Boost on vintage aircraft
Thread Starter
Joined: Feb 2001
Posts: 579
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From: Canada
Boost on vintage aircraft
On warbird era aircraft the index for power was boost, i.e. +14
lbs per sq. in . This boost could be positive or negative.
How does boost compare to a manifold pressure gauge?
What would the boost indicator show when the engine is not running?
Thanks .
lbs per sq. in . This boost could be positive or negative.
How does boost compare to a manifold pressure gauge?
What would the boost indicator show when the engine is not running?
Thanks .
Joined: Dec 1998
Posts: 4,282
Likes: 6
From: Escapee from Ultima Thule
Boost is the inches MP above or below ambient in the induction manifold. The more familiar MP gauge measures actual pressure in the manifold. They're both measuring the same thing - it's just the reference point that changes.
With the engine not running the boost would be zero. In a non-turbo engine it would always be at least slightly negative (think about a 'normal' MAP gauge. When does it ever go above ambient?). In a forced induction engine the boost would go above zero when the turbo- or super-charger is compressing the induction charge.
With the engine not running the boost would be zero. In a non-turbo engine it would always be at least slightly negative (think about a 'normal' MAP gauge. When does it ever go above ambient?). In a forced induction engine the boost would go above zero when the turbo- or super-charger is compressing the induction charge.
Joined: Sep 2001
Posts: 764
Likes: 3
From: UK
Tinstaafl,
Not quite correct in one aspect. As you say, a boost gauge is just a MAP gauge using a different reference. 0 psi boost equates to 30" Hg (1 atmosphere). Therefore, if you have a low pressure day, "static" boost (i.e. with the engine not running) will show slightly less than 0 psi in the same way as a MAP gauge will show less than 30", and vice versa.
IHL,
It is worth remembering that 1 atmosphere is 30" Hg and 14.7 psi. Therefore, as a rough rule of thumb 1 psi boost equates to 2" Hg. Therefore, +14 psi boost is approximately 59" MAP.
Rgds
L
Not quite correct in one aspect. As you say, a boost gauge is just a MAP gauge using a different reference. 0 psi boost equates to 30" Hg (1 atmosphere). Therefore, if you have a low pressure day, "static" boost (i.e. with the engine not running) will show slightly less than 0 psi in the same way as a MAP gauge will show less than 30", and vice versa.
IHL,
It is worth remembering that 1 atmosphere is 30" Hg and 14.7 psi. Therefore, as a rough rule of thumb 1 psi boost equates to 2" Hg. Therefore, +14 psi boost is approximately 59" MAP.
Rgds
L
