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Old 08-21-2009, 01:50 PM   #1
mellephants
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NA SVTF Tuning: AFR for 93 octane?

I have an NA SVTF and the PRP. I just figured I'd share what I did "on the way" to work this morning. Maybe it'll help someone understand a bit more about the tuning process.

I'm running 12.8:1 AFR at high loads (except 12.7:1 for >6500 RPM at 0.9-1.0 Load). I only run 93 Octane gas, and almost always from the same reliable gas station.

I was using really safe spark settings to dial in the MTF, and when that was done I started increasing my timing advance via the Borderline Spark Table. I slowly increased the timing, listening for knock during 3rd & 4th gear WOT pulls after each increase. I started close to stock and made it all the way to the MBT spark from SCT's value file (which is oddly different than stock MBT) before I heard any knock!

Using illinipo's AUX-IN knock sensor idea, I was able to hear a little knock on 3rd and 4th gear WOT pulls (0.95 Load at 6400 RPM and 6700-6900 RPM). Reviewing my datalog confirmed it:



Pulling back 1.5 degrees at >4000 RPM and >0.8 Load, and 0.75 degrees at 0.7 load completely erased that knock.

So, tuning pros, "Am I doing it right?" If I'm screwing up anything obvious, please let me know! Both and are more than welcome.

Also, since I'm new to tuning I could really use some fueling advice: 12.8:1 AFR is a bit rich for an NA Zetec with ~10.3:1 CR, right? Should I try going 13:1 AFR or even leaner because I'm on 93 Octane? If there isn't usually much power there then I'd rather just run a little rich for safety against variables like bad gas, etc...


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Old 08-21-2009, 02:19 PM   #2
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There isnt enough info here to make that decision , a log is needed

A good safe AF is about 13.2 I dont go much more then that on the SVT NA 13.0 is safer

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Old 08-21-2009, 02:59 PM   #3
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The screenshot of the datalog is just to show what knock looks like when datalogging the J&S activity.

The AFR question shouldn't need a datalog; I just want a rough goal. I didn't know where most SVTFs stop making power or become unsafe. Sounds like I'll try at least 13.0, and probably wait for a dyno to measure any power gains before going past that.
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Last edited by mellephants; 08-21-2009 at 04:04 PM.
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