a3dcadman

iTrader: (1)

Part of my motivation for this thread was to find out what others are doing to get better gas mileage while improving their power output.

Are there any other members that have seen positive differences in their mpg after installing the twin power?

chuck

jpandes

If you had a Power FC, you could just turn off the O@ feedback control and tune for 15-17 AFR's. I just datalogged my 45 min commute to work and retuned for 16.3 AFR's in the cruise section. Let's see if I can break 20 MPG in mixed driving...

mibad

I drive the FD for fun, If I wanted to save fuel, I'd drive a Honda.

scotty305

iTrader: (2)

Don't take the "you've gotta pay to play" idea too far. The way I think of it, $1000 saved on fuel is $1000 I can spend on tires and suspension.




Hyperite, do the leaner A/F ratios affect your temperatures adversely? Are you measuring EGT's and such?


-s-

rotarypower101

iTrader: (1)

very subtle Klaus, thanks for a well thought out O2 solution. Enjoy the ease and flexibility every time I get in the car.

adam c

iTrader: (2)

I guess that is your answer. With a properly running ignition, and no other changes, gas mileage is unchanged with the twin power.

dubulup

maybe this is where a MSD (multi spark discharge) amp steps to the plate.

under 3k, you get radid fire (3) hits...and above just one big bang. cleaner burn = not as much fuel needed

a3dcadman

iTrader: (1)

PLEASE NOTE:
phe·nom·e·non ( P ) Pronunciation Key (f-nm-nn, -nn)
n. pl. phe·nom·e·na (-n)
An occurrence, circumstance, or fact that is perceptible by the senses.
pl. phe·nom·e·nons
An unusual, significant, or unaccountable fact or occurrence; a marvel.

Regarding the 20,000 mile ecu "reset". When my car passed the 20k point, I did not detect any differences other than how it started on cold mornings - the idle speed was different during initial warmup - perhaps a/f difference and/or a throttle linkage component (anti-stall dashpot) function was working differently . Another difference was the 3000 rpm stutter when cold was starting to manifest itself occasioally. Other than these symptoms there were no other perceptible differences.
chuck

Sgtblue

iTrader: (16)

^ALSO NOTE:
Pseudo-, combining form: False; adj. a false form; sham; pretended.
Intellect, a great intelligence, high mental ability

***, figurative a stupid, silly, or stubborn person; fool

Hyperite

In an FD, yes...but not boosting. Highway driving purely for the test of gas mileage maximization. With that tune, I was averaging around 27 MPG with normal driving (ie- NOT ***** out racing)

a3dcadman

iTrader: (1)

Thanks for your positive input re: improving power and gas mileage.

I dont find it challenging to duel with an unarmed man but since you find it necessary to cast aspersions on my otherwise impeccable character, I will say this. I dont recall any references made to words pseudo or *** being used anywhere in this thread. Where did you pull those words out of, your *** perhaps, amazing there was room since you seem to be so full of "it", and most should know what "it" is. I also have to ask, is your avatar indicative of your pseudo reality as a wanna be police officer or are you just a real life pig who acts like an ***.

If you have something worthwhile to add to this thread or something showing some level of imagination or intelligence then please do so. I realize that you will probably have to dig deep and have a dictionary nearby, but I do welcome positive feedback.

chuck

a3dcadman

iTrader: (1)

Hey dubulup do you have msd ignition on your 7? Ive used the msd on my boat engine and did get more power thru the rpm range but had no way to judge mpg.

Is there anyone else that has an msd on their engine that has seen more power and better mpg?

Anybody using other ignition systems that may have some input on their power and mpg.

Turbojeff had stated "why wouldnt mazda have spent the extra money on better ignition if there were gains in mpg, since mileage was an issue". Good question, especially since there are others including myself that have seen significant gains.

chuck

chuck

klatinn

Hi,

Adding $0.02 regarding fuel saving with an internal combustion engine in respect to AFRs:

Typical max power is achieved between 12 and 13.5 AFR (piston engine) because that's where flame-front speed maxes out. This therefore requires the lowest ign. advance to hit peak cyl. pressure at the optimum point. Running richer is sometimes neccessary for thermal reasons (lower combustion temps reduce thermally induced knock, but too much advance can cause pressure induced knock).

Min. emissions (minimum CO, NO and HC) is at stoich (14.7).

Best BSFC (brake specific fuel consumption) is typically achieved at 15.2 - 15.4 AFR (may be different for rotaries, could not find any literature for that). This is the point where you create the most hp/hr per pound of fuel burned.

As you need to produce about 20-30 hp when cruising down the highway, you achive best fuel economy when running at best BSFC.
Running leaner means more throttle and HIGHER fuel consumption.

Max CHT (cylinder head temp) is reached at just a tad rich of stoich. EGTs max out at stoich and fall off quickly when leaner. Temps fall slower on the rich side.

All this assumes of course that ign. timing is optimized for each running condition at MBT (minimum best timing). To run leaner, a slight ign. advance is needed for that compared to running at stoich.

With an LC-1 you can of course simulate a Narrowband sensor with a switchpoint at 15.2 -15.4 instead of 14.7. This will allow to run at best BSFC in idle and cruise. You won't pass smog (NOx emissions higher) and throttle response might be reduced, but you will run cooler than at 14.7.

One of our customers did that test on an F350 truck when towing. His fuel milage reportedly increased from about 11 mpg to ~13 mpg, which would be a larger increase than I expected. I assume at the high partial load he was running (towing), his ign. was knock retarded at stoich and with cooler temps on the lean side it adapted to closer to MBT.
Your milage may vary.

Re: ignition systems and effect on fuel consumption. This will only have an effect if you run into the lean burn limit where the mixture is hard to ignite. At the best BSFC point it should have no effect.

Regards,
Klaus

Hyperite

FYI Klaus, a bunch of that stuff you said kinda goes out the door when you change airflow, aka- have no emissions equipment.

klatinn

Hi Hyperite,

No it doesn't. The numbers I cited were from NACA research on aircraft piston engines, confirmed with our own testing (no emissions equipment). The physics and combustion chemistry is the same for car engines. Changing airflow just means you put more or less mix in there. The resulting ratios stay the same. Removing a modern high flow cat will barely change the flows. Removing EGR will increase your combustion temps and cause more NOx, but it does not change the BSFC or lowest emission AFR numbers. A emission controlled car runs at stoich because that's where there are the lowest emissions (pre-cat) and also the mix is such that the cat can do its work. At the stoich point there's just enough oxygen in the exhaust to allow the cat to "burn" CO to CO2 , HC to H2O and CO2, and NO2 + CO to N2 and CO2. A little richer and there's not enough O2 left for it to do it's magic. But all the major chemistry and physics happens pre-cat.
Regards,
Klaus

dubulup

I do run a MSD 6A on the leading coil...I did notice more power, due to better burn and more boost however my MPG drastically went down due to more boost and more time on boost

I have not driven the car in a sane manner to test MPG in many moons. Now that I think about it, the #'s I posted above were pre-AMP'd ignition. I'll give it a try and post something useful...sometime...no promises, the pedal on the right tends to get stuck to the floor.

side note - emissions decreased after the amp.

a3dcadman

iTrader: (1)

klaus,
There was an excellent article in TPR (TUNER PERFORMANCE REVIEWS) magazine a couple of issues ago which discussed the rotary engine and made comparisons to the reciprocal engine.

When comparing thermodynamic cycles, the rotary is 1080 degrees per cycle and the reciprocal was 720 degrees per cycle. So the rotary has 1.5 as much time as the reciprocal to accomplish each stroke.

More time for combustion but also more heat dissipation into the engine, oil, and coolant.

High emmisions from the rotary were attributed to overlap (intake / exhaust). Seems to me that optimized combustion of gas would result in reduced emissions and more power and better mpg.

When considering the info youve presented as applied to the rotary there are probably variables that come to play which dont necessarily comply to your summation. It would however be interesting to see what kind of results with similar testing the fd would produce.

If youre interested in the magazine article but cannot find it, I can send it to you. pm me.

chuck

Hyperite

I wrote that as I was walking out the door and as I was driving I was like "wait...no it doesn't!". All I know is that my cruising BSFC is closer to 16.5 A/F... ie- no added throttle to keep constant speed, and minimal bucking. Also, I don't think emissions increase once you get north of stoich. All the fuel has burned (as in stoich) but you've just got some extra air in there. If I'm wrong on that one, I'd love an explanation!

scotty305

iTrader: (2)

Klaus, have you tested the LC-1 sensor with the Mazda ECU? Our factory fuel-control system is pretty archaic, I wonder how much fuel trim is actually taking place.


-s-

Kento

Combustion in your engine is a result of a molecular reaction induced by pressure and heat (spark). The molecular compounds in fuel combine with the molecular compounds in air to produce the pressure that applies force to the rotor and powers the car. However, not all of these molecules combine into somewhat harmless form, and that depends on the ratio of fuel and air in the combustion chamber. "Stoichoimetric" means the theoretical ratio of air/fuel that will provide the minimum amount of oxygen required for complete reaction of carbon and hydrogen in fuel into CO2 and H2O. Lean a/f ratios result in more nitrogen molecules (air actually has more nitrogen than oxygen) singularly combining with a number of oxygen molecules to form NOx, which through photochemical reaction produces smog, meaning it is considered a bad emission.

Kento

"Time" is a somewhat misleading term in comparing the combustion cycle of a rotary's eccentric shaft with the crankshaft of a piston engine, because you're implying that all piston engine crankshafts turn at the same speed per power stroke. A "long-stroke" engine may end up with the same "thermodynamic cycle time" as a rotary's eccentric shaft going through its three revolutions. It's not so much the "time" as it is the surface area of the respective combustion chambers; a piston engine combustion chamber is perfectly shaped for combustion, as flame fronts travel outward from the spark plug in an expanding circular pattern-- the Wankel's combustion chamber is rectangular, not exactly the most efficient shape for complete combustion, and opening up a whole lot more surface area to absorb combustion heat.
It's not just port overlap, it's the poor thermodynamic efficiency of the combustion chamber, which is the reason for the leading and trailing spark plugs in each one.

a3dcadman

iTrader: (1)

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.

You are obviously very knowledgeable, so perhaps you can answer this question. Is there a 1.3 liter recipro engine for a car that can generate comparable hp to the rotary with similar fuel delivery? Would it be as smooth and quick and be able to sustain as high rpms without being highly modified. I know that some of these new motorcycles that a couple of the guys at work have are phenomenal machines with 15,000 rpm redlines and getting 130 hp from a 900cc engine.

chuck

Kento

By "fuel delivery", if you mean turbocharged, no, I don't believe so, not for cars anyway. Normally aspirated, no way for cars; motorcycle engines, on the other hand, have already made 170hp from less than 1300cc. Of course, there is a huge debate on what is considered the "actual displacement" of a rotary engine that I'd rather avoid like the plague...

a3dcadman

iTrader: (1)

thanks for your input.

hmmm..... this displacement issue.... another thread....... as you probably can tell, I do like to stir things up a bit!
chuck

klatinn

Hi,

Kento is right, I also want to avoid to displacement debate. Also, running lean of stoich produces more NOx, which is a pollutant.

As regards to where the best AFR for max. BSFC for a rotary is, I have no data there. The data I posted also applies only to homogenious charge engine where the mixture in the combustion chamber is everywhere the same.
Some newer stratified charge engines (typically direct injection) create a stoichiometric mixture around the spark plug for easy ignition. The rest of the chamber is filled with air or leftover exhaust gas. This allows them to run efficiently with up to 88 AFR.
A spark ignited engine modifies power not only by the amount of air-fuel mixture, but also by the dynamic compression ratio. The mixture pressure and density is much lower at part throttle. Lower compression means lower efficiency. That's why diesels are so efficient, no throttle.
The long comb. chamber of a rotary means a long flame front travel time. This requires more ign. advance. Ign. advance means pressure buildup before the optimum peak pressure point and therefore means it robs power and increases knock probability. The reason for 2 plugs is to start the flame front from 2 points to minimize burn time.

With the long rectangular combustion chamber of a rotary it should be actually be even easier to set up a stratified charge system with direct injection. I wonder why it has not been tried yet. It should theoretically make a rotary much more efficient at low loads.

Regards,
Klaus