Auto Tech Quiz Game!

  • Thread starter Troux
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My brain's pretty dead right now, so I'll post an easy one.

In what year did the Corvette gain Independant Rear Suspension (IRS)?
 
Time to get this thread where I wanted it: technical!
On a turbocharged motor, as boost rises, what should be done with ignition timing and why?
 
Troux
Time to get this thread where I wanted it: technical!
On a turbocharged motor, as boost rises, what should be done with ignition timing and why?
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Ignition should be advanced rapidly so we can all melt our piston crowns....


:P
 
Yes, jokey/sarcasm.

Ignition timing should be advanced initially (off boost) then when on-boost should be retarded to reduce combustion chamber temperatures thus reduce the chance of pre-detonation/pinging.
 
Well I was more looking for the answer to why it prevents pinging, but you can ask the next question. A pressurized/turbulent mixture is made from compression, which is much easier and quicker to burn than an off-boost mixture.
 
Troux
Well I was more looking for the answer to why it prevents pinging
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I did answer why it helps to prevent pinging, end results it reduces combustion chamber temps.

Troux
A ped/turbulent mixtressurizure is made from compression, which is much easier and quicker to burn than an off-boost mixture.
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Yes so the ignition is retarded so more heat escapes out of the exhaust to reduce combustion chamber temp....... so less heat remains to detonate the more volitile mix.


Anyway someone else can go. :)
 
When you retard the timing you are making the time between the explosions more and the piston will move down in the cylinder a little and give it more time for the cylinder to cool down also because the piston has moved down a little bit the air/fuel ratio is under less pressure and the combustion temps will be less.

I think thats right if I am wrong please feel free to correct me :)
 
Diablomonkey
When you retard the timing you are making the time between the explosions more and the piston will move down in the cylinder a little and give it more time for the cylinder to cool down also because the piston has moved down a little bit the air/fuel ratio is under less pressure and the combustion temps will be less.

I think thats right if I am wrong please feel free to correct me :)
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Usually even if you retard the ignition it is still several degrees before TDC to give the flame front time to travel.

2-8 deg BTDC is very little advance, 10-12 is about normal, and more than 15 is some serious advance.
 
skip0110
Usually even if you retard the ignition it is still several degrees before TDC to give the flame front time to travel.

2-8 deg BTDC is very little advance, 10-12 is about normal, and more than 15 is some serious advance.
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:ouch: I knew that what I was saying was a little off, but thanks for correcting me.
 
Troux
How does retarding ignition let more haet out of the exhaust?
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Here is an example


"As the timing is retarded, PCP is developed later in the cycle. This allows more energy to be lost through conduction into the water jackets because the piston is further down the bore and the rod has a less advantageous angle on the crank pin to deliver force to the crankshaft. Retarded timing also raises the exhaust gas temperature considerably"

http://www.sdsefi.com/meltdown.htm


More heat escapes the combustion chamber (upper cylinder linings, cyl head, sparkplugs, piston crown) hense reducing combustion chamber temp but heats up everything else (Cylinder linings, exhaust (EGT) etc) This is not a real good thing but its only temporary retard on-boost.

Monte Carlo
Was that the question? Who's gonna post the next trivia question???
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Anyone I guess, go ahead.
 
More heat doesn't escape through the exhaust to reduce CC temperature like you said. If the exhaust is hot, everything in your engine is, too. The EGTs are higher BECAUSE CC temperatures are higher. That's the whole point of an EGT gauge in a turbo car. Even if you're not risking detonation from boost pressure, your EGTs may get too high from retarded ignition, and that'll melt your pistons and valves if taken too far. That's why when you see the warning light on your EGT gauge go off, you lift your foot. Retarding ignition makes your combustion chamber hotter, that's a fact.

That's one of the biggest reasons for the engine under covers on modern cars (the plastic cover under your engine). If you're driving over an unkempt road, or a dirt road without one there, it's entirely possible for small rocks hitting the engine to trigger the knock sensor (which retards ignition when it detects pinging), and this can ultimately melt your pistons!
There really isn't any benefit to retarding ignition, it's entirely a safety measure.

I'll go ahead and ask the next one...
When designing an intake manifold (not the intake pipe or filter, but what's after the TB), name three parameters/variables to keep in mind and what they affect, such as the tradeoffs involved in changing that parameter.
 
Troux
More heat doesn't escape through the exhaust to reduce CC temperature like you said. If the exhaust is hot, everything in your engine is, too. The EGTs are higher BECAUSE CC temperatures are higher. That's the whole point of an EGT gauge in a turbo car. Even if you're not risking detonation from boost pressure, your EGTs may get too high from retarded ignition, and that'll melt your pistons and valves if taken too far. That's why when you see the warning light on your EGT gauge go off, you lift your foot. Retarding ignition makes your combustion chamber hotter, that's a fact.

That's one of the biggest reasons for the engine under covers on modern cars (the plastic cover under your engine). If you're driving over an unkempt road, or a dirt road without one there, it's entirely possible for small rocks hitting the engine to trigger the knock sensor (which retards ignition when it detects pinging), and this can ultimately melt your pistons!
There really isn't any benefit to retarding ignition, it's entirely a safety measure.
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Ignition retard does not cause heat. When you lift off the throttle, there is a drop in manifold vacuum, which means less advance (aka more retard), so your logic relating to the turbo engine is invalid. And that engine cover stuff, I am fairly sure is wrong (considering where a knock sensor is located there should be no risk of it being hit by rocks and the engine cover is not doing anything to protect it anyways).

EDIT: Cylinder pressure goes up with advance and so does heat...that is why advance means a hotter burn (as well as more energy extracted from the fuel).
I'll go ahead and ask the next one...
When designing an intake manifold (not the intake pipe or filter, but what's after the TB), name three parameters/variables to keep in mind and what they affect, such as the tradeoffs involved in changing that parameter.
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Runner length affects torque but specifically must be tuned as a Helmholtz resonator for natural supercharging at a certain rpm. The plenum volume is responsible for smoothing off-idle and tip in throttle response. The plenum shape (and height) can add horsepower by allowing more time for the fuel to atomize and resulting in a more even A/F mixture. The runner material can be modified for different heat characteristics. The relative location of runners from adjacent cylinders in the firing order can also be used to improve power by minimizing the power lost when air changes direction as the intake valve snaps closed.
 
Troux
More heat doesn't escape through the exhaust to reduce CC temperature like you said. If the exhaust is hot, everything in your engine is, too. The EGTs are higher BECAUSE CC temperatures are higher. That's the whole point of an EGT gauge in a turbo car. Even if you're not risking detonation from boost pressure, your EGTs may get too high from retarded ignition, and that'll melt your pistons and valves if taken too far. That's why when you see the warning light on your EGT gauge go off, you lift your foot. Retarding ignition makes your combustion chamber hotter, that's a fact.
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Fuel/air burns at a pretty constant rate, so as engine speed picks up the and the fuel can't burn any faster the ignition must advance to keep it burning on time, as the engine speed increases and the pressure builds up (boost, with extra heat of the pre-compressed air) extra heat soaks into the CC until possible pinging, at this point the ignition retards itself allowing more of the heat to be dissipated on the down stroke over a larger area (rather than the upstroke when advanced), this reduces some of the heat in the TDC CC but rather dissapates more in the Cyl linings into the coolant and some extra heat out the exhaust, yes retarded ignition is not good if you can help it and yes it increases EGT's but retarded ignition does not create anymore heat (energy) overall than a advanced igntion would.
 
which type of CVT transmission uses two metal cones with the tips facing eachother in conjunction with two transfer wheels to select input/output ratios?
 
The article VIPER posted
Retarded timing also raises the exhaust gas temperature considerably. This raises the thermal stress on the pistons, spark plugs, valves, exhaust system and turbocharger.
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Anyways, good job, skip, you get the next question.
 
An ECU maintains A/F ratio by monitoring the O2 sensor _____.
As an O2 sensor gets older, the ______ rate slows down.

Same word must work in both sentences.
 
Troux
*Troux's quote*
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Yes, thats right cause thats where much of the heat is going now. More heat is not produced (from the retard) but rather the same heat is delayed and has negative effects in other ways. It is a good way as a quick preventative as the pinging is happening but it is damaging and unefficent for any prolonged period.

lmracer
which type of CVT transmission uses two metal cones with the tips facing eachother in conjunction with two transfer wheels to select input/output ratios?
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Not your shot.
 
skip0110
An ECU maintains A/F ratio by monitoring the O2 sensor _____.
As an O2 sensor gets older, the ______ rate slows down.

Same word must work in both sentences.
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reading?
 
Well, it monitors the A/F ratio my measuring the voltage coming out of the O2 Sensor. As it ages, the voltage will inevitably drop slightly.

That work?
 
Slicks
Well, it monitors the A/F ratio my measuring the voltage coming out of the O2 Sensor. As it ages, the voltage will inevitably drop slightly.

That work?
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While you are basically right, it actually is not looking directly at the voltage but at a different number. Thats why I added the 2nd sentence.

A tech would check this rate to see if your O2 sensor needed replacing. You can read it on a good scan tool.
 
The ECU does monitor the air fuel ratio using the oxygen sensor voltage.

My understanding of what you are getting at with the second part of that question: The narrow band oxygen sensors in cars don't give a good indication of what the air fuel ratio is, just whether it is rich or lean. So the ECU adds fuel when it's lean and takes it away when it's rich... the result is that the air fuel ratio oscillates between slightly rich and slightly lean. A bad oxygen sensor can begin to react slowly to changes in the air fuel ratio, meaning those oscillations become longer than they should be. The ECU does not use the oscillation in voltage to tell if the mixture is rich or lean, but it can be used to detect a bad oxygen sensor.

That's my understanding of it anyway.
 

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