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.

 

Detonation = really bad for rotaries, so extra richness adds some safety to it. May be more to it though.

 

Rich = cooler motor
cooler motor last longer and runs smoother

 

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.

 

could be mis adjusted TPS. Or weak spark, or a few other things. But in general RX-7's run rich.

 

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 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.

 

In N/A applications, BSFC's aren't that far off their piston engine equivalents... so you're wrong on that one.

 

? hmmmm...who gave you this info

 

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 . .

 

there are some chips being sold on ebay that u can solder to ur ecu board that will supposedly do this. specifically for the s4NA's I believe.

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.

 

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.

 

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.

 

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

 

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+

 

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...

 

I've gotten 34mpg out of a GT, non-stock ECU.

 

MAYBE 35...if all you do is drive at 80mph on the freeway.
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

 

Good point. I was talking about OPTIMAL gas mileage, sorry I forgot to mention this. You are right my t2 gets 30 mpg on the freeway at a constant 60-70mph. Back to the beer.

 

with a cone filter, header, and freer flowing exhaust my NA hit 12:1 at 5.5k and was 10:1 by 8k rpms on the dyno with the wideband O2.

 

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

 

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).

 

we drive sports cars' live with it, u want to drive one then pay the price

 

hehehe, ok well while my car was in that rich state at WOT, i got maybe 17-18mpg on a city/highway tank after a tuneup and not too much throttlel. 25-26 on those road trips when i was back in cali. after getting an ignition box in there sometimes i'll see 19-20mpg on combined city/highway driving tanks.

i installed an SAFC after that, but never got back to the dyno. my 5k is around -10% i believe, with 7k at -15% now, and -20% at 8k. i don't shoot those wicked huge flames at 8k shifts anymore, but it still pops and puffs a hell of a lot, and i can feel it keep pulling rather than the torque curve falling off so terribly like that.

 

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 ?