Originally Posted by
kingtal0n
you need a wideband above all else...
This I know and it's coming soon, I was doing the same with the TBSS as I did with my S/C Regal, just looking to get a little more punch until then. I was hoping to add it while doing exhaust, save intalling sensor twice.
I mean your LOL below is correct, and according to above comments from another I did have a couple things I REALLY screwed up, (my fault) like using 1.75 as a PE instead of the 1.175 I'd intended.
LOL @ trims. I have been tuning for 20 years, wide variety of cars and applications. Never used a narrowband or 'fuel trim' on my own vehicle. Modern computer control uses a wideband i.e. Holley & Haltech, are using wideband to target specific a/f ratios in closed loop now. Nobody is using narrowbands or fuel trims... That is a factory implemented feature to use the cheap narrowband sensor and pass emissions. It does not offer performance or economy, neither are found at 14.7:1.
I really don't know how long widebands have been around, I've only been messing with HPT for a couple years, did a couple of my own and helped clean up a few others, and the chart you shared makes total sense, as did your throttle lift comment about not going super lean at throttle lift or "coastdown" even. I've seen the Holley stuff in the past. I just don't know how long ago they began it.
For most cars, you don't need or want to target narrowband a/f ratio when you have a wideband. That ratio is strictly for emissions, and to use the low cost sensor.
leaner A/F gives better economy but raises NOx which can be dangerous if you breath it. So if you have exhaust leaks don't cruise lean I guess.
These I definitely know and I've seen dark green - numbers as well as a few dark reds (not for long, I readjusted. Again, it was my error as I went backwards in my thinking for a brain fart moment and entered some stupid number like 1.0 instead of .01
A typical fuel map for performance engine with wideband only, should be gradually leaner at higher vacuum, until the most high vacuum regions that the engine will touch while you are lifting and the manifold endures low pressure. Those regions should not be very lean due to issues with transient fueling. Sorry this sounds confusing so I will use actual numbers for example
This I actually do understand, but your chart below makes a good starting guide, ESPECIALLY if you stay very close to these.
10-20KPA - most engines, tune to 13.8 to 14.3
20-30KPA - Tune to 14.5 to 14.8 as long as you never touch this while cruising.
30-40KPA - cruise upper limit usually, tune to 14.8 to 15.8
40-50KPA - cruise an idle, light load, lower speeds, tune to 14.7 to 15.2
50-60KPA - some load, just off cruise. Tune to 14.3 to 14.7
60-70KPA - more load, more fuel, tune to 13.5 to 14.5
70-80KPA - closing in on wide open throttle. If you don't care about economy, drop to 12.5 to 12.8, otherwise 12.8 to 13.2 will suffice on moderate compression engines using good fuel quality
80-100KPA - pretty much WOT, use WOT ratio of 12.0 to 12.5 in most engines moderate compression decent fuel (gasoline 93 octane)
boost
100 to 125KPA - low boost can use 12.0 to 12.5 most applications with typical boost compression ratios (8.5 to 9:1 on gasoline)
125KPA to 150KPA - up to 7psi most safe street engines target 12.0 +/- .2 try to keep it as a straight line from this point on
150-200KPA up to 15psi of boost around 11.2 to 11.8 is typical on gasoline fuels with 9:1 compression
From there it just depends how bad the engine needs to cool. Pump fuel 93 octane gasoline won't tolerate high temperature, and the engine won't like being run into the 10's a/f ratio sometimes either, so its a stalemate and you just shouldn't do it. Some engines don't mind super rich 10:1(some subaru apparently) and some engines won't mind the high boost of 25-35psi on 93 octane (4g63 can do it). I personally don't take a gasoline motor much past 20psi of boost unless it has an ambient air temperature inlet (huge intercooler) and piston oil squirters or forged pistons to control the heat input to the piston materials.