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..
Odd problem with TP and Temperature
-
- Knows Some Stuff About 240's!
- Posts: 435
- Joined: Sun Nov 12, 2006 8:33 am
- Location: Kansas City, MO
- Contact:
- Kfred
- Belongs To The TOP CONTRIBUTING MEMBERS!
- Posts: 3513
- Joined: Sun Oct 29, 2006 8:12 am
- Location: Baton Rouge, LA
Re: Odd problem with TP and Temperature
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.
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.
RIP Nate(480sx)...
- sdaigle240
- Belongs To The TOP CONTRIBUTING MEMBERS!
- Posts: 4670
- Joined: Wed Oct 17, 2007 9:53 am
- Location: CONN.
Re: Odd problem with TP and Temperature
***** yeah. love your posts mang.
airman wrote:I'm all about spreadsheets. Bitches love spreadsheets.
schmauster920 wrote:I shall cast my own pistons in the sands of time, then forge them in the depths of hell.. as funds allow
hy35 18psi Build Thread: viewtopic.php?t=38784
RIP MJL best friend of 20 years and the man who showed me 240s