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FD's don't run rich.

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Old 03-30-10, 01:52 PM
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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).



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.



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:



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:



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:



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:



You can see the wideband pegs rich at 10:1, which is very close to the Evo X target AFR table.
Attached Thumbnails FD's don't run rich.-fd_afr.png   FD's don't run rich.-lgt_afr.png   FD's don't run rich.-vr4_afr.png   FD's don't run rich.-z32_afr.png   FD's don't run rich.-evox_afr.png  

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Old 03-30-10, 01:56 PM
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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)."



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.
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Old 03-30-10, 04:43 PM
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Interesting thread
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Old 03-30-10, 05:39 PM
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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?
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Old 03-30-10, 06:19 PM
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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.
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Old 03-30-10, 06:28 PM
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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?
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Old 03-30-10, 07:25 PM
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My FD ran pretty rich on the stock ecu. My gas mileage went up about 20% after installing a PFC.
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Old 03-30-10, 07:33 PM
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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.
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Old 03-30-10, 10:27 PM
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Originally Posted by arghx View Post


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

Attached Thumbnails FD's don't run rich.-f_ratio_emissions.jpg  

Last edited by mdpalmer; 03-30-10 at 10:40 PM. Reason: adding emissions chart
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Old 03-30-10, 11:07 PM
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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
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Old 03-31-10, 01:13 AM
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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 :-)
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Old 03-31-10, 01:41 AM
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Originally Posted by milano maroon
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?
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.

Originally Posted by dguy View Post
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.
Probably due to the overlap.

Originally Posted by mdpalmer
That boost curve looks horrible. Losing 5 or so psi from peak to redline, blah Or maybe that was deliberate by the Mitsu engineers?
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.

Originally Posted by mdpalmer
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...
It's probably the Mitsu lean spool control:



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.

Originally Posted by rdahm View Post
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.
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 **** 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.
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Old 03-31-10, 07:01 AM
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Originally Posted by arghx View Post
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?
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Old 03-31-10, 10:18 AM
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Originally Posted by arghx View Post

Probably due to the overlap.

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).
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Old 03-31-10, 10:48 AM
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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?
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Old 03-31-10, 10:52 AM
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Originally Posted by arghx View Post
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.
That's ok, simple/primitive means less **** to break.

Somewhere out there Howard is having way too much fun spanking GT-R pigs with his "primitive" water/alcohol injected FD.
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Old 03-31-10, 12:21 PM
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Originally Posted by NissanConvert View Post
How big is this library?
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.

Originally Posted by dguy View Post
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).
I definitely agree based on firsthand experience. It's hard to get good throttle response on a ported motor especially.

Originally Posted by no_more_rice View Post
That's ok, simple/primitive means less **** to break..
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 **** 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.

Originally Posted by no_more_rice
Do you have any charts for the 911 TT?
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
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Old 03-31-10, 03:17 PM
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Another excellent thread by Ray. Just updated the FAQ thread with a link to this.
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Old 03-31-10, 06:20 PM
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Originally Posted by arghx View Post
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.
I wonder if any of these more savvy tuners are experimenting with water injection and leaner AFRs....?
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Old 04-01-10, 01:05 AM
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Originally Posted by no_more_rice View Post
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.
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Old 04-01-10, 10:32 AM
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Originally Posted by arghx View Post
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.
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?
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Old 04-01-10, 10:44 PM
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Lightbulb 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.

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Old 04-01-10, 10:54 PM
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i really wish i knew how to read thos maps
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Old 04-02-10, 12:43 AM
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Originally Posted by mdpalmer View Post
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.
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.
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Old 04-02-10, 01:25 AM
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Originally Posted by no_more_rice View Post
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.
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