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Old 01-04-2005, 11:14 AM   #1
erggy
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Default a/f readings during cruise and boost

Just wondering what would be the ideal a/f for the scenarios below:

1. cruising at low TPS 5th gear at about 65-70mph

2. WOT boosting at 1bar with 93 or higher (95) octane fuel (rpm from 4000 to 7000)

3. idle
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Old 01-04-2005, 11:18 AM   #2
TheMadScientist
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#1 and #3 should be right at or very close to 14.7:1

#2 is going to depend on timing but most people shoot for ~11:1

TMS
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Old 01-04-2005, 11:39 AM   #3
erggy
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wow that was quick!! Thanks

For #2 would 12.5-12:1 be too lean? I'm running on octane 95 right now. Also do you know what is the range of the ignition timing for this? (WOT at around 4000-7000)? Thank you again!!
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Old 01-04-2005, 07:04 PM   #4
cdvma
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The range of ignition timing cannot be answered, as that depends on your entire setup as well as the quality of fuel you are running and at what AFR.

"too lean" depends on a lot of things. Most people would consider 12.5-12.1 too lean on a Subaru, but I think its because everyone is used to low 11s or high 10s. Sure its possible, especially with 95 octane and the right timing curve.
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Old 01-04-2005, 07:10 PM   #5
hippy
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What kinda car do you drive?
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Old 01-04-2005, 09:28 PM   #6
erggy
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I drive an MY99 STI ver 6 with VF30, exhaust, downpipe, and EMS (standalone ECU).... this is with 95 octane ^_^


another silly question if i may, why would 12-12.5:1 would be considered "too lean" for subarus and not other turbocharged cars (ie: evos, silvias, etc.)?
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Old 01-04-2005, 11:36 PM   #7
hippy
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It's a heat issue. I'm not so sure about sti's, but when ya get into the upper rpm ranges and higher gears on a usdm wrx, the engine starts to get hot. The longer ya stay there generally, the hotter it gets. It's not that going richer then 12 to 1 will produce any more power then running 12 to 1, cause it probably won't. The extra fuel beyond that is never used. It's just pumped in to the cylinder to absorb some heat, maybe slow down the combustion a bit, and then gets pushed out of the exhaust. The extra fuel helps the engine stay cooler longer. If the engine heats up slower, there's less chance of det in certain situations(maybe all situations, I dunno?).

I've found that to keep the egt's where I want them on my car with 93 octane, I need to keep the a/f ratio at 11.5 to 1 or richer. Your engine might be able to run at 12 to 1, maybe 12.5. Either way, it would probably be safer to start at something like 11 to 1 and work your way up from there. Course this is just my opinion......

peace
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