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Old 10-19-2007, 03:21 PM   #1
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Default Determining appropriate A/F ratios.

You dont have a dyno, and you dont have a knock sensor.

How is tuning accomplished? what is a generally accepted target A/F ratio? Is A/F ratio constant throughout the rev range? How do you know what A/F ratio should be if you are cruising? If a turbo makes full boost at 3000rpm and you are cruising at 4000rpm, the engine doesn't make boost until you step on it?

I am trying to visualize the fuel tables that I see screen shots of, and if I remember correctly it was boost vs rpm. What data and, in what measurement, is filled into the table?
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Old 10-19-2007, 03:22 PM   #2
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14.7:1 cruise and idle. 12:1 in boost.
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Old 10-19-2007, 03:30 PM   #3
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Quote:
Originally Posted by Braineack View Post
14.7:1 cruise and idle. 12:1 in boost.
Who determined this number and how did they come to this optimal conclusion?
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Old 10-19-2007, 03:37 PM   #4
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cause 14.7:1 is the optimal burning ratio for gasoline.

Richening up the mixture to 12:1 results in a slower burn, moving the pressure peak later where there is more leverage and more torque. Anything richer is a waste of gas; it cannot provide any real additional cooling or slow the burn. Anythign leaner and the peak pressure increase, the spark ignites closer to TDC, the air charge is not cooled and you risk detonation.

Last edited by Braineack; 10-19-2007 at 04:18 PM.
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Old 10-19-2007, 03:40 PM   #5
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Brain, Megamanual says going as high as 16:1 in light-load cruise is kosher. Any truth?
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Old 10-19-2007, 03:41 PM   #6
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yes. you dont need more than 2-10hp to cruise, so why waste gas.
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Old 10-19-2007, 03:52 PM   #7
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Quote:
Originally Posted by Braineack View Post
cause 14.7:1 is the optimal burning ratio for gasoline.

Richening up the mixture to 12:1 results in a slower burn, moving the pressure peak later where there is more leverage and more torque. Anything richer is a waste of gas; it cannot provide any real additional cooling or slow the burn.
So pretty much make sure you hit those numbers in the given conditions and thats all she wrote?

What about the numbers in the tables?
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Old 10-19-2007, 04:17 PM   #8
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what numbers in what table?
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Old 10-19-2007, 04:35 PM   #9
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Quote:
Originally Posted by Braineack View Post
what numbers in what table?
Kitchen tables. Have you been reading this thread at all? Try and keep up.
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Old 10-19-2007, 04:43 PM   #10
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ok mr. smart guy. eat off that table.
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Old 10-19-2007, 05:00 PM   #11
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Damn dude. I was just making a joke and I get banned? I was just poking fun because the guy mentions tables out of thin air.

I sent you free **** too. You suck.
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Old 10-19-2007, 05:05 PM   #12
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you didnt sound joking enough :gay: needs more silly gay smilies.


plus your name user name looked exactly like the OP, who i thought i was banning
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Old 10-19-2007, 05:14 PM   #13
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Damn Scot, a bit harsh? He was just following up on the unanswered question in his first post...see the last sentence.

Is your new job making you feel inadequate? :gay:
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Old 10-19-2007, 05:16 PM   #14
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no. i thought the op was being smart with me. i didnt even realize it was someone else.

about the tables. they are a % of fuel. based on rpm vs. MAP. only there to supply to fuel so you can tune it to your given AFR.
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Old 10-19-2007, 05:20 PM   #15
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Scott, you and Loki gotta stop hanging out.
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Old 10-19-2007, 05:30 PM   #16
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so did you unban him or what? i was shocked at your reaction, slo-guy jokes a lot, so i didnt see it coming...
great thread btw, again, im on the learning side, keep the good info pile up in here, im reading carefully...maybe too carefully
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Old 10-19-2007, 05:32 PM   #17
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Quote:
Originally Posted by Braineack View Post
no. i thought the op was being smart with me. i didnt even realize it was someone else.

about the tables. they are a % of fuel. based on rpm vs. MAP. only there to supply to fuel so you can tune it to your given AFR.
Woh, that could have ended badly. Good thing its straightened out.

So is there some sort of mathematical formula you can use to determine the percentage of fuel you would need to create a specific AFR based on rpm and map or is it unique to every car? I know its somewhat interchangeable between miatas, but never perfect unless cars are identical.

I ask because i am curious, can you measure your AFR only once the car is in motion or can you estimate it on the drawing board?
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Old 10-19-2007, 05:36 PM   #18
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You can figure it out with Volumetric Efficencies. Read the fuel tuning section of the megamanual.
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Old 10-19-2007, 05:54 PM   #19
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Quote:
Originally Posted by Ben View Post
You can figure it out with Volumetric Efficencies. Read the fuel tuning section of the megamanual.
Yea thats pretty sweet.
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