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Old 03-04-2008, 09:00 AM   #1
98EJ20
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Default AFR Target

Ive tuned a few Turbo Honda's as well as a few Turbo Toyota Matrix's. I usually tune for 12:1 WOT and monitor knock. I recently picked up a wideband for my 98 RS w/02 WRX swap. I figured I would fine tune the AFR and pick up a couple ponies. It was running 10.8 throughout the band on my XPT stg2 map w/GM BCS. I leaned back to 11.6 where boost spikes, then 12.0 to 6K RPM and 11.6 to redline. Im getting no knock at all and the car definately feels a LOT stronger then before.

When I was talking to ev8siv3 from XPT about this, he suggested running 11.3 to 6K and then 10.8 to redline. Any thoughts on this anyone?
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Old 03-04-2008, 12:52 PM   #2
06rexwagon
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Your egt's are probably really high. On 91 octane I typically run 11:1 and 11.1-11.2 on 93. Just because it's not knocking doesn't mean the egts aren't high enough to do damage.
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Old 03-04-2008, 01:10 PM   #3
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You're going to get different answers from different people. There's more than one way to make power. Personally, I follow the school of thought that both Innovate Motorsports (makers of the LC-1 WBO2) and most of the Japanese do: Fuel is not there for knock control. Combustion is a multi-stage process and the most complete and quickest combustion occurs and Mean Best Torque, usually somewhere between 12 and 13. Richer than that isn't cooling the intake charge to prevent knock, it's making combustion so inefficient that the car doesn't want to knock anymore. Fuel it properly and then set the timing to whatever you have to to make it safe.
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Old 03-04-2008, 02:19 PM   #4
98EJ20
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My EGT's are no higher then 1600 in the up pipe.

And I agree with the above post. From what Ive read and from tuning overtime, AFR can effect knock if youre crazy lean but generally timing is the key. Most resources say 12:1 is ideal for a FI car. But Ive also read other articles stating that some cars like to be ridiculously rich as well, like 10.8 or richer. I guess time will tell then.

Thanks for the input. Just looking for some other peoples perspective and talk it out a bit
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Old 03-04-2008, 03:10 PM   #5
06rexwagon
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1600 at the up pipe is too hot. If you're reading the factory egt probe that's even worse. You need to read your egt at the manifold. 12:1 is ideal, but that's if you have access to c16. Like williaty said, you will get different answers from different people. On my car, I run 11:1 on pump and 11.4:1 with 91+methanol/h20 injection at 24 psi, making 417whp/421wtq.
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Old 03-04-2008, 03:48 PM   #6
98EJ20
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I guess I should specify my boost level too, would def change things a lil. Im running 18psi spike, holding 15 to redline. When I was running 20-21 before I had the AFR around 11.5 to be safe.

I thought the temps at the up pipe would be hotter since it was all merging together? Its not a factory EGT btw, just fyi. Maybe thats my goal this weekend, move the EGT to 1 runner and check it out. Most cars Ive tuned maxed out around 1450-1500 in the runner. Would this be OK on the Sube too?
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Old 03-04-2008, 04:32 PM   #7
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Peak of 1600*F is normally safe for the EJ205's.

93 octane I typically tune for ~11.4:1
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Old 03-04-2008, 06:26 PM   #8
98EJ20
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I usually drive the car very easy and only do a gear or 2 spurts. I plan on drag racing alot this year again and will be running 104 unleaded when I do. But Im considering a bigger turbo before the season starts. I was pretty much just seeing all I could get out of the stock turbo. Its pretty quick in my gutted RS coupe
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