View Full Version : Lets talk turbos..
hondarider552
02-02-2009, 05:30 PM
Ive been asked by James Hess today about the boost pressures of the stock turbo, and the cheetah.
The problem is, is that most people assume 45psi is better than 40psi.
The real story is the amount of air the new turbo flows compared to the old one. lets say you have a stock turbo pushing 40psi vs a cheetah or any other turbo flowing 45psi. Do you have only 5 more psi of air? No. Boost is a restriction of the flow of the turbo.
If you upgrade to a different charger, you reduce the amount of restriction, and gain the CFM of the new turbo. Brody, my friend with a 6.0 has the phat shaft from industrial injection. He sees 36-38psi of boost while on the track, while i see the same and a little more. Does that mean that im as efficient as him? IMO it doesnt.
I also heard from james that he just wants the "whistle" from the turbo. that can be changed in the stock turbo by modding the vane posistions at idle, i have personally done it to mine. You dont have to go out a buy a cheetah just for the sound, you need to do a lot of research.
Lets hear your thoughts guys.
RickDLance
02-02-2009, 05:46 PM
Don't forget drive pressure. ;)
Crazy_Steve
02-02-2009, 06:12 PM
Boost is a restriction of the flow of the turbo.
Boost is the restriction of the flow entering the engine. The turbo is pushing against that.
The bigger turbos can make more boost at a lower turbo rpm (just like a big fan moves more air at a slower rpm than a small fan and a high rpm). Say a stock turbo that can make 40psi of boost spins at x rpm, a bigger turbo (doesnt matter which model gt40, 42, htt etc) can make that same 40 psi at x-y rpm.
I think this is the most important part:
The more psi you have knocking at each cylinders door every time the valves open up, the more air you'll get into the cylinders, regardless of the turbo that is in use. IMO 40psi from the stock turbo and 40psi from any other turbo force an equal amount of air into the cylinders.
hondarider552
02-02-2009, 06:14 PM
Boost is the restriction of the flow entering the engine. The turbo is pushing against that.
The bigger turbos can make more boost at a lower turbo rpm (just like a big fan moves more air at a slower rpm than a small fan and a high rpm). Say a stock turbo that can make 40psi of boost spins at x rpm, a bigger turbo (doesnt matter which model gt40, 42, htt etc) can make that same 40 psi at x-y rpm.
I think this is the most important part:
The more psi you have knocking at each cylinders door every time the valves open up, the more air you'll get into the cylinders, regardless of the turbo that is in use. IMO 40psi from the stock turbo and 40psi from any other turbo force an equal amount of air into the cylinders.
Thanks for posting this steve, you said what i was thinking but couldnt put it to words :lol: :thumb:
I'd suggest that when evaluating a compressor in an application, it's important to consider both boost pressure and charge air temperature. These two variables will give you a very clear idea of the efficiency of the compressor. As a compressor moves out of its efficiency range (that happens at high RPM or high boost), it may still make big boost pressure - but that pressure will be more a function of the heat in the intake charge than its actual mass. Low temperature air is more dense (all other things equal) and cause less boost pressure per unit mass.
Air mass is what makes horsepower.
The turbine side is the next limiting component...
Vrrrooom vrroom!
Nick
Crazy_Steve
02-02-2009, 07:46 PM
I'd suggest that when evaluating a compressor in an application, it's important to consider both boost pressure and charge air temperature. These two variables will give you a very clear idea of the efficiency of the compressor. As a compressor moves out of its efficiency range (that happens at high RPM or high boost), it may still make big boost pressure - but that pressure will be more a function of the heat in the intake charge than its actual mass. Low temperature air is more dense (all other things equal) and cause less boost pressure per unit mass.
Air mass is what makes horsepower.
The turbine side is the next limiting component...
Vrrrooom vrroom!
Nick
X2
x2 on the vroom vrooom too. ):h
MMLMM
02-02-2009, 07:59 PM
Lower psi, less temp.
Bigger turbo moves more air at less psi = less temp.
IOWA LLY
02-02-2009, 08:36 PM
IMO 40psi from the stock turbo and 40psi from any other turbo force an equal amount of air into the cylinders.
Wrong
Lower psi, less temp.
Bigger turbo moves more air at less psi = less temp.
Look at a compressor map reflecting the GT45 at 40psia. Then look at say a GT37 at 40psia. You're spot on bud. It's all about pounds of air a minute. Volume does increase with pressure and, more volume less pressure ( actual engine modifications required ) equal more bang for the boost. We build bigger engines to make bigger power but we also build bigger boost to supplement bigger engines.
Crazy_Steve
02-02-2009, 09:19 PM
Wrong
40psi is 40psi, it doesnt matter what is making the pressure. It's simple physics. If you think thats wrong then idk what to tell you.
A pound of feathers weighs the same as a pound of steel. Thats wrong too huh?
MMLMM
02-02-2009, 09:50 PM
40psi is 40psi, it doesnt matter what is making the pressure. It's simple physics. If you think thats wrong then idk what to tell you.
A pound of feathers weighs the same as a pound of steel. Thats wrong too huh?
Thats not true. Its not even physics....
pV=nRT ;)
hondarider552
02-02-2009, 10:10 PM
y=mx+b
I can do this too ):h
James Hess
02-02-2009, 10:11 PM
OK just to clear something up and make myself not look like a complete idiot(if that can be done) ):h lol i also wanted the extra power from an aftermarket turbo but i was looking forward to a louder whistle also.
Brian i think i was understanding you correctly when we were talking earlier and you and Steve put my thoughts into words better than i could.
The boost pressure(which is the restriction) is the by product of the engine not being able to take all the air being thrown at it right? The intake valves are only open for a certian amount of time and no matter what the boost level your only going to get a certian amount of air into the cylindars short of increasing volume of the engine. Am i on the right track with that?
MMLMM
02-02-2009, 10:15 PM
If your turbo was (and this is an vague example) twice as big (moves twice the amount of volume, you would have to double the volume to maintain the psi of the small turbo.
P2 = P1/(V2/V1)
MMLMM
02-02-2009, 10:16 PM
y=mx+b
I can do this too ):h
thats an equation of a line lol
OK just to clear something up and make myself not look like a complete idiot(if that can be done) ):h lol i also wanted the extra power from an aftermarket turbo but i was looking forward to a louder whistle also.
Brian i think i was understanding you correctly when we were talking earlier and you and Steve put my thoughts into words better than i could.
The boost pressure(which is the restriction) is the by product of the engine not being able to take all the air being thrown at it right? The intake valves are only open for a certian amount of time and no matter what the boost level your only going to get a certian amount of air into the cylindars short of increasing volume of the engine. Am i on the right track with that?
So, if I may, why do we need a charger of any type on our 4 stroke DI engine if only a certain amount of air is able to reach and fill the cylinder? Set your wastegate to open all the time or just remove the wastegate without blocking the hole shut and see how much power is made.
We need boost until boost becomes the enemy.
MMLMM
02-02-2009, 10:24 PM
OK just to clear something up and make myself not look like a complete idiot(if that can be done) ):h lol i also wanted the extra power from an aftermarket turbo but i was looking forward to a louder whistle also.
Brian i think i was understanding you correctly when we were talking earlier and you and Steve put my thoughts into words better than i could.
The boost pressure(which is the restriction) is the by product of the engine not being able to take all the air being thrown at it right? The intake valves are only open for a certian amount of time and no matter what the boost level your only going to get a certian amount of air into the cylindars short of increasing volume of the engine. Am i on the right track with that?
wouldnt you be saying if you can leave the valve open longer, a small turbo can catch up and put the same volume of air in there as a big turbo can in a short amount of time???
If your turbo was (and this is an vague example) twice as big (moves twice the amount of volume, you would have to double the volume to maintain the psi of the small turbo.
P2 = P1/(V2/V1)
I'm not sure I follow you on this one. The way I read this: Double the size of the air compressor doubles the required air volume to create the same pressure?
hondarider552
02-02-2009, 10:26 PM
wouldnt you be saying if you can leave the valve open longer, a small turbo can catch up and put the same volume of air in there as a big turbo can in a short amount of time???
Thats what i got out of it mike.
MMLMM
02-02-2009, 10:28 PM
I'm not sure I follow you on this one. The way I read this: Double the size of the air compressor doubles the required air volume to create the same pressure?
leave temperature out of the equation, yes.
wouldnt you be saying if you can leave the valve open longer, a small turbo can catch up and put the same volume of air in there as a big turbo can in a short amount of time???
Thats what i got out of it mike.
I was thinking: Hmmm.....
If the cylinder is filled to the atmosphere equal to the intake charge, no. A positive pressure differential is required to move the air one way or the other. If the intake valve is open for too long, that rising cylinder pressure, say in a rising piston, would cause the air to move back into the intake manifold at least until the valve is closed.
MMLMM
02-02-2009, 10:40 PM
I was thinking: Hmmm.....
If the cylinder is filled to the atmosphere equal to the intake charge, no. A positive pressure differential is required to move the air one way or the other. If the intake valve is open for too long, that rising cylinder pressure, say in a rising piston, would cause the air to move back into the intake manifold at least until the valve is closed.
true, but valves dont stay open when the piston starts compressing air, lol
S Phinney
02-02-2009, 10:59 PM
The valves can be forced open breifly and allow contamination in the combustion process if the valve springs are not strong enough to hold the boost pressures. The whole exhaust through turbo is pressurized all the time under boost. It is almost too much to understand. Thats why we should talk to the turbo specialist to get the best information when purchasing. Overall use is the main concern when picking any performance improvement.
blksmok
02-02-2009, 11:06 PM
Good discussion guys.
Wrong
Comments like the one above are not helpful. If you identify that someone is incorrect in their thoughts, please feel free to let them know, but explain why it is that their thoughts are incorrect. Just telling someone they are wrong without explaining why doesn't do anyone any good.
Thanks,
James Hess
02-02-2009, 11:09 PM
What i was saying is that is where the restriction(boost) comes from but i guess i understood that all wrong and this redneck needs to stay out of it ):h.
Good topic.:thumb:
Questions we get and comments we see all the time. How much boost you running??? Thats it??? Mine makes more then that!!!! Yes but how much power are you making and what is your drive pressure compared to intake boost psi?
I have seen twin kits time and time again make up in the area of 90 psi but cant make any power while a setup speced out correctly by a supporting Vendor we will leave at large for the time ):h make only a minimal 60 psi and make some serious power.
I might also add all while doing this at 1:1 ratio.
duramaxxx
02-03-2009, 12:49 AM
So basically the real purpose of the turbo is to increase the density of the air not volume or pressure
Crazy_Steve
02-03-2009, 01:42 AM
Thats not true. Its not even physics....
pV=nRT ;)
My bad....
QUANTUM PHYSICS! ):h
MMLMM
02-03-2009, 02:10 AM
My bad....
QUANTUM PHYSICS! ):h
):h
It can be applied in chemistry, which I HATE with a passion.
So basically the real purpose of the turbo is to increase the density of the air not volume or pressure
... pretty much, yeah. :)
More specifically, the purpose of the turbochargers compressor is to increase the mass/sec of the intake charge, or it's mass air flow.
It does this by working through the ideal gas law that Mike posted earlier
P(pressure) X V(volume, which we'll call constant at 6.6L) = n (number of molecules) X R(fudge factor) X T(temperature in Kelvin*)
*Kelvin is a temperature scale you may not be familiar with. 273 K is 0*C and 278K is 5*C ect. This means that in order to double PV, temperature in Kelvin needs to double... So 5*C (278K) would need to 'double' to 283*C (556K) for pressure to double.
PV=nRT describes the relationship of all these variables
V(volume) and R ( fudge factor) will not change on a stock truck so we can pull them out of our discussion.
Our goal is to increase n (air mass) because n = power potential and cleaner burn. We can do that by increasing p (pressure) or decreasing T (tempeature in Kelvin). Unfortunately a Turbocharger increases pressure and raises temperature... good but not great. Therein lies the balance.
Nick
bigbird
02-03-2009, 06:02 PM
... pretty much, yeah. :)
More specifically, the purpose of the turbochargers compressor is to increase the mass/sec of the intake charge, or it's mass air flow.
It does this by working through the ideal gas law that Mike posted earlier
P(pressure) X V(volume, which we'll call constant at 6.6L) = n (number of molecules) X R(fudge factor) X T(temperature in Kelvin*)
*Kelvin is a temperature scale you may not be familiar with. 273 K is 0*C and 278K is 5*C ect. This means that in order to double PV, temperature in Kelvin needs to double... So 5*C (278K) would need to 'double' to 283*C (556K) for pressure to double.
PV=nRT describes the relationship of all these variables
V(volume) and R ( fudge factor) will not change on a stock truck so we can pull them out of our discussion.
Our goal is to increase n (air mass) because n = power potential and cleaner burn. We can do that by increasing p (pressure) or decreasing T (tempeature in Kelvin). Unfortunately a Turbocharger increases pressure and raises temperature... good but not great. Therein lies the balance.
Nick
My head hurts.
I need to stop writing text books.
Sorry Kelly.. http://deephousepage.com/smilies/doh.gif (Doh!)
What i was saying is that is where the restriction(boost) comes from but i guess i understood that all wrong and this redneck needs to stay out of it ):h.
Which one SPECIFICALLY needs to stay out? :hello:
James Hess
02-03-2009, 11:07 PM
Which one SPECIFICALLY needs to stay out? :hello:
ME lol i would probly just muck this thread up for everyone else and confuse everyone. ):h
On another note so i can at least try to understand this, having good boost is ok as long as its not so much to where it heats the intake charge but you also need low drive pressure or what?
Drive pressure is the pressure from the exhaust turning the turbine side right? What is normally seen on these motors with a stocker and what is good, and what is ideal?
The valves can be forced open breifly and allow contamination in the combustion process if the valve springs are not strong enough to hold the boost pressures. The whole exhaust through turbo is pressurized all the time under boost. It is almost too much to understand. Thats why we should talk to the turbo specialist to get the best information when purchasing. Overall use is the main concern when picking any performance improvement.
I personally agree with you on the above. One thing I'd like to add is our use of a charger and their practical use of their charger does not always make " Them " right. Most of the chargers we are running had been designed and tested on gasers or extreme gasers and still unable to run at boost levels we can see. Sorta re-plotting our own compressor maps as well as turbine maps. And now those damn superchargers to confuse me even more ):h.
Thanks Man
NWTDIESEL
02-03-2009, 11:10 PM
Good discussion guys.
Comments like the one above are not helpful. If you identify that someone is incorrect in their thoughts, please feel free to let them know, but explain why it is that their thoughts are incorrect. Just telling someone they are wrong without explaining why doesn't do anyone any good.
Thanks,
Wrong):h
James Hess
02-03-2009, 11:11 PM
Always causin trouble lol ):h.
ME lol i would probly just muck this thread up for everyone else and confuse everyone. ):h
On another note so i can at least try to understand this, having good boost is ok as long as its not so much to where it heats the intake charge but you also need low drive pressure or what?
Drive pressure is the pressure from the exhaust turning the turbine side right? What is normally seen on these motors with a stocker and what is good, and what is ideal?
Oh.... Are you Redneck #1 or Redneck #2? I only ask because I to am a Redneck:thumb:
Building pressure creates heat point blank. So long as the pressurized air into the engine is very close or the same as the ambient air temps into the charger, boost is good, to a point. Because the engine will compress the air charge ( pressurized and cooled by what ever means ), heat will be generated. So to help combat this increased heat, compression ratios are decreased ( other reasons for compression ratios decreased not listed ).
And the high drive pressure question. Some reasons for high drive pressure could be: VVT and programming and trying to drive a charger beyond the compressors " speed limit " and driving the turbine beyond its pounds per ( time ). Many others but those can be a starting point.
true, but valves dont stay open when the piston starts compressing air, lol
You got me there but you know, those custom grinds and well leaking valves and well damn it. I did forget the hypothetical clause didn't I. I was trying to make a for instance with air movement.
):h
MMLMM
02-03-2009, 11:38 PM
Oh.... Are you Redneck #1 or Redneck #2? I only ask because I to am a Redneck:thumb:
Building pressure creates heat point blank. So long as the pressurized air into the engine is very close or the same as the ambient air temps into the charger, boost is good, to a point. Because the engine will compress the air charge ( pressurized and cooled by what ever means ), heat will be generated. So to help combat this increased heat, compression ratios are decreased ( other reasons for compression ratios decreased not listed ).
And the high drive pressure question. Some reasons for high drive pressure could be: VVT and programming and trying to drive a charger beyond the compressors " speed limit " and driving the turbine beyond its pounds per ( time ). Many others but those can be a starting point.
Intercooler......BIGGER and better ):h
Intercooler......BIGGER and better ):h
And it helps to lower the ambient temperature by any means possible.
IOWA LLY
02-04-2009, 12:13 AM
Comments like the one above are not helpful. If you identify that someone is incorrect in their thoughts, please feel free to let them know, but explain why it is that their thoughts are incorrect. Just telling someone they are wrong without explaining why doesn't do anyone any good.
Thanks,
40psi of boost at ~300 degrees, (from say a stock turbo) will be less dense then 40psi of boost at ~175 degrees. (from say a gt42)
Sorry for being short, but 40psi of boost with a stock turbo is not the same as 40psi with a large turbo designed to run those kind of boost levels.;)
Comments like the one above are not helpful. If you identify that someone is incorrect in their thoughts, please feel free to let them know, but explain why it is that their thoughts are incorrect. Just telling someone they are wrong without explaining why doesn't do anyone any good.
Thanks,
40psi of boost at ~300 degrees, (from say a stock turbo) will be less dense then 40psi of boost at ~175 degrees. (from say a gt42)
Sorry for being short, but 40psi of boost with a stock turbo is not the same as 40psi with a large turbo designed to run those kind of boost levels.;)
Ok. Thinking about this: The smaller charger is causing an increased temperature due to friction. More contact with more of the air being compressed causing friction induced heat. Doesn't this go back to a restriction causing the actual pressure increase? The restriction has not changed but Yes, the turbine restriction might have changed. Isn't heat created while compressing or moving the air?
MMLMM
02-04-2009, 01:42 AM
Ok. Thinking about this: The smaller charger is causing an increased temperature due to friction. More contact with more of the air being compressed causing friction induced heat. Doesn't this go back to a restriction causing the actual pressure increase? The restriction has not changed but Yes, the turbine restriction might have changed. Isn't heat created while compressing or moving the air?
compressing a smaller amount of air will build heat faster than compressing greater amount of air.
NWTDIESEL
02-04-2009, 09:56 AM
Ill just add that my little BD supermax could put out 45psi but wasnt as strong/efficent when it was at 38psi. My A5k hits 45psi easy and it feels way way stronger than the BD ever did.
The volume and dense air from the bigger charger makes a HUGE difference.
duramaxxx
02-04-2009, 11:14 AM
... pretty much, yeah. :)
More specifically, the purpose of the turbochargers compressor is to increase the mass/sec of the intake charge, or it's mass air flow.
It does this by working through the ideal gas law that Mike posted earlier
P(pressure) X V(volume, which we'll call constant at 6.6L) = n (number of molecules) X R(fudge factor) X T(temperature in Kelvin*)
*Kelvin is a temperature scale you may not be familiar with. 273 K is 0*C and 278K is 5*C ect. This means that in order to double PV, temperature in Kelvin needs to double... So 5*C (278K) would need to 'double' to 283*C (556K) for pressure to double.
PV=nRT describes the relationship of all these variables
V(volume) and R ( fudge factor) will not change on a stock truck so we can pull them out of our discussion.
Our goal is to increase n (air mass) because n = power potential and cleaner burn. We can do that by increasing p (pressure) or decreasing T (tempeature in Kelvin). Unfortunately a Turbocharger increases pressure and raises temperature... good but not great. Therein lies the balance.
Nick
Isn't (n) the weight of gas
subman
02-04-2009, 01:56 PM
Check out the thread, "drive pressure I don't get it" Very good info there for this thread as well.
MMLMM
02-04-2009, 02:18 PM
Isn't (n) the weight of gas
the number of moles
1 mole = 22.4 litres at S.T.P.
STP is Standard Temperature and Pressure, 0*C and 101.3kPa
or as Nick would say, 273K :)
the number of moles
1 mole = 22.4 litres at S.T.P.
STP is Standard Temperature and Pressure, 0*C and 101.3kPa
or as Nick would say, 237K :)
If you're going to quote me, do it right ;)
273K
MMLMM
02-04-2009, 04:51 PM
If you're going to quote me, do it right ;)
273K
Ahahaha, oops, IDK why I was thinking that lol.
nice catch
fix.t
VABRacing
02-07-2009, 09:52 AM
Ok, this is a good thread. Now 40 psi boost in a stock charger and 40 psi in a larger charger are no where near the same thing. you can significantly increase the volume of air at the same boost number as the stock charger. The reason for this is the compressor map of the turbo flows more to start. But the other big reason is the exhaust turbine and housing. You will never move as much air through a stock charger as you can through a gt42. Thats the reason i feel modified stock chargers are a complete waste of time. But the whole idea is to get as much cool, dense, cfm as possible to make the power. Now thats also where head porting comes in. But we will save that topic for another day! ):h
Ok, this is a good thread. Now 40 psi boost in a stock charger and 40 psi in a larger charger are no where near the same thing. you can significantly increase the volume of air at the same boost number as the stock charger. The reason for this is the compressor map of the turbo flows more to start. But the other big reason is the exhaust turbine and housing. You will never move as much air through a stock charger as you can through a gt42. Thats the reason i feel modified stock chargers are a complete waste of time. But the whole idea is to get as much cool, dense, cfm as possible to make the power. Now thats also where head porting comes in. But we will save that topic for another day! ):h
Not to be a nit pick here, but I think it's important that we not confuse volume with mass in this case. I think that's where a lot of confusion comes from regarding forced induction. The volume isn't changing, but the temperature, and density are.
5 psi and 65psi are the same volume of air with relation to our discussion assuming a constant RPM and engine displacement. Pressure (P), mass/moles/weight (n), and temperature (T) are much different though.
The rest, I pretty much agree with :)
Nick
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