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Old 11-18-2011, 07:34 PM   #1
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Default The "Why is fuel being pulled from my top end" Thread

Many people have noticed that the Autotune feature in TunerStudio has been pulling fuel out their Fuel VE table at high rpm. I've noticed the same thing each and every time I tune the car. Let's get a little discussion going.

IIRC, I've heard some of the hardcore tuners state they it's expected that less fuel is required above 6000 rpm. Others have said that's crazy talk, and the VE table should be increasing all the way to redline.

I did some adjustments to my AFR Target Table today and went out for an autotune. Attached is the results. I've already cleaned up most of the cells <70kPa and <5200rpm. Every time, I get a rich jump from 4000->4600rpm and lean out after about 5500rpm. While logging & viewing the wideband gauge, AFR's are consistent with the targets...just the VE Table 'looks' wacky.

So, let's attack it: what is 'normal' or 'expected.' Should the Autotune leaning be ignored, and high rpm VE Table cells manually increased? Is the tune fine as-is?
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Old 11-18-2011, 07:40 PM   #2
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What are you AFR's up in the higher rpms?
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Old 11-18-2011, 07:58 PM   #3
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That's not totally abnormal. Yours rolls off a bit more than mine, and Jeff's. Several things come into play like the cam and compressor map.

Sorry about the scaling on the RPM, but this is the last dyno log I made from years ago when I made that fuel table.
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Last edited by hustler; 11-18-2011 at 09:07 PM.
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Old 11-18-2011, 08:06 PM   #4
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Stop autotuning. take logs. Are your afrs rich in boost?

Ms2?
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Old 11-18-2011, 10:11 PM   #5
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you make less torque up there... don't you?
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Old 11-18-2011, 10:20 PM   #6
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If your car continued to make more power all the way to redline, then your fuel table wouldn't drop off. Power goes down, so does the fueling. Also as you get beyond the torque peak and piston speed increases, chance of det decreases so you can get away with a little leaner AFR target.
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Old 11-18-2011, 10:30 PM   #7
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Quote:
Originally Posted by y8s View Post
you make less torque up there... don't you?
My car did with the supercharger on, yes.
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Old 11-18-2011, 10:42 PM   #8
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Your "decharged" still? Do u have an egt gauge?
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Old 11-18-2011, 10:52 PM   #9
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Quote:
Originally Posted by cymx5 View Post
IIRC, I've heard some of the hardcore tuners state they it's expected that less fuel is required above 6000 rpm.
Think of the head as a restriction to the flow of air.

As flow (in units of volume per unit of time) across a restriction increases, pressure drop across that restriction also increases. Thus, beyond a certain point, VE does in fact start to fall as RPM increases. This is the reason why peak torque typically occurs somewhere in the middle of the RPM band, and then starts to drop off.

Because of this, we would expect the numbers in the VE table to start getting smaller as RPM continues on beyond the point where peak torque was seen.
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Old 11-21-2011, 08:44 PM   #10
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Logs, currently naturally aspirated. The first log is apparently too large to upload @ 3.8mb...

1) Drive home w/ a few timestamps of WOT & accel enrichments.
2) Idling in the driveway after drive.

There's some obvious chatter on the attached WOT log starting at 6700rpm through redline. Does this read spark issues?
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File Type: msl 0- Idle.msl (704.1 KB, 51 views)
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