quick fuel air ration question

[KillerAngel]

This is just for reference at the moment, i dont plan to mess around with fuel/air stuff yet...

But that said, anyone know the stock fuel air ratio for a '95 engine, and what ratio you think the engine could handle?

As you can see im new to these forums (posting wise anyway) and just tryin to get my bearings. Thanks for any input...

[maxnix]

Yes. Q45tech does. Read his posts. Depends on which ECM.

[elwesso]

The ECU trys to keep AF ratio at 14.7:1 at all times (the stoichiometric ratio)...

generally though, it will run on the rich side, so average, maybe 13:1?

[RobertsnewQ]

Under cruise it's stoich, but at high RPM/load points it goes as rich as 11.0:1.

In my retuned ECUs I go for 12.5-13.0 under power. Picks up quite a bit of power.

Here's a stock 94 fuel map. Low RPM on the bottom, high RPM on top. Low load on left, high load on right.

14.70 14.70 14.70 14.70 14.70 14.70 13.11 12.93 12.84 12.80 12.63 12.42 11.91 11.91 11.91 11.9114.70 14.70 14.70 14.70 14.70 14.70 13.34 13.16 13.07 12.84 12.71 12.50 11.95 11.95 11.95 11.9514.70 14.70 14.70 14.70 14.70 14.70 13.34 13.20 13.11 12.93 12.76 12.59 11.95 11.95 11.95 11.9514.70 14.70 14.70 14.70 14.70 14.70 14.15 13.63 13.39 13.07 12.89 12.76 12.22 12.22 12.22 12.2214.70 14.70 14.70 14.70 14.70 14.70 14.70 14.36 13.49 13.07 13.07 12.76 12.22 12.22 12.22 12.2214.70 14.70 14.70 14.70 14.70 14.70 14.70 14.70 14.04 13.84 13.30 13.07 12.22 12.22 12.22 12.2214.70 14.70 14.70 14.70 14.70 14.70 14.70 14.70 14.70 14.25 13.94 13.30 12.22 12.22 12.22 12.2214.70 14.70 14.70 14.70 14.70 14.70 14.70 14.70 14.70 14.36 14.09 13.63 12.67 12.67 12.67 12.6714.70 14.70 14.70 14.70 14.70 14.70 14.70 14.70 14.70 14.70 14.15 13.68 13.11 13.11 13.11 13.1114.70 14.70 14.70 14.70 14.70 14.70 14.70 14.70 14.70 14.70 14.20 13.78 13.34 13.34 13.34 13.3414.70 14.70 14.70 14.70 14.70 14.70 14.70 14.70 14.70 14.70 14.25 13.84 13.54 13.54 13.54 13.5414.70 14.70 14.70 14.70 14.70 14.70 14.70 14.70 14.70 14.70 14.70 13.54 13.54 13.54 13.54 13.5414.70 14.70 14.70 14.70 14.70 14.70 14.70 14.70 14.70 14.70 14.70 13.54 13.54 13.54 13.54 13.5414.70 14.70 14.70 14.70 14.70 14.70 14.70 14.70 14.70 14.70 14.04 13.54 13.54 13.54 13.54 13.5414.70 14.70 14.70 14.70 14.70 14.70 14.70 14.70 14.70 14.36 14.04 13.54 13.54 13.54 13.54 13.5414.70 14.70 14.70 14.70 14.70 14.70 14.70 14.70 14.70 14.70 14.70 14.70 14.70 14.70 14.70 14.70

[RobertsnewQ]

modified map:14.70 14.70 14.70 14.70 14.70 14.70 13.11 13.07 13.07 13.07 13.07 13.07 13.07 13.07 13.07 13.0714.70 14.70 14.70 14.70 14.70 14.70 13.34 13.16 13.07 13.07 13.07 13.07 13.07 13.07 13.07 13.0714.70 14.70 14.70 14.70 14.70 14.70 13.34 13.20 13.11 13.07 13.07 13.07 13.07 13.07 13.07 13.0714.70 14.70 14.70 14.70 14.70 14.70 14.15 13.63 13.39 13.07 12.93 12.93 12.93 12.93 12.93 12.9314.70 14.70 14.70 14.70 14.70 14.70 14.70 14.36 13.49 13.07 12.93 12.93 12.93 12.93 12.93 12.9314.70 14.70 14.70 14.70 14.70 14.70 14.70 14.70 14.04 13.84 12.93 12.93 12.93 12.93 12.93 12.9314.70 14.70 14.70 14.70 14.70 14.70 14.70 14.70 14.70 14.25 12.67 12.67 12.67 12.67 12.67 12.6714.70 14.70 14.70 14.70 14.70 14.70 14.70 14.70 14.70 14.36 12.67 12.67 12.67 12.67 12.67 12.6714.70 14.70 14.70 14.70 14.70 14.70 14.70 14.70 14.70 14.70 12.67 12.67 12.67 12.67 12.67 12.6714.70 14.70 14.70 14.70 14.70 14.70 14.70 14.70 14.70 14.70 12.80 12.80 12.80 12.80 12.80 12.8014.70 14.70 14.70 14.70 14.70 14.70 14.70 14.70 14.70 14.70 12.80 12.80 12.80 12.80 12.80 12.8014.70 14.70 14.70 14.70 14.70 14.70 14.70 14.70 14.70 14.70 12.80 12.80 12.80 12.80 12.80 12.8014.70 14.70 14.70 14.70 14.70 14.70 14.70 14.70 14.70 14.70 12.80 12.80 12.80 12.80 12.80 12.8014.70 14.70 14.70 14.70 14.70 14.70 14.70 14.70 14.70 14.70 12.80 12.80 12.80 12.80 12.80 12.8014.70 14.70 14.70 14.70 14.70 14.70 14.70 14.70 14.70 14.36 12.80 12.80 12.80 12.80 12.80 12.8014.70 14.70 14.70 14.70 14.70 14.70 14.70 14.70 14.70 14.70 12.80 12.80 12.80 12.80 12.80 12.80

[texasoil]

The modified fuel air ratio map is about what I'd expect to achieve best power--which usually is right around 13 or a little lower,depending on fuel dispersion efficiency. I'm curious to see exhaust gas temperature vs mixture. In high performance aircraft engines, peak power is usually delivered at peak exhaust gas temp to as much as 100 deg F rich of peak EGT, while highest HP-hr/# of fuel is usually about 75 deg F lean of peak EGT. The high performance (rapid response time, high sensitivity @ stoich) O2 sensor system is a big improvement over the EGT method of tuning IMHO.

[KillerAngel]

Rob: Is there a reason you made it rich down low and lean up high? Not sure im following that...

Great info btw... you guys are awesome ;-)

[Q45tech]

Show us injection milliseconds at highest load and 4,000 and 5500>up....11>9.4 millisecs

What most don't understand is how the VE is highest at peak torque [by definition] and slope declines from there. The VVT confuses matters in the area up to and during and just after VVT operation [~~4600] and the 90-93 tuning which results in 2 HP peaks [5500 then a dip and returns at 6,000] depending on air temperature.

Holding A/F constant results in an ever declining injection time from HP peak to redline as the VE declines [less air per gulp] as filling time decreases.

Chassis dyno [ALLOW] accelerates engine TOO FAST in 3rd gear to properly consider the ignition advance.

Many engines after a dyno tune knock and require a 1-2 degree reduction [in 3rd-4th gear] for real world operation in Summer heat.

Lots of difference in a single quarter mile tune and a road course tune where you may be running above 100 mph for more than a second.

Why advance is keyed to coolant temp heavy load raises coolant temp.

[maxnix]

Ooh, I'd like to see the axis coordinates to do a 3D mapping!

[RobertsnewQ]

Rob: Is there a reason you made it rich down low and lean up high? Not sure im following that...

Great info btw... you guys are awesome ;-)

It's the opposite. "down low" i.e. idle & cruise, is bottom left. 'up high' power area is upper right.

Here's the RPM scale:

68006200570053004900440040003600320028002250215016001200800400

And the load (TP = Theoretical Pulsewidth) scale:8 12 16 20 24 28 32 36 40 44 48 52 56 60 64 72

I do all my tuning with a wideband O2 sensor, so I've never really looked at EGTs. I know it's way more critical with turbo cars.

I was going to do some more dyno time this week (I always use a load-cell dyno, NOT an inertial dyno) to tune, but I loaned the Q to my dad and now it's 400 miles away. I'm driving his old Dodge truck so I think he got the better end of that deal.

When I do get around to dynoing it again I will post the numbers. Last time I almost got to 270 at the wheels.

Oh, and as far as the above tables go, they are not EXACTLY what you see out the tailpipe. There are other correction factors out there that have to be turned off to do the AFR table tuning.

One good thing with the 94-95 ECUs is that they have a separate VE table that I do not tweak. The AFRs are much closer to actual.

The 90-93 ECUs do not have a VE table, so all the "fudging" occurs in the fuel tables. They do not always reflect actual AFR.

Incidentally that is also why in the above RPM scale, there is a weird spacing between 2000 and 3000 rpm. THe "pinched' portion of the scale is there to compensate for a VE dip in the stock engine.

[RobertsnewQ]

Here's the RPM scale for a modified 94 ECU (notice no "pinch")

68006200570053004900440040003600320028002400200016001200800400

[maxnix]

Geez, thanks. Going have to look at that in Excel.

All I know the low rpm flat spot is not there any more.

[elwesso]

Yeah Brian, please give us your feedback on the ECU... maybe in a seperate thread?