why do these cars run so rich?
10-07-04, 06:15 PM
#1
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why do these cars run so rich?
I searched and got a ton of post on so many things so I am just asking directly.
that is the one thing I have hated about all my RX7's.
I would like to know why and what I can do about it if anything.
that is the one thing I have hated about all my RX7's.
I would like to know why and what I can do about it if anything.
10-07-04, 06:27 PM
#4
FB+FC=F-ME
Its because the rotary has a very long, thin combustion chamber,which by design is ineffecient.The sliding nature of the rotaries combustion cycle causes a lot of fuel to get piled up at the back of the chamber.This is the reason for the dual sparkplugs and the later "wasted spark" system used on the 2nd-3rd gen engines.If a set amount of fuel is inevitably going to be wasted,then more fuel has to be injected initially, to compensate for that.
Having a peripheral exhaust port doesnt help since all the unburned fuel at the back of the chamber is forced to go out the port,contributing to the extremely high exhaust temps and high smog levels.
The Renesis places its exhaust ports up a bit from the apex running surface so the heavy, wasted fuel mixture can bypass the exhaust port and be reused on the next cycle.This cuts down on the amount of fuel needed to feed the next cycle,plus reduces wasted fuel out the tailpipe.
Having a peripheral exhaust port doesnt help since all the unburned fuel at the back of the chamber is forced to go out the port,contributing to the extremely high exhaust temps and high smog levels.
The Renesis places its exhaust ports up a bit from the apex running surface so the heavy, wasted fuel mixture can bypass the exhaust port and be reused on the next cycle.This cuts down on the amount of fuel needed to feed the next cycle,plus reduces wasted fuel out the tailpipe.
Last edited by steve84GS TII; 10-07-04 at 06:31 PM.
10-07-04, 06:32 PM
#6
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The questions doesn't make any sense.
The cars do NOT normally run rich.
If yours is running rich, something is broken or out of adjustment.
If you're talking about why the engine eats so much gas, this really has nothing to do with running rich.
-Ted
The cars do NOT normally run rich.
If yours is running rich, something is broken or out of adjustment.
If you're talking about why the engine eats so much gas, this really has nothing to do with running rich.
-Ted
10-07-04, 06:41 PM
#7
FB+FC=F-ME
The amount of fuel/air actually burned in the chamber is of a normal mix ratio.But a lot of fuel is left unburned afterwards,because of the chamber design/operation.This the reason why the injectors are so large compared to comparably sized engines.The fuel/air mixture going into ther engine is fuel heavy,but the amount that is comsumed is an average ratio.The rest of the fuel is wasted because of the rotaries design.
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10-07-04, 06:44 PM
#8
I wish I was driving!
Originally Posted by steve84GS TII
The amount of fuel/air actually burned in the chamber is of a normal mix ratio.But a lot of fuel is left unburned afterwards,because of the chamber design/operation.This the reason why the injectors are so large compared to comparably sized engines.The fuel/air mixture going into ther engine is fuel heavy,but the amount that is comsumed is an average ratio.The rest of the fuel is wasted because of the rotaries design.
10-07-04, 07:59 PM
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Originally Posted by steve84GS TII
The amount of fuel/air actually burned in the chamber is of a normal mix ratio.But a lot of fuel is left unburned afterwards,because of the chamber design/operation.This the reason why the injectors are so large compared to comparably sized engines.The fuel/air mixture going into ther engine is fuel heavy,but the amount that is comsumed is an average ratio.The rest of the fuel is wasted because of the rotaries design.
?
hmmmm...who gave you this info
10-07-04, 08:05 PM
#10
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is there anyway to "lean out" the fuel air mixture so that not so much gas is left unburnt. other than getting an safc or soemthing along those lines . .
10-07-04, 08:12 PM
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Originally Posted by Dom_C
is there anyway to "lean out" the fuel air mixture so that not so much gas is left unburnt. other than getting an safc or soemthing along those lines . .
who the hell is saying the NA's don't run rich? I've seen lots and lots of info saying otherwise both on this forum and other websites/forums.
10-07-04, 08:19 PM
#12
I wish I was driving!
Originally Posted by locketine
who the hell is saying the NA's don't run rich? I've seen lots and lots of info saying otherwise both on this forum and other websites/forums.
Stock, they run stoich under cruise. Not rich, not lean, stoich. 14.5:1-14.7:1 Air fuel ratios.
Wanna talk WOT? I've got several datalog's from an NTK UEGO run via a FJO controller and EGT's logged via a RACEPAK system that show the N/A's don't excessively rich under WOT, what have you got other than threads filled with regurgitation? 12.2:1 - 13.0:1 AFR's aren't exactly what I would call excessively rich, especially for stock.
Yes, there is power to be gained be going leaner, but they are by no means excessively rich.
10-07-04, 08:38 PM
#13
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I guess people just don't keep their cars in spec. my car will eat half a tank in 30 minutes of above 5k driving, that's why I believed it, I guess it's time for a cleaning and blueprint of injectors.
10-07-04, 08:40 PM
#14
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Chamber geometry does have something to do with efficiency, but there are other factors involved.
If you calculate exhaust port timing, it's very radical versus most mass produced pistons engines.
This all affects BSFC.
A lot of the combustion power is wasted out the exhaust port.
This is where the newer RX-8 MSP-RE engine shines.
Due to the side port exhaust, a lot more of the combustion chamber is utilized, and efficiency is increased.
No, there is no way to lean out the fuel maps and still have the engine run anywhere near driveable.
You might gain 1 to 2mpg maximum before the engine hesitates noticably.
Addition of a CDI box can do this with minimal fuss.
-Ted
If you calculate exhaust port timing, it's very radical versus most mass produced pistons engines.
This all affects BSFC.
A lot of the combustion power is wasted out the exhaust port.
This is where the newer RX-8 MSP-RE engine shines.
Due to the side port exhaust, a lot more of the combustion chamber is utilized, and efficiency is increased.
No, there is no way to lean out the fuel maps and still have the engine run anywhere near driveable.
You might gain 1 to 2mpg maximum before the engine hesitates noticably.
Addition of a CDI box can do this with minimal fuss.
-Ted
10-07-04, 10:08 PM
#15
Originally Posted by RETed
No, there is no way to lean out the fuel maps and still have the engine run anywhere near driveable.
You might gain 1 to 2mpg maximum before the engine hesitates noticably.
Addition of a CDI box can do this with minimal fuss.
-Ted
You might gain 1 to 2mpg maximum before the engine hesitates noticably.
Addition of a CDI box can do this with minimal fuss.
-Ted
10-07-04, 10:13 PM
#16
Engine, Not Motor
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35MPG in an FC? Hell, I know Prius drivers who don't get that kind of mileage...Of course, the Prius sucks, so...
Anyway....
The main reason these cars "run rich" is because most of them are on crappy 12+ year old sensors. Replace with all new sensors and properly calibrate your TPS and it will make a world of difference. Anyone who has experienced a VERY low mileage 2nd gen or one with a properly tuned standalone knows what I'm talking about...
Anyway....
The main reason these cars "run rich" is because most of them are on crappy 12+ year old sensors. Replace with all new sensors and properly calibrate your TPS and it will make a world of difference. Anyone who has experienced a VERY low mileage 2nd gen or one with a properly tuned standalone knows what I'm talking about...
10-07-04, 10:35 PM
#17
I wish I was driving!
Originally Posted by Aaron Cake
35MPG in an FC? Hell, I know Prius drivers who don't get that kind of mileage...Of course, the Prius sucks, so...
Anyway....
The main reason these cars "run rich" is because most of them are on crappy 12+ year old sensors. Replace with all new sensors and properly calibrate your TPS and it will make a world of difference. Anyone who has experienced a VERY low mileage 2nd gen or one with a properly tuned standalone knows what I'm talking about...
Anyway....
The main reason these cars "run rich" is because most of them are on crappy 12+ year old sensors. Replace with all new sensors and properly calibrate your TPS and it will make a world of difference. Anyone who has experienced a VERY low mileage 2nd gen or one with a properly tuned standalone knows what I'm talking about...
10-08-04, 01:28 AM
#18
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Originally Posted by 1Revvin7
You lost me here. Even if you are talking about just n/a rx7s, this is not what I have found. A stock t2 gets what on the freeway? 20-22mpg? My t2 with haltech gets 30mpg... I believe an n/a with a cdi can get atleast 35+
Step on the brake once, and you're under 30mpg for sure...
Hell, if we're talking about ALL freeway driving, I'm sure this is possible.
But, how many of us drive like this?
Come on, this really isn't realistic, right?
-Ted
Last edited by RETed; 10-08-04 at 01:47 AM.
10-08-04, 01:33 AM
#19
Originally Posted by RETed
MAYBE 35...if all you do is drive at 80mph on the freeway.
Step on the brake once, and you're under 30mph for sure...
Hell, if we're talking about ALL freeway driving, I'm sure this is possible.
But, how many of us drive like this?
Come on, this really isn't realistic, right?
-Ted
Step on the brake once, and you're under 30mph for sure...
Hell, if we're talking about ALL freeway driving, I'm sure this is possible.
But, how many of us drive like this?
Come on, this really isn't realistic, right?
-Ted
10-08-04, 01:34 AM
#20
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Originally Posted by scathcart
Me.
Stock, they run stoich under cruise. Not rich, not lean, stoich. 14.5:1-14.7:1 Air fuel ratios.
Wanna talk WOT? I've got several datalog's from an NTK UEGO run via a FJO controller and EGT's logged via a RACEPAK system that show the N/A's don't excessively rich under WOT, what have you got other than threads filled with regurgitation? 12.2:1 - 13.0:1 AFR's aren't exactly what I would call excessively rich, especially for stock.
Yes, there is power to be gained be going leaner, but they are by no means excessively rich.
Stock, they run stoich under cruise. Not rich, not lean, stoich. 14.5:1-14.7:1 Air fuel ratios.
Wanna talk WOT? I've got several datalog's from an NTK UEGO run via a FJO controller and EGT's logged via a RACEPAK system that show the N/A's don't excessively rich under WOT, what have you got other than threads filled with regurgitation? 12.2:1 - 13.0:1 AFR's aren't exactly what I would call excessively rich, especially for stock.
Yes, there is power to be gained be going leaner, but they are by no means excessively rich.
10-08-04, 01:49 AM
#21
Lives on the Forum
I thought we were talking about getting the best mileage?
Are you guys trying to imply you get better gas mileage by leaning out the fuel delivery at WOT???
Think about that now...
-Ted
Are you guys trying to imply you get better gas mileage by leaning out the fuel delivery at WOT???
Think about that now...
-Ted
10-08-04, 02:04 AM
#22
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i'll bemildly tuning (s-afc) my 91 n/a in upcoming weeks/months; what are good air/fuel numbers to see across the board?
it'd be nice if someone used the graph above and made a realistic, ideal line for the air/fuel. i'd like to think i could lean it out quite a bit compared to the graph above (not sure how my current air/fuels would compare to that one).
it'd be nice if someone used the graph above and made a realistic, ideal line for the air/fuel. i'd like to think i could lean it out quite a bit compared to the graph above (not sure how my current air/fuels would compare to that one).
10-08-04, 03:04 AM
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Originally Posted by RETed
I thought we were talking about getting the best mileage?
Are you guys trying to imply you get better gas mileage by leaning out the fuel delivery at WOT???
Think about that now...
-Ted
Are you guys trying to imply you get better gas mileage by leaning out the fuel delivery at WOT???
Think about that now...
-Ted
Originally Posted by casio
i'll bemildly tuning (s-afc) my 91 n/a in upcoming weeks/months; what are good air/fuel numbers to see across the board?
it'd be nice if someone used the graph above and made a realistic, ideal line for the air/fuel. i'd like to think i could lean it out quite a bit compared to the graph above (not sure how my current air/fuels would compare to that one).
it'd be nice if someone used the graph above and made a realistic, ideal line for the air/fuel. i'd like to think i could lean it out quite a bit compared to the graph above (not sure how my current air/fuels would compare to that one).
Last edited by bingoboy; 10-08-04 at 03:08 AM.
10-08-04, 10:53 AM
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yea, i saw your graph and was like "damn that falls off." but at the same time, i'm not good with reading torque and picturing horsepower, so i cant estimate where your horsepower would fall off (though if i really wanted, i could do the same math formula over and over and get a good idea).
i hope to have the s-afc installed before i get to the dyno. in fact, there's not much reason for me to go before i install it. i have about 1100 miles on my rebuilt n/a, so i'm ready to get a bit of tuning done.
were you not worried about taking out fuel without being on the dyno? obviously there was some you could take out, but 20% is a lot. especially at a "catastrophic" rpm. i'm glad it worked for you, just curious as to how you got to those negative percentages on your safc. bit of trial and error ? guess and check ?
i hope to have the s-afc installed before i get to the dyno. in fact, there's not much reason for me to go before i install it. i have about 1100 miles on my rebuilt n/a, so i'm ready to get a bit of tuning done.
were you not worried about taking out fuel without being on the dyno? obviously there was some you could take out, but 20% is a lot. especially at a "catastrophic" rpm. i'm glad it worked for you, just curious as to how you got to those negative percentages on your safc. bit of trial and error ? guess and check ?