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Old 06-26-2010, 01:53 AM
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Wideband tuning holley 750 at the track...

Took my Vega to the track tonight and logged my runs with my wideband. The 60' times weren't so great. I launch at about 1800 rpm. First gear was rich from 2400-3300 and then it went lean from 3300-4800 before finally leveling out. My question is this... How could I adjust the carb to smooth this out a bit. 2nd and 3rd gears were pretty good. See the attached graph, I circled first gear in red. Here is the quick breakdown of the car:

75 Vega
406 sbc
dart heads
mild cam
performer rpm intake
holley 750 vacuum secondary no choke
th350 2400 stall
ford 9" 373 gears
26x9 slicks

Best run tonight in 100 degree heat:
60' 1.798
330' 5.070
1/8th 7.803 89.88mph
1000 10.154
ET 12.139 @ 113.50 mph
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Old 06-26-2010, 01:59 AM
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If it isn't obvious on the graph... Black is rpm, purple is AFR.
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Old 06-26-2010, 11:35 AM
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Anybody have an ideas? I'd like to go back out to the track this afternoon if I can make some changes. Here is what I figure so far:
1. it is too lean while I'm staged to launch at 1800rpm
2. Too much accelerator pump squirt. It looks like enough to counteract the initial lean condition and then go too rich.
3. Goes lean once again while secondaries are opening

Possibly a power valve that opens sooner would remedy the initial lean condition, then I could work on the accelerator pump?

Last edited by iambigperm; 06-26-2010 at 12:00 PM.
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Old 06-26-2010, 02:15 PM
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The idle afr is right at 14.0 but I had started the log when I was staged so you can't see it. It doesn't lean out until I bring it up off idle. I have ran 11.3 in the quarter with this car exactly as it sits(in Seattle@ sea level and 70 degrees). I don't think the converter is the issue I have ran plenty of 1.6's for 60' times with this one. I was told this was a 2800-3000 stall but I think its a little tighter than that. I had this car running great in Washington, but here in Vegas it is a different ball game.
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Old 06-26-2010, 02:28 PM
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As far as the timing it is 14 degrees at idle, 36 total, all in by 3000.
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Old 06-26-2010, 02:37 PM
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It was a 3310 and I added a rear metering block. The choke horn is gone so most of the numbers are too... I have the carb info written down in my trailer, but that's at work so I'm not going to try to remember it all... I'll get those numbers later today. I did buy the carb brand new as a factory holley unit so most of it is stock aside from the rear metering block and choke horn machined off. I did change the squirter and secondary spring as well, but I haven't drilled any holes or anything.
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Old 06-27-2010, 01:38 AM
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I did a run with the caps on the exhaust and figured out that the oxygen sensor is too close to the dumps to read accurately at low rpm. When I ran the car through the muffler I saw different readings when staged. It was actually about 14:1 @ 1800 rpm, the rest of the run was the same as the log. It did still have the very rich dip right off the line accompanied with a hesitation. I'm going to try a different accelerator pump cam. It has a red cam in it and I'm going to try a pink one. Didn't have any with me though. Only a couple more race days in vegas before we take the summer break for the heat.... After next weekend there isn't any racing until the end of August

As far as your earlier question... I have a Comp XE268 in it. Performer RPM intake.

Thanks for all your help F-Bird!
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