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Old 08-28-2013, 09:59 PM   #226
Commander Keen
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You can have a shorter pulse width and higher duty cycle to achieve the desires AFR.
The only way you can shorten the pulse width while raising the duty cycle is by raising the RPM.

I'm very familiar with ECU operation.

The engine is not just a power source, it's a load and it requires more power to spin itself at higher RPMs. Notice your car takes more throttle to free rev at higher RPMs. Free revving is the point where internal engine losses equal the energy produced by the engine, since no power is taken off the crankshaft (except through accessories).

Producing useful power at 4K RPM requires more fuel than to free rev at 4K RPM. However, the same fuel required to free rev at 4K RPM can produce plenty of useful output power at 1500 RPM.
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Old 08-28-2013, 10:33 PM   #227
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Originally Posted by Commander Keen View Post

The only way you can shorten the pulse width while raising the duty cycle is by raising the RPM.

I'm very familiar with ECU operation.

The engine is not just a power source, it's a load and it requires more power to spin itself at higher RPMs. Notice your car takes more throttle to free rev at higher RPMs. Free revving is the point where internal engine losses equal the energy produced by the engine, since no power is taken off the crankshaft (except through accessories).

Producing useful power at 4K RPM requires more fuel than to free rev at 4K RPM. However, the same fuel required to free rev at 4K RPM can produce plenty of useful output power at 1500 RPM.
Part of your first remark is accurate. You do raise the duty cycle by raising RPM'S, the pulse width is a factor of the TPS or the MAP. I also understand EMS, I have several cars with them.
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Old 08-28-2013, 11:14 PM   #228
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Part of your first remark is accurate. You do raise the duty cycle by raising RPM'S,
Duty cycle and RPM are independent, however the only way to shorten pulse width (on time) while raising the duty cycle (on time / total time) is to raise RPM (reduce off time by a greater percentage than the decrease in on time).
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Old 08-29-2013, 12:05 AM   #229
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Duty cycle and RPM are independent, however the only way to shorten pulse width (on time) while raising the duty cycle (on time / total time) is to raise RPM (reduce off time by a greater percentage than the decrease in on time).
That's not entirely accurate. As RPM'S increase, the time or dead time between each pulse width decreases, thus per the formula the percentage of the duty cycle increases.
What you said is correct all but the first part of the first sentence. I suppose the tach isn't connected to the injectors, so maybe from that standpoint your right. But it takes increasing intake cycles ( thus engine cycles thus engine revolutions which is RPM'S) to increase the duty cycles. This is actually the way you would properly size your injectors. If the duty cycles are 85-90% or more you should look at increasing your injectors size. I think we are somewhat talking about the same thing, however seems like a tangent. We started off talking about mpg's.
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Old 08-29-2013, 06:09 AM   #230
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Originally Posted by G2Spfld View Post
however seems like a tangent. We started off talking about mpg's.
It is argument for arguments sake.

Either the CVT gets better HWY mpg's than the 5 Speed, or it doesn't (evidence from multiple sources say it does, though individuals unhappy with their personal mpg's surmise it does not)

Either the higher HWY mpg's is due to the engine turning lower rpm at highway speeds, or it isn't (still trying to figure out why people are arguing RPM is irrelevant. They seem to think having a lower RPM at highways speeds is a curse, because it requires the car to "downshift", which they then presume means is raises the RPM way higher than a 5 Speed turns, in 5th or 4th -- or others just argue that RPM is unrelated to mpgs)

Either there is more drivetrain/transmission drag from a CVT or from a 5 Speed. Since this isn't measurable, opinions vary.

So which is it, do CVT's suck, or are they better at delivering better MPG's on the highway?

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Old 08-29-2013, 07:17 AM   #231
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Yep, definitely have to use manual mode on anything even slightly resembling an incline. It'll drop down to 5th (CVT) in a stiff breeze.
Mine will lose 10-15mph before kicking down to 5th. I.e. cruising at 55, hit a long steep hill, 5th comes at 40-42.
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Old 08-29-2013, 08:17 AM   #232
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Originally Posted by hemophilic View Post

Mine will lose 10-15mph before kicking down to 5th. I.e. cruising at 55, hit a long steep hill, 5th comes at 40-42.
Mine shifts but doesn't lose over 3 mph
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Old 08-29-2013, 11:37 AM   #233
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That's not entirely accurate. As RPM'S increase, the time or dead time between each pulse width decreases, thus per the formula the percentage of the duty cycle increases.
Assuming a fixed on-time, yes. Assuming a proportional decrease in on-time, duty cycle is unchanged.

Quote:
Either the CVT gets better HWY mpg's than the 5 Speed, or it doesn't (evidence from multiple sources say it does, though individuals unhappy with their personal mpg's surmise it does not)
I believe the 5MT has less internal drag, but may not do as well as the CVT due to significantly shorter overall gearing in 5th. The 5MT loses its mechanical efficiency advantage because it keeps the engine operating in an inefficient RPM range.

Last edited by Commander Keen; 08-29-2013 at 11:51 AM.
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Old 08-29-2013, 01:42 PM   #234
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Assuming a fixed on-time, yes. Assuming a proportional decrease in on-time, duty cycle is unchanged.

I believe the 5MT has less internal drag, but may not do as well as the CVT due to significantly shorter overall gearing in 5th. The 5MT loses its mechanical efficiency advantage because it keeps the engine operating in an inefficient RPM range.
Duty cycle being a percentage based partly on RPM'S in a 4 cycle engine (2 rotations per cycle) I'm not sure I understand your statement. By on time are you referring to time the injector is energized, or the amount of times its energized per cycle? Since the amount if time that exists per cycle decreases as the RPM'S increase, and increases as the RPM'S decrease, I am not sure how the duty cycle can remain unchanged. I can see how the pulse width can remain the same, but the duty cycle will change with engine cycles.
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Old 08-29-2013, 05:06 PM   #235
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On-time is the amount of time it's on for that cycle. By knowing any two of duty cycle, RPM and on-time, you can calculate the third.

This was your original statement:

Quote:
You can have a shorter pulse width and higher duty cycle to achieve the desires AFR.
I said the only way you can meet both of those conditions is by increasing RPM (and therefore decreasing off-time).

Fuel rate is proportional to duty cycle, not pulse width. You can have relatively long pulse widths at low RPMs without consuming large amounts of fuel.
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Old 08-29-2013, 06:50 PM   #236
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On-time is the amount of time it's on for that cycle. By knowing any two of duty cycle, RPM and on-time, you can calculate the third.

This was your original statement:

I said the only way you can meet both of those conditions is by increasing RPM (and therefore decreasing off-time).

Fuel rate is proportional to duty cycle, not pulse width. You can have relatively long pulse widths at low RPMs without consuming large amounts of fuel.
Fuel rate is proportional to duty cycle in the fact that the higher the % of duty cycle the injector has, the more times the pulse width occurred in that given cycle. That is, unless your thinking fuel rate as a measurement of the number of times a given amount of fuel is used. In that case, nice try ;-). The pulse width is the time in ms that the injector is spraying fuel. I think your confusing the two. Duty cycle is % the injector is open vs closed. It's not a measurement of amount of fuel used. Just how many times a given amount of fuel is used per cycle in a percentage not over 100%. So fuel rate is proportional to pulse width directly, as pulse width is the time, in my case, my 1300cc injectors are spraying. Again, duty cycle is the percentage of time it sprays per cycle. Your response to my remark is correct, you just have pulse width and duty cycle confused I believe. I could be wrong, but if I am I've been so very lucky with my high boost high HP cars not leaning out and blowing up. Omg I'd be sick if that happened, :-(

Last edited by G2Spfld; 08-29-2013 at 08:19 PM.
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