Re: TAP vs IA Chip/Boost mods

["Russell S Southerlin" <Russell.S.Southerlin@lmco.com>]

I agree 100% - 1.7 bar is the same pressure at sea level as 5000ft. 

The point I was making was how much turbo boost pressure does it take to get 1.7
bar at sea level vs 5000ft. I know Chad and I think Graydon both have a separate
boost gage that indicates turbo boost gage pressure (I have one also). This is 
what they are refering to when they say the boost was 14 or 15 psi. In any case 
the absolute pressure of 1.7 bar is 1.7*14.7=25.0psi.  

At sea level to get 25.0 psi of pressure the turbo would have to put out 10.3 
psi and atmospheric would contribute 14.7 psi to get 25.0 psi total. 

Now at 5000 ft atmospheric is only about 12.5 psi so to get 25.0 psi total the 
turbo would have to put out 12.5 and atmospheric would contribute 12.5 to give 
you 25.0 total.

Same thing for 1.8 bar (26.5psi)- sea level, turbo=11.8psi atmos=14.7psi; 
5000ft, turbo=14psi atmos=12.5.

**The moral of the story is, your turbo has to work harder at altitude to 
produce the same absolute pressure.


Except for one small problem.  The gauges read absolute pressure vs. zero 
rather than differential pressure vs ambient.
     
Likewise, the chip is calibrated for absolute pressure not some pressure 
above an arbitrary starting point such as ambient pressure.  Thus 1.7 bar 
at Denver is the same pressure as 1.7 bar at Miami.
     
At 10:08 AM 5/21/97 -0700, you wrote: 
>Graydon Wrte:
>> than the TAP box, it was consistant at 14 psi which let me keep my
>> right foot planted at all times. Stock bar guage read 1.7 bar all the 
>
>>Shows the inaccuracy of the stock guage - mine reads 1.9 when the 
>>Autometer guage says 14psi.
>
>Remember we are at 5000 ft. At this altitude Chad's gage is not very far 
>off. 14psi of boost would be right at 1.80bar (12.5 atmos. press @ 
>5000ft + 14psi boost)/14.7psi/bar = 1.80 bar. It was a also a hot day on 
>Sat. (86-87 degf) so this would reduce the 12.5 atmospheric pressure a 
>little.
>
>I think Graydon is in Mich. which is essentially at sea level so 14 psi 
>of boost would be 1.95bar (14.7 + 14)/14.7=1.95
>
>
>
___
   Bob
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