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AFR's and Powah
Ok, this is sorta weird. I was running 8 PSI boost at 12.5:1 AFR's for a couple days. The power was NICE. Now I'm at 10.7 PSI and running 11.5:1 AFR's and I could swear it's not much faster than 8 was at 12.5:1. Feels the same or a spec better yet it's 2.7 pounds more boost....
I'm gonna datalog it tomorrow and make sure I'm still getting 10.7 PSI boost (no boost gauge, I know, gay, but it's a sleeper). But I haven't touched the MBC so it should be the same as ambient temps haven't changed either. Just curious if anyone else has seen a noticeable power difference going from rich to lean or lean to rich? I don't have any dyno proof of course but it sure isn't impressive like it was. Or maybe I'm getting used to it. But I really don't think it's pulling like it should. EDIT: I changed the numbers. Turns out I was running EIGHT pounds before, not 7. So not as big of a difference as I thought.... |
rich is always a bit less power but safe. on my subaru going from 12:1 to 11.25 was a noticeable decrease in power. I really dont think anything is wrong with your car
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is timing optimized at both boost levels?
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Timing table stayed the same when I changed boost and wasn't optimized. Was just surprised that the difference in adding boost and changing AFR's to be richer made for a small HP gain. I edited my first post as I thought I was running 7 before, and that the change in boost was 4 psi, but it was actually only 3.
Here's the timing map I'm running. Attachment 209253 |
richer you go you trade horsepower for torque right?
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Originally Posted by johndoe
(Post 349360)
richer you go you trade horsepower for torque right?
The relationship between HP and torque is fixed. Specifically, HP = (Torque * RPM) / 5250. For any given RPM, you cannot decrease one unit (HP or Torque) without also decreasing the other, nor increase one without the other. If one remains the same, then both remain the same. |
well u know what they say..... when its lean its mean.... but i keep it in the mid 11's to be safe that's what im at.... also you are pulling alot of timming no? at atmospheric im in 29 to 30 adv and for now since my car is only ass tuned (street stuff) im pulling about 1 deg per lbs and i think its safe.... im sure you could bump up that timing a lil. granted you have a big turbo i think you are pull a lil too much. it prob felt nice a 8lbs cuz you had more spark adv.. and that 12afr helped too... you dont really make power off of fuel.. ign is where it at..
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I built a conservative timing map, then tuned fuel on the street. After that I went to the dyno to tweak the IGN and then adjusted fuel. It took five (or six) pulls ($150) and I left with 30 more whp and 20 more ftlbs. The IGN map was the key, but I had no desire to try and tune the IGN on the street while trying to drive. Far easier on the dyno with two people IMO. Final AFR was 11.6-11.8 with 10* advance at peak torque, rising to 19* at 7k rpm on 93 pump.
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needs more advance and less fuel.
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Originally Posted by patsmx5
(Post 349349)
Timing table stayed the same when I changed boost and wasn't optimized. Was just surprised that the difference in adding boost and changing AFR's to be richer made for a small HP gain. I edited my first post as I thought I was running 7 before, and that the change in boost was 4 psi, but it was actually only 3.
1a. boost 1b. compression ratio (lets forget this for now) 3. timing 4. AFR assuming you're only changing each by less than 10% and already in the ballpark of a decent tune. in other words, adding 1.5 psi to a 15 psi car gains more power than adding 1 degree (to 10) of timing if you're below MBT and both increase (or decrease?) power more than changing AFR from 11:1 to 12.5:1 |
Seems to rich to me Pat, im running 12:1 at 15psi.
IMHO anything below 12 is to rich, tune the spark to reduce knock, dont compensate with more fuel. If you have trouble controlling detonation with too much advance get water injection. At least thats my take on it. |
i'm gonna disagree with sam, to a point. i'd rather have the best timing for power than the ideal AFR.
Why: because I think excessive spark retard causes as many problems as it solves. Start pulling timing and leaning things out, and you'll raise EGT and risk burning expensive parts. I dont think running 11ish AFRs is a crime if your spark is well tuned and you're running relatively high boost. |
^ im on the same level as u and cupcar
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Originally Posted by y8s
(Post 349621)
i'm gonna disagree with sam, to a point. i'd rather have the best timing for power than the ideal AFR.
Why: because I think excessive spark retard causes as many problems as it solves. Start pulling timing and leaning things out, and you'll raise EGT and risk burning expensive parts. I dont think running 11ish AFRs is a crime if your spark is well tuned and you're running relatively high boost. I agree with what you say. I guess I'm tuning it a bit rich so I can get spark dialed in. I tune for 11.5, then if I tune spark and it begins running a bit leaner, I won't go too lean as to possibly induce knock. I need to get a new fuel pump in here. I had to dial in a ton of fuel in the VE table to keep AFR's around 11.5:1 in boost over 160kpa. I think I have values around 130%:eek5:. |
Originally Posted by y8s
(Post 349621)
i'm gonna disagree with sam, to a point. i'd rather have the best timing for power than the ideal AFR.
Why: because I think excessive spark retard causes as many problems as it solves. Start pulling timing and leaning things out, and you'll raise EGT and risk burning expensive parts. I dont think running 11ish AFRs is a crime if your spark is well tuned and you're running relatively high boost. But I am not saying to retard the timing and lean out fuel, one or the other. Personally id rather run a more ideal AFR then run a more advanced spark where knock is more prominent. Tossing more fuel then you have to into the exhaust seems like a waste. Also running to rich can hurt power as well. So where is the happy medium? I just think running richer mixture to control detonation is impractical and at that point it makes sense to use water injection. I have noticed better engine performance from more ideal AFR mixtures then more spark, even though I am running a pretty conservative spark map. |
I could run 12.5 AFR at 16psi and not get knock BUT I made way more power with more IGN advance and more fuel, while the EGTs dropped. 11.6-8 was definitely the sweet spot for my car at 16psi after peak torque.
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Originally Posted by m2cupcar
(Post 350102)
I could run 12.5 AFR at 16psi and not get knock BUT I made way more power with more IGN advance and more fuel, while the EGTs dropped. 11.6-8 was definitely the sweet spot for my car at 16psi after peak torque.
I'm no expert in tuning, but from the reading I have done, its always been like "dont run too rich". |
Originally Posted by Saml01
(Post 350109)
Ill trust your experience.
I'm no expert in tuning, but from the reading I have done, its always been like "dont run too rich". |
So where does the knock suppression of richer mixtures come from? If the mixture gets ignited by the spark, a flame front spreads out from the spark plug. This burning mixture increases the pressure and temperature in the cylinder. At some time in the process the pressures and temperatures peak. The speed of the flame front is dependent on mixture density and AFR. A richer or leaner AFR than about 12-13 AFR burns slower. A denser mixture burns faster. So with a turbo under boost the mixture density raises and results in a faster burning mixture. The closer the peak pressure is to TDC, the higher that peak pressure is, resulting in a high knock probability. Also there is less leverage on the crankshaft for the pressure to produce torque, and, therefore, less power. Richening up the mixture results in a slower burn, moving the pressure peak later where there is more leverage, hence more torque. Also the pressure peak is lower at a later crank angle and the knock probability is reduced. The same effect can be achieved with an optimum power mixture and more ignition retard. Optimum mix with “later” ignition can produce more power because more energy is released from the combustion of gasoline. Here’s why: When hydrocarbons like gasoline combust, the burn process actually happens in multiple stages. First the gasoline molecules are broken up into hydrogen and carbon. The hydrogen combines with oxygen from the air to form H2O (water) and the carbon molecules form CO. This process happens very fast at the front edge of the flame front. The second stage converts CO to CO2. This process is relatively slow and requires water molecules (from the first stage) for completion. If there is no more oxygen available (most of it consumed in the first stage), the second stage can't happen. But about 2/3 of the energy released from the burning of the carbon is released in the second stage. Therefore a richer mixture releases less energy, lowering peak pressures and temperatures, and produces less power. A secondary side effect is of course also a lowering of knock probability. It's like closing the throttle a little. A typical engine does not knock when running on part throttle because less energy and therefore lower pressures and temperatures are in the cylinder. This is why running overly-rich mixtures can not only increase fuel consumption, but also cost power. |
Originally Posted by Braineack
(Post 350151)
thug for life.
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m2cup car and y8 are on point... i basically said it in my first post on this topic also....... also i talk to all my friends that work in the tuning industries, motec, efi tech all the time about the race cars and street cars they had played with and they all for street app 11.5-11.8 is best for street. im just getting into the boost stuff now with my own car and playing around. i use to work for a koni cup rx8 team in grand am and i did data acquisition and in charge of the mapping. i achieved 214 to the wheels on a stock rx8 intake and exhaust... and competing with speed source at the time when they were running koni st. anyways getting off topic set your afr's anything under boost 13.8 to 14.7 with the stock spark adv(not sure what 99 is but early 1.8 is about 29-30 at atmos) then pull .75-1.5 per lbs depending on turbo app (meaning size). then go to dyno play with load control (if the dyno has it) watch the live torque and add until it stops and back off a deg or two then go on to next cell. once you do a couple cells you kinda see where you are going and can guess the value close to narrow it down and waist less time...(granted its kinda scary on a turbo car with turbo spooling and waste gate opening). but thats the best way to do it. or the old fashion way.. full throttle pulls and keep bumping up that timming until you start losing torque or not gaining any and back off 1-2 to be safe. then scale your table according. man i could go on all day i got a pool match to go to.
good luck with the tune |
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Ok, I leaned out the AFR table a spec for off boost. It does drive a spec smoother I guess. The car definately feels like it "falls on it's face" when I'm first going into boost and AFR's hit 11:1. I'm gonna change that to 12.5:1 or 12:1 for the first few boost cells. I can tell 11.5:1 is hurting it. Anyways, what I'm running now:
Attachment 209172 |
post up your ign map - afr is nothing without ign when it comes to making power from the afr
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2 Attachment(s)
Originally Posted by m2cupcar
(Post 351556)
post up your ign map - afr is nothing without ign when it comes to making power from the afr
AFR TABLE: Attachment 209170 Timing Table: Attachment 209171 |
is your cpu set at 640x480?
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Originally Posted by Braineack
(Post 351558)
is your cpu set at 640x480?
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That ain't the problem.
A normal 12x12 table gets rendered at 635x407. The ones he posted are 1024x651, including the whitespace. However it appears that they're being upscaled post-capture, due to the uneven stroke width (and antialiasing) of the text. Pat, how are you doing these screencaps? |
that's a lot of advance for 500 and 1000 rpm columns. does the MS use that table for idle? cuz if so, you're idling way advanced. and based on your AFRs, very rich. that lower left corner should be all 10-14 degrees and 14:1 AFRish.
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Originally Posted by y8s
(Post 351579)
that's a lot of advance for 500 and 1000 rpm columns. does the MS use that table for idle?
I think he discussed this earlier (or possibly in another thread) where he's deliberately running a lot of spark advance, and a super-rich mixture, in idle. He was tuning for max vacuum at idle, and that's the setup that achieved it. |
Originally Posted by patsmx5
(Post 351559)
No idea what you're talking about. How do I check?
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I was using what brain said to do: Alt and then print screen. That copys JUST the window that's on top so to speak, rather than the entire screen. Then pasting it in MS Paint. Then making dragging it bigger so it's easier to read and doesn't leave a huge white space of nothing. Is there a better way to do this I assume?
As for the idle advance, I do that because I like how it runs. It's quieter, cooling fans run less and less chance of overheating at idle, more edgy. I get 23-24 kpa total map at idle when fully warmed up. And as Mr. Perez noted, I run these idle cells rather rich too because I don't have a working IAC valve, so when it's 20 or 30 *F out, it idles well. |
Select the corner little box on the edge of the white box (will turn into a double sided diagonal arrow) and shrink it down so it crops around the pasted image :P
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Originally Posted by Braineack
(Post 351592)
Select the corner little box on the edge of the white box (will turn into a double sided diagonal arrow) and shrink it down so it crops around the pasted image :P
So whatcha think of my AFR table now? Look more better? |
it does look better. but there's no reason to run richer than about 13.5 below .001 psi.
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Originally Posted by y8s
(Post 351604)
it does look better. but there's no reason to run richer than about 13.5 below .001 psi.
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thought maximum N/A power/torque was at 13.2ish... but i'm only saying up to 100kpa, not a few psi of boost. I forget what mine is incidentally :)
edit: just looked and I'm a little leaner than I suggest. I probably could use some AFR updating, but I'll probably still aim for around 13:1 and no richer at 100kpa. but it's too cold to go outside. |
Originally Posted by y8s
(Post 351620)
thought maximum N/A power/torque was at 13.2ish... but i'm only saying up to 100kpa, not a few psi of boost. I forget what mine is incidentally :)
To quote Abe in another post:
Originally Posted by AbeFM
(Post 351614)
You can run a LOT leaner at 101. Unless you're NA and trying to make big power. Otherwise I'd run 15.5:1 at 100 kpa.
I think you can rescale, maybe that's only MS-II. As for 13.2 being the number, where did you get that? It's not too far off base from 12.5-13 that I've always heard. Just seems a bit too lean. |
abe's nuts running 15s at 100kpa! Though Ben does run that lean up to about 80 kpa (Ben?) I seem to remember.
a google search turns up the 13.2 number various places. |
Originally Posted by y8s
(Post 351664)
abe's nuts running 15s at 100kpa! Though Ben does run that lean up to about 80 kpa (Ben?) I seem to remember.
a google search turns up the 13.2 number various places. |
at steady cruising speed with very low throttle/high vacuum you should be at 14.5-14.9afr. as you near boost afr should be in the 13 afr range, a few psi of boost 12's, and full boost 100% throttle, i tune for 11.6-11.8 afr. only time i run 12.0-12.3 afr under full boost is at the track (drag racing). and i switch back as soon as i leave. your right about switching to 12.0-12.5 as you come into boost. 11.0 is way too rich at that point.
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Hmm. So I'm reading what I can find, but I'm not finding any badass articles on google yet. But from what I've gathered, older 2 valve engines do make more power running ~12.5:1 where newer 4 valve, fast burn engines make more power running a bit leaner, varying from 13-13.5, many using the 13.2 number. All of this is at atomospheric pressure though.
So here's what I'm thinking now. Now I ran this engine at 190 kpa a few times at 12.5:1, so I know it will do it. (and OMG it pulled like crazy!). But I want to keep it safe for now. So I'm gonna probably tune my VE table to this. Hopefully running a bit leaner at low boost will help it not feel like it "falls on its' face" when I first go into boost, as it does now. Attachment 209166 |
pat I'm liking that map. aside from the earlier discussed idle area of course.
next see if you can find something about leaning slightly as RPMs rise. and conversely richening up the low rpm/high load areas relative to the rest of the map. this is due to knock resistance changing with RPM. (it's also addressed some with spark) but I can't search now, got a gf and dvd waiting for me! ;) |
Originally Posted by y8s
(Post 351664)
abe's nuts running 15s at 100kpa! Though Ben does run that lean up to about 80 kpa (Ben?) I seem to remember.
a google search turns up the 13.2 number various places. Think about it. When you stab the throttle, if anything you're only going to quickly blaze through these cells. And as you're going through them, you have accel enrichment adding extra fuel. FWIW, I watched my car make more power on the dyno in high 11s than mid 12s. I did not believe it until I saw it. Can't wait to get the new car on a load dyno. |
Seemed logical to cross-link this
https://www.miataturbo.net/forum/t29956/#post351847 |
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Here's my latest AFR table. Very similar to the last one I posted. I tuned the car some on the table above this one and now it's a seamless transition going into low boost. It feels "normal", like I just pushed the gas pedal more, rather than boost building. Doesn't fall flat like it did running 11:1. :giggle: Gonna put this table on later and tune some more. But overall, it's getting a lot better.
EDIT: Whoops, for got to post the table... Attachment 209160 |
glad it's workin' for ya. yeah, like i said, i may run 12.5 at the drag track, but change it back to high 11's map before i leave. of course it may run fine and be great at 12.5, but it leaves no room for error. like a bad tank of gas, or big change in temp. or altitude or any little thing that can happen. good luck
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Tuned it to the map above. Yeah, it's awesome. Power at low boost is much better. I did a pull today on the highway in second and it broke the tires loose around 50mph. :eek5: I laughed out loud.
Exactly though, I don't want to get too aggressive and have a little something get off and detonate. I feel pretty comfortable with how it's tuned right now. I may lean it out a spec on the upper boost cells in the future, but not before I completely redo the fuel system. Because as of right now, I loose fuel pressure around 50% duty cycle on the injectors. I'd hate to tune it to run 12.5:1 on a day when it's pumping good, and then one cold day it doesn't hold pressure like before and I run too lean. |
hey pat, I felt like goofing around and adding a little fuel in my super-atmospheric region (90kpa and up) and I dont know if it's the mixture or the 30F air temps but the car seems to pull harder in the midrange as boost is coming on.
it's now basically a ramp from 13.4 at 90 kpa to the mid 11s in the 200kpa region. |
That's good to hear. Basically like the table I posted, but a bit more linear? I think this AFR table is gonna be a keeper. Also, you might appreciate this:
I cranked the car today at 30*F ambient and it idled fairly well at 12.5:1 cold. First time ever it's done that. I think having the spark advanced like I do makes all the difference though. Idling around 22* around 900 RPMs and 12.5:1 and it was solid and smooth. So who knows, maybe I can lean that spot out a bit more. I guess if anything I could lean it out and just dial in a bit more warm up enrichment. But it has been my experience that running high 12's at 100kPa from 400-1400 ish is the best AFR for power and smoothness. Any leaner and I can't get enough spark in there for good grunt, any richer and power falls off. |
who knows. my car idles fine at 14.5:1 and 12 BTDC. and plenty of vac.
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during enrichment 12.5 at idle is fine. i think that's where i'm at. but once warmed up, it should be 14.5-15.1 for sure. same thing when your just cruising (high vac.) at any speed. reason being, that is where your car spends the most time everyday. if your car is too rich in those cells, the extra fuel will wash your cylinders out and you can scour the piston walls and all sorts of other terrible things. i've seen a car that was tuned on a dyno before and never adjusted for cruising/light throttle conditions. his motor lasted 2mos. another was a rotory. he took the ''rotory's like to run rich'' saying too far and killed his apex seals in a few months. those are extreme examples, but you can be ''too rich'' contrary to what any women may have told you! lol
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