K27...Is there any point?
05-30-2004, 08:34 PM
#16
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Since you are going with GURU chips, telling Danno what turbo you are running- he should be able to set up a fuel curve more appropriate to the K27 turbo. The best way to accomplish this is a piggyback fuel control, ala ARC2 or SMT6.
Allways get chips that are very close to the target and then use the piggyback for fine tuning.
Tomas
05-30-2004, 09:28 PM
#17
Mike, even though the boost pressure is the same for both turbos the amount of air going in is not the same. Think of it this way. PSI is a pressure reading which tells how much force the air is at. Imagine if you had a garden hose and measured the pressure of water coming out of it at 5 psi. Now imagine you had a culvert and measured the pressure of water coming out of it at 5 psi. Now which one would fill a 500 gallon tank faster?
It's annoying sometimes when guys ask how much boost you are making and then telling you "That's all? My friends car makes way more boost" They seem to think that more boost = more power. But a hockey puck sized turbo pushing 45 psi will not flow more air than a much larger turbo at 15 psi. So comparing boost numbers is really only relavent when talking about turbo's of the same size/type.
It's annoying sometimes when guys ask how much boost you are making and then telling you "That's all? My friends car makes way more boost" They seem to think that more boost = more power. But a hockey puck sized turbo pushing 45 psi will not flow more air than a much larger turbo at 15 psi. So comparing boost numbers is really only relavent when talking about turbo's of the same size/type.
05-30-2004, 11:57 PM
#18
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Soloracer,
that's not quite correct. Lets say you have two engines of the same flow potential. One has a certain size compressor which is big enough in size to feed the engine 15 psi boost all the way to redline. The other engine has a compressor that's, lets say, 40% bigger, also running 15 psi. Both engines will make the same power.
The real issue, here, is that the K26-6 is just adequate for a stock car. Running any significant more boost quickly renders this turbo too small. Because most of us want to run more than stock boost, we will feel a difference when we go to a bigger compressor; not simply because it's a bigger compressor, but because it's needed to support the flow of higher boost.
that's not quite correct. Lets say you have two engines of the same flow potential. One has a certain size compressor which is big enough in size to feed the engine 15 psi boost all the way to redline. The other engine has a compressor that's, lets say, 40% bigger, also running 15 psi. Both engines will make the same power.
The real issue, here, is that the K26-6 is just adequate for a stock car. Running any significant more boost quickly renders this turbo too small. Because most of us want to run more than stock boost, we will feel a difference when we go to a bigger compressor; not simply because it's a bigger compressor, but because it's needed to support the flow of higher boost.
05-31-2004, 12:01 AM
#19
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Originally posted by TurboTommy
that's not quite correct. Lets say you have two engines of the same flow potential. One has a certain size compressor which is big enough in size to feed the engine 15 psi boost all the way to redline. The other engine has a compressor that's, lets say, 40% bigger, also running 15 psi. Both engines will make the same power.
that's not quite correct. Lets say you have two engines of the same flow potential. One has a certain size compressor which is big enough in size to feed the engine 15 psi boost all the way to redline. The other engine has a compressor that's, lets say, 40% bigger, also running 15 psi. Both engines will make the same power.
PSI does not equal flow, and flow is what makes power.
Think of a magical turbo which creates 15psi without inhibiting the exhaust flow, would it make more power?
05-31-2004, 12:03 AM
#20
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Just to add to Tommy,
the flow rate is only a high as the point of most restriction - Even if one turbo is a culvert pipe and another is a garden hose, if the engine can only flow a certain max rate at a certain pressure.
the flow rate is only a high as the point of most restriction - Even if one turbo is a culvert pipe and another is a garden hose, if the engine can only flow a certain max rate at a certain pressure.
05-31-2004, 02:09 AM
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Originally posted by macnewma
Just out of curiousity, what is does the 7200 on the K27/6 signify? If I should just search, let me know.
Max
Just out of curiousity, what is does the 7200 on the K27/6 signify? If I should just search, let me know.
Max
05-31-2004, 07:20 AM
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Ok, let try to sort this out.
Mass air flow is what makes power. You will need somewhere around 2500 lb of air to operate a 400 hp engine for one hour.
The engine will take in a flow of 2.5 liters * VE every second revolution.
Since the engine itself limits the volume air flow we need to increase the air density to maximize the mass flow.
This can be done in two ways. The first one is obvious, you increase boost. The second one is to decrease air temperature.
As you compress a gas it will at the same time get hotter, this is the way of the nature and nothing we can do about it. However a turbo is not 100% effective, it will always heat the air more than what the gas laws state. This is called adiabatic efficiency and is what is shown in compressor maps.
Since this heating is reducing air density, we want to select a turbo that has the highest efficency for our application.
An example: At 15 psi our stock K26 has it's peak efficiency at an airflow equivalent to about 260 hp at the flywheel. Our engines will produce more power than 260 hp at 15 psi but when you pass this power level the turbos efficiency will fall. We would then gain from a bigger turbo which has higher efficiency which will give cooler and therefore denser air charge.
The tradeoff with the bigger turbo is the it's more inefficient in lower flow situations, giving less power at lower rpm.
Apart from this the compressor efficiency also effects turbine back pressure, but that another story.
Tomas
Mass air flow is what makes power. You will need somewhere around 2500 lb of air to operate a 400 hp engine for one hour.
The engine will take in a flow of 2.5 liters * VE every second revolution.
Since the engine itself limits the volume air flow we need to increase the air density to maximize the mass flow.
This can be done in two ways. The first one is obvious, you increase boost. The second one is to decrease air temperature.
As you compress a gas it will at the same time get hotter, this is the way of the nature and nothing we can do about it. However a turbo is not 100% effective, it will always heat the air more than what the gas laws state. This is called adiabatic efficiency and is what is shown in compressor maps.
Since this heating is reducing air density, we want to select a turbo that has the highest efficency for our application.
An example: At 15 psi our stock K26 has it's peak efficiency at an airflow equivalent to about 260 hp at the flywheel. Our engines will produce more power than 260 hp at 15 psi but when you pass this power level the turbos efficiency will fall. We would then gain from a bigger turbo which has higher efficiency which will give cooler and therefore denser air charge.
The tradeoff with the bigger turbo is the it's more inefficient in lower flow situations, giving less power at lower rpm.
Apart from this the compressor efficiency also effects turbine back pressure, but that another story.
Tomas
05-31-2004, 08:33 AM
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Tomas,
Very nice explanation. One (small) correction is that you are missing one logical step though
Initially you would also look to improve the VE (volumetric efficiency) of the engine. This includes improving airflow into the engine. However in most turbo cars it proves easier/cheaper to skip that step and move straight on to improving the air density through additional boost & cooling.
Very nice explanation. One (small) correction is that you are missing one logical step though
Originally posted by Tomas L
<snip>
The engine will take in a flow of 2.5 liters * VE every second revolution.
Since the engine itself limits the volume air flow we need to increase the air density to maximize the mass flow.
<snip>
<snip>
The engine will take in a flow of 2.5 liters * VE every second revolution.
Since the engine itself limits the volume air flow we need to increase the air density to maximize the mass flow.
<snip>
05-31-2004, 10:31 AM
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Initially you would also look to improve the VE (volumetric efficiency) of the engine. This includes improving airflow into the engine. However in most turbo cars it proves easier/cheaper to skip that step and move straight on to improving the air density through additional boost & cooling.
Tomas
05-31-2004, 11:50 AM
#25
Burning Brakes
7200 Refers to the series compressor; the 7200 is the latest and greatest K27 from KKK/Borg Warner. There are or have been various other versions one that comes to my head is the K27 11/11 there's also a K27-7006, now don't quote me on this cause I'm not 100% sure but I think that part number is a stock replacement for a 930 75 - 89, which was originally known as a 3DLZ.
There's also a newer version of the K27 which is being sold exclusively through Imagine Auto. It's know as the High Flow, do a search on the 911 turbo forum or on turbo911.com for more info.
There's also a newer version of the K27 which is being sold exclusively through Imagine Auto. It's know as the High Flow, do a search on the 911 turbo forum or on turbo911.com for more info.
05-31-2004, 03:02 PM
#26
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Originally posted by Magown
There's also a newer version of the K27 which is being sold exclusively through Imagine Auto. It's know as the High Flow, do a search on the 911 turbo forum or on turbo911.com for more info.
There's also a newer version of the K27 which is being sold exclusively through Imagine Auto. It's know as the High Flow, do a search on the 911 turbo forum or on turbo911.com for more info.
05-31-2004, 03:55 PM
#27
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I checked their web page
www.imagineauto.com
They are selling the K27/6-7200-- for $890 new. I have one, it is only oil cooled but a great upgrade
the K27/6 HF sells for $1495 and they promise the quick spool like the K27/6-7200 and the high end better than a K29 - wow
I have dealt with them on ebay a few times and they are really great to deal with. Stephen (ebay name is porschePhD) is a great guy. I am sure he is on rennlist too.
www.imagineauto.com
They are selling the K27/6-7200-- for $890 new. I have one, it is only oil cooled but a great upgrade
the K27/6 HF sells for $1495 and they promise the quick spool like the K27/6-7200 and the high end better than a K29 - wow
I have dealt with them on ebay a few times and they are really great to deal with. Stephen (ebay name is porschePhD) is a great guy. I am sure he is on rennlist too.
06-02-2004, 12:22 AM
#30
Three Wheelin'
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When people say it flows more air, is it just that it flows air that is cooler, thus having a greater density? By adding less heat, a larger compressor acts as a larger intercooler in some sense?