Why do people think a turbo cares about engine RPM?
02-02-2012, 09:05 AM
#21
Teching In
Join Date: Nov 2011
Posts: 14
Likes: 0
Received 0 Likes
on
0 Posts
I am going to second that!
I think its funny that everyones arguing about it when the OP was really correct with the exception that airflow can result in a different power level on a given engine. It should be pretty close but depending on the Volumetric Effeciency of the engine to begin with. Xcfm = Yhp But the VE has a curve to with a turbo engine and when the Turbo goes out of its sweet spot it starts to hurt total VE.
Its kinda hard to wrap your head around for some people but it makes me laugh.....people that are ignorant should shut up and go read a book. I am sure other experienced people share my setiment - Were happy to share knowledge and experience but when people start spouting nonsense as gospel...well we just chuckle and move on to the next post.....
I think its funny that everyones arguing about it when the OP was really correct with the exception that airflow can result in a different power level on a given engine. It should be pretty close but depending on the Volumetric Effeciency of the engine to begin with. Xcfm = Yhp But the VE has a curve to with a turbo engine and when the Turbo goes out of its sweet spot it starts to hurt total VE.
Its kinda hard to wrap your head around for some people but it makes me laugh.....people that are ignorant should shut up and go read a book. I am sure other experienced people share my setiment - Were happy to share knowledge and experience but when people start spouting nonsense as gospel...well we just chuckle and move on to the next post.....
02-02-2012, 10:47 AM
#22
TECH Apprentice
S372 on a little eng vs big, I will try to make this simple
6l 8cyl 10psi equals 700hp, at 10psi compressor is not in a good spot
2l 4cyl 40psi equals 700hp, compressor is very happy up here working good in the island.
Both have 40psi of back pressure at this level to spin the bugger. Now which has the better PR and PR between the two sides? This is a very crude example so go do some more reading.
6l 8cyl 10psi equals 700hp, at 10psi compressor is not in a good spot
2l 4cyl 40psi equals 700hp, compressor is very happy up here working good in the island.
Both have 40psi of back pressure at this level to spin the bugger. Now which has the better PR and PR between the two sides? This is a very crude example so go do some more reading.
Its kinda hard to wrap your head around for some people but it makes me laugh.....people that are ignorant should shut up and go read a book. I am sure other experienced people share my setiment - Were happy to share knowledge and experience but when people start spouting nonsense as gospel...well we just chuckle and move on to the next post.....
Harsh, BUT very true....
02-02-2012, 10:59 AM
#24
TECH Addict
iTrader: (2)
Join Date: Oct 2004
Location: Miami, Fl.
Posts: 2,890
Likes: 0
Received 0 Likes
on
0 Posts
Interesting... and here I thought forums where designed for like minded I dividuals to ask questions and learn something along the way.
Though I agree that some folks will just repeat what they hear (we are all quilty of that at point or another) .... it doesn't help with comments that start the bs that gets a thread locked. Whatever happened to if you have nothing good to say then don't say anything at all?
Anyways, hopefully we can continue on but I fear that this post is just gonna male it worst.
Back to the topic:
Is it safe to say that a turbo is "happiest" at higher psi/turbine speeds much like an engine is at wot?
Though I agree that some folks will just repeat what they hear (we are all quilty of that at point or another) .... it doesn't help with comments that start the bs that gets a thread locked. Whatever happened to if you have nothing good to say then don't say anything at all?
Anyways, hopefully we can continue on but I fear that this post is just gonna male it worst.
Back to the topic:
Is it safe to say that a turbo is "happiest" at higher psi/turbine speeds much like an engine is at wot?
02-02-2012, 11:05 AM
#25
Not always. It just depends on the particular turbo. For turbos where you have a compressor map, you can see what pressure ratio it is most efficient. There are many turbos out though (many custom combos) that compressor maps are unavailable. There is a pretty cool tool by Borg Warner called "Matchbot" that can plot some of their turbos on your combo. It is kind of optimistic, but it will give you a good starting point.
02-02-2012, 11:11 AM
#26
A hot air ballon at 20psi vs a birthday baloon at 20 psI..
Key words are in the acronym. Pounds per square inch.. If there are 1000 inches. @10 psi. That 10000 pounds of outward force. If there is 100 square inches @10 psi thats 1000 pounds of force.
Hence why less bost is required on larger motors.
Also turbos aside, motors being equal in everyway, 5000 rpm is gling to burn considerably less fuel then 10000 rpm. More fuel being burned = more exhaust.
This thread reminds me of tbe perpetual motion thread last year.
Key words are in the acronym. Pounds per square inch.. If there are 1000 inches. @10 psi. That 10000 pounds of outward force. If there is 100 square inches @10 psi thats 1000 pounds of force.
Hence why less bost is required on larger motors.
Also turbos aside, motors being equal in everyway, 5000 rpm is gling to burn considerably less fuel then 10000 rpm. More fuel being burned = more exhaust.
This thread reminds me of tbe perpetual motion thread last year.
02-02-2012, 11:31 AM
#29
You guys seriously need to do some research instead.of being arm chair philosophers about this ****.
There is plenty of literature available based on facts and real world R&D for anyone who actually wants to learn.
02-02-2012, 04:32 PM
#35
On The Tree
Join Date: Jan 2012
Location: Elswhere
Posts: 158
Likes: 0
Received 0 Likes
on
0 Posts
Maybe incorrect; but two engines moving similar amounts of air, with similar pressure at combustion, and similar exhaust setups will produce similar exhaust volume, pressure, and velocity. That part is still true. And yes, now I know that the 2 engines won't move similar amounts of air with a turbo designed for the 4.8. Cause I did read.
02-02-2012, 06:55 PM
#37
TECH Regular
Thread Starter
iTrader: (2)
Join Date: Oct 2010
Location: Denver, CO.
Posts: 430
Likes: 0
Received 0 Likes
on
0 Posts
Ok guys, I understand that more RPM's equals more air flow. But again, why would a turbo care about the RPM's of an engine? It DOESN'T. It only cares about a VOLUME of exhaust entering the turbine. The force that hits the turbine wheel is a volume of exhaust which has nothing to do with RPM.
90% of the people that told me I was wrong in this thread, spouted off a bunch about this that and the other thing, but failed to even mention RPM of an engine.
For example... The above is all very true information, but not once is RPM even mentioned.
This is why a 2JZ spins to 10,000rpm and can push a 90mm turbo but a say a 427 only spins to 6,000rpm can max out a 90mm turbo. Again, RPM has nothing to do with it. It is about exhaust volume, which can be translated (in a vague way) to horsepower.
When you go on Precision Turbo's website (or most turbo sites) to shop for a turbo, do they categorize their turbo's based on RPM or on a horsepower level?
So this is EXACTLY what I was stating... RPM has NOTHING do do with it. It is ALL about exhaust VOLUME.
90% of the people that told me I was wrong in this thread, spouted off a bunch about this that and the other thing, but failed to even mention RPM of an engine.
S372 on a little eng vs big, I will try to make this simple
6l 8cyl 10psi equals 700hp, at 10psi compressor is not in a good spot
2l 4cyl 40psi equals 700hp, compressor is very happy up here working good in the island.
Both have 40psi of back pressure at this level to spin the bugger. Now which has the better PR and PR between the two sides? This is a very crude example so go do some more reading.
6l 8cyl 10psi equals 700hp, at 10psi compressor is not in a good spot
2l 4cyl 40psi equals 700hp, compressor is very happy up here working good in the island.
Both have 40psi of back pressure at this level to spin the bugger. Now which has the better PR and PR between the two sides? This is a very crude example so go do some more reading.
This is why a 2JZ spins to 10,000rpm and can push a 90mm turbo but a say a 427 only spins to 6,000rpm can max out a 90mm turbo. Again, RPM has nothing to do with it. It is about exhaust volume, which can be translated (in a vague way) to horsepower.
When you go on Precision Turbo's website (or most turbo sites) to shop for a turbo, do they categorize their turbo's based on RPM or on a horsepower level?
So this is EXACTLY what I was stating... RPM has NOTHING do do with it. It is ALL about exhaust VOLUME.
02-02-2012, 07:01 PM
#38
Ok guys, I understand that more RPM's equals more air flow. But again, why would a turbo care about the RPM's of an engine? It DOESN'T. It only cares about a VOLUME of exhaust entering the turbine. The force that hits the turbine wheel is a volume of exhaust which has nothing to do with RPM.
90% of the people that told me I was wrong in this thread, spouted off a bunch about this that and the other thing, but failed to even mention RPM of an engine.
For example... The above is all very true information, but not once is RPM even mentioned.
This is why a 2JZ spins to 10,000rpm and can push a 90mm turbo but a say a 427 only spins to 6,000rpm can max out a 90mm turbo. Again, RPM has nothing to do with it. It is about exhaust volume, which can be translated (in a vague way) to horsepower.
When you go on Precision Turbo's website (or most turbo sites) to shop for a turbo, do they categorize their turbo's based on RPM or on a horsepower level?
So this is EXACTLY what I was stating... RPM has NOTHING do do with it. It is ALL about exhaust VOLUME.
90% of the people that told me I was wrong in this thread, spouted off a bunch about this that and the other thing, but failed to even mention RPM of an engine.
For example... The above is all very true information, but not once is RPM even mentioned.
This is why a 2JZ spins to 10,000rpm and can push a 90mm turbo but a say a 427 only spins to 6,000rpm can max out a 90mm turbo. Again, RPM has nothing to do with it. It is about exhaust volume, which can be translated (in a vague way) to horsepower.
When you go on Precision Turbo's website (or most turbo sites) to shop for a turbo, do they categorize their turbo's based on RPM or on a horsepower level?
So this is EXACTLY what I was stating... RPM has NOTHING do do with it. It is ALL about exhaust VOLUME.
02-02-2012, 07:07 PM
#40
TECH Regular
Thread Starter
iTrader: (2)
Join Date: Oct 2010
Location: Denver, CO.
Posts: 430
Likes: 0
Received 0 Likes
on
0 Posts
I am going to second that!
I think its funny that everyones arguing about it when the OP was really correct with the exception that airflow can result in a different power level on a given engine. It should be pretty close but depending on the Volumetric Effeciency of the engine to begin with. Xcfm = Yhp But the VE has a curve to with a turbo engine and when the Turbo goes out of its sweet spot it starts to hurt total VE.
I think its funny that everyones arguing about it when the OP was really correct with the exception that airflow can result in a different power level on a given engine. It should be pretty close but depending on the Volumetric Effeciency of the engine to begin with. Xcfm = Yhp But the VE has a curve to with a turbo engine and when the Turbo goes out of its sweet spot it starts to hurt total VE.
I was trying to stay away from getting too technical about it to keep the arguing to a minimum. Meaning, I understand that different engines have different VE's. Some engines don't even hit peak VE until they hit a tuned RPM that can be VERY high (F1 cars for example).
That is why I tried to keep my original post dumbed down to it's basic form.
Again though, the turbo doesn't know that it is getting exhaust volume from CID, RPM and VE. It only knows how much exhaust volume is hitting the turbine. The exhaust could be coming from something other than an engine all together; Say a massive storage tank of compressed gas. In which case, you could out flow the turbo by introducing a specific gas volume.