Interested About manifold Pressure

[BrettMiller]

High Manifold Pressure? 40 PSI too high?

So i have an 08 with full deletes and had a Race ME programer and never had a problem but now that I am Running a Smarty JR my Edge Insight CTS keeps alerting me that my manifold PSI is going over 40 PSI is this a normal thing that I should not worry about? or is there something to do to fix this problem? any info would be great!

 

[Bob4x4]

External wastegate

 

[BrettMiller]

External wastegate

What exactly are you talking about Bob4x4? im trying to decide what to do to fix this im not looking to hop this thing to the max im just not sure what to do with my high manifold pressure it show 13.2psi just sitting at an idle and my boost is at 0 so im not sure what to think should i change my air filter i have not changed it in about a year (since i bought it) it has not sucked the gauge on the filter box down at all so i figured it probably still good am I wrong?

 

[RustyJC]

....it show(s) 13.2psi just sitting at an idle and my boost is at 0....

Sounds like one (the Insight CTS) is reading in PSIA and the other (the boost gauge) in PSIG. PSIA (pounds per square inch absolute) = PSIG (pounds per square inch gauge) + atmospheric pressure

If that's the case, then 40 PSIA manifold pressure (using your 13.2 PSI you're seeing at your elevation) would equal 26.8 PSIG manifold pressure.

Rusty

 

[BrettMiller]

Sounds like one (the Insight CTS) is reading in PSIA and the other (the boost gauge) in PSIG. PSIA (pounds per square inch absolute) = PSIG (pounds per square inch gauge) + atmospheric pressure

If that's the case, then 40 PSIA manifold pressure (using your 13.2 PSI you're seeing at your elevation) would equal 26.8 PSIG manifold pressure.

Rusty

Thanks for that bit of info Rusty! that is interesting i never thought of it that way i know that the the Insight says the the MAP (Manifold Air Pressure) is all pulled from the ECU threw calculations

and what not so I am beginning to wonder if that is off or what the deal is there I am going to try changing my air filter out and seeing what that is cause both the MAP and the Boost pressures I

am getting off of the Insight so is one a more accurate number than the other?

 

[RustyJC]

If the Insight is displaying MAP sensor data, then it's displaying Manifold Absolute Pressure (MAP), or PSIA. That's not necessarily better or worse than the readout on your boost gauge, just a different measurement baseline.

Rusty

 

[BrettMiller]

If the Insight is displaying MAP sensor data, then it's displaying Manifold Absolute Pressure (MAP), or PSIA. That's not necessarily better or worse than the readout on your boost gauge, just a different measurement baseline.

Rusty

Rusty, do you think that it is something to worry about? i changed my air filter and it dropped to about 12.5 PSI so I still curious as to if the Manifold Pressure would be to much at 40? or what does anybody think I just don't want to Blow a gasket or anything of that sort.

 

[DonFitzwater]

If you don't want to blow a head gasket.........you should have left it stock.

 

[SierraRam]

If you don't want to blow a head gasket.........you should have left it stock.

14.7 psia is the standard atmospheric pressure at sea level with slight variances due to weather (barometric pressure). So subtract 14.7 from you MAP pressure to see the pressure in PSIG (pounds per square inch gage) this should match your boost gage reading.

 

[RustyJC]

14.7 psia is the standard atmospheric pressure at sea level with slight variances due to weather (barometric pressure).

As you imply, atmospheric pressure varies with elevation as well. 13.2 PSIA (see post #3) equates to 3000 ft elevation above sea level - see HERE. Therefore, the PSIA to PSIG correction factor will vary with altitude (among other things).

Rusty

 

[AH64ID]

The CTS should have the option to show you boost vs MAP pressure.

 

[cerberusiam]

The CTS is known for not correcting for ambient pressure correctly and setting off the alarm. Set the alarm at 15 over what you want it to go off at.

 

[BrettMiller]

14.7 psia is the standard atmospheric pressure at sea level with slight variances due to weather (barometric pressure). So subtract 14.7 from you MAP pressure to see the pressure in PSIG (pounds per square inch gage) this should match your boost gage reading.

Thank You Guys this is more what I was trying to figure out so really i don't have a problem except i need to set my alarm to a higher number to compensate for the atmospheric pressure as i am

roughly about 3000-3800 above sea level so this explains everything I was kinda worried i had something going on that I had no idea about. THANKS GUYS!!! this is why I love the TDR Community!

You all are a great bunch!

 

[BrettMiller]

Thanks everyone I am more relieved now! A+++++ to all of you guys!!!

 

[cerberusiam]

Setting the alarm higher is the fix but it has nothng to do with the altitude. You would have to do the same thing at sea level becasue the CTS is not working correctly. It is trying to combine ambient and boost and that is what messes it up. Boost is nothing more than pressure differential from ambient to manifold pressure, the CTS is reading MAP and not adjusting for ambient when comparing for the alarms. It may display boost correctly but the alarm routine does not reduce MAP signal by ambient signal and it reads high all the time.

 

[RustyJC]

Setting the alarm higher is the fix but it has nothng to do with the altitude.

Well, actually, it does. If one set the alarm at 40 PSIA MAP, that would equate to 25.3 PSIG boost at sea level (14.7 PSIA), but 29.9 PSIG boost at 10,000 feet (10.1 PSIA), so for a given alarm setting, boost (pressure above ambient) will increase as altitude increases and ambient atmospheric pressure decreases.

Rusty

 

[cerberusiam]

Well, actually, it does. If one set the alarm at 40 PSIA MAP, that would equate to 25.3 PSIG boost at sea level (14.7 PSIA), but 29.9 PSIG boost at 10,000 feet (10.1 PSIA), so for a given alarm setting, boost (pressure above ambient) will increase as altitude increases and ambient atmospheric pressure decreases.

No, the differential gets wider as altitude increases IF NOTHING ELSE CHANGES. The pressure density drop will also drop boost at the almost the same ratio. 25 lbs of boost will actually drop to around 20 lbs given the same exhaust flow. Less air to compress at altitude will require more compressor speed to to generate the same density. Will have to run more rpms to make the same power but that will just bring boost back to 25 psi and the differential is now only 10 istead of 15. One could go almost to 30 psi before the alarm triggered.

 

[RustyJC]

The alarm is only measuring MAP - manifold absolute pressure. The point is that the boost pressure (PSIG) at which the MAP-sensing alarm is triggered will vary with altitude since boost is only the differential between manifold absolute pressure and ambient atmospheric pressure. How the boost is made (higher turbo speed to compensate for lower air density, etc.) has nothing to do with the MAP signal - the MAP sensor just sees absolute pressure in the manifold. Higher boost (differential) is required at altitude to produce a given manifold absolute pressure due to the lower ambient atmospheric pressure since MAP (PSIA) = ambient atmospheric pressure (PSIA) + boost (differential pressure, PSIG or PSID), and ambient atmospheric pressure decreases as altitude increases.

We're actually saying the same thing - the engine will see more boost at altitude (29.9 PSIG) than it will at sea level (25.3 PSIG) when the alarm triggers at 40 PSIA. Or, to put it another way, if the alarm triggers at 25.3 PSIG boost at sea level, it won't trigger at 25.3 PSIG boost at 10,000 ft since MAP would be 25.3 PSIG + 10.1 PSIA = 35.4 PSIA MAP at 10,000 ft altitude, falling short of the 40 PSIA trigger point.

Rusty

 

[cerberusiam]

Yes you are correct, I did not explain that MAP will fall at the same ratio as boost because both are tied to compressor efficiency which is variable by altitude.

Setting the alarm for sea level conditions will not be affected by altitude is what I meant. At sea level the turbo is efficient to about 35-37 psi so adjusting alarm level to boost + 14 psi should suffice. At higher altitudes it will never approach alarm condition in normal circumstances. If one lived at 8-10k feet then adjusting the alarm to boost +10 might be a good idea. Anything under 5k feet setting at 50 psi should be sufficient.