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how to read af rations?

Old 08-04-2005, 10:58 PM
  #1  
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Default how to read af rations?

anyone have a write up on whats good and whats bad on air/fuel rations...i know most people say "12.5" but I wanna know how it works so when I take a crack at tuning my car, I will be on the right track.
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Old 08-05-2005, 12:57 AM
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Default Re: how to read af rations?

It varies a little based on load, rpm and a few other factors.

basically...

14.7 at light load
13.5 at medium load
12.5 at high load
12.0 in boost

This is a VERY general to display it...
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Old 08-05-2005, 01:19 AM
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Default Re: how to read af rations?

16.0 at light load, NA of course..........with 8 degrees extra timing.........

Just got 53 mpg last tankful, blundar is itching to wideband the D15!!!!!!

539.3 mile, 10.175 gallons, 53.0 mpg..........

once up into normal powerband (above 3500) typical fuel maps getting about 145 chp from a 102 chp motor when it was stock......should be right at 122-124 whp, likely 130 whp with the next cam upgrade.
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Old 08-05-2005, 02:02 AM
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Default Re: how to read af rations?

Originally Posted by Mista Bone
16.0 at light load, NA of course..........with 8 degrees extra timing.........

Just got 53 mpg last tankful, blundar is itching to wideband the D15!!!!!!

539.3 mile, 10.175 gallons, 53.0 mpg..........

once up into normal powerband (above 3500) typical fuel maps getting about 145 chp from a 102 chp motor when it was stock......should be right at 122-124 whp, likely 130 whp with the next cam upgrade.
god damn. thats better then a 3cyl metro
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Old 08-05-2005, 07:10 AM
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Default Re: how to read af rations?

i usually tune for

15:1 light load
14:1 medium load
13.5 heavy load
12.5 transition in to boost
12.0 up to about 7psi
11.7 8-12 psi
11.5 over 12 psi
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Old 08-05-2005, 10:07 AM
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Default Re: how to read af rations?

Originally Posted by Mista Bone
16.0 at light load, NA of course..........with 8 degrees extra timing.........

Just got 53 mpg last tankful
I got 40 mph (with AC off) from the D15B7 Blundy gave me, stock P06 fuel map and ignition timing at cruise jacked to ~54 degrees.

Key to really big mpg gains is massive part throttle EGR with lotsa ignition advance. Planning on plumbing a Ford EGR valve/solenoid setup into the beater deluxe for highway cruises. Flip a switch, and switched ECU programs +l opening up the EGR.

Originally Posted by 45psi
god damn. thats better then a 3cyl metro
My Metro got 58 mpg. 89 LXi, my first car @ 18. Looking to buy a 95 Metro at the yard - good body, fucked engine - and swap in a Suzuki Swift GTi drivetrain + boost. If a rattletrap CRX can hurt so many ppl's feelings, imagine what a ------- METRO would do.

Originally Posted by projekteg
i usually tune for

15:1 light load
14:1 medium load
13.5 heavy load
12.5 transition in to boost
12.0 up to about 7psi
11.7 8-12 psi
11.5 over 12 psi
Good rule of thumb, yup, but I normally look at the system's dynamics first, and psi second.

Big turbo, lots of high efficiency parts, big power setup going to make a lot of power off of "small psi" I like to go a little richer under boost due to heat generated in the chamber from all that power. Trav-*** was running a little leaner at boost transition, but immediately went to high 11's AFRs, and was running 10.5's over 12 psi.

Small turbos that push a lot of heat but not a lot of power, I like to go richer under boost because of all the heat you're shoving into the combustion chamber. The small power setups can tax an engine as much or more than a big power setup. Between small turbines restricting exhaust (heat) flow from the engine, higher average charge temps from the small compressor exacerbated by ppl thinking that since it's a small turbo they only need a small IC (double whammy), and the fact that a slower engine takes more time to accelerate which gives the combustion chamber more time to really soak up some heat and form hot spots. Hell, Vizard's holy chant was that TIME was one of the Big Three factors in detonation, and the poor HMT guys running IHIs have time in abundance. Another good example of this, if you'll forgive my citing Jewburner Technology, is the VW 1.8T - after 3800 rpms or so AFRs dive into the 9.x:1 range to combat the tiny turbo restrictive turbine/manifold/no power lotsa heat syndrome. In the age of emissions, even if you are only graded on closed loop emissions, an OEM does this for a reason!

Well rounded setups I'd follow your guide pretty close.

YAAAAAARR!!11
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Old 08-05-2005, 10:11 AM
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Default Re: how to read af rations?

Refer to that last big passage for why I snicker a little bit when people bitch about D15 rods not holdoing together at 8-10 psi. I remember Jajogon citing rod knock - a sure sign of bearing damage from detonation, and not a problem with the rod itself. Those that detonate harder would probably fold the rod first - still not a problem with the rod. Might not be capable of holding 1.9 million JDM hp, but can probably hold 1.4... :P
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Old 08-05-2005, 02:52 PM
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Default Re: how to read af rations?

Originally Posted by Mista Bone
Just got 53 mpg last tankful, blundar is itching to wideband the D15!!!!!!
Dave is a **** about part throttle. ...I think it stems from his constant desire to beat the smog testers from his modified ECUs, and no cat turbo systems. ...he's done it a few times. I think he loves to "Dare" them to fail him.
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