View Poll Results: Which year to build a SC for
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To build a supercharger kit or not?
12-22-2004, 01:13 PM
#62
Banned
Originally Posted by 1999Porsche911
The is no way to increase the volume of air in the cylinders without compression unless you're going to bore them out or put a shorter crank in..
12-22-2004, 01:51 PM
#63
Race Car
Resonance charging, which is on the 996 intake, does NOT increase the volume of air that goes into the cylinders. Physics does not allow this. The valve simply opens and closes at predetermined power levels to create an increase in turbulance of the air being thrown into the engine. It also seres as a means of adjusting the length of the intake. Kinda like putting and high rise intake under an old carb systems.
Only by compression can more air be put into the same cylinders.
Only by compression can more air be put into the same cylinders.
12-22-2004, 01:55 PM
#64
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Just got around to reading all this....
The advantage of the centifuge blower is that it can move more CFM than the eaton. (At least the Eaton units I have used). There IS boost at ALL engine speeds as long as you are at WOT or accelerating rapidly enought to lose vacuum. Cruising at any speed is like driving a stock motor because all boost is bypassing the intake.
Why in the heck would all boost be bypassing the intake if you're at part throttle? You have a blow off valve that opens when the throttle is closed (i.e. between shifts), but if you're cruising at a fairly high rpm, the thing should most definitely be making boost.
Highway gas mileage is increased by about 10%. Open the throttle and the boost is immediately in the cylinder. The centrifuge SC with a proper aftercooler will keep the intake air at about 20 degrees F above ambient temperature so heat is not a concern.
This obviously depends on the supercharger size, intercooler size, etc etc. Centrifugal compressors do operate more efficiently than other supercharger designs, but they kinda suck IMHO because they build boost on an exponential curve relative to RPM, you don't get significant boost until the upper rpm band (not much low end improvement).
The about of boost is directly related to the RPM of the blower. A boost of 6 psi at 7,000 RPM will be reduced to (the square of 6) 2.5 psi at 3500 RPM and is linear in between. The power curve is smooth and even.
What's a square of 6? You mean power of 6? Does this vary with compressor/housing design?
Having used both, I prefer the centrifuge blower because of the power curve and the amount of air it can compress compared to the Eaton.
I disagree, IMHO centrifugals are an 'easy way' to SC an engine. They can fit into a tight engine bay easier, and *can* produce more peak power - but their power curve sucks. If you want to use a centrifugal compressor, go the extra mile and use a turbocharger setup - much much better (although more complex and expensive). Positive displacement superchargers are definitely the way to go for the guy who just wants a solid %50 or so gain. Those looking for big power may want to look at turbochargers.
The advantage of the centifuge blower is that it can move more CFM than the eaton. (At least the Eaton units I have used). There IS boost at ALL engine speeds as long as you are at WOT or accelerating rapidly enought to lose vacuum. Cruising at any speed is like driving a stock motor because all boost is bypassing the intake.
Why in the heck would all boost be bypassing the intake if you're at part throttle? You have a blow off valve that opens when the throttle is closed (i.e. between shifts), but if you're cruising at a fairly high rpm, the thing should most definitely be making boost.
Highway gas mileage is increased by about 10%. Open the throttle and the boost is immediately in the cylinder. The centrifuge SC with a proper aftercooler will keep the intake air at about 20 degrees F above ambient temperature so heat is not a concern.
This obviously depends on the supercharger size, intercooler size, etc etc. Centrifugal compressors do operate more efficiently than other supercharger designs, but they kinda suck IMHO because they build boost on an exponential curve relative to RPM, you don't get significant boost until the upper rpm band (not much low end improvement).
The about of boost is directly related to the RPM of the blower. A boost of 6 psi at 7,000 RPM will be reduced to (the square of 6) 2.5 psi at 3500 RPM and is linear in between. The power curve is smooth and even.
What's a square of 6? You mean power of 6? Does this vary with compressor/housing design?
Having used both, I prefer the centrifuge blower because of the power curve and the amount of air it can compress compared to the Eaton.
I disagree, IMHO centrifugals are an 'easy way' to SC an engine. They can fit into a tight engine bay easier, and *can* produce more peak power - but their power curve sucks. If you want to use a centrifugal compressor, go the extra mile and use a turbocharger setup - much much better (although more complex and expensive). Positive displacement superchargers are definitely the way to go for the guy who just wants a solid %50 or so gain. Those looking for big power may want to look at turbochargers.
12-22-2004, 02:09 PM
#66
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1999911
"Only by compression can more air be put into the same cylinders."
I have a feeling that it has to do with Volumetric efficiency. Very well designed heads can achieve up to 130% VE in a certain rev bands. This is achieved by creating partial vacuum during part of the exhaust cycle. The partial vacuum, of course depends heavily on valve timing etc etc. Herein lies the skill in NA engine head design. You refer to 'resonance charging'. This is very much about tuning intake lengths to create pressure waves. Both inlets and exhaust tuning can achieve these 'physically ipossible' VE's WITHOUT compresion - though in reality compression is exactly what you get by tuning the exhaust & inlets. Read up on Walter Karden, the East German engineer at MZ who first developed the expansion chamber exhaust for 2 stroke engines.
So, what I believe any S/C setup can achieve is high VE across the rev range. With very low boosts, you are effectively getting 130%+ VE across the whole trev range. The heads can then flow more air, so you can burn more fuel & air.
You clearly have alot of practical S/C experience. However, some of your statemets concerning hte laws of physics need examining. In the case of internal combustion engine design, you may also wish to consider the laws of thermodynamics....
JohnFM
"Only by compression can more air be put into the same cylinders."
I have a feeling that it has to do with Volumetric efficiency. Very well designed heads can achieve up to 130% VE in a certain rev bands. This is achieved by creating partial vacuum during part of the exhaust cycle. The partial vacuum, of course depends heavily on valve timing etc etc. Herein lies the skill in NA engine head design. You refer to 'resonance charging'. This is very much about tuning intake lengths to create pressure waves. Both inlets and exhaust tuning can achieve these 'physically ipossible' VE's WITHOUT compresion - though in reality compression is exactly what you get by tuning the exhaust & inlets. Read up on Walter Karden, the East German engineer at MZ who first developed the expansion chamber exhaust for 2 stroke engines.
So, what I believe any S/C setup can achieve is high VE across the rev range. With very low boosts, you are effectively getting 130%+ VE across the whole trev range. The heads can then flow more air, so you can burn more fuel & air.
You clearly have alot of practical S/C experience. However, some of your statemets concerning hte laws of physics need examining. In the case of internal combustion engine design, you may also wish to consider the laws of thermodynamics....
JohnFM
12-22-2004, 02:18 PM
#68
Banned
Originally Posted by 1999Porsche911
Resonance charging, which is on the 996 intake, does NOT increase the volume of air that goes into the cylinders.
12-22-2004, 02:24 PM
#69
Race Car
But that's precisely what's it's there for.
So, please explain to me how you would get moire air into a set sized cylinder without compressing it? It cannot be done. You can change the raio of the various gases in the air, but you cannot increase the total volume.
So, please explain to me how you would get moire air into a set sized cylinder without compressing it? It cannot be done. You can change the raio of the various gases in the air, but you cannot increase the total volume.
12-22-2004, 02:27 PM
#70
Banned
Originally Posted by 1999Porsche911
But that's precisely what's it's there for.
So, please explain to me how you would get moire air into a set sized cylinder without compressing it? It cannot be done. You can change the raio of the various gases in the air, but you cannot increase the total volume.
So, please explain to me how you would get moire air into a set sized cylinder without compressing it? It cannot be done. You can change the raio of the various gases in the air, but you cannot increase the total volume.
12-22-2004, 02:38 PM
#71
Race Car
Flatair:
Why in the heck would all boost be bypassing the intake if you're at part throttle? You have a blow off valve that opens when the throttle is closed (i.e. between shifts), but if you're cruising at a fairly high rpm, the thing should most definitely be making boost.
Connect a vaccum gauge to your engine and see if you have engine vacuum while cruising at 100 mph. If you do (and you should) there is little to no boost entering the engine. The by-pass vale IS ALWAYS OPEN when there is vacuum.
What's a square of 6? You mean power of 6? Does this vary with compressor/housing design.
No I DO mean the square of 6.
I disagree, IMHO centrifugals are an 'easy way' to SC an engine. They can fit into a tight engine bay easier, and *can* produce more peak power - but their power curve sucks. If you want to use a centrifugal compressor, go the extra mile and use a turbocharger setup - much much better (although more complex and expensive). Positive displacement superchargers are definitely the way to go for the guy who just wants a solid %50 or so gain. Those looking for big power may want to look at turbocharger.
And just WHY would you want a power curve that "SUCKS"? No Turbo Charger of the same boost will come close to giving you the low end power that a Cetrifuge blower will. The power curve of the centrifuge is as smooth as you can get. Also, having a boost level of more than 2.5 at 3500 rpm on a static engine of 11.3:1 is hardly a low boost level.
But we each have our own preference, but having installed and run all the various SC's available, I will stay with the cetrifuge style.
Why in the heck would all boost be bypassing the intake if you're at part throttle? You have a blow off valve that opens when the throttle is closed (i.e. between shifts), but if you're cruising at a fairly high rpm, the thing should most definitely be making boost.
Connect a vaccum gauge to your engine and see if you have engine vacuum while cruising at 100 mph. If you do (and you should) there is little to no boost entering the engine. The by-pass vale IS ALWAYS OPEN when there is vacuum.
What's a square of 6? You mean power of 6? Does this vary with compressor/housing design.
No I DO mean the square of 6.
I disagree, IMHO centrifugals are an 'easy way' to SC an engine. They can fit into a tight engine bay easier, and *can* produce more peak power - but their power curve sucks. If you want to use a centrifugal compressor, go the extra mile and use a turbocharger setup - much much better (although more complex and expensive). Positive displacement superchargers are definitely the way to go for the guy who just wants a solid %50 or so gain. Those looking for big power may want to look at turbocharger.
And just WHY would you want a power curve that "SUCKS"? No Turbo Charger of the same boost will come close to giving you the low end power that a Cetrifuge blower will. The power curve of the centrifuge is as smooth as you can get. Also, having a boost level of more than 2.5 at 3500 rpm on a static engine of 11.3:1 is hardly a low boost level.
But we each have our own preference, but having installed and run all the various SC's available, I will stay with the cetrifuge style.
12-22-2004, 02:41 PM
#72
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Resonance charging, which is on the 996 intake, does NOT increase the volume of air that goes into the cylinders.
Ok let me get this straight, you're saying resonance charging does *not* increase the volume (i.e. amount) of the air that goes *into* the cylinders? Wanna bet on that one?
Ok let me get this straight, you're saying resonance charging does *not* increase the volume (i.e. amount) of the air that goes *into* the cylinders? Wanna bet on that one?
12-22-2004, 02:42 PM
#73
Rennlist Lifetime Member
Thread Starter
98993,
Keep in mind this truly was a question to the masses of do we build it. Lets say I could nothing more than what TPC has done performance wise. Are you guys wanting something else that is done with a more efficient system and with true programming and larger injectors?
I can see how one misread my statement. Of course there are always those that look at a tuner and go OH another one of those guys. I pride my self on being an owner and modifying every car I have owned (over 30 Porsches) and actually build motors and fix stuff
I will also be the first to admit if it doesn't achieve the numbers I am expecting. I have not built the kit as one could gather so it is all speculation based on some other things I have done. I do the math and look at the numbers, but I am also one that says AH screw it! Let me build it and see if it works. A common ground for argument among my engineering buddies.
I will try to did up some Authors and old books I have that go into great detail of what we are talking about. If you are interested.
1999P, you know as well as I do you can not have one without the other. To say you can only increase volume without pressure is not what I am saying. If that was the case I could re-market the Eram. I think that was what it was called. The little blower that didn't create pressure yet was supposed add volume to the system. Without the pressure you will not raise the CR. You need apx and this is a loose number 3psi to every 1 point increase. This changes based on the VE of the motor. But that is a pretty good number to start with. Interesting enough I keep running into CRs under boost that I can't believe. Look at the new TT. We run 9:4:1 static. We have run as much as 1.9 bar under testing and still maintained a decent CCT and AFR. (read:lots of fuel mods)The ultimate issue we have is the thermal temps of the air-cooled. Same issue we have always had whether it was a turbo or not. Volume does matter as well as pressure. Take the 930 for example. You run a 3LDZ stock then switch to a K27 which is a bigger compressor and turbine. The net increase is apx 35 HP at the same boot level. Nothing else changed other than the volume. Being CIS typically no more fuel requirement is needed as the law of pneumatics dictates the plate will drop or pull through the cone as needed. I will not create any more confusion by going into the heat saturation from over spinning. People should know though over spinning to small of a wheel off the map will create a heat situation and cause the result to go backwards in gains.
Bottom line is all I want to know is is this something we should build. if I am wrong then I will admit it. Bottom line. I am not so arrogant that I will not take responsibility. I also have enough experience to know that I am not nuts. At least not about this.
Now if I could just figure out how to keep subscribed to this thread. Think I would rather tune an ECU.
Keep in mind this truly was a question to the masses of do we build it. Lets say I could nothing more than what TPC has done performance wise. Are you guys wanting something else that is done with a more efficient system and with true programming and larger injectors?
I can see how one misread my statement. Of course there are always those that look at a tuner and go OH another one of those guys. I pride my self on being an owner and modifying every car I have owned (over 30 Porsches) and actually build motors and fix stuff
I will also be the first to admit if it doesn't achieve the numbers I am expecting. I have not built the kit as one could gather so it is all speculation based on some other things I have done. I do the math and look at the numbers, but I am also one that says AH screw it! Let me build it and see if it works. A common ground for argument among my engineering buddies. I will try to did up some Authors and old books I have that go into great detail of what we are talking about. If you are interested.
1999P, you know as well as I do you can not have one without the other. To say you can only increase volume without pressure is not what I am saying. If that was the case I could re-market the Eram. I think that was what it was called. The little blower that didn't create pressure yet was supposed add volume to the system. Without the pressure you will not raise the CR. You need apx and this is a loose number 3psi to every 1 point increase. This changes based on the VE of the motor. But that is a pretty good number to start with. Interesting enough I keep running into CRs under boost that I can't believe. Look at the new TT. We run 9:4:1 static. We have run as much as 1.9 bar under testing and still maintained a decent CCT and AFR. (read:lots of fuel mods)The ultimate issue we have is the thermal temps of the air-cooled. Same issue we have always had whether it was a turbo or not. Volume does matter as well as pressure. Take the 930 for example. You run a 3LDZ stock then switch to a K27 which is a bigger compressor and turbine. The net increase is apx 35 HP at the same boot level. Nothing else changed other than the volume. Being CIS typically no more fuel requirement is needed as the law of pneumatics dictates the plate will drop or pull through the cone as needed. I will not create any more confusion by going into the heat saturation from over spinning. People should know though over spinning to small of a wheel off the map will create a heat situation and cause the result to go backwards in gains.
Bottom line is all I want to know is is this something we should build. if I am wrong then I will admit it. Bottom line. I am not so arrogant that I will not take responsibility. I also have enough experience to know that I am not nuts. At least not about this.
Now if I could just figure out how to keep subscribed to this thread. Think I would rather tune an ECU.
12-22-2004, 02:46 PM
#74
Rennlist Lifetime Member
Thread Starter
FWIW only the NA cars have the resonance charging. Both the 993 and 996 use the same intake as the 963/993 (pre96) and the prts are blocked off. Different theory alltogether in the turbo cars.
Oops, I also forgot to add, yes we will use a centrifugal blower that is similar to what Renntech has used on the Benz. I know you know what I am talking about.
Oops, I also forgot to add, yes we will use a centrifugal blower that is similar to what Renntech has used on the Benz. I know you know what I am talking about.