Re: how is boost measured?

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Re: how is boost measured? Posted by Dean [Email] (more from Dean) on Sat, 1 Apr 2006 15:36:25

In Reply to: how is boost measured?, LesH, Sat, 1 Apr 2006 14:22:01 Members do not see ads below this line. - Help Keep This Site Online - Signup

The sensor is refered to as a manifold absolute pressure sensor. So the reference pressure is fixed at a full vacuum.

The T5 boosted to a given absolute pressure. But in damp or hot weather, the mass air flow was lower and the power and responsiveness suffered. But in cold weather, the power increased greatly.

The T7 has (depending on year), one or two MAP sensors and a MAF. The system then boosts to a mass air flow target and temperature changes do not affect power very much. This mass air flow target is also known as a torque target or limitation. That is not really true, but is roughly true. If one lowers intake, IC or exhaust restrictions, one gets more (moderate) power from the same mass air flow, as the turbo then works less hard and the wastegate can then be more open, and the exhaust manifold pressure is then reduced, which translates directly onto increased power. There are some other secondary benefits as well. Note that at 15PSI of boost, the exhaust manifold pressure could be around 30PSI. So these "turbine" backpressures are significant and boost is not for free.

So when one talks about how boost is measured, one first needs to if boost targets are pressure or mass air flow. In this case, mass air flow is relative to one combustion chamber cycle or load.

Posts in this Thread:

how is boost measured?, LesH, Sat, 1 Apr 2006 14:22:01
- Power Loss at altitude, nikos, Sat, 1 Apr 2006 18:09:17
  - also intercoolers become less efficient, jak , Sat, 1 Apr 2006 21:22:51
    - keeping it simple, vigge, Sat, 1 Apr 2006 23:28:09
      - I would never argue how much is lost, jak , Sun, 2 Apr 2006 09:13:06
      - To add to the above, Vigge, Sun, 2 Apr 2006 08:32:25
    - Re: also intercoolers become less efficient, soneway, Sat, 1 Apr 2006 23:26:46
- Re: how is boost measured?, Dean, Sat, 1 Apr 2006 15:36:25 <-- Viewing This Message
  - Less oxygen per volume..., John Williams , Sun, 2 Apr 2006 09:07:57
  - Re: how is boost measured?, Vigge, Sun, 2 Apr 2006 03:23:34
    - Re: how is boost measured?, Dean, Mon, 3 Apr 2006 23:03:04
    - short overlap :-), jak , Sun, 2 Apr 2006 21:13:34
    - Re: how is boost measured?, vigge, Sun, 2 Apr 2006 08:28:04
      - thats a valid point on pre turbine exaust pressure, jak , Sun, 2 Apr 2006 11:57:31
        oops, jak , Sun, 2 Apr 2006 11:59:46
        A good link about this, SteveW, Sun, 2 Apr 2006 16:12:00
        02 not constant by volume..., John Williams , Mon, 3 Apr 2006 08:17:06
        Finally a way to understand this oxygen per volume., John Williams , Mon, 3 Apr 2006 08:55:40
        Re: Finally a way to understand this oxygen per volume., vigge, Mon, 3 Apr 2006 12:13:55
        do you have the slip on this viggen at 5000 feet?, jak , Mon, 3 Apr 2006 20:35:00
        Re: do you have the slip on this viggen at 5000 feet?, vigge, Mon, 3 Apr 2006 23:20:55
        yeah I asked back trhen but never got them, jak , Mon, 3 Apr 2006 23:28:52
        I dissagree, SteveW, Mon, 3 Apr 2006 14:24:49
        Re: I dissagree, Vigge, Mon, 3 Apr 2006 22:47:36
        Ok, SteveW, Mon, 3 Apr 2006 16:31:38
        Re: Ok, vigge, Mon, 3 Apr 2006 23:18:32
        Re: Finally a way to understand this oxygen per volume., John Williams , Mon, 3 Apr 2006 14:14:43
        Re: Finally a way to understand this oxygen per volume., vigge, Mon, 3 Apr 2006 23:26:31
        Ok Vigge, will you help me figure all this out?, John Williams , Tue, 4 Apr 2006 09:11:44
        Re: Ok Vigge, will you help me figure all this out?, Vigge, Tue, 4 Apr 2006 10:04:26
        Re: Ok Vigge, will you help me figure all this out?, John Williams , Tue, 4 Apr 2006 15:48:46
        Re: Ok Vigge, will you help me figure all this out?, vigge, Wed, 5 Apr 2006 13:35:56
        Re: Ok Vigge, will you help me figure all this out?, John Williams , Wed, 5 Apr 2006 14:07:39
        Re: Ok Vigge, will you help me figure all this out?, Vigge, Wed, 5 Apr 2006 14:20:01
        Well, I will say this, its hot!!!, John Williams , Fri, 7 Apr 2006 08:22:42
        Re: Well, I will say this, its hot!!!, vigge, Fri, 7 Apr 2006 12:23:30
        Re: Well, I will say this, its hot!!!, John Williams , Sat, 8 Apr 2006 06:07:04
        Re: Well, I will say this, its hot!!!, vigge, Sat, 8 Apr 2006 12:24:38
        Mid-way on delivery pipe is 142F, John Williams , Sun, 9 Apr 2006 13:03:59
  - absolute pressure, jak , Sat, 1 Apr 2006 21:11:16
    - Re: absolute pressure, TML , Mon, 3 Apr 2006 02:15:43
      - yeah I think you are rite pre98, jak , Mon, 3 Apr 2006 09:22:35

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