PCM Diagnostics & Tuning HP Tuners | Holley | Diablo

Explain map at idle

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Old Oct 20, 2010 | 02:57 PM
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Default Explain map at idle

I am a bit confused on the physics of map, I know at idle you want the most vacuum possible.

I assume that means you want the highest map possible at idle.


At the same time, isn't vacuum a pressure difference? So does thy mean you want the map reading as low as possible? Meaning a greater pressure difference between the engine and atmosphere?
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Old Oct 20, 2010 | 03:02 PM
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Wow, subscribed for this one.
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Old Oct 20, 2010 | 03:32 PM
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U got it!
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Old Oct 20, 2010 | 03:58 PM
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Highest vacuum is lowest MAP.

The less air (hence fuel) you need the more efficient you
are. That's about as good a measure as you can get, for
idle tweaking.

Of course the same also holds for part throttle loads like
towing, if you could get the load steady enough to be
useful in tuning you could maximize fuel economy by
chasing it to minimum there too.
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Old Oct 20, 2010 | 04:02 PM
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Originally Posted by jimmyblue
Highest vacuum is lowest MAP.
this

the camshaft plays a large role in how much vacuum you'll end up with at idle, my 224 cam was around 40 kpa, my larger 233/239 cam is around 50-55kpa at idle
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