Help me understand something regarding boost...
Help me understand something regarding boost...
So if my boost gauge is reading 9PSI, this is 9PSI of boost that the engine has not used. Therefore if I help my engine to breath better by doing mods like cams, manifold, decat...etc, my boost reading will actually go down because the engine is able to consume more of that boost - but I will make more power.
If this is true (which i guess it is), then why would I (or anyone for that matter) want to generate more boost if their engine is not making full use of what they are already making?
Probably a n00b question, but its buggin me
OK, I've read in a few places now that the PSI readouts you see on boost gauges are not an indication of how much power you're making (in a roundabout way), but how much boost is LEFT after the engine can consume what it can.
So if my boost gauge is reading 9PSI, this is 9PSI of boost that the engine has not used. Therefore if I help my engine to breath better by doing mods like cams, manifold, decat...etc, my boost reading will actually go down because the engine is able to consume more of that boost - but I will make more power.
If this is true (which i guess it is), then why would I (or anyone for that matter) want to generate more boost if their engine is not making full use of what they are already making?
Probably a n00b question, but its buggin me
the way i understand it. (and please stop reading if im teaching you to suck eggs)
In a NA car when the inlet valve opens the air is "sucked" in by the vacuum left from the piston pulling down. so it will just pull in the amount of air at atmospheric pressure (0barG) that the space allows. so say hypothetically its 1 litre per cylinder it will suck in 1 litre of air at atmospheric pressure.
In a forced induction car when the inlet valve opens, the air is forced in by the positive pressure from the turbo and is compressed in the cylinder instead of sucked in at atmospheric pressure.
Think of a 1 litre bottle. normally if you just screw a top on you get one litre of air inside.
If you compress it in at 1bar then you get more volume than 1 litre of air in there, say 2 litres worth, but at pressure; so therefore more Oxygen for the more powerful bang.
Hope that makes sense to everyone else
![[Image: LexuS-Copy.jpg]](http://i65.photobucket.com/albums/h204/Sparkystav/LexuS-Copy.jpg)
Read my thread here: The Evolution of my Turbo Lexus from NA-Supercharged-Twin Turbo-Massive Single
Please leave your comments.
Sparkystav
31-05-2018, 11:41 AM #2Hmm, doesnt seem right to me.
the way i understand it. (and please stop reading if im teaching you to suck eggs)
In a NA car when the inlet valve opens the air is "sucked" in by the vacuum left from the piston pulling down. so it will just pull in the amount of air at atmospheric pressure (0barG) that the space allows. so say hypothetically its 1 litre per cylinder it will suck in 1 litre of air at atmospheric pressure.
In a forced induction car when the inlet valve opens, the air is forced in by the positive pressure from the turbo and is compressed in the cylinder instead of sucked in at atmospheric pressure.
Think of a 1 litre bottle. normally if you just screw a top on you get one litre of air inside.
If you compress it in at 1bar then you get more volume than 1 litre of air in there, say 2 litres worth, but at pressure; so therefore more Oxygen for the more powerful bang.
Hope that makes sense to everyone else
Read my thread here: The Evolution of my Turbo Lexus from NA-Supercharged-Twin Turbo-Massive Single
Please leave your comments.
But then that kinda throws this out:
Quote:What the Boost Gauge is really telling you
A lot of people believe the boost gauge measures supercharger output. It doesn't.
The boost gauge measures pressure. Pressure is caused by a restriction to flow. The engine is that restriction to flow.
While the supercharger is spinning and making up air, the engine is also running and inhaling, and the boost gauge only shows the remainder. In other words: The boost gauge only shows WHAT'S LEFT after the engine consumes what it can.
Supercharger output MINUS engine consumption = what's left to display on the gauge.
Sometimes we get a call from an enthusiast who has just added headers, or cams, or a larger intake and now sees his boost gauge is lower than it used to be. They call thinking they did something wrong. Quite the opposite – they have removed restrictions to air flow in their motor, and although the supercharger is producing as much air as it did before, the engine can now use more of it. The HP of this engine has gone up, and the boost gauge will have gone down.
Now that you understand that, we can tell you that a low boost gauge number is either:
1) an engine that has little restriction and is breathing well (this is a GOOD thing) or
2) a supercharger that is sized too small for the size of the engine it is bolted to.
3) a supercharger spinning too slowly to match its output to engine needs.
Thats exactly how I understood it too! So 9PSI = the air is compressed to 9PSI and therefore it creates a much more powerful explosion than air at atmospheric pressure.
But then that kinda throws this out:
Quote:What the Boost Gauge is really telling you
A lot of people believe the boost gauge measures supercharger output. It doesn't.
The boost gauge measures pressure. Pressure is caused by a restriction to flow. The engine is that restriction to flow.
While the supercharger is spinning and making up air, the engine is also running and inhaling, and the boost gauge only shows the remainder. In other words: The boost gauge only shows WHAT'S LEFT after the engine consumes what it can.
Supercharger output MINUS engine consumption = what's left to display on the gauge.
Sometimes we get a call from an enthusiast who has just added headers, or cams, or a larger intake and now sees his boost gauge is lower than it used to be. They call thinking they did something wrong. Quite the opposite – they have removed restrictions to air flow in their motor, and although the supercharger is producing as much air as it did before, the engine can now use more of it. The HP of this engine has gone up, and the boost gauge will have gone down.
Now that you understand that, we can tell you that a low boost gauge number is either:
1) an engine that has little restriction and is breathing well (this is a GOOD thing) or
2) a supercharger that is sized too small for the size of the engine it is bolted to.
3) a supercharger spinning too slowly to match its output to engine needs.
IS 200 Sport with a few mods, Standardish IS-F. The IS250 SE-L with a few mods has gone to a new home.[SIGPIC][/SIGPIC]
If the supercharger or turbo is supplying more than enough volume than the engine is capable of ingesting then the pressure between the turbo/charger stays fairly constant doesn't it? It would only decrease if the constant charge to the cylinder isn't capable of keeping up with the volume ingested by the engine.
IS 200 Sport with a few mods, Standardish IS-F. The IS250 SE-L with a few mods has gone to a new home.[SIGPIC][/SIGPIC]
yes i see his point it you have a set output like you do from a charger and you loose boost because of better flow. this doesnt happen with a turbocharger because your wastegate will still open at the set pressure unlike a supercharger which spins at a set speed (provided its run at max output and doesnt use a wastegate or similar)
And he's of right about the restriction to flow, in that it has no where to go. so in theory that is right, your showing whats left,
BUT again, whats left is what is forcing the air into the engine each time a valve opens so bigger boost is better.
Read my thread here: The Evolution of my Turbo Lexus from NA-Supercharged-Twin Turbo-Massive Single
Please leave your comments.
Sparkystav
31-05-2018, 12:55 PM #5Jim, he makes sense in what he says BUT for point one.
yes i see his point it you have a set output like you do from a charger and you loose boost because of better flow. this doesnt happen with a turbocharger because your wastegate will still open at the set pressure unlike a supercharger which spins at a set speed (provided its run at max output and doesnt use a wastegate or similar)
And he's of right about the restriction to flow, in that it has no where to go. so in theory that is right, your showing whats left,
BUT again, whats left is what is forcing the air into the engine each time a valve opens so bigger boost is better.
Read my thread here: The Evolution of my Turbo Lexus from NA-Supercharged-Twin Turbo-Massive Single
Please leave your comments.
The pressure is the same from the output of the charger as it is in the chamber as there are wastegates to regulate the pressure to a set max.
The psi guage doesn't measure how much air there is, merely the pressure of the air that is there - so in practice I don't believe that it is a measure of unused boost.
speedfreek
31-05-2018, 01:21 PM #6Exactly as I see it Stav.
The pressure is the same from the output of the charger as it is in the chamber as there are wastegates to regulate the pressure to a set max.
The psi guage doesn't measure how much air there is, merely the pressure of the air that is there - so in practice I don't believe that it is a measure of unused boost.
[SIZE=3]'93 Mazda Eunos Roadster Turbo[/SIZE]
(Current project)
Sparkystav Jim, he makes sense in what he says BUT for point one.
yes i see his point it you have a set output like you do from a charger and you loose boost because of better flow. this doesnt happen with a turbocharger because your wastegate will still open at the set pressure unlike a supercharger which spins at a set speed (provided its run at max output and doesnt use a wastegate or similar)
And he's of right about the restriction to flow, in that it has no where to go. so in theory that is right, your showing whats left,
BUT again, whats left is what is forcing the air into the engine each time a valve opens so bigger boost is better.
Right gotcha, I think I've got it straight in my head now.
Higher PSI numbers are desirable, because even though the boost gauge is effectively measuring the PSI of the air that is not being used by the engine at that moment in time, the fact that the air is compressed to xPSI will be relative to power output when the engine does ingest that air.
It all sounds rather simple when you think it through properly, but the comments from a few people and the one pasted above had me veering off in a different direction.
Bottom line....I shall order the 14PSI pulley and the Meth injection kit. And I shall have fun.
Sparkystav Jim, he makes sense in what he says BUT for point one.
yes i see his point it you have a set output like you do from a charger and you loose boost because of better flow. this doesnt happen with a turbocharger because your wastegate will still open at the set pressure unlike a supercharger which spins at a set speed (provided its run at max output and doesnt use a wastegate or similar)
And he's of right about the restriction to flow, in that it has no where to go. so in theory that is right, your showing whats left,
BUT again, whats left is what is forcing the air into the engine each time a valve opens so bigger boost is better.
Right gotcha, I think I've got it straight in my head now.
Higher PSI numbers are desirable, because even though the boost gauge is effectively measuring the PSI of the air that is not being used by the engine at that moment in time, the fact that the air is compressed to xPSI will be relative to power output when the engine does ingest that air.
It all sounds rather simple when you think it through properly, but the comments from a few people and the one pasted above had me veering off in a different direction.
Bottom line....I shall order the 14PSI pulley and the Meth injection kit. And I shall have fun.
![[Image: tempsig2.jpg]](http://i121.photobucket.com/albums/o227/84stoney/tempsig2.jpg)
ad: It was a tough call to make, but the Supercharged IS200 is being retired. 
I can understand the fact that the engine is the restriction creating the pressure, and that if the engine is "freed" up a bit the pressure will decrease, but does that necessarily mean that the engine is suddenly producing more power? Surely that would be only if the charger has surplus power to give that is currently unused?
But yeah it would make no sense if the pressure gauge which simply measures pressure was telling you how much pressure was in reserve (how would it work that out?), rather than the actual pressure in the system.
2002 '02' IS200 SE Auto - DVD Satnav with Voice Activation - [COLOR="Blue"]Strathcaron Blue - Parking Sensors - 5000K HIDs with Anti-Glare Bulbs - PIAA 6500K Main Beams - LED Sidelights - Mirror/Sunroof Closure - TTE Styling Kit - 18" Styling Kit Alloys with nitrogen filled Goodyear Eagle F1 Asymmetric Tyres - Bluetouch Multimedia Kit - Gromaudio AUX in - Black painted calipers with silver Lexus decals - 12 LED Dome Light - 96 LED Boot Light - Stainless Steel Sport Sill Plates - PIAA Silicone Wipers[/COLOR]
I have barely any knowledge on this subject so forgive me if this is a total newbie question but I'm slightly confused by the conclusion made in that quote you posted.
I can understand the fact that the engine is the restriction creating the pressure, and that if the engine is "freed" up a bit the pressure will decrease, but does that necessarily mean that the engine is suddenly producing more power? Surely that would be only if the charger has surplus power to give that is currently unused?
But yeah it would make no sense if the pressure gauge which simply measures pressure was telling you how much pressure was in reserve (how would it work that out?), rather than the actual pressure in the system.
2002 '02' IS200 SE Auto - DVD Satnav with Voice Activation - [COLOR="Blue"]Strathcaron Blue - Parking Sensors - 5000K HIDs with Anti-Glare Bulbs - PIAA 6500K Main Beams - LED Sidelights - Mirror/Sunroof Closure - TTE Styling Kit - 18" Styling Kit Alloys with nitrogen filled Goodyear Eagle F1 Asymmetric Tyres - Bluetouch Multimedia Kit - Gromaudio AUX in - Black painted calipers with silver Lexus decals - 12 LED Dome Light - 96 LED Boot Light - Stainless Steel Sport Sill Plates - PIAA Silicone Wipers[/COLOR]
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