[Diy_efi] Re: Question about speed density, etc.

[Eric D Byrd]

Not sure how this is unclear... boost pressure is not identically equal
to manifold pressure, because the throttle body comes before the
manifold, but after the intake piping from the compressor.  Consider 2
situations.  12 psi boost, 60% throttle position, 5000 rpm;  and 12 psi
boost, 100% throttle position, 5000 rpm.  The latter would occur just
after you punched the throttle.  The simple fact that you suddenly get
crushed back in your seat is what proves your air mass flow has
increased.  But this is because your manifold pressure has increased. 
Your wastegate holds boost at 12 lbs because that's what a wastegate's
job is.  But the throttle body's job is to throttle back the intake
pressure to the level you set with your foot.  On most cars, that is the
only way to control engine power.  Throttling the flow, by definition,
also reduces manifold pressure.  For a given volume flow of air, which is
fixed by the engine's displacement and the rPM, the only way to control
power is by varying the density, which you do by varying pressure
*behind* the throttle body, in the manifold.

On Sun, 27 Oct 2002 20:55:11 -0600 "arnie" <arnie_ at charter.net> writes:
> quote:
> > Right, I was going to say that;  boost pressure is not manifold 
> pressure,
> 
> ?????
> 
> GAS
> 
> ----- Original Message ----- 
> From: "Eric D Byrd" <klox at juno.com>
> To: <diy_efi at diy-efi.org>
> Sent: Sunday, October 27, 2002 7:32 PM
> Subject: Re: [Diy_efi] Re: Question about speed density, etc.
> 
> 
> > Right, I was going to say that;  boost pressure is not manifold 
> pressure,
> > because  MAP is taken after the TB.  If you are at part throttle 
> at 12
> > psi and you floor it, MAP goes up simply because the throttle is 
> opened,
> > even though your wastegate controls boost pressure with precision.
> 
> 
> 
> _______________________________________________
> Diy_efi mailing list
> Diy_efi at diy-efi.org
> http://www.diy-efi.org/mailman/listinfo/diy_efi
> 


________________________________________________________________
Sign Up for Juno Platinum Internet Access Today
Only $9.95 per month!
Visit www.juno.com

_______________________________________________
Diy_efi mailing list
Diy_efi at diy-efi.org
http://www.diy-efi.org/mailman/listinfo/diy_efi