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Old 11-29-2004, 01:18 PM   #1
jblaine
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Default Let's talk AFRs

I'd like to start a discussion about AFRs for turbo models (93 octane, no WI, etc).

I am gathering (keeps being reinforced over and over) that running anything richer than roughly 11.3:1 in our cars is a total waste of gas during open-loop fueling (in any temperatures). That number already includes plenty of cooling fuel.

That is, more specifically, people using 11.0:1 as "absolute leanest" then adding "cooling fuel" to get to 10.5:1 are completely overkilling it.

Comments? Thoughts? Speculation? Theory?
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Old 11-29-2004, 02:03 PM   #2
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Are you talking about 2.5 or 2.0? Actually I should be more specific, are you talking about the 257, 207, or the 205.

I tend to run the 207 and the 257 leaner, with better results than the 205. That is partially based on my willingness to run the 207 and the 257 hotter than the 205.

Something to think about is how much are you loosting power wise, and how much are you loosing gas mileage wise by running the car that much richer. On some cars I have seen very minimal losses when adding in the little extra fuel. In those cases it just makes sense to leave a little more cushion. Honestly I have never tried a gas mileage comparison to see if that little extra fuel has a significant impact on mileage. On my personal car I get bad mileage and I am still running it leaner than I would a customers car. It may be that I would get even worse mileage, but I doubt that is possible.
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Old 11-29-2004, 02:23 PM   #3
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I'm suggesting this across all of the engines you mentioned, including the EJ205 -- that roughly 11.3:1 is a safe/cool AFR to target.

Don't get me wrong, I'm not one to nitpick/monitor MPG figures in sportscars, but at some point you are needlessly throwing away money. My main intention for this thread isn't really about fuel economy as much as it is about reevaluating historical trends/beliefs for accuracy and sanity.
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Old 11-29-2004, 04:14 PM   #4
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I think it's a great question, that touches many topics. I like focusing on the fuel component of our engines every once in awhile instead of the very popular induction component. Obviously if you are detecting detonation (or pre-ignition) at 11:1 you have to do something.

To me, an AFR maximum of 11:1 is a noble one. For me the question is: are you "substantially better off" with higher boost if that means dropping below AFR 11:1, than you would be in improving the temperature of the charge to maintain that AFR ratio? This question, we ask ourselves all the time.

For the sake of argument, lets say you have a choice: you can add 25% more boost or cut 25% of the fuel (roughly AFR 10:1-->12.5:1) because you have lowered the temperature at the intake manifold (and/or increased octane). Which will give you more power? Which is the cheaper modification? Which is simplest?

No simple answers here. Downward force on the piston is what we are after. I don't think many of us know what would happen if we could run "rich best torque" conditions. Dumping more fuel to save us from detonation, but also killing more power seems like a "no win" solution to the det problem.

I can feel the flames lapping at my toes already.
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Old 11-29-2004, 05:08 PM   #5
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Jup... The richest I typically will run a car is 11:1, On average, a car will run anywhere from 11.3 to 11.5:1 AFR's. That's on EJ205's.

257's seem to do decent in the low to mid 11's as well.

Another thing to talk about is the obvious pumping loss of unburnt fuel. 10.8:1 feels substantially different from even 10.9:1, the next major jump as measured by ass is in the 11.3 range. Then 11.8-12:1.

207's are animals.. hell we had one running 13:1 at 22 PSI on a 39 and it never had an issue.

VE, such a wonderful thing.

I personally run around 11.2:1 on my 257, but that's in part to chicago's HORRIBLE winter gas, compression, etc. That's not using WI btw..

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Old 11-29-2004, 05:29 PM   #6
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Quote:
Originally Posted by RiftsWRX
chicago's HORRIBLE winter gas
Quote:
Originally Posted by RiftsWRX
chicago's HORRIBLE winter gas
Quote:
Originally Posted by RiftsWRX
chicago's HORRIBLE winter gas
thats been my mantra for the past couple weeks. all of a sudden, the crossover hesitation that i rid my car of months ago creeped its way back in to terrorize me.
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Old 11-29-2004, 05:45 PM   #7
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Hell... and everyone thought I was crazy in the CtA thread, LOL.
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Old 11-29-2004, 06:41 PM   #8
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How's the bambino Jorge? Are you getting sleep yet?
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Old 11-29-2004, 06:54 PM   #9
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He's actually doing pretty good. If we bed him down around 10-11PM he sleeps through to 4-6 am

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Old 11-29-2004, 07:56 PM   #10
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Like ya first said, it's for cooling. That might not be the only effect of fueling beyond 12 to 1, but it's what we're looking to get out of the extra fuel(from what I've been told). Just like starting with a lower boost or less timing to avoid knock, fuel is no different. Having extra fuel to keep the engine running cooler then it needs to be is safer then always walking the line of death. Adding fuel to be more conservative beyond 11 to 1 is pretty normal from what I've seen with our cars. I've heard people say that they've seen the stock ecu run richer then 10 to 1 at boost, and that's at lower boost levels then many people run. Ya might not need to add so much fuel to keep the egt's where you want, but it helps the engine stay cooler for longer.

If ya never get out of third or never run the car hard for more then 14 seconds at a time, you could obviously run leaner then if you're gonna be running in higher gears for longer periods of time. On my car though, things get pretty hot above 5500rpm in fourth. It also seems like my engine is happier when the egt's are lower. Ie- the engine seems to handle more timing, and knocks a lot less when the egt's rise slower and stay lower. As always, this is just what I've seen/heard......

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Old 11-29-2004, 08:33 PM   #11
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So I guess the million dollar question is: how much does adding fuel past 11:1 actually improve knock resistance. Or how much extra timing or boost can you run say when going from 11:1 to 10.9:1 and further 10ths to make up for the power loss of running rich?

Obviously at some point you will reach a point of diminishing returns.

Say you've found the edge while running 11:1 and are looking to create a bulletproof daily driver tune. Is it better to add some fuel (how much?), pull a couple degrees of timing, or reduce the boost? Or some combination of the above?

Keep in mind that another drawback of dumping extra fuel into the combustion chamber has more negative effects than just fuel consumption. Any blowby that occurs now contains more fuel which will get into the oil as well as increase deposits inside the engine. But how much?
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Old 11-30-2004, 11:05 AM   #12
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Besides blowby, you have pumping losses, misfire issues, fouling, and a slew of issues. Personally... If you can't get away with running at least low 11's, or you have EGT issues... improve flow (exhaust housings, etc), or turn down the boost. If you have that taken care of and still can't run those ratio's, then increase the octane, cause you're gone beyond the usuable tolerance of the fuel you're using.

One proper fuel curve
One proper timing curve
One proper boost curve

Period...

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Old 11-30-2004, 11:59 AM   #13
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Why draw the line at low 11's though? Why not say that if ya can't keep the egt's normal at 12 to 1, then turn down the boost? Is there a big difference between 11 and 10.5 to 1? I've heard people saying that they've seen a stock wrx run richer then 10 to 1 at boost. Does that mean subaru's doing something wrong? I've run my car anywhere from 9.5 to 11.8 to 1 on 93 octane(not including water injection, but including n2o), and haven't had any fouling or misfire issues<knocks on wood>. Probably woulda sucked if that did happen though. Not sayin that anyone out there should run 9.5 to 1, but it could be better then the alternative in certain situations(like det, or rediculous egts). Point being is imo a/f ratio's are setup/tuner specific.

Some people might run 23psi or more with the setup that's on my car(poor turbo) and need more fuel to combat the added heat generated by running running more boost then I would. Another thing to think about is that if you always tune close to the edge, when things change a little(and chances are they will especially if you tune really close to the edge) you could end up in trouble. Maybe that's why wrx's run so rich stock(maybe there are other reasons, but that's not the point)? I just don't see how 10.5 to 1 is that much worse for an engine then 11 to 1, especially when it can help ya run more boost with less chance of melted/cracked piston/cracked head/broken........

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Old 11-30-2004, 12:40 PM   #14
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Nobody's saying 10.5:1, specifically, is "worse for an engine" than 11:1.

At some point, you are needlessly wasting fuel and decreasing torque for no reason.

This is not a mysterious magical number. It's visible via torque and EGT readings while not knocking.

Running a turbo past its efficiency range, or at 23psi, on pump gas is beyond the scope of this thread as it's already left the realm of good tuning. If you can't run 11.0:1 at Xpsi, but can run 10.5:1 at Xpsi... consistently over and over on a dyno with a scorching engine... and actually make more knock-free torque on PUMP gas, knock yourself out It's your engine.
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Old 11-30-2004, 12:47 PM   #15
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Quote:
Originally Posted by drees
So I guess the million dollar question is: how much does adding fuel past 11:1 actually improve knock resistance. Or how much extra timing or boost can you run say when going from 11:1 to 10.9:1 and further 10ths to make up for the power loss of running rich?
Yes

Quote:
Say you've found the edge while running 11:1 and are looking to create a bulletproof daily driver tune. Is it better to add some fuel (how much?), pull a couple degrees of timing, or reduce the boost? Or some combination of the above?
Yes
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Old 11-30-2004, 12:51 PM   #16
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Quote:
Originally Posted by jblaine
I'd like to start a discussion about AFRs for turbo models (93 octane, no WI, etc).

I am gathering (keeps being reinforced over and over) that running anything richer than roughly 11.3:1 in our cars is a total waste of gas during open-loop fueling (in any temperatures). That number already includes plenty of cooling fuel.

That is, more specifically, people using 11.0:1 as "absolute leanest" then adding "cooling fuel" to get to 10.5:1 are completely overkilling it.

Comments? Thoughts? Speculation? Theory?
If we were willing to run our turbochargers at peak efficiency then we could easily run AFRs in the 12:1 range but since we make substantially more power for every pound of boost added we choose to quench knock with fuel. You will also significantly add more power by advancing timing but again you need fuel to reduce knock.

There is no universal truth other than what Jorge stated and that there is one ideal timing curve, AFR curve, and boost curve, for a given engine, parts, and fuel that equals optimal power. The problem is that all those targets change given different parts and fuel. Itís up to the tuner to decide how much power and how much safety margin to leave in. Get any of these things wrong and you can ruin an engine running too lean or too rich, too much timing or too little timing, or too much boost.

If I had to have only one gauge for tuning it would be EGT. EGTs relay how complete the combustion process is and whether you have the proper ignition timing to AFR ratio regardless of boost pressure.

Thanks,
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Old 11-30-2004, 01:09 PM   #17
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Quote:
Originally Posted by Element Tuning
If we were willing to run our turbochargers at peak efficiency then we could easily run AFRs in the 12:1 range but since we make substantially more power for every pound of boost added we choose to quench knock with fuel. You will also significantly add more power by advancing timing but again you need fuel to reduce knock.
Phil, thank you for commenting. We've covered quite a bit more than this, and my original generalized post, in the thread already. If you have the time to read it and comment more specifically, it would be appreciated.
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Old 11-30-2004, 02:15 PM   #18
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Here's an example to show where when you eliminate something in the tune things dramatically change. I don't have my water injection turned on in this log, just to show how the car needs to adapt everything else being equal. Add to this the fact that our gas here is HORRID, and you can see why the timing that is being run, is being run.

Code:
4115  -7.9 2.6  17  00    00   W/B  +41.2   33.3 ECU.   +0.0 ECU.   3.0  13.65 
 4368  -6.3 3.4  87  10    00   W/B  +23.8   27.3 ECU.   +0.0 ECU.   3.6  13.84 
 4432  -3.8 3.7  93  10    00   W/B  +19.8   36.4 ECU.   +0.0 ECU.   3.8  14.37 
 4522  -0.4 4.0  95  20    00   W/B  +16.8   48.2 ECU.   +0.0 ECU.   4.1  13.12 
 4789  +4.5 4.2  93  40    00   W/B  +14.9   58.0 ECU.   +0.0 ECU.   4.3  10.86 
 4887  +8.0 4.4  95  60    00   W/B  +10.6   68.9 ECU.   +0.0 ECU.   4.5   9.99 
 5042 +11.9 4.6  95  70    00   W/B   +9.9   75.2 ECU.   +0.0 ECU.   4.5  10.02 
 5175 +14.7 4.5  93  80    00   W/B  +10.4   77.8 ECU.   +0.0 ECU.   4.6  10.30 
 5159 +16.6 4.6  95  90    00   W/B  +10.4   75.5 ECU.   +0.0 ECU.   4.5  10.65 
 5282 +18.0 4.6  95  90    00   W/B  +10.6   74.2 ECU.   +0.0 ECU.   4.6  10.95 
 5359 +18.4 4.6  95  90    00   W/B  +11.0   78.2 ECU.   +0.0 ECU.   4.6  11.05 
 5299 +19.0 4.6  93 100    00   W/B  +11.1   79.6 ECU.   +0.0 ECU.   4.6  11.11 
 5482 +18.8 4.6  94  90    00   W/B  +11.0   78.7 ECU.   +0.0 ECU.   4.6  11.14 
 5583 +18.2 4.7  95  80    00   W/B  +11.4   76.5 ECU.   +0.0 ECU.   4.6  11.14 
 5592 +18.2 4.7  95  90    00   W/B  +11.7   79.5 ECU.   +0.0 ECU.   4.6  11.18 
 5592 +18.2 4.6  94 100    00   W/B  +11.9   77.9 ECU.   +0.0 ECU.   4.6  11.27 
 5555 +19.2 4.7  94 100    00   W/B  +11.4   80.3 ECU.   +0.0 ECU.   4.7  11.33 
 5767 +19.4 4.7  94  90    00   W/B  +12.0   79.7 ECU.   +0.0 ECU.   4.7  11.33 
 5767 +19.6 4.7  94  90    00   W/B  +12.4   77.9 ECU.   +0.0 ECU.   4.7  11.37 
 5847 +19.8 4.7  94 100    00   W/B  +12.3   80.0 ECU.   +0.0 ECU.   4.7  11.39 
 5707 +19.0 4.7  94  90    00   W/B  +13.0   78.6 ECU.   +0.0 ECU.   5.0  11.43 
 5952 +19.0 4.7  94  80    00   W/B  +13.7   79.4 ECU.   +0.0 ECU.   4.7  11.45 
 5747 +18.4 4.7  94  80    00   W/B  +14.0   78.3 ECU.   +0.0 ECU.   4.7  11.45 
 5995 +17.8 4.7  93  90    00   W/B  +14.2   80.8 ECU.   +0.0 ECU.   4.7  11.48 
 6038 +17.8 4.7  93  90    00   W/B  +14.3   77.1 ECU.   +0.0 ECU.   4.7  11.48 
 5995 +18.2 4.7  93  90    00   W/B  +14.4   81.7 ECU.   +0.0 ECU.   4.7  11.48 
 6150 +18.2 4.7  94  90    00   W/B  +14.7   76.9 ECU.   +0.0 ECU.   4.7  11.49 
 6071 +18.2 4.7  94  90    00   W/B  +14.6   78.5 ECU.   +0.0 ECU.   4.7  11.45 
 6116 +18.2 4.7  93  90    00   W/B  +15.0   80.1 ECU.   +0.0 ECU.   4.7  11.45 
 6161 +18.0 4.7  93  90    00   W/B  +14.5   78.6 ECU.   +0.0 ECU.   4.7  11.48 
 6325 +18.4 4.7  93  90    00   W/B  +16.9   82.5 ECU.   +0.0 ECU.   4.7  11.45 
 6361 +18.0 4.7  93  90    00   W/B  +27.3   81.9 ECU.   +0.0 ECU.   4.7  11.48 
 6535 +18.0 4.7  98  90    00   W/B  +17.7   79.1 ECU.   +0.0 ECU.   4.7  11.48 
 6301 +18.2 4.7  93  90    00   W/B  +17.6   82.8 ECU.   +0.0 ECU.   4.7  11.48 
 6459 +18.2 4.7  93  90    00   W/B  +24.2   81.0 ECU.   +0.0 ECU.   4.7  11.49 
 6447 +18.4 4.7  93  90    00   W/B  +14.1   77.2 ECU.   +0.0 ECU.   4.7  11.45 
 6410 +18.2 4.7  93  90    00   W/B  +14.4   81.5 ECU.   +0.0 ECU.   4.7  11.45 
 6706 +18.2 4.7  93  80    00   W/B  +14.2   78.7 ECU.   +0.0 ECU.   4.7  11.49 
 6523 +18.4 4.7  93  90    00   W/B  +14.3   77.8 ECU.   +0.0 ECU.   4.7  11.49 
 6574 +18.0 4.7  97  90    00   W/B  +14.0   82.1 ECU.   +0.0 ECU.   4.7  11.52 
 6613 +18.2 4.7  92  80    00   W/B  +14.3   79.3 ECU.   +0.0 ECU.   4.7  11.53 
 6301 +18.0 4.7  93  80    00   W/B  +14.6   79.6 ECU.   +0.0 ECU.   4.7  11.53 
 6930 +17.8 4.7  61  90    00   W/B  +14.8   83.0 ECU.   +0.0 ECU.   4.7  11.56
The AFR's in question are perfect for either summer gas and no WI, or winter gas and WI, and the way the flash is setup, it is only at a IAM of 9 at even 14 degrees of advance, so when the fuel, and WI are on par, there is enough room left even in flash to learn up to that point.

EGT's at this point STILL are only 1560 at the top of 3rd, even at 15 degrees of advance hehe, and at 11.5:1. So while it sounds low, the gauges, logs, and butt sure don't tell me something is wrong.

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Old 11-30-2004, 02:27 PM   #19
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EGT is a great "check" on the WB readings, after all you haven't calibrated the WB, and a Type K thermocouple is much simpler (and usually NIST certified) than a WB.

How much power is left "on the table" when AFR is 10.5:1 compared to the ideal. I'd say alot--like 20%, that's 60 hp on a 300 hp (crank) engine.....and so on. More boost is just easier to add than solutions that reduce knock likelihood (race fuel, giant intercoolers, water injection, water-air IC...other elaborate schemes).

Even if the timing is perfect, turbo is efficient, FMIC in place, etc...."safe" tunes by excellent tuners, still seem to drop below 11:1. At some point AFR reaches a threshold where, any lower, and power is lost above what can be gained with the additional boost. That threshold seems to occur around 11:1, but most people drop it a bit further for "safety" into the high tens. In other words, if you are dropping below the high tens over a large RPM range (caveat), then lowering boost and raising AFR might yield more power than keeping the boost up.

We pay guys like Phil to make choices for us becuase they have reams of data to draw upon. I'm not saying, it's ever like falling off a log, but Phil can quickly run the variables and make a great guess at the "best". I think for Phil it's more like Zen. We can come up with the same "ideal" curves for our parts, but some "rules of thumb" like jblaine has proposed are excellent crutches to use for those of us that have not tuned a 1000 WRX's.

Maybe this "rule of thumb" is: "consider turning boost down if AFRs are consistantly below 10.5, and timing is in range"

Or: "below 11:1 AFR, you are just throwing fuel at a problem that lies elsewhere (boost or charge cooling)"

Maybe another one can be: "timing on the EJ engines normally ranges from......."

Thank you too Phil. Your comments add credibility to the discussion. Mine only add suspicion
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Old 11-30-2004, 02:36 PM   #20
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Jorge adds credibilty I still just add suspicion.

Jorge, do you think a "professional" tuner would put your tune out on the streets. Are you detecting any knock even after several loggings? Looks like none in this one.

Is this your SBR GT-11 tune?

Wait a minute, is that your timing column in the middle? No its on the far left, right?
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Old 11-30-2004, 02:43 PM   #21
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Yes, I just took that log a few minutes before I posted it. Just went to the gas station and filled the tank with 93 v-power (shell), just to have max weight in the car.

The tune is setup to be robust enough to protect itself (as you see it doing), It WANTS to run 20-24 degrees of timing with the WI turned on.

When it comes to flashes, I like this tune (I did it myself), because it offers me the most flexability for the times when I need to fall back from the UTEC (as I have to now, due to lack of OLF support for an automatic).

FYI, my wife's car is flashed in a much less broad version of my car, and it's been that way for almost a year, and she's had no issues, and it defineately knows how to take advantage of a tank of 100 if she wants to play with us sometimes, or just take my son to my parents for the day. heh.

EDIT: and yes... that's the GT30R-11 with UR785CC injectors. They're perfect.. as you can see I'm in the low 80's at redline. Just how they should be.

Jorge (RiftsWRX)
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Old 11-30-2004, 02:46 PM   #22
drees
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Quote:
Originally Posted by RiftsWRX
Here's an example to show where when you eliminate something in the tune things dramatically change. I don't have my water injection turned on in this log, just to show how the car needs to adapt everything else being equal. Add to this the fact that our gas here is HORRID, and you can see why the timing that is being run, is being run.
So in your case, you chose to drastically reduce timing instead of reducing boost or adding fuel. That is probably one of the lowest timing curves I've seen (if I'm reading that UTEC log right) with 10* at 5k RPM and only 14-15* at redline. Stock, the ECU will run around 25* at redline. What's your timing at 3k (and when does that turbo spool?)

What happens if you richen it up to 10.8:1 from low-mid 11:1, how much more timing can you run? How does the power output compare? It does seem that you've got optimal conditions for high EGTs (low timing, high boost and not too rich) yet your EGTs are OK.
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Old 11-30-2004, 02:59 PM   #23
RiftsWRX
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'07 Honda FIT sport (5MT)

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Quote:
Originally Posted by drees
So in your case, you chose to drastically reduce timing instead of reducing boost or adding fuel. That is probably one of the lowest timing curves I've seen (if I'm reading that UTEC log right) with 10* at 5k RPM and only 14-15* at redline. Stock, the ECU will run around 25* at redline. What's your timing at 3k (and when does that turbo spool?)

What happens if you richen it up to 10.8:1 from low-mid 11:1, how much more timing can you run? How does the power output compare? It does seem that you've got optimal conditions for high EGTs (low timing, high boost and not too rich) yet your EGTs are OK.
Well... 25 degrees is arbitrary.. if you notice, I'm basically MAXING the MAF sensor at 4.7 volts. I'm riding 290+g/sec all the time on boost. When you're moving that much air, you don't need as much timing...

Remember.. timing is just a crutch for poor VE, something also apparent in EGT. But of course... if the AFR's dropped you could equalize timing again. the 14 degrees is a failsafe in case water runs out, or in this case, I blatently turned the system off.

And >10.9:1 runs like ass hehe. Lowest I'll go is ~11:1.

Jorge (RiftsWRX)
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Old 11-30-2004, 03:11 PM   #24
bboy
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So that is your timing column, boost is on the far left.
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Old 11-30-2004, 03:16 PM   #25
jblaine
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*cough*topic*cough*
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