sar

iTrader: (1)

Dang, you got me on a misunderstanding - I said after, not during but my example of a valve on the spark plug side could not have made it any clearer.

Your whole concept is based off of a blown engine. A blown engine essentially has no compression chamber as with no seals it is conencted with the intake and exhaust ports.

Furthermore, you make no mention of preventing this unfueled rotor from receiving air only to comrpess and expel that gas. By making the compression event have a hole in it you eliminate all compression resistance. Keeping all air at 1atm is probably the best convention of maintaning a constant air volume. Unless you want to close the intake and exhaust ports, which would be extremely more difficult.

My statement is directly inline with the idea of turning an engine over with a spark plug removed is a lot easier than turning one over with both plugs in.

I don't think you understood my post at all. You have to disable air changes when you disable cylinders and this is why the different companies have different methods of "pinning" the camshafts. "In addition to stopping combustion in these cylinders, energy is also saved by not pumping air through these cylinders. Th"

http://www.greencar.com/index.cfm?content=features46

Terrh

iTrader: (7)

in my experience, probably driving 50,000hwy KM (thats like what, 100 tanks of gas at least)
my (stock ecu, upgraded intake and exhaust) TII had the best fuel economy cruising at 3500ish RPM in 5th. I've tried everywhere from 80km/h to 160km/h cruising. Best fuel economy always seemed to happen around 140km/h. Fuel economy declines drastically above 150km/h.

Even in my FB I should note that this was the case - the faster I went the better on fuel it was.

I realize this may not "make sense" when comparing to other cars but all I can state is what happened with me - I don't know why this is or why it isn't - but if everyone else seems to have similar experiences then I'd say it can't just be a fluke with my car, since alot of the board members that have actually TRIED THIS and have EXPERIENCE AND KNOWLEDGE IN THE SUBJECT AT HAND tend to have more weight than theroies and experience in other cars.

Unless you've commuted at 90mph and experienced worse milage, you can't say otherwise.

As far as diesels lackingg engine brakingg goes - I dunno on that either. I had a b2200 diesel that was pretty much bone stock, 2.2 liter n/a diesel.

The gas pedal on it functioned differently than it did on a car - it was more like a "request for revs pedal" - press it down and the engine will rev higher, let go and the revs will drop. If it would rev to say, 2500 with no load, it would probably go 2500 in 5th just the same with the same amount of gas pedal usage. And if I let go, it would slow down pretty quick.
Also, it got BY FAR the best milage at about 70km/h in 5th. And REALLY terrible gas milage anywhere above 110km/h. But it was ancient, diesel, and brick shaped Not an FC, or even similar.

sar

iTrader: (1)

Peak torque is found via point of the most volumetric efficiency - therefore the closer you are to 4000 rpm (on an s5) (if it weren't for the ecu and 5th/6th ports) the more efficient your engine will run due to the rate of the expansion of the gases.

While the air compression losses may be less noticeable at higher rpm 3500 rpm is not that many rpm to be turning..


If you're running on a megasquirt you could retune this to work the best; go to 4000 rpm (s5) for volumetric eff. and keep electronically activated 5th/6ths closed when on one rotor. All of this while using a wideband o2 sensor to keep a perfect lamda.

Sideways7

iTrader: (7)

That may be the most effecient operating speed of the engine, but drag increases greatly at speed.

iceblue

Seems like 98% of this thread is full of worthless crap.

Rotorgod has been working on this for some time now.

In 1981 Mazda did just this at another time. They installed a valve that cut both FUEL and AIR going into the rear rotor on deaccel. This improved the gas mileage by 20%

Cutting the fuel during cruise is a good concept but will require allot more load to be placed on the one rotor b/c there is allot of MAS to keep in motion. Now if you reach a speed that creates both little drag and low load it could work. If you have ever drove on one rotor you would know how hard it is to accel. I was unable to build any boost on 1 rotor and took around 1mi to reach 45mph and was very hard to surpass it all at WOT. Now once in motion like I said maybe but it will be hard for the motor to keep up.

Running premix will not load the motor up with oil but the OMP will. However I do not know if the lack of premix running in that rotor will cause premature wear due to pore lubrication on the apex seals and housing.

Syonyk

Fine. Drag increases with speed. Nobody's arguing that. And, apparently, on an RX-7, engine efficiency gains at higher RPM more than make up for the increased drag.

Unless you can explain why basically everyone who has tested this is seeing best economy around 90mph/3500 RPM, I'm going to kindly tell you to stop arguing. I see significantly better fuel economy cruising at high speed, as does everyone else. Will 3500 RPM in 4th provide better economy? Possibly, but it's not a useful speed for most people.

The reason exceeding 3500 RPM makes fuel economy drop like a rock is that the ECU shifts into a differnt map. With the O2 sensor working, the ECU shifts into open loop mode (and fuel dump mode) at 3500 RPM or so. Even with a SAFC-II or such and no O2 sensor connected, the ECU shifts into a different map, and adds a lot more fuel.


The rotor lubrication with premix is the only reason I was thinking of cycling the firing rotor.

Again, this would only be used at cruise, once up to speed. I don't know if I can make enough power on one rotor for it to work, but I think it might be possible.

-=Russ=-

iceblue

The O2 sensor is not used outside of closed loop. So ^ is incorrect. The only reason the fuel drops is b/c the secondary injectors kick on at 3.8k RPM this is a long known fact, when cruising keep the secondary’s off and you will get allot bettor fuel mileage. Unless your speed increases greatly to counter that increasing your distance traveled per amount of fuel delivered.

It really doesn’t matter what speed you are doing as long as you are at a cruise with minimal drag and the secondary’s off you will have good gas mileage.

I don’t know about you buy 80mph is 4k RPM in 5th for me with 4:10s so I don’t know where this 3.5 at 90mph is coming from.

Syonyk

The problem is that the secondaries come on at 3644 RPM or so, and the fuel economy & mixture shift occurs below that (according to my SAFC-II, not the stock tach). I believe the fuel maps change before the secondaries come on. Also, the secondaries when they come on, split the previous duty cycle in half. So no more or less fuel is being injected after the switchover.

I have an 88 SE, and 3500 RPM in 5th is about 90mph. The TIIs have a different 5th gear ratio (shorter), and I didn't think the stock rear end was a 4.1...

-=Russ=-

Terrh

iTrader: (7)

TII speed/RPM is really easy to figure out if you work in km/h.

every 500RPM is 20km/h in a TII.

so 80km/h (50mph) is 2000
and 160km/h (100mph) is 4000.

140km/h (~88mph) = 3500.

iceblue

The secondarys come on at 3.8 with a bias of a vacuum amount you must be seeing a certain amount of vacuum or boost for the S to come online anyways the ECU will override its preset 3.8, as well there is no fuel map on a FC there is also no fuel economy switch.

So there is no map there is no O2 signal in this rpm range so there is no exact. The car simply runs richer when the secondarys come online even though they drop the P duty cycle in half.

DemonicPupil

That's gotta suck. 5th gear, 80mph for my 86 and 87 NA's are 3000rpm.

iceblue

^ That’s around 60mph for me. Anyhow we all know how accurate the FC Speedo is.

I did drive by one of them cop thingy’s that tell you your sped and 2.5rpm is 50mph for me.

scathcart

Been there, tried it.
N/A cannot do it, even at WOT.
TII can only do it at WOT and full boost... which means no closed loop, and very rich.
Before we keep discussing this, try it. It'll take you, what, maybe 30 mins max to setup a series disconnect for the primary injector?

I don't believe this is true.
None of the second gens I have ever driven have ever acted this way, and I have extensively tested this with the stock ECU's (logging, of course).
I think this is a situation where one person says it happens, so everyone repeats it.
As I've found, the differences between driving 65 mph and 85 mph is 1-2 mpg in fuel economy, so driving faster does not significantly decrease fuel economy.
I think part of the problem is the driver's. At 65 MPH, people tend to surge on the throttle, whereas at 85 mph, with the increased wind resistance, throttle position is much more constant.

When you keep going on about the engine efficiency change being the main contributing cause to the higher fuel economy at higher engine speeds... Honestly, how much do you really think the volumetric and combustion efficiency changes over 500 rpm? How do you think this is any different from a piston engine which shares nearly identical traits?
If its the aerodynamics that makes all the difference, why don't the V-8 swappers find optimum fuel economy at 90 mph? If its the engine efficiency peak occuring at 3500-4000 rpm, why don't any of the 4-cylinder imports show the same traits you're claiming exist?

Furthermore, I think you guys are placing an awful lot of faith into closed loop mode. How much of a difference do you really think it makes at cruise to have the O2 sensor providing feedback or not?
Again, try it. Throw in the dataloggit, and report back.
(Its pretty minimal.. usually 1 mpg lower.)

scathcart

Different overdrive gearing.
S4's had 0.711:1, S4 TII's had 0.756:1.

With stock tire sizes, he would be at 88 mph at 3500 rpm, just as he said.

You would be at 94 mph in 5th gear at 4000 rpm.
So either your tires are much smaller than stock, or your speedo is wrong. 14 mph at those speeds is pretty significant.

Carzy Driver

This is a very good idea, but raises a big red flag for me and others that premix with the OMP removed. 2 others have mentioned this before me. I believe that with a fuel cut on any rotary that's premixed would be bad, this is common knowledge.

Syonyk

What part of "cycling the firing rotor every 5-10 seconds to make sure both rotors stay at temperature and lubricated" was missed? That's exactly why I'm planning to cycle rotors.

-=Russ=-

Syonyk

That's reasonable. I was assuming a NA could hold the speed. If I get some time later this week, I'll rig up a quick injector cut down in the footwell & test stuff out. You're right, if a NA can't hold a reasonable speed on one rotor, it's a non-issue.

The throttle position could definitely be part of the issue, but I discovered this on my own before hearing other people try it, and it confused the **** out of me for a while. My highway economy for the past 6 months has been disturbingly low, and I couldn't figure out why until this weekend, when I was cruising back at 85-90, and the economy was back where it should be.

However, I've made runs with an O2 sensor check light connected, and been very gentle on the throttle to make sure I stay in closed loop mode as much as possible, and I still see better economy at higher speeds.

This is just what I've observed with the SAFC-II's readings - I'm running a significantly higher manifold pressure at higher speed (50-55% vs 25-30%), and I suspect the S4 intake runners are tuned for something closer to 3500 RPM than 3000. 500 RPM is apparently reasonably significant in that band.


Aerodynamics don't make the difference. I don't think it's a case of the rotary getting "really good" at 3500 RPM, I think it's much more a case of "not sucking nearly as much" at 3500 RPM. I know it's not a magic engine, and I know that there's significantly more drag at 90 than at 65, which is why this is so confusing. The only conclusion I've been able to come to is that at 65-70mph the engine is being not terribly efficient, and at 90, the engine is operating at or near peak efficiency.

Actually, I just place faith in the ECU's fuel maps where closed loop mode should be. I've found I get better economy with the O2 sensor disconnected & the SAFC-II leaning things out to somewhat lean of stoich at cruise. I do know that, at least on mine, I have to pull 15% or so out at cruise RPM to get to stoich from where the ECU runs without the O2 sensor, so it's fairly rich in that map normally.

-=Russ=-

Terrh

iTrader: (7)

I leaned my car out a TON at cruise on my SAFC - up to 30% in some areas... the stock map is really rich.

this is really easy to test, btw.

Set your TPS up so that it's in the "1 rotor" mode at like 1/3 throttle. Since the ecu does this anyways at really light throttle, just make it think that you're at really light throttle when you aren't. I know when my TPS was misadjusted that I was running on one rotor a lot putzing around town.

Carzy Driver

Even with cycling, that's still 5-10 seconds of bare metal, slightly unlubricated contact. cruising at 3.5k RPM, 5 sec. is 291 revs with 10 sec. at 583, for me that too many unlubricated revs. IMHO, for those of us that premix, this has accelerated seal wear written allover it.

Syonyk

It's no worse than engine braking from highway speed. Two-stroke oil leaves a lubricating film behind, and I'll engine brake down from 90mph, blip the throttle every 10 seconds or so to downshift, and touch the brakes around 5mph.

http://fc3spro.com/TECH/FAQ/premix.html covers this - the premix will still lubricate fine for a while with no additional injection.

The non-firing rotor is also not dealing with any combustion pressures - it's just spinning, and the seals are being forced out by spring pressure only (and any centripetal forces). It's nothing like the loads of combustion pressure.

-=Russ=-

MattB

80 mph is 3500 for me in my 87 TII...

MARTIN

First of the compression does make a difference. This is just stupid... I've driven the car with full compression in the rotor w/o fuel.... (messed up inj clips.) And the car couldnt feel any slower... YOU DO HAVE TO KEEP IT AT OR NEAR WOT TO GET ANYWHERE NEAR 50MPH. I dont even remember if it got to 50MPH. Like stated above, one side with no compression will spin significantly easier than it having comp. This is just rediculous. Drop it..

ilike2eatricers

I'll vouch for this as I've had the same experience (dead primary injector drivers on rear rotor). Couldnt have said it better. just leave it alone.

Mura

Really? I get the opposite. I get better gas mileage going 70, than I would going 85 - 90. Going to Gainesville which is a 2hr drive, going there at 70mph, by the time I got there, I would be prety much at a half a tank. Going between 85-90, I'm at a quarter tank once i get there. And the most i've been able to get up to was 103(auto). I hate Auto. I'm going to go out and see if I can get pass 103 now.

scathcart

On stock size tires, 3500 rpm ona TII would be ~84 mph.