What happens under "boost" conditions?
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Senior Member
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From: Virginia
What happens under "boost" conditions?
I'm new to forced induction with my Lightning and was wondering if someone could shed a little more light on what boost really is and when it occurs. I haven't been able to find much about this in searches. What functionally/technically is happening when:
a) I roll into the throttle and at 3000 rpm and the boost gauge reads zero or a level of vacuum
versus
b) when I romp on the pedal and at 3000 rpm I get an actual boost reading (2, 4, 8+ lbs, whatever).
????
In both situations, is the the same amount of air being "forced" through the intake, or under boost is it pushing more air through and how so? BTW, I understand the concept of the supercharger being driven by the belt as engine speed increases and that the the rotor (?) spins and forces air out of it and through the intercooler. Thanks for any info!
a) I roll into the throttle and at 3000 rpm and the boost gauge reads zero or a level of vacuum
versus
b) when I romp on the pedal and at 3000 rpm I get an actual boost reading (2, 4, 8+ lbs, whatever).
????
In both situations, is the the same amount of air being "forced" through the intake, or under boost is it pushing more air through and how so? BTW, I understand the concept of the supercharger being driven by the belt as engine speed increases and that the the rotor (?) spins and forces air out of it and through the intercooler. Thanks for any info!
Last edited by Slick_Sammy; Sep 13, 2004 at 08:35 PM.
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From: DETROIT, (formerly Eaton County, Michigan)
instead of a boost gauge think of it as a vacuum gauge.
On the bottom of the s/c is a bypass valve, when it opens the air the air recirculates and doesn't create boost.
that valve is controlled by vacuum. on the drivers ide of the s/c is a boost actuator that opens and closes that valve.
when at idle and NOT ACCELERATING hard (accelerate slowly) the engine stays in vacuum. and the valve remains OPEN (no boost)
when you hammer it, the engine is not in vacuum (forgot the technical name) and the boost actuator operates and closes that vavle.
when the valve on the bottom of the s'c closes, the air being sucked into the s/c can only go into the engine and BOOST is created.
start your truck, pop the hood, find the trottle body and give the engine alittle throttle (rev it up)
With a flash light look at the boost actuator (drivers side of supercharger) and watch it open and close (go up and down) that is openin gn and closing the vavle on the bottom of the supercharger.
with that valve closed, all that air is being forced into the engine.
the quicker the a/c spins, the more boost (up to a point).
With the valve opened, it doesn't matter how fast the a/s is spinning, the air is recirculating and NOT being forced into the engine.
HOPE THIS HELPS... only basics
On the bottom of the s/c is a bypass valve, when it opens the air the air recirculates and doesn't create boost.
that valve is controlled by vacuum. on the drivers ide of the s/c is a boost actuator that opens and closes that valve.
when at idle and NOT ACCELERATING hard (accelerate slowly) the engine stays in vacuum. and the valve remains OPEN (no boost)
when you hammer it, the engine is not in vacuum (forgot the technical name) and the boost actuator operates and closes that vavle.
when the valve on the bottom of the s'c closes, the air being sucked into the s/c can only go into the engine and BOOST is created.
start your truck, pop the hood, find the trottle body and give the engine alittle throttle (rev it up)
With a flash light look at the boost actuator (drivers side of supercharger) and watch it open and close (go up and down) that is openin gn and closing the vavle on the bottom of the supercharger.
with that valve closed, all that air is being forced into the engine.
the quicker the a/c spins, the more boost (up to a point).
With the valve opened, it doesn't matter how fast the a/s is spinning, the air is recirculating and NOT being forced into the engine.
HOPE THIS HELPS... only basics
Senior Member
Joined: Mar 2002
Posts: 11,153
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From: Selden NY
Great explanation l-menace
That settles it, I'm welding my Butterfly Closed, and I'm going to get me a Boost Storing Canister
OR SOMETHING ???
and then save up all my Boost, AND THEN WAM release it when I race Gator
Sammy, here's a Pic of the bottom of our S/C
Notice the Butterfly l-menace speaks of
You also notice how one S/C has been modified (Ported)
(Made Larger) to allow more Air/Boost to pass through it.
Many L's have this Mod, good for @ 2lb's of extra Boost,
and 20-40 HP more
(and I was only kidding about saving my boost) hehehehe......
That settles it, I'm welding my Butterfly Closed, and I'm going to get me a Boost Storing Canister
OR SOMETHING ???
and then save up all my Boost, AND THEN WAM release it when I race Gator
Sammy, here's a Pic of the bottom of our S/C
Notice the Butterfly l-menace speaks of
You also notice how one S/C has been modified (Ported)
(Made Larger) to allow more Air/Boost to pass through it.
Many L's have this Mod, good for @ 2lb's of extra Boost,
and 20-40 HP more
(and I was only kidding about saving my boost) hehehehe......
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Joined: May 2004
Posts: 440
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The whole point of the recirculating air when not at WOT is for efficiency. There is no need to build boost when at part throttle or idle and burn more fuel and create heat continously from compressing.
This is the same reason for nitrous being used at WOT. A lot of people think nitrous needs to be used at WOT and this is not true. But why use nitrous that costs money at part throttle when you have a lot more throttle left that brings in more air for FREE. Nitrous can actualy be activated at idle if done properly as this would be no different then opeing the throttle more and bringing in more oxygen.
This is the same reason for nitrous being used at WOT. A lot of people think nitrous needs to be used at WOT and this is not true. But why use nitrous that costs money at part throttle when you have a lot more throttle left that brings in more air for FREE. Nitrous can actualy be activated at idle if done properly as this would be no different then opeing the throttle more and bringing in more oxygen.