the bypass and allow the turbine to spin faster and longer. More speed means more friction at the hubs, and that puts more strain and heat on the oil lubing the bearings. (Can someone tell me why Audi would even think of using anything but synthetic?!?!?).
Interesting side theory is that a chip can increase turbine speed, keeping it within the design limits, without undue harm. But opening up the exhaust may increase the rate at which the turbos spool up (faster boost) and cause damage.
My conclusions:
Any modification that makes the turbos spin faster than stock, presents an increased chance of failure.
Synthetics are looking better than ever. Why chance it? even when stock? Why push oil changes past 4 or 5,000 miles? Seems crazy to me.
It's really all in the wastegate. The WG is upstream of the turbine, and it allows the engine exhaust to bypass the turbo when boost hits a certain level (computer determined). Chips change the bypass and allow the turbine to spin faster and longer. More speed means more friction at the hubs, and that puts more strain and heat on the oil lubing the bearings. (Can someone tell me why Audi would even think of using anything but synthetic?!?!?).
Interesting side theory is that a chip can increase turbine speed, keeping it within the design limits, without undue harm. But opening up the exhaust may increase the rate at which the turbos spool up (faster boost) and cause damage.
My conclusions:
Any modification that makes the turbos spin faster than stock, presents an increased chance of failure.
Synthetics are looking better than ever. Why chance it? even when stock? Why push oil changes past 4 or 5,000 miles? Seems crazy to me.