Big HP #s
10-12-2006, 12:34 AM
#26
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i think the renesis could handle 400 hp. i dont think the compression ratio is a limiting factor. the saleen S7? that super half million dollar car has a compression ration of 13:1 i think, and its a twin turbo high boost monster.
what i do think is a limiting factor on the renesis is heat. i dont have a temp gauge on mine, but i hear that it runs into the 200 degree range on longer drives. add lots of boost and things are going to get hot under hood. i dont think it would be a practical car to drive everyday. to be truthful i dont think it would last 10000 miles.
its just a matter of time.
what i do think is a limiting factor on the renesis is heat. i dont have a temp gauge on mine, but i hear that it runs into the 200 degree range on longer drives. add lots of boost and things are going to get hot under hood. i dont think it would be a practical car to drive everyday. to be truthful i dont think it would last 10000 miles.
its just a matter of time.
10-12-2006, 07:58 AM
#27
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Originally Posted by turbosa22c
i think the renesis could handle 400 hp. i dont think the compression ratio is a limiting factor. the saleen S7? that super half million dollar car has a compression ration of 13:1 i think, and its a twin turbo high boost monster.
what i do think is a limiting factor on the renesis is heat. i dont have a temp gauge on mine, but i hear that it runs into the 200 degree range on longer drives. add lots of boost and things are going to get hot under hood. i dont think it would be a practical car to drive everyday. to be truthful i dont think it would last 10000 miles.
its just a matter of time.
what i do think is a limiting factor on the renesis is heat. i dont have a temp gauge on mine, but i hear that it runs into the 200 degree range on longer drives. add lots of boost and things are going to get hot under hood. i dont think it would be a practical car to drive everyday. to be truthful i dont think it would last 10000 miles.
its just a matter of time.
Have you owned one before?
Are you a mechanical engineer?
10-12-2006, 08:41 AM
#28
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sometimes less is better.............
actually I'm runing my car on the 420 to 450 hp range........................
(rich as a pig, with a 10.0 FAR) because it transfer better the power.
when I run the car with +525hp is so difficult to don't spin the tires.
believe or not we use both car's (rgonza and mine) as daily driven car's, of course we have
pick ups and we also use them, but if we whant we use the RX8's everyday,
for example I used mine for 3 moths practically every day. the only problem is that gives 12 mpg.
with the 20B swap we can use the cars with only 400 hp but the good news is that the power is there if we whant more hp we just increase the boost. We don't need race fuel we use 93 octane pump gasoline.
Manuel
actually I'm runing my car on the 420 to 450 hp range........................
(rich as a pig, with a 10.0 FAR) because it transfer better the power.
when I run the car with +525hp is so difficult to don't spin the tires.
believe or not we use both car's (rgonza and mine) as daily driven car's, of course we have
pick ups and we also use them, but if we whant we use the RX8's everyday,
for example I used mine for 3 moths practically every day. the only problem is that gives 12 mpg.
with the 20B swap we can use the cars with only 400 hp but the good news is that the power is there if we whant more hp we just increase the boost. We don't need race fuel we use 93 octane pump gasoline.
Manuel
10-12-2006, 11:44 AM
#29
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IVE owned rotaries for 17 years. i ve turbo charged my 1st gen with a 12a streetport using a weber blow through. fabbing my own parts. ive put turbo rotaries into mazda b2200 trucks,porsche 911, toyota starlet, corolla. i still have turbo FC thats boosting pretty good right now. and of cousre i have my 8. no i dont have a engineering degree. i dont theorize about how to do things i just do it. you can sit there a trying to figure how its going to work. in reality how many rotary hot rodders out there that build their own turbo systems are engineers?
10-12-2006, 01:33 PM
#31
One would think there is a significant amount of difference from having a 400 whp 20b and a 400 whp renensis. To make the Ren high boost friendly, it might be as simple as changing rotors for lower compression, adding beefy seals, redoing fuel delivery, and slapping a big turbo on there. With a turbo that doesn't really spool below 4k rpms, it would probably drive decently on the street assuming you don't heavily port it. Using the stock compression ratio, you'd be looking at pretty high charge temps before ignition. As you compress a gas, it heats up. Get the gas hot enough, you get detonation where it auto-ignites often destroying a motor. You run more fuel to absorb some of that heat. Fuel is heavier than air. Running rich also costs you some power as during your power "stroke" the unburnt fuel absorbs some of the heat.
So I guess the answer is "maybe". With enough time, money, and effort, you can do just about anything. Where the line of what is practical and what is no longer a stock engine has yet to be seen.
Edit: I am an engineer but experience is so much more important than a college degree. I'm also bored at work.
So I guess the answer is "maybe". With enough time, money, and effort, you can do just about anything. Where the line of what is practical and what is no longer a stock engine has yet to be seen.
Edit: I am an engineer but experience is so much more important than a college degree. I'm also bored at work.
Last edited by maxxdamigz; 10-12-2006 at 01:37 PM.
10-12-2006, 04:28 PM
#32
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Originally Posted by MazdaManiac
Why do I keep seeing this junk about the "compression ratio" being a limiting factor - especially from seemingly knowledgable people?
The combustion process doesn't care how the charge got so dense - whether it is from static or dynamic compression inside or outside the combustion chamber.
More static compression just means less boost is needed to achieve the same combustion pressure.
The combustion process doesn't care how the charge got so dense - whether it is from static or dynamic compression inside or outside the combustion chamber.
More static compression just means less boost is needed to achieve the same combustion pressure.
10-12-2006, 06:17 PM
#33
The main advantage to low compression/high boost is it is safe - it is easier to pull boost on knock than lowering the static compresion.
However, that is mostly an OEM strategy do deal with owner knumbskullitude and bad gas.
For the aftermarket (where, presumably, the owner is at least aware of what he is putting in his tank and what the risks are), that kind of caution is counterproductive.
However, that is mostly an OEM strategy do deal with owner knumbskullitude and bad gas.
For the aftermarket (where, presumably, the owner is at least aware of what he is putting in his tank and what the risks are), that kind of caution is counterproductive.
10-13-2006, 05:23 PM
#34
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I dont see the problem.. Just port the intake so it close late.
By doing this you get higher CFM, lower CR and less pumping losses. Typical Miller cycle.
By doing this you get higher CFM, lower CR and less pumping losses. Typical Miller cycle.
10-13-2006, 11:03 PM
#40
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Originally Posted by zoom44
at least a few of us are saying the same thing. ive been saying the above in every one of these threads but people always argue with me.
)Don't you need to pump a greater volume of air/fuel into a low compression engine to reach the same pressure as a high compression engine at the time of ignition? It would seem to me that a high compression engine would require less volume to reach the same pressure.
If that is the case, then the low compression engine would have more potential to produce power because it has the greater air/fuel charge, albeit at the same pressure?
I am quite prepared to be wrong on this, its just something that I had in the back of my mind that needed straightening out.
Last edited by Rotorpsycho; 10-13-2006 at 11:54 PM.
10-14-2006, 09:56 PM
#41
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Originally Posted by Rotorpsycho
Ive been thinking about this (no, I'm not at all qualified to do so )
Don't you need to pump a greater volume of air/fuel into a low compression engine to reach the same pressure as a high compression engine at the time of ignition? It would seem to me that a high compression engine would require less volume to reach the same pressure.
If that is the case, then the low compression engine would have more potential to produce power because it has the greater air/fuel charge, albeit at the same pressure?
I am quite prepared to be wrong on this, its just something that I had in the back of my mind that needed straightening out.
)Don't you need to pump a greater volume of air/fuel into a low compression engine to reach the same pressure as a high compression engine at the time of ignition? It would seem to me that a high compression engine would require less volume to reach the same pressure.
If that is the case, then the low compression engine would have more potential to produce power because it has the greater air/fuel charge, albeit at the same pressure?
I am quite prepared to be wrong on this, its just something that I had in the back of my mind that needed straightening out.
That i why those large displacement motors make so much power with little boost. they got a lot of air/fuel to burn.
the lower is your compression, the more air/fuel you can push into the chamber without detonating it. it is that simple.
I an way, by decreasing the compression you are increasing the displacement.
Last edited by rotorocks; 10-14-2006 at 09:58 PM.
10-14-2006, 10:36 PM
#42
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something doesn't make sense here. If CR and boost give the same density of charge as Mazdamaniac points out, why wouldn't people just make N/A cars that have very long strokes, run like 16:1 compression and achieve the same horsepower as the equavelant turbo? Asides from the fact that you're reciprocating the mass more it would seem that would be better for the engine because that would be like having "static boost" in a high HP car.
(side question: is the longer stroke used in diesels for creating 20:1 comression what causes the high torque of diesels; because they have more movement of mass?)
maybe something to do with flame propogation at different pressures? Anyone a chemist?
Also, on Zoom's comment, how could a difference in compression NOT change power if power scales w/ pressure as Mazdamaniac said?
Very confused......
Actually
(side question: is the longer stroke used in diesels for creating 20:1 comression what causes the high torque of diesels; because they have more movement of mass?)
maybe something to do with flame propogation at different pressures? Anyone a chemist?
Also, on Zoom's comment, how could a difference in compression NOT change power if power scales w/ pressure as Mazdamaniac said?
Very confused......
Actually
10-14-2006, 10:45 PM
#43
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Wait, what rotorocks said makes to most sense yet.
Let's say 30 psi ignitioni compression:
N/A: all 30 PSI generated by stroke, giving mass X of charge at volume Y
cut compression in half, same chamber generates 15 psi by doubling length of chamber (probably actually a power law, but eh...)
Turbo: 15 psi boost, 15 psi stroke = 30 psi. Now mass 2X at volume 2Y. So you've doubled charge by 1/2 compression and adding boost.
HOWEVER: I may have dammed my own idea b/c how do you change CR w/o altering displacement due to stroke? Dammit! I'm still confused.
Let's say 30 psi ignitioni compression:
N/A: all 30 PSI generated by stroke, giving mass X of charge at volume Y
cut compression in half, same chamber generates 15 psi by doubling length of chamber (probably actually a power law, but eh...)
Turbo: 15 psi boost, 15 psi stroke = 30 psi. Now mass 2X at volume 2Y. So you've doubled charge by 1/2 compression and adding boost.
HOWEVER: I may have dammed my own idea b/c how do you change CR w/o altering displacement due to stroke? Dammit! I'm still confused.
10-14-2006, 11:04 PM
#44
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I Figured It Out!!!!!
Compression of gasses does follow a power law (Boyle's Law?), and therein lies the key.
To reduce the pressure of a highly compressed gas in a chamber would require only a small change in volume.....the equivalent of adding on a thick head gasket or whatever. So basically stroke doesnt change at all so your combustion stroke is the same regardless of pressure.
However, since boost happens on the intake stroke, it gets to take advantage of filling a very large chamber with ~15 psi of charge (a lot more fuel and air than N/A on intake). Then it compresses to an ALMOST IDENTICAL FINAL VOLUME to create identical pressure as the N/A setup, but this time with a hell of a lot more charge, and it gets to enjoy the same length of stroke. I'm guessing flame propogation is not drastically altered by pressure and thus what controls power is mass of charge and length of stroke (for two identical engine blocks)
Since the turbo gets more mass at a nearly identical stroke, it wins in power. It would seem that this would continue to make sense until you reached some breaking point in the power law curve. In english this means it makes damn good sense to lower compression in a boosted car as much as possible because that means you will just get to dump exponentially more charge in there for the same final pressure, up until some esoteric point that a chemist could figure out (4:1?)
Make sense everyone? Zoom44, Mazdamaniac, agree? disagree?
To reduce the pressure of a highly compressed gas in a chamber would require only a small change in volume.....the equivalent of adding on a thick head gasket or whatever. So basically stroke doesnt change at all so your combustion stroke is the same regardless of pressure.
However, since boost happens on the intake stroke, it gets to take advantage of filling a very large chamber with ~15 psi of charge (a lot more fuel and air than N/A on intake). Then it compresses to an ALMOST IDENTICAL FINAL VOLUME to create identical pressure as the N/A setup, but this time with a hell of a lot more charge, and it gets to enjoy the same length of stroke. I'm guessing flame propogation is not drastically altered by pressure and thus what controls power is mass of charge and length of stroke (for two identical engine blocks)
Since the turbo gets more mass at a nearly identical stroke, it wins in power. It would seem that this would continue to make sense until you reached some breaking point in the power law curve. In english this means it makes damn good sense to lower compression in a boosted car as much as possible because that means you will just get to dump exponentially more charge in there for the same final pressure, up until some esoteric point that a chemist could figure out (4:1?)
Make sense everyone? Zoom44, Mazdamaniac, agree? disagree?
10-15-2006, 02:52 AM
#45
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Originally Posted by flomulgator
Compression of gasses does follow a power law (Boyle's Law?), and therein lies the key.
To reduce the pressure of a highly compressed gas in a chamber would require only a small change in volume.....the equivalent of adding on a thick head gasket or whatever. So basically stroke doesnt change at all so your combustion stroke is the same regardless of pressure.
However, since boost happens on the intake stroke, it gets to take advantage of filling a very large chamber with ~15 psi of charge (a lot more fuel and air than N/A on intake). Then it compresses to an ALMOST IDENTICAL FINAL VOLUME to create identical pressure as the N/A setup, but this time with a hell of a lot more charge, and it gets to enjoy the same length of stroke. I'm guessing flame propogation is not drastically altered by pressure and thus what controls power is mass of charge and length of stroke (for two identical engine blocks)
Since the turbo gets more mass at a nearly identical stroke, it wins in power. It would seem that this would continue to make sense until you reached some breaking point in the power law curve. In english this means it makes damn good sense to lower compression in a boosted car as much as possible because that means you will just get to dump exponentially more charge in there for the same final pressure, up until some esoteric point that a chemist could figure out (4:1?)
Make sense everyone? Zoom44, Mazdamaniac, agree? disagree?
To reduce the pressure of a highly compressed gas in a chamber would require only a small change in volume.....the equivalent of adding on a thick head gasket or whatever. So basically stroke doesnt change at all so your combustion stroke is the same regardless of pressure.
However, since boost happens on the intake stroke, it gets to take advantage of filling a very large chamber with ~15 psi of charge (a lot more fuel and air than N/A on intake). Then it compresses to an ALMOST IDENTICAL FINAL VOLUME to create identical pressure as the N/A setup, but this time with a hell of a lot more charge, and it gets to enjoy the same length of stroke. I'm guessing flame propogation is not drastically altered by pressure and thus what controls power is mass of charge and length of stroke (for two identical engine blocks)
Since the turbo gets more mass at a nearly identical stroke, it wins in power. It would seem that this would continue to make sense until you reached some breaking point in the power law curve. In english this means it makes damn good sense to lower compression in a boosted car as much as possible because that means you will just get to dump exponentially more charge in there for the same final pressure, up until some esoteric point that a chemist could figure out (4:1?)
Make sense everyone? Zoom44, Mazdamaniac, agree? disagree?
Cheers flomulgator
10-15-2006, 03:10 AM
#46
The problem with your comparisons is that you are changing the displacement.
The only difference between high and low compression motors of the same displacement is the final volume.
The inital volume is the same.
So, you can stuff the same amout of air in either by whatever means you desire.
However, the high compression motor will have a higher intial pressure at combustion.
So, yes you can stuff more air/fuel into a lower compression motor to acheive the same initial pressure at combustion, but the amount of work done will be the same because of the pressure differential.
The lower differential also leads to poorer combustion and a lower effective VE.
Also, for drivabiility purposes, low static compression sucks off-boost.
BTW - the flame front speed is affected greatly by pressure.
The only difference between high and low compression motors of the same displacement is the final volume.
The inital volume is the same.
So, you can stuff the same amout of air in either by whatever means you desire.
However, the high compression motor will have a higher intial pressure at combustion.
So, yes you can stuff more air/fuel into a lower compression motor to acheive the same initial pressure at combustion, but the amount of work done will be the same because of the pressure differential.
The lower differential also leads to poorer combustion and a lower effective VE.
Also, for drivabiility purposes, low static compression sucks off-boost.
BTW - the flame front speed is affected greatly by pressure.
10-15-2006, 03:54 AM
#47
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Originally Posted by MazdaManiac
The problem with your comparisons is that you are changing the displacement.
The only difference between high and low compression motors of the same displacement is the final volume.
The inital volume is the same.
So, you can stuff the same amout of air in either by whatever means you desire.
However, the high compression motor will have a higher intial pressure at combustion.
So, yes you can stuff more air/fuel into a lower compression motor to acheive the same initial pressure at combustion, but the amount of work done will be the same because of the pressure differential.
The lower differential also leads to poorer combustion and a lower effective VE.
Also, for drivabiility purposes, low static compression sucks off-boost.
BTW - the flame front speed is affected greatly by pressure.
The only difference between high and low compression motors of the same displacement is the final volume.
The inital volume is the same.
So, you can stuff the same amout of air in either by whatever means you desire.
However, the high compression motor will have a higher intial pressure at combustion.
So, yes you can stuff more air/fuel into a lower compression motor to acheive the same initial pressure at combustion, but the amount of work done will be the same because of the pressure differential.
The lower differential also leads to poorer combustion and a lower effective VE.
Also, for drivabiility purposes, low static compression sucks off-boost.
BTW - the flame front speed is affected greatly by pressure.
Therefore:
I dont understand how more fuel/air at the same combustion pressure as less fuel/air will result in the same work done?
Displacement I thought was related to bore and stroke. If you were to (for example sake) reduce the stroke length to reduce compression you have created a lower compression motor without increasing displacement but allowing higher initial boost.
Zoom44 alludes to this kinda thing in this thread (compression/displacement) https://www.rx8club.com/series-i-tech-garage-22/displacment-100746/
Last edited by Rotorpsycho; 10-15-2006 at 04:30 AM.
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