Gas Mileage Improved - The Answer Youve Been Waiting For
10-17-05, 05:13 PM
#51
Rotary Enthusiast
Originally Posted by a3dcadman
Kento,
Good points!
re: Time. Let me clarify, I failed to mention that both engines working at similar rpm.
Another comparison would be that the reciprocal burns its fuel for approx 25% of the thermodynamic cycle where the rotary at the leading plug burns its fuel for approx 70% of the cycle and the trailing for approx 30% of the cycle. More time to burn the fuel, more heat, more energy output....
chuck
Good points!
re: Time. Let me clarify, I failed to mention that both engines working at similar rpm.
Another comparison would be that the reciprocal burns its fuel for approx 25% of the thermodynamic cycle where the rotary at the leading plug burns its fuel for approx 70% of the cycle and the trailing for approx 30% of the cycle. More time to burn the fuel, more heat, more energy output....
chuck
Regardless of bore/stroke ratio, if you are running the same road speed as a piston engined car (behind you), and he is turning 2/3 the rpms you are, then his pistons will have the same cycle time (secs) as each rotor face in your rx7 (I think that was Kento's point?). And Kento is correct that shape and are are the main chamber performance issues, not cycle time due to the 3 rev engine cycle.
But you will have to clarify your 25% vs (30%,70%) comparison. Does not sound right to me.
10-17-05, 06:57 PM
#52
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"actual displacement" should not be a real factor for this particular topic IF you are explaining thermodynamic properties of combustion engines in general. whether the engine is a two cycle 4 cycle, rotary, diesel, ethanol,normally aspiration, forced induction etc. thermodynamics explains that combustion engines will only attain 50% maximum efficiency due to loss in energy from heat and chemical reactions. whenever there exists an exothermic reaction (reactions in which there heat transfer exists) 100% total efficiency in terms of energy can never be attained. Friction and heat transfer do play a role in exothermic reaction part of the thermodynmic equation as Kento has explained.
In simple terms: internal combustion engines, no matter what shape, will always have energy and efficiency loss due to heat transfer.
now, if you are comparing the energy output in terms engine types, the rotary engine is very efficient in terms of getting the most energy out of the least amount of space, moving parts, combustion reactions and movement cycles. but that does not necessarily mean that you are getting the best milage efficiecy, as described by Klauss' explanation. but milage is excellent if you view it to the benefit of getting the most energy output per drop of gasoline, it's just the rate at which gasoline is consumed is faster. this comes back to how the engine was designed, what materials were used, the static equations for the epitrochoid etc. and the natural properties of the combustion reaction.
the term effieciency needs to be defined to the topic at had or else people will interject and miscontrue the whole subject. (although i maybe one of those people that have in this case...) the more variables you introduce to a problem or topic, the more complex the issue becomes to try to resolve the issue.
the displacement issue should not be introduced as it would definetely be another topic in comparisons in efficiency between other engine types.
if you get 24-25mpg with a forced induction rotary engine, woo hoo!!! that's great! the average mpg for vehicles in the US is less than 15mpg.
back to the original topic...
i have a twin power unit in my 2nd gen. I noticed a slight increase in milage, but it's more likely for maintaining milage than making milage since the car is getting old. rather, it was a positive by-product from the original reason why i installed one in to my car. i put on the twin power more for ignition efficiency rather than gas milage since i wanted to run higher boost with colder plugs. twin power does prevent spark knock at higher RPMs. work for me.
someone earlier in this thread said that if the ignition system is already running optimal, then you should get the best milage already. i agree, to a certain point. remember, the OE manufacturer will most likely run an A/F ratio on a more conservative for a factor of safety. generally the more dialed in you are on the optimal A/F ratio ( there will be different theories on this topic for sure but that's for another thread), your factor of saftey lessens. but again, no matter how well you target your A/F, the design of the engine will still limits you to a certain maximum which would probably never be as efficient in milage efficiency compared to a reciprocating engine.
iridium plugs are great, only if you match the correct plugs for your own application. they do infact last longer than platinums or stock. if you put too cold of a plug, you will definitely not have enough spark at low temps, therefore incomplete combustion, therefore wasting fuel, therefore having worse milage.
if the twin power works for you as a milage fixer upper, great! i am sure there are people who say they have experienced it as well, and there are others who will think it's snake oil.
my bad for the long as post... i was bored at work...
In simple terms: internal combustion engines, no matter what shape, will always have energy and efficiency loss due to heat transfer.
now, if you are comparing the energy output in terms engine types, the rotary engine is very efficient in terms of getting the most energy out of the least amount of space, moving parts, combustion reactions and movement cycles. but that does not necessarily mean that you are getting the best milage efficiecy, as described by Klauss' explanation. but milage is excellent if you view it to the benefit of getting the most energy output per drop of gasoline, it's just the rate at which gasoline is consumed is faster. this comes back to how the engine was designed, what materials were used, the static equations for the epitrochoid etc. and the natural properties of the combustion reaction.
the term effieciency needs to be defined to the topic at had or else people will interject and miscontrue the whole subject. (although i maybe one of those people that have in this case...) the more variables you introduce to a problem or topic, the more complex the issue becomes to try to resolve the issue.
the displacement issue should not be introduced as it would definetely be another topic in comparisons in efficiency between other engine types.
if you get 24-25mpg with a forced induction rotary engine, woo hoo!!! that's great! the average mpg for vehicles in the US is less than 15mpg.
back to the original topic...
i have a twin power unit in my 2nd gen. I noticed a slight increase in milage, but it's more likely for maintaining milage than making milage since the car is getting old. rather, it was a positive by-product from the original reason why i installed one in to my car. i put on the twin power more for ignition efficiency rather than gas milage since i wanted to run higher boost with colder plugs. twin power does prevent spark knock at higher RPMs. work for me.
someone earlier in this thread said that if the ignition system is already running optimal, then you should get the best milage already. i agree, to a certain point. remember, the OE manufacturer will most likely run an A/F ratio on a more conservative for a factor of safety. generally the more dialed in you are on the optimal A/F ratio ( there will be different theories on this topic for sure but that's for another thread), your factor of saftey lessens. but again, no matter how well you target your A/F, the design of the engine will still limits you to a certain maximum which would probably never be as efficient in milage efficiency compared to a reciprocating engine.
iridium plugs are great, only if you match the correct plugs for your own application. they do infact last longer than platinums or stock. if you put too cold of a plug, you will definitely not have enough spark at low temps, therefore incomplete combustion, therefore wasting fuel, therefore having worse milage.
if the twin power works for you as a milage fixer upper, great! i am sure there are people who say they have experienced it as well, and there are others who will think it's snake oil.
my bad for the long as post... i was bored at work...
10-18-05, 01:28 AM
#53
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hks fc3s,
You can be bad and bored all you want cause the info you provided is definitely great stuff. With regard to the twin power as a mileage fixer upper, for me the increased mileage that came with better performance was a nice benefit which was unexpected and welcome considering the escalating jump in fuel prices recently. The hks twinpower was installed to resolve the hi rpm breakup I was experiencing at stock boost levels and slightly higher.
thanks for you input
chuck
You can be bad and bored all you want cause the info you provided is definitely great stuff. With regard to the twin power as a mileage fixer upper, for me the increased mileage that came with better performance was a nice benefit which was unexpected and welcome considering the escalating jump in fuel prices recently. The hks twinpower was installed to resolve the hi rpm breakup I was experiencing at stock boost levels and slightly higher.
thanks for you input
chuck
10-18-05, 01:32 AM
#54
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"now, if you are comparing the energy output in terms engine types, the rotary engine is very efficient in terms of getting the most energy out of the least amount of space...."
Very True.
"... but that does not necessarily mean that you are getting the best milage efficiecy, as described by Klauss' explanation."
Also True.
".. but milage is excellent if you view it to the benefit of getting the most energy output per drop of gasoline, ..."
Trouble. This defines the BSFC (thermal) rating for the engine ... how many lbs fuel to get 1 hp at the crank. FD rating hovers near .6 (thirsty, not excellent), piston turbos range from .45 to .55, and na pistons below .45 (camel like).
---------------------------------------------
Twinpower will help mpgs in cars with an ign problem, but not all have that problem, so gains will be little in those cases.
Very True.
"... but that does not necessarily mean that you are getting the best milage efficiecy, as described by Klauss' explanation."
Also True.
".. but milage is excellent if you view it to the benefit of getting the most energy output per drop of gasoline, ..."
Trouble. This defines the BSFC (thermal) rating for the engine ... how many lbs fuel to get 1 hp at the crank. FD rating hovers near .6 (thirsty, not excellent), piston turbos range from .45 to .55, and na pistons below .45 (camel like).
---------------------------------------------
Twinpower will help mpgs in cars with an ign problem, but not all have that problem, so gains will be little in those cases.
10-18-05, 02:18 AM
#55
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hey kevink2,
If you are interested, heres a link to the article I mentioned earlier that covers a comparison of the rotary to the reciprocal engine. Its a pretty good general discussion of function and the pros and cons of the rotary. The question of what percentage of the cycle is devoted to burning the fuel, comparing rotary to recipro is covered as well.
http://www.tprmag.com/issue/11/11_rotary_1.shtml
Dont most basically stock fds experience this hi rpm breakup problem to some degree. My car is tuned and relatively new despite the fact that is a 93. I just turned 40,000 miles and got it less than 2 years ago with 19,000 miles. The engine has not been thrashed by the first owner or me and it has been kept very well maintained. This ignition breakup I had experienced is not due to a worn engine or engine components. My guess is that it was a result of a less than optimum stock igniton setup.
chuck
If you are interested, heres a link to the article I mentioned earlier that covers a comparison of the rotary to the reciprocal engine. Its a pretty good general discussion of function and the pros and cons of the rotary. The question of what percentage of the cycle is devoted to burning the fuel, comparing rotary to recipro is covered as well.
http://www.tprmag.com/issue/11/11_rotary_1.shtml
Dont most basically stock fds experience this hi rpm breakup problem to some degree. My car is tuned and relatively new despite the fact that is a 93. I just turned 40,000 miles and got it less than 2 years ago with 19,000 miles. The engine has not been thrashed by the first owner or me and it has been kept very well maintained. This ignition breakup I had experienced is not due to a worn engine or engine components. My guess is that it was a result of a less than optimum stock igniton setup.
chuck
10-18-05, 03:12 AM
#56
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kevinK2,
you are definitely right about the BSFC Thermal of approximately 0.6 on a ealier model FD 13b-rew engine with an 8 bit ecu processor.
But also please remember that the BSFC rating is much better with the middle model and late model FD engines that were offered in Japan that came with slightly better engine, drivetrain, and cooling components. not to mention that they came with 16bit processors and a refined base map for the stock ecu. also, the better octane levels and and more refined fuels offered in japan. the power rating on the japan model FD for the later models were at 280PS. (for argument's sake 1hp approximatley 1ps, in acutality 1ps=.99hp) the 280hp rating was a conservative number to advertise... the actual hp to the crank was acutally pushing close to 300hp. the final models that came out in the last year the FD was offered before being discontinued had 300+hp. (this also included the other J-super cars in Japan such as the the STI, EVO, GT-R and the Supra) therefore the BSFC should be approximately 10-15% better... there is a history behind the 280ps limit to japanese passenger vehicles, but that was probably covered in another thread somewhere. could be covered later if desired.
it's kind of hard to compare the FD rotary turbo engine to all piston engines in general... especially because mazda being the only manufacturer for the rotary engine in mass quanties in our current time, is being compared to ALL others! the arguement was for the most current rotary engine design as an internal combustion engine in general. if you consider the most optimal design of the rotary engine and the most optimal design of a reciprocating engine, then that's a different story and a whole new debate.
unfortunately there is no official measurements for response, therefore being subjective.... if response had a truely defined measurement to add to an engine's overall efficiency, then this debate would even more insteresting. well in my opinion at least.
yes i also totally agree with your last comment as well with the twin power.
BTW
i wish i had an FD like all y'all but i am still a die hard FC nut. hope that doesn't change my comments as being valid! (^_^)
you are definitely right about the BSFC Thermal of approximately 0.6 on a ealier model FD 13b-rew engine with an 8 bit ecu processor.
But also please remember that the BSFC rating is much better with the middle model and late model FD engines that were offered in Japan that came with slightly better engine, drivetrain, and cooling components. not to mention that they came with 16bit processors and a refined base map for the stock ecu. also, the better octane levels and and more refined fuels offered in japan. the power rating on the japan model FD for the later models were at 280PS. (for argument's sake 1hp approximatley 1ps, in acutality 1ps=.99hp) the 280hp rating was a conservative number to advertise... the actual hp to the crank was acutally pushing close to 300hp. the final models that came out in the last year the FD was offered before being discontinued had 300+hp. (this also included the other J-super cars in Japan such as the the STI, EVO, GT-R and the Supra) therefore the BSFC should be approximately 10-15% better... there is a history behind the 280ps limit to japanese passenger vehicles, but that was probably covered in another thread somewhere. could be covered later if desired.
it's kind of hard to compare the FD rotary turbo engine to all piston engines in general... especially because mazda being the only manufacturer for the rotary engine in mass quanties in our current time, is being compared to ALL others! the arguement was for the most current rotary engine design as an internal combustion engine in general. if you consider the most optimal design of the rotary engine and the most optimal design of a reciprocating engine, then that's a different story and a whole new debate.
unfortunately there is no official measurements for response, therefore being subjective.... if response had a truely defined measurement to add to an engine's overall efficiency, then this debate would even more insteresting. well in my opinion at least.
yes i also totally agree with your last comment as well with the twin power.
BTW
i wish i had an FD like all y'all but i am still a die hard FC nut. hope that doesn't change my comments as being valid! (^_^)
10-18-05, 09:16 AM
#57
Rotary Enthusiast
Originally Posted by a3dcadman
hey kevink2,
If you are interested, heres a link to the article I mentioned earlier that covers a comparison of the rotary to the reciprocal engine. Its a pretty good general discussion of function and the pros and cons of the rotary. The question of what percentage of the cycle is devoted to burning the fuel, comparing rotary to recipro is covered as well.
http://www.tprmag.com/issue/11/11_rotary_1.shtml
Dont most basically stock fds experience this hi rpm breakup problem to some degree. My car is tuned and relatively new despite the fact that is a 93. I just turned 40,000 miles and got it less than 2 years ago with 19,000 miles. The engine has not been thrashed by the first owner or me and it has been kept very well maintained. This ignition breakup I had experienced is not due to a worn engine or engine components. My guess is that it was a result of a less than optimum stock igniton setup.
chuck
If you are interested, heres a link to the article I mentioned earlier that covers a comparison of the rotary to the reciprocal engine. Its a pretty good general discussion of function and the pros and cons of the rotary. The question of what percentage of the cycle is devoted to burning the fuel, comparing rotary to recipro is covered as well.
http://www.tprmag.com/issue/11/11_rotary_1.shtml
Dont most basically stock fds experience this hi rpm breakup problem to some degree. My car is tuned and relatively new despite the fact that is a 93. I just turned 40,000 miles and got it less than 2 years ago with 19,000 miles. The engine has not been thrashed by the first owner or me and it has been kept very well maintained. This ignition breakup I had experienced is not due to a worn engine or engine components. My guess is that it was a result of a less than optimum stock igniton setup.
chuck
I've read this before. Jim Mederer is a chief engineer and cofounder of Racing Beat. Only issue I had was his suggestion that ~20 deg btdc was a significant timing limitation. That's crank degrees, which translates to 30 deg BTDC as far as the rotor's cycle. Not so bad.
The point he as making on burn cycle was that since 3 faces/pistons share the same spark plug, it will be exposed to hot power stroke gagses 3 x 25% or 75% of the time, vs 25% on a piston engine that does not share plugs or combustion chambers. It's no like there is more time to burn fuel than we already have discussed. He was talking about overheating/cooling the plugs.
My FD with intake and exhaust mods did not have high rpm ign problems with stock ignition. When I had a reman installed, I elected to go with Taylor cables as a maintenance move, and left the stock coils in. Top end is still fine.
10-18-05, 09:41 AM
#58
Rotary Enthusiast
Originally Posted by HKS FC3S
...... But also please remember that the BSFC rating is much better with the middle model and late model FD engines that were offered in Japan that came with slightly better engine, drivetrain, and cooling components. not to mention that they came with 16bit processors and a refined base map for the stock ecu. also, the better octane levels and and more refined fuels offered in japan. the power rating on the japan model FD for the later models were at 280PS. (for argument's sake 1hp approximatley 1ps, in acutality 1ps=.99hp) the 280hp rating was a conservative number to advertise... the actual hp to the crank was acutally pushing close to 300hp. the final models that came out in the last year the FD was offered before being discontinued had 300+hp. (this also included the other J-super cars in Japan such as the the STI, EVO, GT-R and the Supra) therefore the BSFC should be approximately 10-15% better...
http://www.rx7.net.nz/newrx7.htm
"BTW i wish i had an FD like all y'all but i am still a die hard FC nut."
At least you will not have to struggle with whether to go single or not!
FC's are nice, although when I test drove a new one, I thought the body style was somewhat "sampled" from the 944 ....
10-19-05, 12:15 AM
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boost increase was possible because of a better design in the rotor seals and the refined map using a 16bit ecu. i've seen japanese engineering articles (a magazine called jidousha kougaku) explaining the differences between the earlier, mid, and late models. nevertheless the differences enabled the increase in injector duty cycle as well as fuel pressure to support higer duty cycle to allow for more boost. You mentioned in your earlier post that the BSFC was a direct correlation to lbs of fuel per 1hp, and that was what my explanation was based upon.
the hp numbers that i was talking about were not what the maker advertised numbers were (280ps), but actual empirical numbers from experiments. unfortunately my argument can proabably go out the door because i don't have the actualy aritcles and conversations that i base my words upon. most of the info i got was from actual engine dyno numbers, talking to various tuners and actual mazda engineers from my old job...
but 1 thing is for sure. back when cars were said to be rated 280 Subaru at one point in time got in trouble by the gov't for marking their Impreza WRX STI (GC model i believe the ver.IV, 1 body style before the current) as 280ps, when it wheel dyno'd at 295. Similar situations with the GT-R and EVO 6 7 and 8 as well. the max 280 rule for japanese makers were based upon an unwritten sanction by the US after WWII to prevent the japanese to making engines powerful enough for airplanes. of course now that rule is now being ignored as the first advertised japanese passenger vehicle more than 280ps ( Honda Legend 300ps) at the end of 2004.
but i digress! and yes the body style was most likely influenced by the 944. i have not problem with that tho, since i think the FC is better looking and that design was based on PORCHE! FD's though are damn sexy no doubt.
the hp numbers that i was talking about were not what the maker advertised numbers were (280ps), but actual empirical numbers from experiments. unfortunately my argument can proabably go out the door because i don't have the actualy aritcles and conversations that i base my words upon. most of the info i got was from actual engine dyno numbers, talking to various tuners and actual mazda engineers from my old job...
but 1 thing is for sure. back when cars were said to be rated 280 Subaru at one point in time got in trouble by the gov't for marking their Impreza WRX STI (GC model i believe the ver.IV, 1 body style before the current) as 280ps, when it wheel dyno'd at 295. Similar situations with the GT-R and EVO 6 7 and 8 as well. the max 280 rule for japanese makers were based upon an unwritten sanction by the US after WWII to prevent the japanese to making engines powerful enough for airplanes. of course now that rule is now being ignored as the first advertised japanese passenger vehicle more than 280ps ( Honda Legend 300ps) at the end of 2004.
but i digress! and yes the body style was most likely influenced by the 944. i have not problem with that tho, since i think the FC is better looking and that design was based on PORCHE! FD's though are damn sexy no doubt.
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