7psi with big turbo diff as with small right?
07-19-2004, 06:56 PM
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7psi with big turbo diff as with small right?
Im trying to explain to my friend why a big turbo will make more power than a small turbo at the same boost level? Is it because of the amount of air that the bigger compressor can flow?
07-19-2004, 07:09 PM
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Re: 7psi with big turbo diff as with small right? (tegsedan)
he thinks that 7 psi is 7 psi no matter what turbo. i no this isnt right. someone please help me in explaining why this is?
07-19-2004, 10:18 PM
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Re: (tegsedan)
Its not that simple...A smaller compressor wheel may flow more air at 7psi than a larger compressor wheel at the same 7psi...The larger and/or more aerodynamic wheel will flow more air at higher pressures where the smaller compressor wheel will simply "chop" the air...
07-19-2004, 10:36 PM
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Re: (Sunrise City Rider)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Sunrise City Rider »</TD></TR><TR><TD CLASS="quote">Its not that simple...A smaller compressor wheel may flow more air at 7psi than a larger compressor wheel at the same 7psi...The larger and/or more aerodynamic wheel will flow more air at higher pressures where the smaller compressor wheel will simply "chop" the air...</TD></TR></TABLE>
Nice description. Also, two similarly sized turbos with different wheel trims will flow different cfms at the same pressure ratio. Put simply, if a large turbo has a tight A/R, it may flow less than a smaller turbo with a larger A/R. Learn how to read compressor maps, they help clarify things a lot.
Nice description. Also, two similarly sized turbos with different wheel trims will flow different cfms at the same pressure ratio. Put simply, if a large turbo has a tight A/R, it may flow less than a smaller turbo with a larger A/R. Learn how to read compressor maps, they help clarify things a lot.
07-19-2004, 10:50 PM
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Re: (Sunrise City Rider)
If you take a normally asperated engine, it will make different power levels by changing to different exhaust and intake components, even though it is always running at the same 'boost' (+0psi). In the same way, on an FI car the turbo is part of the both the exhaust and intake. So when you change it, naturally you can make different power levels at the exact same boost level.
Also if you have a restrictive turbine wheel/housing, it can limit flow through the engine, while the measured pressure in the intake side of the engine can be just as high or higher, compared with a turbine that is less restrictive.
Also if you have a restrictive turbine wheel/housing, it can limit flow through the engine, while the measured pressure in the intake side of the engine can be just as high or higher, compared with a turbine that is less restrictive.
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07-19-2004, 11:46 PM
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Re: (Slammd Sol)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Slammd Sol »</TD></TR><TR><TD CLASS="quote">put 7psi through a straw, then put 7psi through something larger like a paper towel roll.. which will end up having more air flowed through it within a set time.</TD></TR></TABLE>
Too bad this analogy is completely wrong, since the straw is your engine, and unless you increase the displacement, it will never be a paper towel.
The reason the bigger turbo will make more power at a given boost level is because it will not have to spin as quickly, and will heat up the air less. For every ~11ºF you drop the intake temps, you gain 1% power.
Talking about CFM is really confusing, and dumb, in my opinion. One should talk about lb/min of air, since this takes density, and thus temperature, into account. ANY tiny turbo that can make Xpsi on a given engine will flow just as much CFM at Xpsi as any other much larger turbo. It will just be more dense with the larger turbo, thus higher lb/min.
Too bad this analogy is completely wrong, since the straw is your engine, and unless you increase the displacement, it will never be a paper towel.
The reason the bigger turbo will make more power at a given boost level is because it will not have to spin as quickly, and will heat up the air less. For every ~11ºF you drop the intake temps, you gain 1% power.
Talking about CFM is really confusing, and dumb, in my opinion. One should talk about lb/min of air, since this takes density, and thus temperature, into account. ANY tiny turbo that can make Xpsi on a given engine will flow just as much CFM at Xpsi as any other much larger turbo. It will just be more dense with the larger turbo, thus higher lb/min.
07-20-2004, 08:38 AM
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Re: (ion_four)
Ion four is right about temperature of course, but there are other things that cause 7psi to make less or more power with one turbo than with another turbo.
I'll say it like this to take temperature out of the equation: A turbocharged engine can make less power at the same lb/ft of air, than the same engine under identical conditions with a different turbo.
Think of pumping losses on a n/a engine when energy is used to push air through things. There are similar losses when pushing air through the blades of a turbine. There are also pumping losses on the compressor and intake side of things, and these losses are different from turbo to turbo.
I'll say it like this to take temperature out of the equation: A turbocharged engine can make less power at the same lb/ft of air, than the same engine under identical conditions with a different turbo.
Think of pumping losses on a n/a engine when energy is used to push air through things. There are similar losses when pushing air through the blades of a turbine. There are also pumping losses on the compressor and intake side of things, and these losses are different from turbo to turbo.
07-20-2004, 08:41 AM
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Re: (mos)
7 PSI IS 7PSI NO MATTER WHAT. but the amount of horsepower made at 7psi isnt always gonna be the same . it all has to do with the size of a turbo. bigger turbo = more flow= more hp. plain and simple
07-20-2004, 09:32 AM
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Re: (itr206)
I dont know much about the flow maps and such but i have taken a centrifugal pump course for my degree as a mechanical engineer at cal poly, slo. Yes, 7 lbs/in^2 in a small turbo is the same as 7lbs/in^2 in a big turbo since they are just a pressure. But I guess the power would come from the volumetric flow rate the turbo would push into the cylinders. Volumetric flow rate is a velocity times Area. The Area i would assume would remain constant through out the process (engine) but the velocity would definitely change depending on the turbo wheel size. To calculate the velocity is pretty complex since it depends on so many factors including the geometry of the wheel, efficiency, blah blah. But i could estimate it by taking the max velocity of both wheels and assuming that constant. Velocity would be the radius of the turbing wheel times the revolutions measured in rads/sec. The revolutions of the wheel would have to be the same since they are both being powered by the exiting gases of the same engine. What would increase the velocity of the flow of air would be the radius of the wheel. If you ahve more velocity you have more volumetric flow rate. Having a bigger turbo would get you more air inside the cylinders at a faster rate and thus creating more power at the same pressure.
I hope this helps.
I hope this helps.
07-20-2004, 11:53 AM
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Re: (CalGSR99)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by CalGSR99 »</TD></TR><TR><TD CLASS="quote">I dont know much about the flow maps and such but i have taken a centrifugal pump course for my degree as a mechanical engineer at cal poly, slo. Yes, 7 lbs/in^2 in a small turbo is the same as 7lbs/in^2 in a big turbo since they are just a pressure. But I guess the power would come from the volumetric flow rate the turbo would push into the cylinders. Volumetric flow rate is a velocity times Area. The Area i would assume would remain constant through out the process (engine) but the velocity would definitely change depending on the turbo wheel size. To calculate the velocity is pretty complex since it depends on so many factors including the geometry of the wheel, efficiency, blah blah. But i could estimate it by taking the max velocity of both wheels and assuming that constant. Velocity would be the radius of the turbing wheel times the revolutions measured in rads/sec. The revolutions of the wheel would have to be the same since they are both being powered by the exiting gases of the same engine. What would increase the velocity of the flow of air would be the radius of the wheel. If you ahve more velocity you have more volumetric flow rate. Having a bigger turbo would get you more air inside the cylinders at a faster rate and thus creating more power at the same pressure.
I hope this helps. </TD></TR></TABLE>
First, you want to stay away from using the term volumetric flow rate since it is the density of the air that is really important. The term mass flow rate is more appropriate. They are afterall related by density.
Regardless, you are correct in stating that the "velocity" of the air flowing through the system is what makes the difference.
The difference between a large and small turbo would be the actual wheel speed at a given pressure ratio. The larger turbo with greater flow capacity will be more efficient than the smaller turbo under some operating conditions and less efficient under others. It all comes down to what the wheel speed is at the given pressure ratio and flow rate. Too high and you are out of peak efficiency range, too low and you aren't there either.
Conservation of mass is the governing rule behind why small turbos behave differently as compared to larger turbos. This is also why larger turbos are more efficient at higher flow rates. They allow more mass to exit the system so that more mass can enter to make more power. Then engine feeds off of itself which is why large turbos look so peaky on the dyno. The increase in power is exponential.
I hope this helps.
</TD></TR></TABLE>First, you want to stay away from using the term volumetric flow rate since it is the density of the air that is really important. The term mass flow rate is more appropriate. They are afterall related by density.
Regardless, you are correct in stating that the "velocity" of the air flowing through the system is what makes the difference.
The difference between a large and small turbo would be the actual wheel speed at a given pressure ratio. The larger turbo with greater flow capacity will be more efficient than the smaller turbo under some operating conditions and less efficient under others. It all comes down to what the wheel speed is at the given pressure ratio and flow rate. Too high and you are out of peak efficiency range, too low and you aren't there either.
Conservation of mass is the governing rule behind why small turbos behave differently as compared to larger turbos. This is also why larger turbos are more efficient at higher flow rates. They allow more mass to exit the system so that more mass can enter to make more power. Then engine feeds off of itself which is why large turbos look so peaky on the dyno. The increase in power is exponential.
07-20-2004, 12:52 PM
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Re: (pngfolife)
Absolutely right, density is one of the most important factors to produce power if it's denser.
But the question was why a bigger turbo would produce more power than a smaller turbo operating at the same pressure. I dont see how a bigger turbo is going to have any affect on air density. Air density will remain constant for both turbos since they will operate at the same pressure and external temperature. Yes, mass flow rate is more appropriate to say.
Personally, i like it when things are straightforward and simple. So here goes, a bigger turbo will push air faster into the cylinders than a smaller turbo can, eventhough the engine is at the same boost.
But the question was why a bigger turbo would produce more power than a smaller turbo operating at the same pressure. I dont see how a bigger turbo is going to have any affect on air density. Air density will remain constant for both turbos since they will operate at the same pressure and external temperature. Yes, mass flow rate is more appropriate to say.
Personally, i like it when things are straightforward and simple. So here goes, a bigger turbo will push air faster into the cylinders than a smaller turbo can, eventhough the engine is at the same boost.
07-20-2004, 01:12 PM
#14
to make the kid understand....... simple words:
a bigger turbo at the same Psi level as the smaller one will push (cram) more air into the cylinders than the smaller....... more air+gas=more power
a bigger turbo at the same Psi level as the smaller one will push (cram) more air into the cylinders than the smaller....... more air+gas=more power
07-20-2004, 01:33 PM
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Re: (CalGSR99)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by USDM 4G VTEC »</TD></TR><TR><TD CLASS="quote">to make the kid understand....... simple words:
a bigger turbo at the same Psi level as the smaller one will push (cram) more air into the cylinders than the smaller....... more air+gas=more power
</TD></TR></TABLE>
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by CalGSR99 »</TD></TR><TR><TD CLASS="quote">
Personally, i like it when things are straightforward and simple. So here goes, a bigger turbo will push air faster into the cylinders than a smaller turbo can, eventhough the engine is at the same boost.</TD></TR></TABLE>
Unfortunately this is not that simple. Under certain conditions a smaller turbo may be able to make more power than a larger one, at the same manifold pressure. Calgsr, you go from your first post which makes things more complicated than they are, to this next post trying to make things simpler than they really are... I should have stayed away from this thread
a bigger turbo at the same Psi level as the smaller one will push (cram) more air into the cylinders than the smaller....... more air+gas=more power
</TD></TR></TABLE>
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by CalGSR99 »</TD></TR><TR><TD CLASS="quote">
Personally, i like it when things are straightforward and simple. So here goes, a bigger turbo will push air faster into the cylinders than a smaller turbo can, eventhough the engine is at the same boost.</TD></TR></TABLE>
Unfortunately this is not that simple. Under certain conditions a smaller turbo may be able to make more power than a larger one, at the same manifold pressure. Calgsr, you go from your first post which makes things more complicated than they are, to this next post trying to make things simpler than they really are... I should have stayed away from this thread
07-20-2004, 02:32 PM
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Re: (mos)
"Under certain conditions a smaller turbo may be able to make more power than a larger one, at the same manifold pressure"
Wow! Thats so helpful! Under "certain circumstances" anything can happen. If the planets are aligned perfectly, if there is a full moon, and if the weather is a certain condition..... Do you know even know what the certain circumstances are??? There are very few things that are simple, stop stating the obvious.
If you want to help the kid maybe you should explain your "certain circumstances" with facts? Also, keep in mind that we are explaining the general case of big turbos compared to smaller turbos. I'm sorry if our answers were too complicated for you.
Wow! Thats so helpful! Under "certain circumstances" anything can happen. If the planets are aligned perfectly, if there is a full moon, and if the weather is a certain condition..... Do you know even know what the certain circumstances are??? There are very few things that are simple, stop stating the obvious.
If you want to help the kid maybe you should explain your "certain circumstances" with facts? Also, keep in mind that we are explaining the general case of big turbos compared to smaller turbos. I'm sorry if our answers were too complicated for you.
07-20-2004, 08:49 PM
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Re: (CalGSR99)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by CalGSR99 »</TD></TR><TR><TD CLASS="quote">I'm sorry if our answers were too complicated for you.</TD></TR></TABLE>
Damn, no need to get all pissy with me. What I mean by 'certain circumstances' is: at low pressure, say 6 or 7psi, (per the thread title) at a moderate rpm, where a smaller turbo is in its peak efficiency range, where a large turbo isnt there yet. Those circumstances seem to be pretty damn common around these parts.
In my previous posts I'm genuinely trying to help this guy understand the answer to his question. I used to believe 7psi made the same power as 7psi no matter which turbo you run. It took a while for me to realize why this is not true... and its not just about temperature like I once believed.
If you go back and read my posts above you may see that I am trying to put things is a way easy to understand. For me thinking about pumping losses on a normally asperated engine was easiest. I'll be happy if anything I've typed helps some person understand more about this subject. Thats the reason I posted here. I'm wrong sometimes, I'm not always right, and I'm always learning from this forum. Your response makes me sorry I said anything at all.
Damn, no need to get all pissy with me. What I mean by 'certain circumstances' is: at low pressure, say 6 or 7psi, (per the thread title) at a moderate rpm, where a smaller turbo is in its peak efficiency range, where a large turbo isnt there yet. Those circumstances seem to be pretty damn common around these parts.
In my previous posts I'm genuinely trying to help this guy understand the answer to his question. I used to believe 7psi made the same power as 7psi no matter which turbo you run. It took a while for me to realize why this is not true... and its not just about temperature like I once believed.
If you go back and read my posts above you may see that I am trying to put things is a way easy to understand. For me thinking about pumping losses on a normally asperated engine was easiest. I'll be happy if anything I've typed helps some person understand more about this subject. Thats the reason I posted here. I'm wrong sometimes, I'm not always right, and I'm always learning from this forum. Your response makes me sorry I said anything at all.
07-20-2004, 10:48 PM
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Re: (mos)
Sorry about that. Didnt mean to come at you the wrong way. I'm learning too but i like it when people explain what they are trying to say. I guess I was just going nuts at work.
Again, Thanks bro.
Again, Thanks bro.
07-21-2004, 10:37 AM
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Re: (mos)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by mos »</TD></TR><TR><TD CLASS="quote">What I mean by 'certain circumstances' is: at low pressure, say 6 or 7psi, (per the thread title) at a moderate rpm, where a smaller turbo is in its peak efficiency range, where a large turbo isnt there yet.</TD></TR></TABLE>
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by pngfolife »</TD></TR><TR><TD CLASS="quote">The larger turbo with greater flow capacity will be more efficient than the smaller turbo under some operating conditions and less efficient under others. It all comes down to what the wheel speed is at the given pressure ratio and flow rate. Too high and you are out of peak efficiency range, too low and you aren't there either.</TD></TR></TABLE>
Damn, I hate quoting myself...
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by pngfolife »</TD></TR><TR><TD CLASS="quote">The larger turbo with greater flow capacity will be more efficient than the smaller turbo under some operating conditions and less efficient under others. It all comes down to what the wheel speed is at the given pressure ratio and flow rate. Too high and you are out of peak efficiency range, too low and you aren't there either.</TD></TR></TABLE>
Damn, I hate quoting myself...
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