Compression Ratios and Forced Induction
10-04-2008, 11:53 PM
#161
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Well, for example, Peak Sierra is 94%+ Prolylene Glycol, the rest is water and additives. You are not going to see a noticeable difference between 94% and 99%.
http://www.peakantifreeze.com/msds/msds_sierra.pdf
Glycol has lower thermal conductivity and lower specific heat compared to pure water. But hey its your money and it sounds like you have already made up your mind. Go for it.
http://www.peakantifreeze.com/msds/msds_sierra.pdf
Glycol has lower thermal conductivity and lower specific heat compared to pure water. But hey its your money and it sounds like you have already made up your mind. Go for it.
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10-05-2008, 12:06 AM
#162
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As I mentioned, I've been using it for a good while. I am just surprised more folks don't try it.
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10-05-2008, 12:42 AM
#163
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What surprises me is the lack of testing for the less-head-hotspotting-less-detonation claim.
Testing it should be easy compared to some of the other tests they do like changing turbos. All you need to do is dyno tune a high compression turbo'ed motor with a decent cooling system, with 91 craptane on a hot day and turn up the boost until the motor is knock limited. Then swap in the Evans and repeat... and again with Sierra LOL.
GRM started a build with Evans on a Mustang, promising to test it, but the project never seemed completed. I never found out what happened.
Having said that, Evans coolant is very popular with the rotary crowd because their engines are very sensitive to knock.
Testing it should be easy compared to some of the other tests they do like changing turbos. All you need to do is dyno tune a high compression turbo'ed motor with a decent cooling system, with 91 craptane on a hot day and turn up the boost until the motor is knock limited. Then swap in the Evans and repeat... and again with Sierra LOL.
GRM started a build with Evans on a Mustang, promising to test it, but the project never seemed completed. I never found out what happened.
Having said that, Evans coolant is very popular with the rotary crowd because their engines are very sensitive to knock.
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10-05-2008, 12:53 AM
#164
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Despite what Evans says, pure glycol does not cool an engine as well as a water mix, or better yet pure water with a surfactant/rust inhibitor like water wetter. Period. So to answer your question speaking for myself, the reason I don't use it is that I know it will not improve cooling, but will actually worsen cooling.
If you think it works for you, great. Enjoy
If you think it works for you, great. Enjoy
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10-05-2008, 12:59 AM
#165
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What surprises me is the lack of testing for the less-head-hotspotting-less-detonation claim.
Testing it should be easy compared to some of the other tests they do like changing turbos. All you need to do is dyno tune a high compression turbo'ed motor with a decent cooling system, with 91 craptane on a hot day and turn up the boost until the motor is knock limited. Then swap in the Evans and repeat... and again with Sierra LOL.
Testing it should be easy compared to some of the other tests they do like changing turbos. All you need to do is dyno tune a high compression turbo'ed motor with a decent cooling system, with 91 craptane on a hot day and turn up the boost until the motor is knock limited. Then swap in the Evans and repeat... and again with Sierra LOL.
AFAIK, there is not a medium of measurement that you could apply to -all- engines so that you could have an idea of how much it would help. FWIW, I should not have been able to advance my VW 1.8 to 56* total without detonation (42 or 44 is stock max); while not scientific, that is a definite improvement. I've confirmed with an OE knock-box control that I do not have any knock BTW.
To the point of obvious damage? If so, that would seem to support their claims too. I know, not very empirical, but....
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10-05-2008, 01:11 AM
#166
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Despite what Evans says, pure glycol does not cool an engine as well as a water mix, or better yet pure water with a surfactant/rust inhibitor like water wetter. Period. So to answer your question speaking for myself, the reason I don't use it is that I know it will not improve cooling, but will actually worsen cooling.
You can lead a horse to water, but...
I've offered evidence to the contrary; it's one thing to not find it compelling, it's another to state that it is wrong without any posts/pages to help support it. You don't have to use it, do what you like; just don't tell me it doesn't work better if you've never tried it.
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10-05-2008, 01:21 AM
#167
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C. A discussion of what Evans NPG+ waterless coolant is and how it
works as compared to water-based coolants:
All commercially available automotive antifreezes and coolants (more than 250 brands), except Evans coolants, are water-based. Water is good because it is cheap and because it has excellent thermal conductivity in its liquid state. On the other hand, water is a poor choice because the boiling point of water is too low. There is very little separation between the operating temperature of the coolant and the boiling point of water (for the pressure of the system). The boiling point of water is the failure temperature for a cooling system using a water-based coolant because water vapor has almost no thermal conductivity. Water is aggressive toward cooling system metals. Water acts as an electrolyte, promoting electrolysis between dissimilar metals within the cooling system.
Although water-based coolants are mostly 50% glycol and 50% water, the failure temperature is the boiling point of water, not the boiling point of the mixture. Some locations within the cylinder head generate so much heat that some of the nearby coolant boils, even though the bulk coolant is below the boiling point of the mixture of glycol and water. When local coolant boils, the resulting vapor is nearly 100% water vapor because of fractional distillation. The water portion is far more volatile and is liberated as water vapor. The glycol portion remains in the solution.
If the coolant that is surrounding the water vapor is above the boiling point of water, the water vapor cannot condense. Under this condition, the water vapor makes an insulating
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barrier between hot metal and liquid coolant, causing the temperature of the metal to spike to high levels. Figure 2 compares the thermal conductivity of Evans NPG+ waterless coolant to the liquid and vapor phases of 50%/50% EGW.
Water-based coolant must be kept cold enough to avoid pump cavitation. Action of the coolant pump creates a low pressure area at the pump inlet. Pump cavitation occurs when coolant near its boiling point encounters the low pressure area and flash vaporizes within the pump. The gas pocket in the pump causes the pump to stop functioning and coolant circulation to stop. Coolant pump cavitation leads directly to catastrophic cooling system failure with the coolant being expelled from the system as steam pressure exceeds the pressure relief setting of the cap.
Water-based coolant must be kept cold enough to avoid afterboil. Afterboil occurs after shut-down of a stressed engine when the coolant is near its boiling point and residual heat remains in the cylinder head or in an auxiliary circuit such as an EGR cooler. Upon shut-down the coolant pump ceases to circulate coolant through the cooling system. Residual heat boils the stagnant coolant, making steam pressure that exceeds the pressure relief setting of the cap. Coolant is pushed out of the system.
Fig. 2 Thermal Conductivity of the Liquid and Vapor Phases of Water-Based Coolant vs. NPG+(The vapor phase of water-based coolant has almost no thermal conductivity.)0.0000.0500.1000.1500.2000.2500.3000 .3500.4000.450212216220224228232236240244248252256 260264268272276280284288Temperature ( Degrees F )Thermal Conductivity (W/EGW 50%/50%, 15 PSIGEvans NPG+, any pressure
A cooling system using water-based coolants is burdened by the requirement to keep the coolant below the boiling point of water for the pressure of the system under all operating conditions and after shut-down. This task is difficult because the coolant frequently operates close to the boiling point of water.
5
The primary purpose of any engine cooling system is to keep engine metal temperatures under control. In order to accomplish that with water-based coolant, significant energy must be expended to keep the coolant cold enough so that it remains functional.
The most important operational feature of Evans NPG+ waterless coolant is its huge separation between the operating temperature and the boiling point of the coolant, on the order of at least 100o F.
The huge separation between the operating temperature and the boiling point of Evans NPG+ unlocks a Reserve Capacity that already exists in systems designed for water-based coolants. Any cooling system designed to keep coolant below the boiling point of water for the pressure of the system under all operating conditions and after shut-down is liberated from those requirements when the coolant is changed to Evans NPG+. The same sized cooling system can accommodate a broader range of temperatures safely. When ambient temperatures happen to be higher, there are no failures due to the boiling point of water. In a 100o F environment a radiator that is 230o F can dissipate 22% more heat than the same one at 205o F.
Evans NPG+ prevents hot spots in the engine. The huge separation between the operating temperature and the boiling point of Evans NPG+, on the order of at least 100o F, provides an environment where any locally generated coolant vapor immediately condenses into adjacent liquid coolant. Vapor cannot build into an insulating barrier and contact between hot metal and liquid coolant is maintained at all times. Metal temperatures are under control at all times.
works as compared to water-based coolants:
All commercially available automotive antifreezes and coolants (more than 250 brands), except Evans coolants, are water-based. Water is good because it is cheap and because it has excellent thermal conductivity in its liquid state. On the other hand, water is a poor choice because the boiling point of water is too low. There is very little separation between the operating temperature of the coolant and the boiling point of water (for the pressure of the system). The boiling point of water is the failure temperature for a cooling system using a water-based coolant because water vapor has almost no thermal conductivity. Water is aggressive toward cooling system metals. Water acts as an electrolyte, promoting electrolysis between dissimilar metals within the cooling system.
Although water-based coolants are mostly 50% glycol and 50% water, the failure temperature is the boiling point of water, not the boiling point of the mixture. Some locations within the cylinder head generate so much heat that some of the nearby coolant boils, even though the bulk coolant is below the boiling point of the mixture of glycol and water. When local coolant boils, the resulting vapor is nearly 100% water vapor because of fractional distillation. The water portion is far more volatile and is liberated as water vapor. The glycol portion remains in the solution.
If the coolant that is surrounding the water vapor is above the boiling point of water, the water vapor cannot condense. Under this condition, the water vapor makes an insulating
4
barrier between hot metal and liquid coolant, causing the temperature of the metal to spike to high levels. Figure 2 compares the thermal conductivity of Evans NPG+ waterless coolant to the liquid and vapor phases of 50%/50% EGW.
Water-based coolant must be kept cold enough to avoid pump cavitation. Action of the coolant pump creates a low pressure area at the pump inlet. Pump cavitation occurs when coolant near its boiling point encounters the low pressure area and flash vaporizes within the pump. The gas pocket in the pump causes the pump to stop functioning and coolant circulation to stop. Coolant pump cavitation leads directly to catastrophic cooling system failure with the coolant being expelled from the system as steam pressure exceeds the pressure relief setting of the cap.
Water-based coolant must be kept cold enough to avoid afterboil. Afterboil occurs after shut-down of a stressed engine when the coolant is near its boiling point and residual heat remains in the cylinder head or in an auxiliary circuit such as an EGR cooler. Upon shut-down the coolant pump ceases to circulate coolant through the cooling system. Residual heat boils the stagnant coolant, making steam pressure that exceeds the pressure relief setting of the cap. Coolant is pushed out of the system.
Fig. 2 Thermal Conductivity of the Liquid and Vapor Phases of Water-Based Coolant vs. NPG+(The vapor phase of water-based coolant has almost no thermal conductivity.)0.0000.0500.1000.1500.2000.2500.3000 .3500.4000.450212216220224228232236240244248252256 260264268272276280284288Temperature ( Degrees F )Thermal Conductivity (W/EGW 50%/50%, 15 PSIGEvans NPG+, any pressure
A cooling system using water-based coolants is burdened by the requirement to keep the coolant below the boiling point of water for the pressure of the system under all operating conditions and after shut-down. This task is difficult because the coolant frequently operates close to the boiling point of water.
5
The primary purpose of any engine cooling system is to keep engine metal temperatures under control. In order to accomplish that with water-based coolant, significant energy must be expended to keep the coolant cold enough so that it remains functional.
The most important operational feature of Evans NPG+ waterless coolant is its huge separation between the operating temperature and the boiling point of the coolant, on the order of at least 100o F.
The huge separation between the operating temperature and the boiling point of Evans NPG+ unlocks a Reserve Capacity that already exists in systems designed for water-based coolants. Any cooling system designed to keep coolant below the boiling point of water for the pressure of the system under all operating conditions and after shut-down is liberated from those requirements when the coolant is changed to Evans NPG+. The same sized cooling system can accommodate a broader range of temperatures safely. When ambient temperatures happen to be higher, there are no failures due to the boiling point of water. In a 100o F environment a radiator that is 230o F can dissipate 22% more heat than the same one at 205o F.
Evans NPG+ prevents hot spots in the engine. The huge separation between the operating temperature and the boiling point of Evans NPG+, on the order of at least 100o F, provides an environment where any locally generated coolant vapor immediately condenses into adjacent liquid coolant. Vapor cannot build into an insulating barrier and contact between hot metal and liquid coolant is maintained at all times. Metal temperatures are under control at all times.
A higher value of a given measure is not always better, not under all circumstances. A 350 hp vehicle against my 105 hp truck is not necessarily faster; what does each weigh? IOW, if you look at the graph, water/AF mix might be better up to a point, but after that it is much worse that PG. While water/AF mix might make it run cooler, from an efficiency standpoint, it is less efficient than PG.
Again, if you don't like it, don't use it; just don't tell me 'it don't work.'
Last edited by fahrvergnugen; 10-05-2008 at 02:05 AM. Reason: Clarity
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10-05-2008, 01:04 PM
#168
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What compression ratio does Top Fuel run? 6.5:1. Why? Because they want to be slower?
This argument seems kind of silly given the small turbos and low boost that is common in the Miata community. Of course at 7psi on a 25lb turbo a 9.5:1 compression is better than 8:1. But the fact of the matter is, that if you want to get serious about making power on a built motor you'll find a higher compression ratio hampers you more than helps. The question is, do you want to go fast? And how is that going to be easiest and most feasible? The answers don't often include a high compression ratio, even if on paper it seems like it'd be best.
Don't take my word for it, build a 12.5:1 motor, get a 75lb turbo and crank the boost up to 45psi- you'll never get it tuned right.
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10-05-2008, 02:36 PM
#169
Yeah, it's just that simple. Of course you're right but at some point you'll find that there is no tune good enough even on 116. At least not with the tools Miata drivers are typically using.
What compression ratio does Top Fuel run? 6.5:1. Why? Because they want to be slower?
This argument seems kind of silly given the small turbos and low boost that is common in the Miata community. Of course at 7psi on a 25lb turbo a 9.5:1 compression is better than 8:1. But the fact of the matter is, that if you want to get serious about making power on a built motor you'll find a higher compression ratio hampers you more than helps. The question is, do you want to go fast? And how is that going to be easiest and most feasible? The answers don't often include a high compression ratio, even if on paper it seems like it'd be best.
Don't take my word for it, build a 12.5:1 motor, get a 75lb turbo and crank the boost up to 45psi- you'll never get it tuned right.
What compression ratio does Top Fuel run? 6.5:1. Why? Because they want to be slower?
This argument seems kind of silly given the small turbos and low boost that is common in the Miata community. Of course at 7psi on a 25lb turbo a 9.5:1 compression is better than 8:1. But the fact of the matter is, that if you want to get serious about making power on a built motor you'll find a higher compression ratio hampers you more than helps. The question is, do you want to go fast? And how is that going to be easiest and most feasible? The answers don't often include a high compression ratio, even if on paper it seems like it'd be best.
Don't take my word for it, build a 12.5:1 motor, get a 75lb turbo and crank the boost up to 45psi- you'll never get it tuned right.
Makes about 1150whp...and runs 11:1 CR.
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10-05-2008, 04:26 PM
#171
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You are beginning to look like a shill by the way.
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10-05-2008, 09:04 PM
#172
Yeah, it's just that simple. Of course you're right but at some point you'll find that there is no tune good enough even on 116. At least not with the tools Miata drivers are typically using.
What compression ratio does Top Fuel run? 6.5:1. Why? Because they want to be slower?
This argument seems kind of silly given the small turbos and low boost that is common in the Miata community. Of course at 7psi on a 25lb turbo a 9.5:1 compression is better than 8:1. But the fact of the matter is, that if you want to get serious about making power on a built motor you'll find a higher compression ratio hampers you more than helps. The question is, do you want to go fast? And how is that going to be easiest and most feasible? The answers don't often include a high compression ratio, even if on paper it seems like it'd be best.
Don't take my word for it, build a 12.5:1 motor, get a 75lb turbo and crank the boost up to 45psi- you'll never get it tuned right.
What compression ratio does Top Fuel run? 6.5:1. Why? Because they want to be slower?
This argument seems kind of silly given the small turbos and low boost that is common in the Miata community. Of course at 7psi on a 25lb turbo a 9.5:1 compression is better than 8:1. But the fact of the matter is, that if you want to get serious about making power on a built motor you'll find a higher compression ratio hampers you more than helps. The question is, do you want to go fast? And how is that going to be easiest and most feasible? The answers don't often include a high compression ratio, even if on paper it seems like it'd be best.
Don't take my word for it, build a 12.5:1 motor, get a 75lb turbo and crank the boost up to 45psi- you'll never get it tuned right.
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10-05-2008, 09:29 PM
#173
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Um, 25lb/min. I find it more useful than talking in terms of all the different compressor wheels to choose from. Do you even know what you're talking about?
I do, however, love being told I don't know what I'm talking about by people who've made 185-205hp in their lives. Fantastic.
I do, however, love being told I don't know what I'm talking about by people who've made 185-205hp in their lives. Fantastic.
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10-05-2008, 10:43 PM
#174
Um, 25lb/min. I find it more useful than talking in terms of all the different compressor wheels to choose from. Do you even know what you're talking about?
I do, however, love being told I don't know what I'm talking about by people who've made 185-205hp in their lives. Fantastic.
I do, however, love being told I don't know what I'm talking about by people who've made 185-205hp in their lives. Fantastic.
And by the way, since this thread was originally about making more power across a broader rpm range, I would think that you'd want more info choosing a turbo than max volume capabilities. That might play a factor into the tuning - you think?
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10-05-2008, 11:07 PM
#175
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Hey dumbass, I'm not choosing a turbo based on max volume capabilities, I'm using max volume capabilities as an easy way to describe a turbo for simplicity sake. Now calm you angry noob *** down.
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10-05-2008, 11:20 PM
#176
Newb on this forum or not, don't make assumptions on someone's ability or past accomplishments on building a high hp engine. If you want to compare resumes on that subject, I'd be more than happy to. Fact is, high compression w/ high boost can be successfully achieved within reason and will give a much broader power curve than an engine with a lower static compression ratio. I've done it.
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10-05-2008, 11:44 PM
#177
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I guess I want to know what you see as high boost and compression ratio. And also what fuel you're using. Assuming you're not talking about you're diesel when you say you've done it, tell me about what you've done with high boost and compression. I'm willing to listen.
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10-06-2008, 12:13 AM
#178
I guess I want to know what you see as high boost and compression ratio. And also what fuel you're using. Assuming you're not talking about you're diesel when you say you've done it, tell me about what you've done with high boost and compression. I'm willing to listen.
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10-06-2008, 12:18 AM
#179
And by the way, I wouldn't start comparing my truck to turbo charged gas engines, I only stated I had it to make you aware that I might have a little bit of knowledge when it comes to turbos.
That would be a good example of high compression and high boost though.
17.2:1 static compression with 65psi total boost.
That would be a good example of high compression and high boost though.
17.2:1 static compression with 65psi total boost.
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10-06-2008, 12:49 AM
#180
I don't know where this thread ended up, I skimmed things pretty heavily, but I support the theory that a low compression ratio motor will spool faster. In a Carnot cycle you've got 2 phases, Isothermal compression/expansion and adiabatic compression/expansion. So that is broken up into 2 parts, P dv and Cv dt. Unfortunately humans suck so we don't get all the energy out of each chemical burn to put it to work. The Carnot cycle is more like a fairy tale but we can use it for fundamental understanding in this case.
By increasing the compression ratio we increase the capacity to do mechanical work and thus P dv is transmitted into power. Having 2 engines exactly the same and mitigating the increase in volumetric efficiency we see that we cannot spontaneously generate joules. Therefore the energy we get from P dv must be subtracted from Cv dt. That basically means the cylinder temperatures must go down. So in a high compression motor by default there is less energy to power the turbine that feeds from this waste energy. I would also wager that whoever designed the aftermarket pistons that done that compression lowering probably didn’t know nearly as much about efficient combustion systems as Mazda so it’s likely the turbulence used by the head to atomize and create favorable flame front conditions is not fully intact. This also reduces efficiency further adding to the Cv dt term, and more areas of the cylinder which will burn later in the exhaust pipe.
Also I would like to add that low compression motors using detonation limited gas should make more power because T will rise as compression goes up (duh), so the high compression motor is limited. This however becomes the low compression motors nemeses as BMEP goes very high and the gas becomes more detonation resistant. The low compression motor simply cannot convert enough of the heat in a race motor in order to keep parts from becoming molten. This is amplified by the inefficiency of any otto-cycle based motor which is already 30/70 on a good day.
By increasing the compression ratio we increase the capacity to do mechanical work and thus P dv is transmitted into power. Having 2 engines exactly the same and mitigating the increase in volumetric efficiency we see that we cannot spontaneously generate joules. Therefore the energy we get from P dv must be subtracted from Cv dt. That basically means the cylinder temperatures must go down. So in a high compression motor by default there is less energy to power the turbine that feeds from this waste energy. I would also wager that whoever designed the aftermarket pistons that done that compression lowering probably didn’t know nearly as much about efficient combustion systems as Mazda so it’s likely the turbulence used by the head to atomize and create favorable flame front conditions is not fully intact. This also reduces efficiency further adding to the Cv dt term, and more areas of the cylinder which will burn later in the exhaust pipe.
Also I would like to add that low compression motors using detonation limited gas should make more power because T will rise as compression goes up (duh), so the high compression motor is limited. This however becomes the low compression motors nemeses as BMEP goes very high and the gas becomes more detonation resistant. The low compression motor simply cannot convert enough of the heat in a race motor in order to keep parts from becoming molten. This is amplified by the inefficiency of any otto-cycle based motor which is already 30/70 on a good day.
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