Buttercup

The PCM does control the AFR, but it does so only in closed loop. WOT is not closed loop. In your case what will happen is that the PCM will get less fuel during normal driving and will gradually richen the mixture up. Fuel corrections made during part throttle can definately affect fuel at WOT. You should've taken it for a drive, giving it different conditions to relearn the fuel corrections and then plopped it back on the dyno to confirm the numbers, they will have changed, how much depends on many variables.

The other concern I'd have is too wide a range of adjustments of fuel pressure without correcting the fuel constants in the PCM will bring the fuel corrections closer to their limits. If the limits are reached it will also affect part throttle.

94formulabz

I can see it happening. Not all based on the XE cam, but if his valve lash was set tight he would have dropped off harder then expected. Just a suggestion.

BTW, nice numbers RealQuick

Beast96Z

I ran my XE 230/236 up to 66-6800 all the time in my set-up. I pulled my old dyno graphs out, and it didn't drop in power till 6500 rpm's. XE lobes are pretty tame to some of the lobes that are on the market today. As far as lobes go, I wouldn't run anything less than a XE lobe. In a proper set-up, the power shouldn't drop to hard. If you plan out the gears, to cross the line at peak RPM, you should easily out run a car with a similar cam on a weaker lobe. Simply because your low-end power comes in much sooner. These cams have great potential. I don't see why people are scared of them?? Mine made 397/365 to the wheels and held a excellent torque band from way down low!

RealQuick

I took it for a ride on the way home and the part throttle was definitely better. More crisp throttle response and it lost the soggy feeling down low. Believe it or not, 6th gear actually had some pull to it.

So, WOT isnt gonna change back on me? Also, how does part throttle affect full throttle? I need enlightening.

Buttercup

Hang with me, I'm not a very good teacher

The PCM supplies the fuel it *thinks* the engine needs. When in closed loop it monitors the O2 sensor feedback. If there's oxygen present it assumes that the engine is running lean, so it adds fuel until the excess oxygen is gone, then it assumes it's rich and pulls fuel out. It does this back and forth rapidly bouncing very closely around 14.7:1 AFR. So it doesn't have to relearn everytime the engine is ran, the PCM stores this correction information in memory. This is what's called a fuel trim. This number is stored in memory and is basically just a multiplier. The PCM takes what it thinks the engine needs, and then multiplies that amount of fuel by this correction factor, if the correction factor (fuel trim) is correct than everything will look perfect and it won't change the fuel trim any further. It constantly updates this fuel trim when in closed loop. You can think of the fuel trim as simply a percentage, the PCM looks at airflow, determines how much fuel to inject to match the airflow, and before it injects that fuel it mulitplies the amount by the fuel trim because it knows it needs it from the previous engine cycle.

When the engine goes WOT it no longer uses the O2 sensors, because they are only accurate at 14.7:1 AFR. However, it can use the fuel trim that's been stored in memory. If the engine was running rich, it basically ignores the fuel trim and supplies the fuel it thinks the engine needs without any correction (because running too rich doesn't destroy anything), if the PCM had to add fuel because of a lean condition during closed loop, it will use that same correction factor at WOT. If this happens, it takes what it believes it should inject and adds a little more because it knows it was running lean.

The problem with adjusting things like fuel pressure on the dyno without having the computer learn if it's rich or lean is that later while driving it WILL correct for it. It will use a different fuel trim once it has time to learn it than what was being used on the dyno. There are also limits to how much the PCM will correct for. In the tuning world we like to aim for just a tad rich, that way it always defaults to no correction at WOT (consistency) and yet has lots of room for correction on either side of rich or lean. You can crank the pressure up beyond what the PCM will correct for and you'll run rich all the time, even in closed loop, likewise with a lean condition. This is probably why it felt "soggy" before, it was running rich all the time!

The reason you were rich at WOT before was because at 55psi of fuel pressure it saw the engine running rich during closed loop. At WOT it doesn't apply a correction when rich (refer to above). So it was adding the fuel it needed to PLUS you added a bunch of fuel through the high pressure. As it stands now you may always get the right amount of fuel you saw on the dyno, you might go richer, you might go leaner, it depends on these fuel trims and some other stuff that gets even more complicated. I'm sure you're better off then you were before but don't count on it being quite as exact as you'd like. Truly the best method for tuning is via PCM reprogramming, it will supply the right amount of fuel at idle, cruise, and WOT... consistently.

NiteRider

I do belive my lash was set tigther then usual. Thanks for the reminder.

jkipp84

J -

Great numbers dude!

RealQuick

Buttercup - Thanks! That was more clear. I am gonna get a new program from madwolf next week and hit the dyno again.

John - Thanks bud.

RealQuick

Buttercup - @ WOT I hit 41-42 degrees of timing. Is that too much?