Theory question on boost.
08-02-2007, 12:49 AM
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Theory question on boost. Ive heard that a certain amount of boost let use 14 pounds can be less efficient on one setup and more efficient on another setup. If there is 14 pounds of boost in the intake isnt that always the same. Why is it that some people with different turbos or superchargers with the same boost level make different power
with every thing else equal.
Im in the process of my first turbo project and i was told the turbo maxed out at 14psi but wasnt very efficient at 14psi. What exactly does not efficient mean, its always 14 psi right?
Thanks
Alex
with every thing else equal.
Im in the process of my first turbo project and i was told the turbo maxed out at 14psi but wasnt very efficient at 14psi. What exactly does not efficient mean, its always 14 psi right?
Thanks
Alex
08-02-2007, 01:10 AM
#2
Efficiency is used in discribe several different things. Usually with ls1 motors it is related to exhaust backpressure and compressor flow..a turbo can lose power at 16 psi compared to 14 psi if the charge is super-heated. Same thing with the exhaust side....if the exhaust side of the turbo is small for the motor it is installed on, it can cause huge backpressure which chokes power.
08-02-2007, 07:09 AM
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Also, you mentioned 14psi on Supercharger vs. Turbo...
The turbo car will typically create more power b/c the turbo is more efficient.. It actually takes horsepower to spin the supercharger, therefore decreasing the efficiency
The turbo car will typically create more power b/c the turbo is more efficient.. It actually takes horsepower to spin the supercharger, therefore decreasing the efficiency
08-02-2007, 08:32 AM
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Because different turbos and superchargers have a different mass flow rate at different boost pressures. Boost pressure doesn't create more power, mass flow rate of air creates more power because it allows you to combine more fuel with it for a given AFR, therefore you are releeasing more energy per combustion event. This is a simplification, because the pressure does affect things like the intake tract air dynamics and fuel atomisation that also affect power production, but I think the simple answer that I gave you is the one that you are looking for.
If all that mattered was boost pressure, nobody would be using big turbos, everyone would be running tiny turbos for the quicker response.
If all that mattered was boost pressure, nobody would be using big turbos, everyone would be running tiny turbos for the quicker response.
08-02-2007, 11:35 AM
#7
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1) 14 psi with you running a T76 is different than if you were running a 88mm thumper. For example my turbo is a lot bigger. But you need to be in the efficiency range of a given turbo to make good power as well. I'm sure someone can chime in and state it better than me.
2) Boost is a value. Kurt from W2W summed it up best once, when he told me that 15psi could effectively double my engine horsepower since I'm cramming double the amount of air through it. It's a good rule of thumb.
2) Boost is a value. Kurt from W2W summed it up best once, when he told me that 15psi could effectively double my engine horsepower since I'm cramming double the amount of air through it. It's a good rule of thumb.
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08-02-2007, 12:36 PM
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Originally Posted by BlackScreaminMachine
Boost/PSI is just a simple matter of how restrictive the entire system is given the size of the motor. As the previous poster stated, there are differences.
08-02-2007, 12:49 PM
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You also have to think about the restrictions in the exhaust (turbine efficency). One turbo might be able to make 15 lbs boost w/ 40 psi exhaust pressure, and another make 15 w/ 50 psi exhaust pressure. That is going to play into the BIG equation.
08-02-2007, 07:43 PM
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Just as stated, boost is a measurement of restriction. This is not something you should be after. Flow is what you should be looking for both on the intake and exhaust side. Boost will find it's way in on it's own. Keep the backpressure on your exhaust as low as possible along with running a properly sized turbo to keep it within it's efficiency range and IAT temps as low as possible and you can't really go wrong.
08-02-2007, 07:58 PM
#11
Originally Posted by SPRAYED 01
If there is 14 pounds of boost in the intake isnt that always the same. Why is it that some people with different turbos or superchargers with the same boost level make different power
with every thing else equal.
with every thing else equal.
08-02-2007, 10:17 PM
#12
boys, Boys, BOYS!!! (Did anyone get the Robocop reference?)
PV = NRT
14 PSI @ 250 Degrees F is NOT equal to 14 PSI @ 95 Degrees F
Thermal and mechanical efficiency are your friends! Whatever is the most efficient will make the most power (and, get the best gas mileage too!).
Now, let the flaming ensue from those who have faster cars than me and therefore must know more about all things automotive than all automotive engineers combined!
PV = NRT
14 PSI @ 250 Degrees F is NOT equal to 14 PSI @ 95 Degrees F
Thermal and mechanical efficiency are your friends! Whatever is the most efficient will make the most power (and, get the best gas mileage too!).
Now, let the flaming ensue from those who have faster cars than me and therefore must know more about all things automotive than all automotive engineers combined!
08-03-2007, 01:07 AM
#14
Some of the other posters here have done a great job of explaining boost related backpressure or boost stacking and how it affects efficiency.
Remember that an engine is basically an air pump (although simplistic, it helps us understand the function better).
The more air VOLUME that you can move through the engine, the more power it will develop. Now increasing pressure usually results in increased volume only if the engine can move the higher volume through it.
Volume flow is measured in CFM (cubic feet per minute). Now imagine you have two pieces of pipe. One is 1 inch in diameter and the other is 2 inches in diameter. If we force air through the two pipes at 14psi, which one will move more volume? The 2 inch, of course. The reason being is that it takes a larger volume of air to pressurize the 2 inch pipe to 14psi than the 1 inch pipe.
The same thing applies to a combustion engine. An engine with better flowing heads, intake, and exhaust will flow more volume of air at 14psi than one with restrictive respective parts. Since it flows more volume, it will produce more power.
Remember that an engine is basically an air pump (although simplistic, it helps us understand the function better).
The more air VOLUME that you can move through the engine, the more power it will develop. Now increasing pressure usually results in increased volume only if the engine can move the higher volume through it.
Volume flow is measured in CFM (cubic feet per minute). Now imagine you have two pieces of pipe. One is 1 inch in diameter and the other is 2 inches in diameter. If we force air through the two pipes at 14psi, which one will move more volume? The 2 inch, of course. The reason being is that it takes a larger volume of air to pressurize the 2 inch pipe to 14psi than the 1 inch pipe.
The same thing applies to a combustion engine. An engine with better flowing heads, intake, and exhaust will flow more volume of air at 14psi than one with restrictive respective parts. Since it flows more volume, it will produce more power.
08-03-2007, 01:44 PM
#15
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Originally Posted by Dan Stewart
Some of the other posters here have done a great job of explaining boost related backpressure or boost stacking and how it affects efficiency.
Remember that an engine is basically an air pump (although simplistic, it helps us understand the function better).
The more air VOLUME that you can move through the engine, the more power it will develop. Now increasing pressure usually results in increased volume only if the engine can move the higher volume through it.
Volume flow is measured in CFM (cubic feet per minute). Now imagine you have two pieces of pipe. One is 1 inch in diameter and the other is 2 inches in diameter. If we force air through the two pipes at 14psi, which one will move more volume? The 2 inch, of course. The reason being is that it takes a larger volume of air to pressurize the 2 inch pipe to 14psi than the 1 inch pipe.
The same thing applies to a combustion engine. An engine with better flowing heads, intake, and exhaust will flow more volume of air at 14psi than one with restrictive respective parts. Since it flows more volume, it will produce more power.
Remember that an engine is basically an air pump (although simplistic, it helps us understand the function better).
The more air VOLUME that you can move through the engine, the more power it will develop. Now increasing pressure usually results in increased volume only if the engine can move the higher volume through it.
Volume flow is measured in CFM (cubic feet per minute). Now imagine you have two pieces of pipe. One is 1 inch in diameter and the other is 2 inches in diameter. If we force air through the two pipes at 14psi, which one will move more volume? The 2 inch, of course. The reason being is that it takes a larger volume of air to pressurize the 2 inch pipe to 14psi than the 1 inch pipe.
The same thing applies to a combustion engine. An engine with better flowing heads, intake, and exhaust will flow more volume of air at 14psi than one with restrictive respective parts. Since it flows more volume, it will produce more power.
Well done.
Volume not pressure; Actually the number of Moles of O2 consumed per unit time, but we don't want to make people remember their chemistry and physics classes or Avogadro's Number...
Remember, efficiency and amount/volume.
A more efficient setup will make more power with the same volume of O2 used, while a greater volume of O2 used can overcome a lack of efficiency. That's why a weaker car can win at the dragstrip if the suspension, tires, and gearing are more efficient at getting the power to the track vs. a very strong car which spins the tires.
That's why turbo guys like turbos vs. superchargers - they (typically) are more efficient by virture of zero drag on the engine.
08-03-2007, 01:45 PM
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Originally Posted by Dan Stewart
Some of the other posters here have done a great job of explaining boost related backpressure or boost stacking and how it affects efficiency.
Remember that an engine is basically an air pump (although simplistic, it helps us understand the function better).
The more air VOLUME that you can move through the engine, the more power it will develop. Now increasing pressure usually results in increased volume only if the engine can move the higher volume through it.
Volume flow is measured in CFM (cubic feet per minute). Now imagine you have two pieces of pipe. One is 1 inch in diameter and the other is 2 inches in diameter. If we force air through the two pipes at 14psi, which one will move more volume? The 2 inch, of course. The reason being is that it takes a larger volume of air to pressurize the 2 inch pipe to 14psi than the 1 inch pipe.
The same thing applies to a combustion engine. An engine with better flowing heads, intake, and exhaust will flow more volume of air at 14psi than one with restrictive respective parts. Since it flows more volume, it will produce more power.
Remember that an engine is basically an air pump (although simplistic, it helps us understand the function better).
The more air VOLUME that you can move through the engine, the more power it will develop. Now increasing pressure usually results in increased volume only if the engine can move the higher volume through it.
Volume flow is measured in CFM (cubic feet per minute). Now imagine you have two pieces of pipe. One is 1 inch in diameter and the other is 2 inches in diameter. If we force air through the two pipes at 14psi, which one will move more volume? The 2 inch, of course. The reason being is that it takes a larger volume of air to pressurize the 2 inch pipe to 14psi than the 1 inch pipe.
The same thing applies to a combustion engine. An engine with better flowing heads, intake, and exhaust will flow more volume of air at 14psi than one with restrictive respective parts. Since it flows more volume, it will produce more power.
08-03-2007, 04:29 PM
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Ya, thanks alot
That makes alot of sense.
Basically the person i bought my turbo kit from make 550hp and 650ftlbs on a mustang dyno. He used a stock cam,ls1 intake and stock heads. i was trying to figure out if my ls6 intake better heads and cam would make a big difference in power.
Im using ported and polished 241s with a 224/228,585,590 on a 115lsa.
That makes alot of sense.
Basically the person i bought my turbo kit from make 550hp and 650ftlbs on a mustang dyno. He used a stock cam,ls1 intake and stock heads. i was trying to figure out if my ls6 intake better heads and cam would make a big difference in power.
Im using ported and polished 241s with a 224/228,585,590 on a 115lsa.
08-05-2007, 08:26 PM
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Originally Posted by SPRAYED 01
Ive heard that a certain amount of boost let use 14 pounds can be less efficient on one setup and more efficient on another setup. If there is 14 pounds of boost in the intake isnt that always the same. Why is it that some people with different turbos or superchargers with the same boost level make different power
with every thing else equal.
with every thing else equal.
Peter
http://www.airpowersystems.com/350z/turbo_flow.htm
08-05-2007, 08:53 PM
#19
I can give you real world findings on my car this is a supercharged car but it shows what better flow can do for you. The only thing I changed in my setup was the heads they flow about 35 cfm better than my old heads and I picked up about 35 rwhp peak and 60 rwhp under the curve. I also lost 3 pounds of boost from the better flowing heads also.
08-06-2007, 10:37 AM
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Originally Posted by SSANDTA
I can give you real world findings on my car this is a supercharged car but it shows what better flow can do for you. The only thing I changed in my setup was the heads they flow about 35 cfm better than my old heads and I picked up about 35 rwhp peak and 60 rwhp under the curve. I also lost 3 pounds of boost from the better flowing heads also.