Odd problem with TP and Temperature

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ICEMAN.KCMO
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Odd problem with TP and Temperature

Post by ICEMAN.KCMO »

So here is my issue. I am running a basic daughterboard with a tune i have put together. Runs great except it seems the TP shifts with te weather. Some days at 14psi the max TP will be 67 and others it will be 74. on my setup that is a large jump. It moves my timing into an area that is too retarded. when i re tune for that, some days i will get knock.





Long story short my TP (load scale) is moving from day to day. mainly with temperature. any suggestions? When i get home, I will post a copy of my tune..
Steve.
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Kfred
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Re: Odd problem with TP and Temperature

Post by Kfred »

At lower ambient temperatures the TP should be higher for a given manifold pressure. Changing TP with ambient temperatures should be expected.

Pressure * Volume = Moles * Gas Constant * Temperature
PV = nRT
Rearranged:
n = P*V/(R*T)

For a given pressure and volume, the moles of air increases as temperature decreases. Thus, more fuel needs to be added at cooler intake air temps and your theoretical pulse width goes up. If you tuned your computer for X* of timing at 14psi on a 85F day, you want it to give less timing at 14psi on a 50F day. The mass of air you charge into your cylinders is what matters for power, not the manifold pressure.
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sdaigle240
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Re: Odd problem with TP and Temperature

Post by sdaigle240 »

***** yeah. love your posts mang.
airman wrote:I'm all about spreadsheets. Bitches love spreadsheets.
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