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So WHY is my car quicker under partial acceleration off the line?

 
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Old 16 Aug 2009, 12:22 pm
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Default So WHY is my car quicker under partial acceleration off the line?

My car is officially quicker accelerating under partial throttle than full throttle from a stop. Why the hell is this?? I've done a lot of monitoring and testing and it's certain.

Now, if I'm moving then it's DEF quicker under full throttle.
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Old 16 Aug 2009, 12:31 pm
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Default Re: So WHY is my car quicker under partial acceleration off the line?

Do you have an intake or K&N filter? I bet either one would help.
Does it miss or skip?
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Old 16 Aug 2009, 12:39 pm
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Default Re: So WHY is my car quicker under partial acceleration off the line?

Because the PCM limits timing advance to 23 degrees in open loop; above 85% throttle. Up to 85%, you can get as much as 37 degrees advance.
Also, intake air vacuum is higher with the throttle plate partially open. Wide open throttle lowers the intake vacuum, and thus lowers air velocity until the RPMs increase to compensate.
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Old 16 Aug 2009, 01:37 pm
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Default Re: So WHY is my car quicker under partial acceleration off the line?

Quote:
Originally Posted by quicksilverdon View Post
Do you have an intake or K&N filter? I bet either one would help.
Does it miss or skip?
Yep I've got an aem short ram intake. The car did this before and after the intake.

Quote:
Originally Posted by MX-5 View Post
Because the PCM limits timing advance to 23 degrees in open loop; above 85% throttle. Up to 85%, you can get as much as 37 degrees advance.
Also, intake air vacuum is higher with the throttle plate partially open. Wide open throttle lowers the intake vacuum, and thus lowers air velocity until the RPMs increase to compensate.
I've never in my life heard of a car thats slower in partial throttle than full throttle lol. Very good info though. How can this be altered? How can the PCM be programmed to allow more timing? I bet that would alter the performance of this car EXPONENTIALLY if that could be fixed.
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Old 16 Aug 2009, 04:45 pm
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Default Re: So WHY is my car quicker under partial acceleration off the line?

Alteration to the intake with a combination of computer work. Velocity, pressure, timing, etc...The list can go on. On one of my old race bike (RVF400), it had staggared velocity stacks to provide an even acceleration force. This was needed to keep the V4 from choking from low rpm acceleration. In order to fix that issue will take some experimentaion. Not unless someone figured it out already...

The intake manifold design isn't designed to win any races.... If you can use a programmer to adjust timing. There is a good possibility to get some addition perfromance out of it. Programming the ECU itself, I haven't come across that yet for an N/A engine.
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Old 16 Aug 2009, 08:49 pm
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Default Re: So WHY is my car quicker under partial acceleration off the line?

Interesting. Good information.

So the entire intake manifold is the culprit then? Hmm.

Where could I find a different, more efficient or power-producing intake manifold?
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Old 17 Aug 2009, 02:32 am
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Default Re: So WHY is my car quicker under partial acceleration off the line?

I've noticed the same thing as well, but have just become accustomed to it. Mine's an N/A '01 with a short ram intake, and it's scared me a couple times.

I live in Tampa, FL now, and traffic going into my apartment complex is a bitch (for lack of a better term). So, when I see a gap as I'm waiting in the median to turn, I go for it. A couple of times though, I've floored the PT due to the speed of oncoming traffic and I wind up sitting there, hairs on the back of neck raised, saying 'What the..?' and making sure I actually hit the accelerator with my foot, and not just the floor. :/ It sucks.

But like you'll find with most of the PCM issues with PTs, Chrysler has the parameters locked up like Fort Knox.. though someone might have a fix for it.
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Old 17 Aug 2009, 07:00 am
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Default Re: So WHY is my car quicker under partial acceleration off the line?

^Same here... i'm at a super busy Army base, so when i see an opperunity, I seize it. And like you say, I worry GREATLY until the car reaches 3200rpm's or so. It almost feels like I pulled out into traffic and didn't hit the gas to move anywhere else.

Though, you gotta admit when the car hits about 3200rpm's that SRI sounds GREAT doesn't it??
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Old 17 Aug 2009, 09:31 am
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Default Re: So WHY is my car quicker under partial acceleration off the line?

NA Cruiser and "quicker off the line" made me LOL.
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Old 17 Aug 2009, 10:27 am
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Default Re: So WHY is my car quicker under partial acceleration off the line?

Quote:
Originally Posted by 85_305 View Post
Interesting. Good information.

So the entire intake manifold is the culprit then? Hmm.

Where could I find a different, more efficient or power-producing intake manifold?
No the N/A manifold is pretty good, compared to the metal turbo one. The holy grail of manifolds for these cars is the turbo plastic.

Better flow more even flow than both the N/A plastic and Turbo Metal which is also a big weight and heat holder in the engine bay.
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