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MAP sensor calibration?

Practical Reflash Tuning

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I want to verify the MAP reading at idle - inches hg on a vacuum gauge to kpa in HPTuners scanner:

100 kpa in Scanner with Key on engine off

11" hg vacuum on the gauge - 70 kpa in Scanner

13" hg vacuum on the gauge - ~55 kpa in Scanner

Does this look correct?

My setup 468 BBC with AFR 265 ovals and perf cam (229/.600/109) 0411 PCM with a LS1 cal file for a 2002 Camaro.

Since 1" hg = 3.38639 kPa, you are pretty close.

100 kpa - (11" hg x 3.3869) = 62.75 kpa

100 kpa - (13" hg x 3.3869) = 55.98 kpa

Here is a google search to lots of calculators to help you with this:


Thanks, I was missing the "-" operator. Now it makes more sense.

So it's close, but it's not accurate. How do I get it to be more accurate so that I'm adjusting the correct cells in the tables, or does it matter?

Depending on engine cam overlap, manifold, sensor placement, (etc) I think it's difficult sometimes to get a stable pressure reading. So comparing two sources and having them within 10% or so, seems OK in my book. Any error you have will just be "baked" into any table changes you make.

Do you have any way to confirm that the barometric pressure was actually 100 kpa? Since I used that in the equation, if it was really 102, then your average error would have been less.

Any chance the scanner data is not actually in kpa, but actually more like map/baro (or percent gauge pressure), so then 100 would equal the current baro pressure?

Eh, it is what it is, I suppose.

I have a gauge that shows kPa, and it's also listed in the chart vs. Time. Both read between 100 and 101 with K-O-E-O.

I also have a channel for MAP in psi and Baro in psi. Both read 14.6 psi.

I have an even bigger problem that causes hard start. It either starts perfectly fine, or backfires through the TB. I have a Holley EFI 95mm TB, and it hates to start unless I set the throttle opening at about 6 turns, or a mixture of throttle set screw and idle bleed screw. Right now it seems to start OK if I have the throttle butterfly open 5 turns with the air bleed screw out 1 turn. Of course it idles at 1,500.

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