FD's don't run rich.
 

Well, they don't run richer under boost than comparable turbo piston engines. The only solid data I've seen that may indicate the factory ECU's target AFR is the fuel table in the basemap of the Power FC (INJ map of default calibration, target AFR view).

https://www.rx7club.com/attachment.p...1&d=1269973955

The boxed area is about where a stock FD will run (Y axis is boost, x axis rpm). You can see the AFR is at least as rich as the mid 10's. Anecdotal evidence indicates that the factory ECU runs similar to this target table. Let's compare this to a turbo piston engine making similar power, a 2005 Subaru Legacy 2.5 GT boxer rated at 250bhp.

https://www.rx7club.com/attachment.p...1&d=1269973955

X axis is load (a function of airflow/rpm), y axis is rpm. The target AFR values are similar. Let's look at one of the FD's contemporaries, the 3 liter Z32 300zx twin turbo:

https://www.rx7club.com/attachment.p...1&d=1269973955

X axis is theoretical pulsewidth (a function of airflow/rpm), Y axis is rpm. AFR's look very similar to the FD. This engine was rated at 300bhp. Another 3 liter twin turbo V6:

https://www.rx7club.com/attachment.p...1&d=1269973955

2nd generation 3000GT VR-4. X axis is rpm, Y axis is load (a function of airflow/rpm). This engine is rated at 320bhp. The last car is the 2 liter 291bhp Evo X:

https://www.rx7club.com/attachment.p...1&d=1269973955

This engine runs really rich, richer than 10:1 AFR, but it also runs over 20psi peak boost from the factory. I realize that I have been posting target AFR tables, but on stock cars these AFR tables are usually pretty close to the measured AFR. Here is the boost and AFR curve on a stock Evo X:

https://www.rx7club.com/attachment.p...1&d=1269667955

You can see the wideband pegs rich at 10:1, which is very close to the Evo X target AFR table.

ok, but where does the FD actually run rich relative to normal piston engines? At low loads, especially idle. Mazda engineers discussed this in their 2004 SAE paper on the Rx-8 Renesis engine, "Developed Technologies of the New Rotary Engine (Renesis)."

https://www.rx7club.com/attachment.p...1&d=1269975324

The smog pump on the FD is used to dilute this rich mixture during low load so that the engine could pass emissions. Mazda redesigned the exhaust ports on the Rx-8 so that they can idle at a normal AFR, similar to a piston engine. Thus the airpump on the Rx-8 is only used to improve warmup emissions.

Interesting thread

I just installed an AEM UEGO wideband in my pretty much stock FD and noticed it doesn't run nearly as rich as I originally anticipated. I see about 11.1 at WOT, the richest I have seen is 10.9 maybe for a second.

It's well known other factory turbo cars are tuned stupid rich to avoid warranty claims and protect engines. Like the map you posted for Evo's which run into the low 9's at WOT. The Mazdaspeed 6 and 3's also run even into the high 8's at WOT!

It's been my understanding manufactures do this to protect motors from overboosting conditions, bad gas, etc anything that can threaten a factory boosted motor, bu it seems to me running a car at 9:1 in boost could lead to a lot of carbon build up?

Although the rich AFR may be partially for safety, its main purpose is to keep cat temperatures down and reduce NOx emissions. The knock control is the main thing to protect an engine, whether it's an FD or a piston motor. The Evo knock control is actually very sophisticated and has adjustable sensitivity and filters. The FD has knock control but only on the factory computer.

arghx - why do you suppose apexi is running so rich in the N1 and N2 columns, especially the vacuum cells? is this the target map you use when tuning?

and would you change the targets if you found you were idling in N2/P7 or N3/P7?

My FD ran pretty rich on the stock ecu. My gas mileage went up about 20% after installing a PFC.

Compare 'accel' trims to most piston engines and you'll notice the 13b and all other peripheral exhaust rotaries run extremely rich on tip in. I can't say for certain about the side port engines as I've never tuned one.

P.S. I think this is more telling of the Japanese style of forced induction tuning than the amount of fuel used in a 13B map.

That boost curve looks horrible. Losing 5 or so psi from peak to redline, blah :( Or maybe that was deliberate by the Mitsu engineers? Also, there looks to be a bit of a delay between the richening and boost and 3800 rpm, @ peak boost AFR is about 11.5 and then flattens to 10 as boost falls off. Not sure if that is an artifact of having the WBO2 in the tailpipe (was it?) or a measurement problem...

Richness to keep the rotary REW motor happy @ low loads and idle makes sense to me, just based on my own experience. Lately in my car, I've been running high 10's/low 11's AFR on 91 octane from 10-14 psi boost stock turbos on the street w/ no problems yet. I've run 10-11 psi on a road course for about 10-15 minutes at a time @ 10.5-11 AFR w/o incident. Ambient temps are in 40-80*F range, water, oil, air temps are "reasonable" (water < 220*F, oil < 240*F, air < 60*F). Although I have hit maxima beyond those values for short periods...

Again, thanks for posting this info Raymond, I personally find it extremely valuable and enlightening. Looking outside of the rotary realm can teach you a lot. Not sure how many of you have the book, but in "Street Turbocharging" by Mark Warner, there is a chart on page 94 (in the water injection chapter) which shows a relationship between AFR and cooling effect. If you run 11:1 on pump and then richen it up to 10:1 on the same fuel, the cooling effect of the fuel is about 10% (you remove 10% of the heat from the combustion chamber). The neat thing about the chart is how much more heat you can remove with water... not sure what assumptions were built into the chart, but it's something to chew on. I will scan it in sometime and post it up.

EDIT: another thing, RE: NOx emissions.. arghx is right, if you go too lean on AFR past stoich (14.7:1 on pump gas), your NOx will go up (to a point) and probably EGT as well.... see attached chart for NOx, etc.

https://www.rx7club.com/attachment.p...2&d=1270006778

info regarding the cooling effects of water and gas can be found in one of howard coleman's very enlightening threads, here:
https://www.rx7club.com/3rd-generation-specific-1993-2002-16/making-case-rotary-powered-fd-fix-806104/page18/
check post 440

off tangent for a moment, but arghx, you post some of the most interesting threads on FDs and you dont own one. Im afraid to think of the genius you would post if you had one.

OR owning one ruins all the anticipation and desire to study it ;-)

carry on the good work. i read your threads :-)

It could be that rich to account for fluctuations with the weather (IAT sensor heatsoak) that would result in an unacceptably lean/unstable idle. Remember that the PFC and series 6 ECU are not learning computers (no fuel trims). I don't use that AFR table exactly, but there's nothing really wrong with it. If you could tune a modded engine to hit those exact AFR's in each of those cells you'd be doing ok in terms of safety and driveability as long as the timing ok.

Probably due to the overlap.

Newer turbo cars do that. They wind out a smaller turbo to give low end torque.
I've argued with Subaru owners over this. It's just a preference, although they don't see it that way. Even when they put bigger turbos in, they usually taper the boost down because of the way they chose to size that turbo.

So that type of boost curve is intentional. It is achievable because modern OEM boost controllers are very precise, far better than anything you can buy aftermarket. On Subarus they use rpm vs throttle position for target boost, then two tables to set the acceptable highest and lowest wastegate duty cycle values to achieve those targets. Then a proportional-integral controller gives closed loop correction, on top of IAT and water temp adjustment. What's cool is that there are maps that vary the integral and proportional gains based on boost error/deviation from the target. All the standalones (Haltech, AEM) only let you set one value for the PID coefficients.

On the Mitsus, the boost controller is less sophisticated and uses a target engine load value instead of a target boost (Nissan does this too). USDM Evos don't have MAP sensors really. The closed loop is just proportional control only from what I've seen. It still seems to work though. I'd post up the tables I have but I don't want to clutter the thread too much.

It's probably the Mitsu lean spool control:

https://www.rx7club.com/attachment.p...1&d=1270016612

The Subarus have a factory wideband as the front O2 sensor. They use a closed loop/open loop delay counter that is incremented when certain load and TPS conditions are met. On the Subaru side a lot of people turn this off completely because they worry about the leaner mixture. But Subaru owners/tuners are often paranoid. I just cut the delay timer in half, it helps with safety without wasting too much fuel. GM's have a "power enrichment" mode (and have had that for many years) where the target AFR's shift for WOT and high load operation, so the AFR's are leaner when power enrichment isn't triggered.

The R35 GT-R's are sophisticated; they run in closed loop all the time, even WOT, with one wideband for each cylinder bank. And the timing maps are not the traditional table of commanded spark timing BTDC vs rpm and load/boost. They are actually based on calculated flame front speed, although I don't think this is completely understood yet. When you mess with these newer cars you start to realize just how insanely primitive the FD and the PFC really are.

I almost own one. I have a friend with an FD who travels a lot for work. In fact, he's the guy who got me into Rx-7's six years ago. We keep our cars in the same garage. I drive his car more than he does these days and I help him work on it. That's where I have all these random logs of sequential turbo stuff. Also, you'd be amazed how much shit you can learn when you are bored at work and have access to university databases of journal articles. I do come from a family of scientists and engineers. Believe it or not though I had a History degree in college, which taught me how to do research with proper sources.

I have a huge pdf library of this kind of random crap, anybody is welcome to PM me if you want some esoteric reading material.

When I was poor and my car garage bound I found myself doing a lot of this. How big is this library?

It most definitely is from overlap, as well as a such a long combustion chamber. I'm just pointing out that at sustained loads the rotary isn't much different however when you really get down into the nitty gritty of tuning a rotary map or carb from scratch you'll notice all the extra fuel goes into the accelerator trims (or jets as the case may be).

All turbo cars, and even supercharged waverunners like the Yamaha FZR and Kawasaki Ultra 260, run pig rich at full load, and they all suffer ungodly fuel dilution as a result. That's the main reason I bought an n/a car (S2000) as my daily driver. No fuel dilution, oil looks great after 5k miles. Don't try that with any forced induction motor.

Do you have any charts for the 911 TT?

That's ok, simple/primitive means less shit to break.

Somewhere out there Howard is having way too much fun spanking GT-R pigs with his "primitive" water/alcohol injected FD.

Over 4 gigs. Now that includes technician training programs from a few manufacturers, the SAE standards handbook as of 2008, instructions and writeups for most boost controllers and widebands, a ton of saved maps for various cars, random research and SAE papers. I've also got a gazillion service manuals and technical manuals for DSM, Evo, STi, 3000GT, FB-FD Rx-7, R31-R34 Skyline, various Hondas/Acuras, BMW N54 twin turbo engine, Porsche 944. It's decently organized but there are a lot of little papers/pdfs that I have thrown into a misc folder.

I definitely agree based on firsthand experience. It's hard to get good throttle response on a ported motor especially.

the more modern OEM systems have a lot more failsafes, like adaptive learning to maintain consistent operation as ambient conditions change. Look through even the series II Rx-8 engine controls and you'll see what I mean (Rx-8 service highlights, PM me if interested). I don't agree that there is less shit to break. Drive-by-wire on the Rx-8's for example eliminates a lot of the idle problems associated with dirty ISC valves, misadjusted throttlebodies, etc. Mail order tuning (email somebody your logs and they email you back a map) is common on newer cars, something that is practically unthinkable on an Rx-7.

You should see the kind of things that Subaru owners get away with. Some of the less knowledgeable will put a full catless exhaust on their car without proper boost control tuning and overboost like hell. Then they just throw a code, while on an FD you blow a motor. The Subaru ECU will dump fuel in, turn off boost control altogether, and pull a ton of timing (both immediately and through long term learning) when they detect that kind of problem.

It's hard to find stuff for European cars, especially really expensive ones. The shops that have disassembled the ECUs don't sell DIY tuning packages, and there really aren't any active open source projects. There are a few charts on this site for some older non turbo 911's:

http://www.911chips.com/fuelmaps.html

Another excellent thread by Ray. Just updated the FAQ thread with a link to this.

I wonder if any of these more savvy tuners are experimenting with water injection and leaner AFRs....?

It's not uncommon to run 30+ psi with that type of setup on newer turbo 4 cylinders (Evo, STi, etc). It's all over evolutionm.net and nasioc.com in dedicated sections.

Also, my comment about mistakes Subaru owners make (resulting in knock) was to point out the failsafes in newer cars, not to bash anyone. There are people making uninformed modification choices among any group of enthusiasts. It's interesting though to hear Evo owners talk about their car running rich under boost (every stock turbo car does that) and Subaru owners talking about how their engine can't handle much knock (durability is all relative). Those have been perennial complaints among turbo Rx-7 owners.

Right, but is anyone experiementing with leaner AFRs? Latent heat capacity of water far exceeds that of gas, so why do we still need pig rich AFRs?

cooling effect, rich AFR vs. water injection
 

See pic. This is out of Mark Warner's "Street Turbocharging" book, page 94. Like I said before, I don't know what assumptions were built into this chart. Oh, and to correct a statement I said earlier: you don't remove 10% of the heat from the combustion chamber, you remove ~10% more heat @ 10:1 vs. 11:1.

https://www.rx7club.com/attachment.p...6&d=1270179582

i really wish i knew how to read thos maps

Thanks....this is what I'm driving at: more tuners need to focus on "sane" AFRs in the high 12s/low 13s range with water injection, which will greatly reduce fuel dilution, keep the oil from becoming grossly contaminated and stay in grade much longer. Most people change their oil every 5-7k+ miles with UOAs that look great. I'm tired of pitch black, 5+% fuel dilution oil after 1000 miles....it's insane.

Do it and report back.

You would probably find ECUProject.com interesting. A friend and I started it because Saab tuners were charging $1,000+ for what was mostly crappy recycled tuning. The group of guys that got involved cracked Saab's Trionic 5 and Trionic 7 management system. Software is free, and you can use common market BDM devices and/or CAN bus interfaces (to monitor and modify RAM in realtime). It's pretty cool! Literally, you can tune your own car, full access to everything, stock ECU, with a well documented real time interface for $150 to buy the CAN device and an hour to splice into the bus.

The Trionic systems were and are way advanced for their time. T5 is pressure-based, T7 is mass-based. Both don't use knock sensors and have a single crank sensor and synch themselves with rotation during startup. They use the spark plugs as realtime sensors to determine the combustion charasteristics (as well as knock) on a per instance basis, post combustion, by ion analysis. I believe BMW has licensed the technology and is using it on their M6 V-10 engines.

I have a stock internal 2001 2.0L running a Mitsubishi 19T compressor wheel (15T is stock) that made 310whp and 320ft-lb torque at 22psi during the last dyno (Dynojet) on 93 octane pump gas, at a steady 12.5:1 under boost. Stock compression ratio is 8.8:1. (I've since damaged something internally experimenting with higher boost, but it's mechanical breakage from torque onset, not pre-detonation or knock, stock engine with 147,000 miles).


Anyway, now that I've found and fixed the wiring problem on the boost controller on my FD (caused 2 boost overshots, didn't find it the first time), I'll have a chance to really work through the dual S-HSV direct port water injection system that I've built. Of course, that's after I replace the broken apex seal from the last boost overshoot....*sigh*.

Before the boost overshoot, on 93 pump gas, I was running 20psi with knock numbers in the 'teens running about 12.0:1 AFR and 50/50 water/denatured alcohol.

It seems like the root issue with the rotary is the lack of sufficient heat rejection and a corresponding increase in combustion volatility, tendency to knock and pre-combust, because of: 1. the fact that there's more ignition events per comparable combustion surface per crank revolution, and 2. compounded because of limited rotor cooling, and increased heat retention.

With some extra heat rejection and the stock 9.2-9.3:1 CR there shouldn't be any problem at all running more correct AFR's on these things under boost.

Now that I have the boost control issue solved I hope to hear back from Sven soon regarding delivery on a single NRS 3mm 2-piece so I can get this thing back together and keep testing. :)

why didn't you have any overboost protection set up? fuel or spark cut? It kills me that people would rather run no overboost fuel protection at all than hit even a fuel cut

Heh heh, sometimes I forget about the big heads around here; you rotary guys can sure be nasty for no reason. :) Consider for a second that I'm coming from the world of modern and effective engine management systems that work well. It just might be possible that it didn't occur to me that it's necessary or a good idea to add a hard external cut of some sort.

So! Thanks for the suggestion, seriously. I have a hobbs switch and a n/c relay laying around, won't be hard to add pressure-based ignition cut; good idea.

Send me a PM if you're interested in any of the Saab control stuff. Saab is/was a pioneer when it comes to turbos and control; the Trionics really are one of the most advanced systems around, and we made them open. It's no problem for me to send some .bin files to you to look at in the free programming suites; there are some white papers detailing the ion technology that you might find interesting too. The suites are so good you can even look at the reverse compiled code if you want to take it to that level, that may be a little beyond what your interests-are though.

Also, you guys probably know this already, but when tuning with one of the wideband setups using the common Bosch wideband probes (VW, AEM, Innovate, etc.) your wideband signal is only going to be good down to 9.8-10.2 or so because the probe goes blind, lower than that and your reading is nonsense no matter what the displayed reading says, limited by the sensor. Seems like Arghx is showing targeted values on the control request side, but just realize that you actually can't even measure as low as some of the requested values with a common WBAFR setup. Setting targeting that low doesn't make sense anyway unless you're trying to control heat, and if that's the case, a little water is a much much better tool.

http://img.villagephotos.com/p/2004-...mp_Current.gif

(picture borrowed from here: http://www.daytona-sensors.com/tech_wego.html)

I can't think of a turbo car that doesn't have a fuel cut from the factory. On those cars without a MAP sensor the fuel cut is based on a max signal from the airflow meter. For example, on the Evo 8, 3000GT, etc the fuel cut is when the signal frequency is above something like 2400 hertz. Cars with a factory MAP sensor usually have the fuel cut based on boost. The 2nd gen FC3S turbo had fuel cat back in 1986 (it was like 8.5psi). Any Subaru will have boost-based fuel cut and knock-based boost cut. Ignition cut works too. A fuel cut is built into the Power FC and people just disable it completely. Part the reason for that is the fact that the PFC manual from Apex'i actually tells you to do that if you are using an external boost controller. And that's just silly. I've hit overboost fuel cut plenty of times. It's not good

Will do.

Got your PM, I'll send you some .bins and a link to the software download later today. You should probably get both the T5 and T7 suites to look at the difference, compare/contrast.

As for the a hard fuel cut, I didn't say that Saabs don't have one, I said that I'm used to a control system that works well. The knock control schemes in Trionic are very effective so it's rare to hit a fuel cut. In fact, I've never hit a fuel cut tuning on my own car.

And actually, now that you mention it, I met up with Chuck down here back a few years ago, and I think he disabled my fuel cut; since then I've re-scaled for 3bar, converted to e85, changed injectors, basically everything is different, but I know I didn't add fuel cut. I totally forgot about that. I agree with you, I'll have to go check through the settings again. I like the idea of ignition cut a little better, probalby do both I think.

having seen a few of each, id say that the subaru engine is more fragile than the rotary, the piston ring lands are very weak, even STOCK cars can break them. i'm in CA, so we have 87 octane that acts like 85 octane, our subaru dealers stock the ring set....

or data point 2, on the subaru engine, there is a freeze plug on the block that lets you change pistons without taking the rest of the short block apart, no other engine is like that.

by contrast, its very rare to see an FD with the factory main cat have an apex seal failure.

Lots of good info, Thanks Guys.

Barry

Here's more to consider. This is a chart of WOT AFR's on a completely stock Series I Rx-8:

https://www.rx7club.com/attachment.p...1&d=1271052890

Source data is attached. I got that from somebody on rx8club if I remember correctly. AFR is measured with the factory Rx-8 wideband.

Here's the target AFR table for a 175hp nonturbo Subaru Outback:

https://www.rx7club.com/attachment.p...1&d=1271052890

The Rx-8 is maybe a little richer than that in some places, but it also revs a lot higher and higher rpms usually have a richer commanded AFR in stock calibrations. Now here's the target WOT AFR table on a 2007 C6 Z06:

https://www.rx7club.com/attachment.p...1&d=1271052890

The Z06 is actually tuned richer than the Rx-8. So that's two naturally aspirated engines that make either way less or way way more power than the Renesis while still running AFR's in a similar range.

rich AFR ZO6?
 

Speaking of ZO6, check out the linked dyno video. I'm pretty sure this ZO6 was stock, and tailpipe AFRs were in the 10's!! Not sure if that's normal or not, or how reliable the dyno's air/fuel readings are. When I ran my car, the tailpipe AFR was indicating a little richer than my wideband upstream of the cat, maybe by 0.2-0.5. Go to 1:17 in the video. Car made insane power too, wonder how much more he could get if he leaned it out some...

http://www.youtube.com/watch?v=Ca3baOfF1P8

its also lean before it goes WOT...

Maybe i'm missing something about this thread, but I've ran 4cyl and 6 cyl turbo Honda engines at 12.5:1 on 91 octane, something you don't ever want to do on a rotary, hence why they run rich.

Hondas do seem to tolerate a little leaner mixture on lower octane fuel. But you also have to be careful doing a comparison because of differences in overall combustion chamber pressure due to lower flowing turbos. Also, for comparison purposes no Hondas came with a turbo from the factory except for the RDX--and the RDX was tuned to AFR's in the low 10's. http://www.turbomagazine.com/tech/tu...ash/index.html

so Honda did the same thing as every other manufacturer

the thread title should be changed to FD's don't run rich comparatively

way back in the day we tuned the Na FC ITS/PS1 car on the dyno, with a haltech. it made best power @13.1 afr, more fuel lost power, less fuel lost power.

the current car is an integra with a non vtec b18. for the 08 25 hours of thunderhill, the tune was about 13.3 afr, and we actually broke stuff with detonation http://picasaweb.google.com/MWStockl...40827802289746

for 09 we again tuned it on the dyno, the stock map ran in the mid 12's (like 12.4) at high rpm WOT, and MADE MORE POWER than the 13.3 map....

we eventually ended up with a nice 139fwhp tune that was around 13.1, or THE SAME as the rx7

links to pics of the racing is in the siggy