Not that extreme of a backfire, just the little exhaust leak hiccupy ones. The mixture isn't exactly right, but I haven't yet figured out how to control it to the level that would be required to get it right.

The MAF temp sensor is reading non-conductive and higher resistance is colder temps. My thought is that either the ECU sees that as being super duper cold and it's giving it a richer mixture to compensate for colder, more dense air or it's gone into a failsafe mode where it richens the mixture in case it's super cold. Either way, it's definitely running rich, and if I lean it out any more, the idle starts to break up. Hopefully when I get a fully functioning MAF in there it'll smooth everything out and I can lean it back to a more appropriate level.

 

Your getting 20 mpg, thats fairly decent for a FC, i usually only average 19, but i know mines running rich cause my oil REEKS of gas, enough that it makes me uneasy

Also, N/As run really rich thanks to the ECU, its natural for them

 

I filled the tank yesterday, and got 20.217. I know that's probably pretty decent, but you have to consider the effect altitude has on NA fuel economy. We have less air for a given volume of air (3% delta per 1K' for about a 15% reduction in available air where I live compared to sea level), and so there's less fuel introduced per stroke. That results in a decrease in available power, but also an increase in fuel economy typically to the tune of around 3 mpg in this general range (to wit, my old 4Runner got 23 mpg consistently compared to an average of 19-20 mpg for similarly equipped models). Adjusted accordingly, I'm a little off what I should be at.

The exhaust is nauseating as it sits, and it has the exhaust hiccups. I just sent HRnico PayPal for the MAF, and I intend to do that and fuel filters at the same time along with an adjustment of the whole mess. Hopefully I can get the exhaust smell and backfires to a minimum and fuel economy to a maximum. I have a noisy throwout bearing, and the input shaft bearing on the 3-4 shaft is pretty loud. Those things are not helping my case, but they'll roll along just fine for a while like that. Meanwhile, I need to get back to the truck project so I can get it done before winter, and that means I need to wrap up the heavy RX7 fiddling.

 

20 mpg (non-highway driving) is pretty bloody good, imo.
I've averaged about 17-18mpg over the last seven years.

Hope that AFM solves your problem.

 

It's a pretty mixed tank. An unfortunate number of really short trips (you know where the FLAPSes all are in relation to my place, the grocery stores are only the next set of lights down) and quite a lot of revs (it's hard to resist when it's fully up to temp) with a few trips up to Boulder and down to Denver thrown in for good measure. I imagine if my wife were taking it to and from work every day (mostly highway and a more timid driver), it'd probably get closer to 23. If I could get all my little mechanical foibles ironed out and get a solid tune (and maybe do something about the transmission bearings) I could get closer to 25. I know I'm having issues because it's a very smooth and balanced engine, and it's telling me (through the vibrations) that it's a little unhappy about something. If I could pick up another good NA trans for cheap without having to ship something so heavy and bulky (shouldn't be too hard since everyone wants to go turbo), I could probably get this guy pretty close to 30 mpg with a good amount of meddling. There is a lot of fuel being wasted in the emissions systems.

 

30mpg...dream on.

 

I don't see why not. OE EPA MPG rating was 17/24. I'm currently getting 20-22 with almost all city driving, lots of revs, and a drivetrain that's constantly telling me its unhappy. I haven't even started trying to tune it because I haven't even fully got it baselined. Add to that equation the fact that this was a sports car tuned for hp AND it has some really crappy emissions systems that burn a lot of fuel. The cats require unburnt fuel in order to work, so that's extra fuel in the mix. The air pump and EGR similarly require mixtures that are too rich. Emissions systems require extra fuel to work. The irony of emissions requirements is that the tail pipe emissions are cleaner at the expense of engine efficiency. It would be far easier, cheaper, more efficient, and with better engine life if we could just tune to better emissions, but people are idiots and don't maintain their ****. Up here (Clokker is probably the only person that will really get this), you can smell a carbureted anything from 100 yards because people are far too stupid to tune their **** for altitude.

With my 20 mpg, the exhaust is eye watering... Maybe this is the direction I head with this car. A proof of concept that these things can be efficient and clean. Since they're tuned for power, you can bet the best case scenario has them at a 13:1 AFR throughout the RPM band (I'm probably seeing high single digits at best right now). That nets you power and keeps temps in check. Taking a page from the aircraft book of tuning though, 17:1 has you a few hp down, but just as cool. Aircraft people discuss AFR in terms of ROP/LOP; Rich Of Peak and Lean Of Peak respectively where the "Peak" is EGR. They run ROP for power when taking off, etc. and LOP for everything else for efficiency, reliability, and to keep things cool and happy. For some reason, tribal knowledge holds that anything north of (some arbitrary AFR below stoichiometric) will run hot and break things. This simply isn't true. Temps are highest at stoichiometric, but they cool off on a similar curve above it just as below. I tune all my carbs to 17:1 idle and 17:1 cruise (progression circuit or primary depending on the type of carb) with a 13:1 in the (mains/secondary) for power. I also throw in a few extra degrees of timing (in addition to those that get thrown in to compensate for altitude). This nets cool temps, crisp throttle response, power where you need it and fuel efficiency where you need it and a crisp clean exhaust note and no smell to boot. I call it a "street tune" compared to a "power tune" or a "hypermile tune" where you'd be all 13/17:1 AFR respectively.

There will certainly be hurdles that will have to be overcome if I take that path to any degree. For starters, I need to figure out the rest of the eletrickery and be able to make sense of what systems are doing what and how they do it. Then I'll have to figure out what I can bin and how to have better control over fuel and timing (running more lean means you can run more timing). I need to read all the way through the ECU tuning thread, and being able to control mixture and timing will be key. If I'm fully reliant on stock systems, yeah 30 mpg is not going to happen. 25 mpg is totally doable though, and I'll probably be there with nothing more than a solid baseline.

Regardless, this is likely a down the road affair. I need to get my truck painted, wired, assembled, and get an engine in it all before winter, and that's going to be a pretty significant challenge on its own. I doubt I'll spring for a new exhaust on the Rat this summer with all the truck expenses, so I won't be able to do anything about the exhaust backfires save just lean it out a bit. Fuel filters, MAF, and seeing what I can do about the rest of the electronics are about as far as I'll likely go for now.

 

a rotary won't tune to those same AFR targets as a piston engine, although process to get to a safe lean mixture is the same.

 

Why not?

I can imagine some limitations due to the port fuel injection and the spark plug holes allowing some HC to cross over to the exhaust portion of the housing* causing HC emissions trouble, but I don't see why it would have any unusual issues running a lean mixture. The HC issues might even self rectify if there's enough remaining oxygen available after combustion... Emissions self-rectification.

*Is there a term for the rotary equivalent of a stroke? People get all uppity if you say "crankshaft" instead of "e-shaft", but there seems to be far less of a differential in reality there than in the "stroke" moniker...

 

the rotary is a 4 stroke engine, the same as a piston engine, however there are two differences. the piston engine has all 4 strokes in one place, and the rotary has each stroke in a different physical location. the intake is on one side, and the spark plugs are on the other.

the other difference is that the rotors are geared 3:1 to the e shaft, so the e shaft spins 3 times for each rotation of the rotors. this makes the stokes 270 degrees long, which is great for the intake, power and exhaust strokes and bad for the compression stroke. there is more time for the seals to leak, and there are also more of them.

for the mixture differences, the square combustion chamber leaves pockets of unburned mixture at the corners, and its pretty free to fall out into the exhaust (the Rx8 goes to a side port, and these gasses are recycled). also the exhaust port has pretty radical timing, so it lets a lot of exhaust gasses back in, like a giant EGR valve. at low rpm this means its not a very optimal place for stable combustion, and it needs richer mixtures to not misfire. this is why there is an airpump, it delivers some fresh air into the exhaust port. it also evens out the mixture the cat sees.

 

I know this. I figured since an e-shaft ≠ crankshaft despite being essentially exactly the same save a much shorter throw, that there must be some sort of stroke equivalent since there aren't any strokes at all in a rotary so much as degrees of rotation and there is an actual factual difference. Maybe instead of "stroke" there's a term like "swept quadrant" or "sector" or something similarly pedantic. Or maybe there's not... Maybe it's like van vs. bus in the VW world, where unless you're in the UK, a VW Type 2 is never called a van, always a bus because technically it was a station wagon and other pedantry, but really it doesn't matter and no one cares because it's just a way to differentiate the subsection of the automotive hobby (that said, I'm completely guilty of the van/bus distinction).

A cylindrical combustion chamber also has corners, and the longer effective stroke would help mitigate any differences here. That sounds more like an issue of swirl than anything though. Lacking a more thorough background in fluid dynamics though, I'm not sure how to process that off the top of my head.

This helps explain why they're so dirty from an emissions perspective, but why would that prevent a lean mixture? O2 sensors detect available oxygen in the exhaust gasses, not unburnt hydrocarbons. If we assume a tune for economy versus emissions, this should have no bearing.

 

the E shaft/crankshaft thing is silly, the E shaft just has short throws, it would work in a reciprocating engine, i think.

the rotary does have strokes, there are BDC's and TDC's, its just like a piston engine in fact, is just that TDC of the compression stroke happens a foot away from TDC on the exhaust stroke.

actually we can skip the theory, and go right to empirical test data. the R100 SAE paper lists some emissions numbers, and they are right in line with what we got testing my T2.

at idle, with no emissions controls, the 10A emits ~2500ppm of unburned HC's. if you add the airpump, it drops to ~1900HC's. adding the thermal reactor to ~200ppm HC's.

 

The "e-shaft" as a crankshaft in a piston engine would absolutely work, it would just have nearly zero torque due to such a short through. On the plus side, piston speed and rod angle would be dramatically reduced, so redline would be sky high (on your two cylinders). My comment was primarily based on the pedantry surrounding the "e-shaft" when the differences are precisely nil whereas there are actually no physical strokes. The "intake stroke" is really just 90° (or however many) of rotor rotation. If there was a real method to the pedantry, there would be some alternate name for the intake stroke and I would have been called out when I said it in the original post where it came up. It seems the pedantry is more communal desire for difference than actual hard factual differentiation. Going forward, I'm dropping the "e-shaft" moniker for the rote silliness of it.

So those two parts alone are sufficient to pass any smog test around here... Interesting. Are those numbers with stock tune? What's the AFR of an NA engine at idle with a stock tune? That is something that is of acute interest. There's no use attempting any real tuning until I get the rest of the machine happy though...

 

maybe instead of stroke, they should say phase or something, the rotary does have strokes, just like a piston engine, there is a big chamber volume @BDC, and a small one at TDC, it just isn't and up and down stroke, like things that have up and down strokes.

So those two parts alone are sufficient to pass any smog test around here... Interesting. Are those numbers with stock tune? What's the AFR of an NA engine at idle with a stock tune? That is something that is of acute interest. There's no use attempting any real tuning until I get the rest of the machine happy though...[/QUOTE]

i suspect yes, although it doesn't mention what that is.

best idle AFR will be in the 12.2-12.8 area, over about 1100rpm and low load is 14.7:1 stock, and it'll run a bit leaner. at high load the stock ECU map is in the 14's up to about 3500, and then dips down into the mid 12's all the way to redline.

with the airpump, you'd tune idle to about 16:1 as the airpump air is injected in front of the O2 sensor.

 

If I were to apply my standard tuning methodology to this platform, I'd see ~17:1 at idle and up through the convenience of the secondary injectors coming online at 3500 (though I thought it was 3800), or throttle was somewhere between 1/2 and 3/4 travel, at which point it would dip down to about ~13:1 to help with the extra load. The result is a nice lean and clean burn until you are actually wanting extra power (as indicated by load visa vis throttle position and RPM). With the secondary injectors and intake ports on these engines, the resulting feel would be like a subtle surrogate turbo lag. Just getting that dialed in is good for 3-5 mpg in daily driving without a noticeable drop in power or performance save that throttle response crisps up and the exhaust sounds better and more defined.

Anything between the mid-13s through mid-15s I generally try to avoid to keep temps down. The transition is usually the difficult part to get right since you want to go from a high AFR to a low. If the specs you have there are stockish, that reinforces my expectations of what I'm feeling/seeing/smelling. It's just too rich pretty much everywhere save up high in the RPM band which is where it wants to be and seems most happy.

Where this methodology could fall flat is with the charge that gets from the compression stroke into the power/exhaust stroke through the spark plug holes. It wouldn't be a whole lot, but that could cause an artificially lean reading as the wasted fuel reacts with the remaining oxygen in the exhaust gases. On the other hand, that extra available oxygen from the lean tune could potentially help tremendously with emissions sans the standard emissions kit.

 

All this talk about "tuning" and AFR's is great but with your stock ECU there ain't **** you can do besides making sure the input/output devices are right.

Watching AFR in real time is essentially a lesson in futility.

 

For now, it's purely theoretical. It will probably continue to be for quite a while too since this car is about to take a back seat and just drive for a while. Eventually though, I'll take the time to sit down and figure out what's up with all the electronic crap and see what can be done. I still need to read and digest the stock ECU tuning thread in its entirety, and then there's the whole "physicist next door" angle and all the stuff we've been talking about lately with FPGAs. It might not be as hard as you think. It's probably harder than I think.

 

What part of the 7 experience has been easier than you expected?

Bueller?
Bueller?

 

its all in the training manual Index of /rx7manual/manuals/Training Manual

we're the Australian version BTW

 

It's been a helluva lot easier than the truck was if you can believe that. The truck almost broke me.

 

Truck is in pieces, so there's still time.

 

Don't jinx it!

 

Busy weekend! As Clokker mentioned in his build thread, we met up yesterday at Clokker's favorite junkyard, and I've got to say... That is the ritziest junkyard I've ever seen! Seriously. They've had an interior decorator or something in there to great effect! The yard itself was decent enough as well. I was actually able to find a few good parts to get what I needed done! I got some Integra window scrapers, some rubber wire pass throughs, some bushings for the fuel filter mount, and found some hood pins for my truck! $15 all in.

After that, we parted ways. He did his experimental intake thing, and I replaced my fuel filters. The Tank sock was easy enough, but the replacement part was clocked a few degrees off. There was enough play in the plastic of the new sock to force it to work, so it did. The old sock was in pretty good shape, so that was almost assuredly not my issue anyway. On the engine compartent filter, part of my problem was that the rubber bushings that hold the thing to the body were trash (which was the primary purpose of the visit to the yard). I was able to get one of them out, but the other wouldn't budge for anything. All that's left is a thin hexagonal plate, and I just couldn't get anything on there well enough within the available space to get it to budge... It had been in there for some unknown period of time with no mounts, so hopefully it'll last a while with the one.

Today I flushed the clutch (still had some brake fluid left over from the brake flush), adjusted the clutch play, and adjusted the brake pedal play. Then I removed the aftermarket fog lights. They were a pretty clean and well integrated install, so I'm thinking they might have been a dealer option or something like that. I actually almost stopped removing them at one point because I thought they were part of the original harness. They were completely non-functional and causing rust, so they came out regardless.

While I was in there, I found these:

This is right up front behind the bumper and under a set of relays. Three plugs, nothing plugged into them, and nothing nearby that looks like it might do so. Further, I can't think of anything they might be used for up there, but with all the relays...

I finished off the weekend copying Clokker's window treatment.

The Integra window moulding took some massaging (which was expected and guided by Clokker's advice), but worked beautifully. I was actually surprised at how transformative such a simple job could be. The old mouldings were rusty, crusty, cracked and gross. The rubber didn't contact the glass really anywhere. The new rubber obviously looks much better, but with some massaging and adjusting the rubber actually has a chance to do its job! The rustiness right there at the car's "eyes" had much more of an effect on the aesthetic than I gave it credit for. Replacing it with the clean black happy rubber was a huge improvement, and has helped me figure out exactly where I want to take the build.

 

Yeah, that place is my Walmart/PepBoys/Summit playground.
You may also now understand why I rarely know what car donated what part...after walking past a few hundred cars, briefly glancing in the engine bay and then moving on, they all blend together.
Or maybe my whole life is a continuous "senior moment" now and I don't know it.


Took a nap, actually.

Please share the new mission statement with the class.

 

Finish making it happy electrically and mechanically. At this point, that means adjusting the rear hatch release lever by the driver's seat, cleaning and greasing the sunroof, and a bunch of solder work. It also means I likely need a new transmission and maybe differential at some point in the not super distant future. The 3/4 input shaft bearing is pretty loud, and I don't think it's long for this world. I don't intend to go turbo with it or anything, just make it mechanically sound, so I'm hoping I can round up a decent used NA transmission somewhere close sometime soon for a reasonable price. Then do the 5-lug brake conversion and replace all the suspension bushings while I'm in there. Then I need to find some decent seats, round up all the broken interior plastics, and dye everything black. The last thing will be to plasti-dip the car the dark gray color they have that's all but identical to the color it actually is. At that point, it'll be one seriously happy little car that should last as long as I need it to while being reasonably economical and fun to drive.