My quest for better fuel milage
09-12-11, 10:41 AM
#52
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'active fuel management ' is an interesting fuel economy strategy used by a few OEM's
i have driven 25+ km on one rotor due to igniter fail and suffered no engine issues
( i have only dual igniter wasted leading DF ignition )
they don't shake massively like a blown rotor , but you are fully aware of the change in NVH
the one rotor operation was/is a feature of the decel /anti backfire/buck strategy in many production rotaries
however traditionally there is usually heavy enrichment on the rotor that runs
and you may find the result is almost counter productive to keep smooth while under load and not decel
you also will find a NA single rotor in a heavy car ( FC ! ) will struggle to maintain 90 kmh
it would be worthy of a look see at a workable result
but i think it may be a long path not in the realm of the stock ecu or with 2 rotors
but i think you gave mazda a great reason to build us all 3-4 rotor engines with active fuel management
------------
however lean burn tricks on an FC ECU are relatively easy
using the 5th gear switch
trip a pair of changeover relays to bypass the leading coil resister to hot the spark
and enable the lambda trim resister / rheostat
trip also a standard relay to enable the water injection
set up the water injection flow with a pill or valve and adjust the flow to control exhaust temps/ ignition beak-down point and adjust for the lambda trim ratio
am expecting the spark will give up after a point
and / or need a few tricks but you will get a reasonable result as there is much reserve in the FC NA ignition
( being the same ignition used on the turbo and capable of pushing reasonable boost )
i have driven 25+ km on one rotor due to igniter fail and suffered no engine issues
( i have only dual igniter wasted leading DF ignition )
they don't shake massively like a blown rotor , but you are fully aware of the change in NVH
the one rotor operation was/is a feature of the decel /anti backfire/buck strategy in many production rotaries
however traditionally there is usually heavy enrichment on the rotor that runs
and you may find the result is almost counter productive to keep smooth while under load and not decel
you also will find a NA single rotor in a heavy car ( FC ! ) will struggle to maintain 90 kmh
it would be worthy of a look see at a workable result
but i think it may be a long path not in the realm of the stock ecu or with 2 rotors
but i think you gave mazda a great reason to build us all 3-4 rotor engines with active fuel management
------------
however lean burn tricks on an FC ECU are relatively easy
using the 5th gear switch
trip a pair of changeover relays to bypass the leading coil resister to hot the spark
and enable the lambda trim resister / rheostat
trip also a standard relay to enable the water injection
set up the water injection flow with a pill or valve and adjust the flow to control exhaust temps/ ignition beak-down point and adjust for the lambda trim ratio
am expecting the spark will give up after a point
and / or need a few tricks but you will get a reasonable result as there is much reserve in the FC NA ignition
( being the same ignition used on the turbo and capable of pushing reasonable boost )
i just got an S5, and this is pre tune up, but it does the 1 rotor operation in town a lot, it'll only maintain about 20mph though, any more and it goes into normal 2 rotor operating
09-12-11, 06:25 PM
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09-12-11, 08:40 PM
#57
Wow, lots more good information here since I posted last!!
OK so to answer some stuff-
The mirrors WERE a bad idea- lol. I can see cars that are aside & behind me, but they go out of vision after dropping back about 3 car lengths. 99% of the time this isn't a bad thing, but in the rare time that someone's hauling *** up from behind in another lane, you'll have NO idea unless you turn around. It's kindof like riding a bicycle w/ no mirrors... feasible, and not a big deal, but sucks in any kind of traffic. Will be going back to the T2 mirrors, so I'm glad I didn't do anything that's irreversible.
When I rebuilt my engine, I actually swapped to a manual rack. My power rack was poorly depowered and had a TON of play in it. Worse than anything I'd ever driven. And the pump/bracket/lines were all absent as well. The 3 other 7's I'd owned before were manual, so I would prefer to keep the tradition alive
I also had the injectors cleaned and tested about 8k miles ago, so they're fresh.
Hozzman- you know you're totally right about the speedo, damn mine is off. I was next to a new civic today (06? plus), as a friend showed me that they're "rolling calibrators" with their GIANT digi speed readout. At 70 mph on my speedometer, the civics shows 66. I've swapped transmissions a few times, but dumped the original, so I don't have a gear for it. Shouldn't be tough to find one though.
My interior is super mint, so I'd rather keep it all there. That, AC, and the enkeis are the only things staying for sure, lol.
The talk about going into lean burn & single rotor operation has really got to be a way to go! This may become my post graduation project. On track for Dec '11, doing mechanical engineering.
OK so to answer some stuff-
The mirrors WERE a bad idea- lol. I can see cars that are aside & behind me, but they go out of vision after dropping back about 3 car lengths. 99% of the time this isn't a bad thing, but in the rare time that someone's hauling *** up from behind in another lane, you'll have NO idea unless you turn around. It's kindof like riding a bicycle w/ no mirrors... feasible, and not a big deal, but sucks in any kind of traffic. Will be going back to the T2 mirrors, so I'm glad I didn't do anything that's irreversible.
When I rebuilt my engine, I actually swapped to a manual rack. My power rack was poorly depowered and had a TON of play in it. Worse than anything I'd ever driven. And the pump/bracket/lines were all absent as well. The 3 other 7's I'd owned before were manual, so I would prefer to keep the tradition alive
I also had the injectors cleaned and tested about 8k miles ago, so they're fresh.
Hozzman- you know you're totally right about the speedo, damn mine is off. I was next to a new civic today (06? plus), as a friend showed me that they're "rolling calibrators" with their GIANT digi speed readout. At 70 mph on my speedometer, the civics shows 66. I've swapped transmissions a few times, but dumped the original, so I don't have a gear for it. Shouldn't be tough to find one though.
My interior is super mint, so I'd rather keep it all there. That, AC, and the enkeis are the only things staying for sure, lol.
The talk about going into lean burn & single rotor operation has really got to be a way to go! This may become my post graduation project. On track for Dec '11, doing mechanical engineering.
09-12-11, 09:39 PM
#60
op, you dont want to raise the idle using a throttle bypass (bac valve). From my experience, factory closed loop is activated under these conditions:
TPS above 0 %
rpms below 3500
load under 0 psi (not sure what the cutover is for n/a)
when you stay on the throttle while idling, you are keeping TPS above 0%, so the ecu thinks you are cruising and stays in closed loop. if you want to stay in closed loop at idle, try misadjusting your TPS so that it never goes below the threshold (im not exactly sure what it is, experimentation is needed). There may be a minimum RPM threshold too, but just using bac valve alone to raise idle will not keep you in closed loop. problem with this is you will never go into decel fuel cut, which will also waste gas
from my experience, as others have mentioned the biggest difference in mpg is weight and, at higher speeds, aerodynamics. shedding weight will make the biggest difference. timing also, but since you dont have a standalone that will be difficult.
if you do have standalone, the timing is key. I noticed a mpg difference just changing split from +5 to 0 degrees. if i keep it at around 55 mph, i get around 30mpg. this is a streetported S4 turbo. I I run about 30deg adv at 3krpm, 0 split, closed loop fuel. expect better with high comp rotors
some other things i wanted to try is electric water pump and throttle dependent accessories.. im thinking you could ditch the thermostat, and use water pump speed as temp control. activate the alternator and a/c only under cruise and decel. but yeah my next engine build im going high comp rotors with water injection to have best of both worlds.. reliable power and economy
TPS above 0 %
rpms below 3500
load under 0 psi (not sure what the cutover is for n/a)
when you stay on the throttle while idling, you are keeping TPS above 0%, so the ecu thinks you are cruising and stays in closed loop. if you want to stay in closed loop at idle, try misadjusting your TPS so that it never goes below the threshold (im not exactly sure what it is, experimentation is needed). There may be a minimum RPM threshold too, but just using bac valve alone to raise idle will not keep you in closed loop. problem with this is you will never go into decel fuel cut, which will also waste gas
from my experience, as others have mentioned the biggest difference in mpg is weight and, at higher speeds, aerodynamics. shedding weight will make the biggest difference. timing also, but since you dont have a standalone that will be difficult.
if you do have standalone, the timing is key. I noticed a mpg difference just changing split from +5 to 0 degrees. if i keep it at around 55 mph, i get around 30mpg. this is a streetported S4 turbo. I I run about 30deg adv at 3krpm, 0 split, closed loop fuel. expect better with high comp rotors
some other things i wanted to try is electric water pump and throttle dependent accessories.. im thinking you could ditch the thermostat, and use water pump speed as temp control. activate the alternator and a/c only under cruise and decel. but yeah my next engine build im going high comp rotors with water injection to have best of both worlds.. reliable power and economy
09-13-11, 08:15 AM
#62
op, you dont want to raise the idle using a throttle bypass (bac valve). From my experience, factory closed loop is activated under these conditions:
TPS above 0 %
rpms below 3500
load under 0 psi (not sure what the cutover is for n/a)
when you stay on the throttle while idling, you are keeping TPS above 0%, so the ecu thinks you are cruising and stays in closed loop. if you want to stay in closed loop at idle, try misadjusting your TPS so that it never goes below the threshold (im not exactly sure what it is, experimentation is needed). There may be a minimum RPM threshold too, but just using bac valve alone to raise idle will not keep you in closed loop. problem with this is you will never go into decel fuel cut, which will also waste gas
from my experience, as others have mentioned the biggest difference in mpg is weight and, at higher speeds, aerodynamics. shedding weight will make the biggest difference. timing also, but since you dont have a standalone that will be difficult.
if you do have standalone, the timing is key. I noticed a mpg difference just changing split from +5 to 0 degrees. if i keep it at around 55 mph, i get around 30mpg. this is a streetported S4 turbo. I I run about 30deg adv at 3krpm, 0 split, closed loop fuel. expect better with high comp rotors
some other things i wanted to try is electric water pump and throttle dependent accessories.. im thinking you could ditch the thermostat, and use water pump speed as temp control. activate the alternator and a/c only under cruise and decel. but yeah my next engine build im going high comp rotors with water injection to have best of both worlds.. reliable power and economy
TPS above 0 %
rpms below 3500
load under 0 psi (not sure what the cutover is for n/a)
when you stay on the throttle while idling, you are keeping TPS above 0%, so the ecu thinks you are cruising and stays in closed loop. if you want to stay in closed loop at idle, try misadjusting your TPS so that it never goes below the threshold (im not exactly sure what it is, experimentation is needed). There may be a minimum RPM threshold too, but just using bac valve alone to raise idle will not keep you in closed loop. problem with this is you will never go into decel fuel cut, which will also waste gas
from my experience, as others have mentioned the biggest difference in mpg is weight and, at higher speeds, aerodynamics. shedding weight will make the biggest difference. timing also, but since you dont have a standalone that will be difficult.
if you do have standalone, the timing is key. I noticed a mpg difference just changing split from +5 to 0 degrees. if i keep it at around 55 mph, i get around 30mpg. this is a streetported S4 turbo. I I run about 30deg adv at 3krpm, 0 split, closed loop fuel. expect better with high comp rotors
some other things i wanted to try is electric water pump and throttle dependent accessories.. im thinking you could ditch the thermostat, and use water pump speed as temp control. activate the alternator and a/c only under cruise and decel. but yeah my next engine build im going high comp rotors with water injection to have best of both worlds.. reliable power and economy
My father's told me there are O2 sensors w/ heated elements inside, to get them up to reading temperature faster, and I wondered if anyone had put them in FC's, and if it would indeed go into closed loop quicker? I found a few pieces of interest:
http://www.rx7.org/Robinette/o2_sensor.htm seems alot of race FD guys install them, as the heated element allows the use of race fuel containing lead. Non-heated O2s tend to foul out from the lead VERY fast. Looks like Napa part # OS204, for an 86 Ford Escort.
I also found this thread in searching: https://www.rx7club.com/3rd-generation-specific-1993-2002-16/best-o2-sensor-use-430044/
In particular, post #9 was of value to me: "Not sure on the FD, but on the FC the ECU would use the O2 sensor's output as soon as it was heated up and in range, even if the engine was still cold. In theory, this could help fuel economy."
Maybe the heated element wire will eliminate the 5 minute wait time to get into closed loop? Anyone here have thoughts? I'm anxious to try it out, may even pick one up on the way back from class.
GXL90RX7- 30 on a ported turbo is insane. This proves how "safe" the stock computer ran the AFR's! Thanks for the info, you've definitely giving me an excuse to go turbo in the future.
09-13-11, 08:43 AM
#63
Carbs are simple, eliminate unnecessary wiriring and sensors that could fail, and you don't need a laptop (with m$oft windoze) and ecu tuner and ecu and a degree to tune it. They do just fine. Rb hasn't provided any mpg numbers, but rotary shack says their custom kits can get up to 30+ highway. Might want to inquire. It's an option.
09-13-11, 09:36 AM
#64
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Carbs are simple, eliminate unnecessary wiriring and sensors that could fail,
And there's just so much about an EFI system that fails, all the time. I mean, just look at the posts on this forum. EFI parts are failing every minute...there's post after post after post about....uh, the TPS going out of adjustment on a 20+ year old system?
and you don't need a laptop (with m$oft windoze)
and ecu tuner
and ecu and a degree to tune it.
They do just fine. Rb hasn't provided any mpg numbers, but rotary shack says their custom kits can get up to 30+ highway. Might want to inquire. It's an option.
And then at WOT, drop back to AFRs and timing that are going to both give maximum power and fuel economy, also wideband corrected in real time?
And then at idle, automatically seek out the leanest mixture to maximize idle fuel economy as well?
09-13-11, 09:50 AM
#65
Sure, there are some components on the 20+ year old EFI systems (which was relatively new in 198x) that are prone to failure because of hundreds of thousands of miles of heat and weather, but really in the long run, there have been far less EFI system problems than ever on carburetors.
The only advantage of carburetors is for people who are scared by wires and circuits. FI works at a higher fuel pressure, therefore better fuel atomization, therefore a more complete combustion of fuel. Also, those pesky sensors provide feedback to constantly adjust for different conditions, as Aaron already said. With a carburetor, the best you can hope for is a local ballpark, then it has absolutely zero feedback to make any adjustment. I'd much rather have a system that works on actual conditions, rather than pre-set adjustments made back when the carburetor was installed, and that applies to both HP and economy.
By the way, I have no degree. And I tune my own ECU (which cost NEW less than $450, including wiring harness and sensors) with a $20 laptop and a free tuning software...
The only advantage of carburetors is for people who are scared by wires and circuits. FI works at a higher fuel pressure, therefore better fuel atomization, therefore a more complete combustion of fuel. Also, those pesky sensors provide feedback to constantly adjust for different conditions, as Aaron already said. With a carburetor, the best you can hope for is a local ballpark, then it has absolutely zero feedback to make any adjustment. I'd much rather have a system that works on actual conditions, rather than pre-set adjustments made back when the carburetor was installed, and that applies to both HP and economy.
By the way, I have no degree. And I tune my own ECU (which cost NEW less than $450, including wiring harness and sensors) with a $20 laptop and a free tuning software...
09-13-11, 10:14 AM
#66
i run into far more carburetion issues than with EFI, carbs are junk collectors and where does the junk go from the float? right into the jets.. carbs are inefficient because they are poor fuel atomizers, the more fine the mist of fuel is, the cleaner it burns, which is why EFI is superior and gets better fuel mileage.
a quick lesson in fuel combustion:
liquid fuel is not what burns, the vapor that fuel gives off is what burns. so for efficiency the closer you get the fuel to a true vapor form, the better it will yield for economy. carburetors basically shoot a stream of fuel into the intake throat, which eventually somewhat vaporizes, injectors spray a fine mist which is much closer to a vapor form than a stream of fuel. even closer yet is direct port injection, like diesels, which spray the fuel directly into the combustion chamber and atomize it instantly. direct injection is VERY costly because of the pressures involved, direct injection systems run anywhere from 1,000psi to 10,000psi or higher(several thousand psi can cut off limbs if even a pinhole fracture exposes in the system so they must be VERY well built and the pump takes alot of abuse, which is why newer diesels with the higher pressure have so many fuel pump problems).
but you simply can't adapt that concept, higher fuel pressure in an EFI system does not = more power and mileage. moving the injectors further down the system and atomizing it more comprehensively does.
some people have claimed to have built carburetors that atomize so efficiently that they can get better fuel mileage than EFI and even direct port injection, yet you don't see those carbs out there. because they were based off of conspiracy theory lies. someone in a garage in some small town builds a car that gets 100mpg, where dozens of factories paying millions to develop better fuel economy cars cannot, i simply call it BS from someone trying to get attention.
a quick lesson in fuel combustion:
liquid fuel is not what burns, the vapor that fuel gives off is what burns. so for efficiency the closer you get the fuel to a true vapor form, the better it will yield for economy. carburetors basically shoot a stream of fuel into the intake throat, which eventually somewhat vaporizes, injectors spray a fine mist which is much closer to a vapor form than a stream of fuel. even closer yet is direct port injection, like diesels, which spray the fuel directly into the combustion chamber and atomize it instantly. direct injection is VERY costly because of the pressures involved, direct injection systems run anywhere from 1,000psi to 10,000psi or higher(several thousand psi can cut off limbs if even a pinhole fracture exposes in the system so they must be VERY well built and the pump takes alot of abuse, which is why newer diesels with the higher pressure have so many fuel pump problems).
but you simply can't adapt that concept, higher fuel pressure in an EFI system does not = more power and mileage. moving the injectors further down the system and atomizing it more comprehensively does.
some people have claimed to have built carburetors that atomize so efficiently that they can get better fuel mileage than EFI and even direct port injection, yet you don't see those carbs out there. because they were based off of conspiracy theory lies. someone in a garage in some small town builds a car that gets 100mpg, where dozens of factories paying millions to develop better fuel economy cars cannot, i simply call it BS from someone trying to get attention.
Last edited by RotaryEvolution; 09-13-11 at 10:24 AM.
09-13-11, 11:14 AM
#67
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I don't see how fuel injection is superior in every way. It has been mainly adopted due to emission regulations in my eyes.
Carbs are simple, eliminate unnecessary wiriring and sensors that could fail, and you don't need a laptop (with m$oft windoze) and ecu tuner and ecu and a degree to tune it. They do just fine. Rb hasn't provided any mpg numbers, but rotary shack says their custom kits can get up to 30+ highway. Might want to inquire. It's an option.
Carbs are simple, eliminate unnecessary wiriring and sensors that could fail, and you don't need a laptop (with m$oft windoze) and ecu tuner and ecu and a degree to tune it. They do just fine. Rb hasn't provided any mpg numbers, but rotary shack says their custom kits can get up to 30+ highway. Might want to inquire. It's an option.
I know that your saying carbies are nice and simple - sure they are, you can tune it with a box of jets, another box of emulsion tubes, air correction jets, a dyno, AFR gauge, a few screw drivers, and a whole weekend!
So now you have your carby running well, how do you do your timing? Distributor, thats how.
Distributors are the worst bloody things on the planet, and if you say something like "Electronic distributors are much better" NO THEY ARE NOT!!
They still use springs and vacuum to try figure out whats going on inside the motor.
Prime example.
My suzuki swift runs carby and dizzy.
the PO got it tuned with a broken thermostat, and the car is always running cold. Today in traffic i finally got the car up to operating temp, and the bloody thing detonated its head off untill i got the temp back down!
If i had a computer running the show, it would have known that i was pinging, and backed the timing off.
Dont even get me started on bloody automatic chokes!!
Last edited by tlmitf; 09-13-11 at 11:18 AM.
09-13-11, 12:04 PM
#69
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09-13-11, 03:07 PM
#70
Jesus is the Messiah
Adjusting the nut behind the wheel is the best improvement to MPG usually.
So you'll need gauges to help you make decisions.
You've already got something like an AFR, next you might want a vac gauge.
I highly recommend getting a real-time mileage calculator like the MPGuino.
The best MPG I ever tagged was an average 32MPG on my megasquirted 'vert - all highway with the top down and average speed of 65mph. That was with MS1. 16.2:1 on some spots on cruise.
The stock computer runs pretty rich in even in closed loop, esp with the outside air being mixed in on some of our cars. (13.8 or so with outside air)
Ditch the SAFC option, I gag whenever I read that, esp in reference to MPG.
Now with the newer MSs you can set up timed injection to better "shape" the intake charge, play with negative timing split, and go full sequential injection instead of batch. Those kinds of changes can really help that hard to improve city MPG, as well as smoothing out the overall feeling of the engine.
MS is not the only ECU that can do this kind of stuff, it's just the one that I use.
Combining this with full timing control and a non-restrictive exhaust, and you'll see same the gains I did.
So you'll need gauges to help you make decisions.
You've already got something like an AFR, next you might want a vac gauge.
I highly recommend getting a real-time mileage calculator like the MPGuino.
The best MPG I ever tagged was an average 32MPG on my megasquirted 'vert - all highway with the top down and average speed of 65mph. That was with MS1. 16.2:1 on some spots on cruise.
The stock computer runs pretty rich in even in closed loop, esp with the outside air being mixed in on some of our cars. (13.8 or so with outside air)
Ditch the SAFC option, I gag whenever I read that, esp in reference to MPG.
Now with the newer MSs you can set up timed injection to better "shape" the intake charge, play with negative timing split, and go full sequential injection instead of batch. Those kinds of changes can really help that hard to improve city MPG, as well as smoothing out the overall feeling of the engine.
MS is not the only ECU that can do this kind of stuff, it's just the one that I use.
Combining this with full timing control and a non-restrictive exhaust, and you'll see same the gains I did.
09-13-11, 04:51 PM
#71
yeah closed loop should activate in under 3 seconds from open loop condition, once warmed up. back when i was running the factory ecu, then only thing that would keep it from going in closed loop, other than what i mentioned above, was very light throttle.. for some reason the AFRs would drop into 10's just before decel fuel cut. but it would go right back into closed loop easily
i wish i could experiment with negative split but the e6k only goes down to zero split
i wish i could experiment with negative split but the e6k only goes down to zero split
09-13-11, 06:05 PM
#72
S4 NA, using the pressure sensor, Lo-Hi changeover at 70% "Throttle", -7% correction on Lo-Thr 0-3600RPM, 0% correction on Hi-Thr.
Overall on the tanks I usually get 2-3MPG more, and manage 300mi per tank.
09-13-11, 06:15 PM
#73
I'm curious as to why not? I've been running an SAFC2 for around 5 months and it's certainly helped my fuel economy..
S4 NA, using the pressure sensor, Lo-Hi changeover at 70% "Throttle", -7% correction on Lo-Thr 0-3600RPM, 0% correction on Hi-Thr.
Overall on the tanks I usually get 2-3MPG more, and manage 300mi per tank.
S4 NA, using the pressure sensor, Lo-Hi changeover at 70% "Throttle", -7% correction on Lo-Thr 0-3600RPM, 0% correction on Hi-Thr.
Overall on the tanks I usually get 2-3MPG more, and manage 300mi per tank.
09-13-11, 06:32 PM
#74
^_^" I did forget a couple little details on my setup.. I started using the SAFC on my old [totally stock S4] engine, and I wasn't keeping track of the economy at the time, but I was getting close to 300/tank.
About a month after I got the SAFC, I lost a coolant channel [I'd just done the vinegar coolant system trick, which pushed it over the edge..] So the engine was rebuilt with better condition S4NA plates, 77K mi FD housings [32% less friction, no exhaust diffusers], brand new Atkins apex seals/springs, and S5 NA rotors.
Exhaust is a FULL Racing Beat NA system [Collected header-Presilencer-catback]
So, there are a couple other tricks, but I was running the SAFC past -10% on the old engine for similar economy.
About a month after I got the SAFC, I lost a coolant channel [I'd just done the vinegar coolant system trick, which pushed it over the edge..] So the engine was rebuilt with better condition S4NA plates, 77K mi FD housings [32% less friction, no exhaust diffusers], brand new Atkins apex seals/springs, and S5 NA rotors.
Exhaust is a FULL Racing Beat NA system [Collected header-Presilencer-catback]
So, there are a couple other tricks, but I was running the SAFC past -10% on the old engine for similar economy.