target a/f ratio and boost

Jaxx · 08-05-2003, 01:53 PM

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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bobsterswrx · 08-05-2003, 11:22 PM

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

NavyBlueSubaru · 08-07-2003, 09:59 AM

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

RiftsWRX · 08-07-2003, 10:12 AM

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

Austin · 08-07-2003, 12:29 PM

Jared - I tune for 10.8 - 11.0 up to about 5800rpm, then work down to ~10.5 @ 7200rpm.

skywalker · 08-07-2003, 09:19 PM

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.

MAD REX · 08-07-2003, 11:35 PM

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.

skywalker · 08-08-2003, 02:46 PM

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.

08-05-2003, 01:53 PM	#1
Jaxx NASIOC Supporter Member#: 177 Join Date: Aug 1999 Chapter/Region: NWIC Location: Boise,Idaho,USA Vehicle: The 93 Imp W/EJ20K flat black	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 * Registered users of the site do not see these ads.

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08-05-2003, 11:22 PM	#2
bobsterswrx Scooby Newbie Member#: 31555 Join Date: Jan 2003	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

08-07-2003, 09:59 AM	#3
NavyBlueSubaru Scooby Specialist Member#: 22127 Join Date: Jul 2002 Chapter/Region: South East Location: Oviedo, FL Vehicle: 2013 BMW 335i Sedan Estoril Blue	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

08-07-2003, 12:29 PM	#5
Austin Scooby Guru Member#: 7089 Join Date: May 2001 Chapter/Region: NWIC Location: Moscow, ID Vehicle: 05 Legacy GT Sedan 07 4Runner Limited	Jared - I tune for 10.8 - 11.0 up to about 5800rpm, then work down to ~10.5 @ 7200rpm.

08-07-2003, 09:19 PM	#6
skywalker Scooby Specialist Member#: 1990 Join Date: Jul 2000	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.

08-07-2003, 11:35 PM	#7
MAD REX Scooby Specialist Member#: 18163 Join Date: Apr 2002 Location: Denver Vehicle: 2002 2.5 WRX MBP	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.

08-08-2003, 02:46 PM	#8
skywalker Scooby Specialist Member#: 1990 Join Date: Jul 2000	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.