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Old 08-05-2003, 02:53 PM   #1
Jaxx
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Default target a/f ratio and boost

is there a chart of some kind that showes desired a/f in relation to boost

or is this a lean-till-it pings sort of thing
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Old 08-06-2003, 12:22 AM   #2
bobsterswrx
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Most of the tuners I talk to set A/F based on octane used. You can run higher ratios with C16 vs pump gas. For 91 we are at appox 10.5-10.7:1 and at 95 oct we are closer to11:1. I noticed as we increased boost we did not need to increase fuel much once we had a good map for the fuel we were using. I'm not an expert but 2+2 usually = 4 and that's what I observed.
Bob
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Old 08-07-2003, 10:59 AM   #3
NavyBlueSubaru
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Using 93 octane i like to run around 12.5:1 afr at full boost, i.e. 18psi. This is water injection, of course heh I think turboxs aims for 10.5 - 10.7 :1 as their afr for most of their stages.

Jeff
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Old 08-07-2003, 11:12 AM   #4
RiftsWRX
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Quote:
Originally posted by NavyBlueSubaru
Using 93 octane i like to run around 12.5:1 afr at full boost, i.e. 18psi. This is water injection, of course heh I think turboxs aims for 10.5 - 10.7 :1 as their afr for most of their stages.

Jeff
LOL! was going to say... until I saw the water injection comment hehe

11.3-11.5 is "doable" on 93, just takes vigilant tuning... for a race type map that's ok... but day to day your stock internals won't like the 1600+egt's for very long.

Jorge (RiftsWRX)
www.ProjectWRX.com
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Old 08-07-2003, 01:29 PM   #5
Austin
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Jared - I tune for 10.8 - 11.0 up to about 5800rpm, then work down to ~10.5 @ 7200rpm.
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Old 08-07-2003, 10:19 PM   #6
skywalker
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I have been doing pretty well running 11.5:1 on California 91 octane gas.

Though if you are speaking theoretically the optimal level is 14.5:1 for most power. Of course we all know that this doesn't happen in real life. There are a lot of factors and lots of those factors come down to the reliablility of the engine itself. I have noticed some Subaru engines just don't like to run 11.5:1 at all, just the way it is. But some can go up to 12.5:1 like my RS with a Turbo Kit, loved it right there, and I was making lots of power.

The EGT's would reach about 1600 max, but that was fine for what I was doing. That is another thing to watch out for, if you want your EGT lower add more fuel. Of course doing this you lose power. Bigger bang causes more power but more heat.
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Old 08-08-2003, 12:35 AM   #7
MAD REX
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What about afr's when off boost?


I have a 18g that doesn't start making positive boost til 3k rpm's or somewhere around there.

I've been watching the Utec dashboard and when I'm at WOT from 1500 rpm's to 3000 the afr is about 13.1:1 to 13.3:1

Is that too high to low or ok? I'm trying to get it to spool faster.
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Old 08-08-2003, 03:46 PM   #8
skywalker
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The only way to really know if it is too high or not is to measure your EGT's also and to check the spark plugs to see how they look. From my initial guess though you are probably running a little leaner then you should.

Does the car ping at all? What O2 sensor are you reading off of, the front or rear? That makes a difference also.

Just some things to think about.
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