Sag/bog after shift at WOT

I have a '69 Dart with a 340/904 combination. I am having a problem with a sag in acceleration at WOT after the 1-2 shift and as the race night progresses it gets worse with the same problem after the 2-3 shift. There is even some misfiring out the open exhaust. I have gone through the Holley 830 Annular carburetor and found nothing. I reset the float height with no benefit. I have cleaned the fuel cell, installed a new filter (100 micron) between the cell and pump; again no better. I replaced all the braided fuel lines with new lines, no help. I replaced the pump and regulator, no help. I tested the volume of fuel and the pump can provide one gallon of fuel every 19 seconds. I have played with various fuel pressure staying close to about 6.5-7psi, no help. I have been running the same setup for years, an Edlebrock headed 340 with a .557 MP camshaft and for the last three weeks I have had this problem. I have gone from the 11.40s to 11.60s and 114mph to 111-112mph. The entire fuel system has been replaced except the Holley 830. I have gone through the MSD distributor, checking the pickup and it was good. I replaced the cap, rotor, plug wires, and plugs, no benefit. I used another ballast and MP Chrome box to see if the Dart would pick up and that did not work. I have changed the actual fuel I use (93 octane). I did a compression test and it was 75psi on the first puff and 175psi after five puffs (cylinder 6 was only 170psi). I did leak down testing and every cylinder was 3% or less. Any ideas? I am running out of them.

Thanks,

Chris

Quote:

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I have a '69 Dart with a 340/904 combination. I am having a problem with a sag in acceleration at WOT after the 1-2 shift and as the race night progresses it gets worse with the same problem after the 2-3 shift. There is even some misfiring out the open exhaust. I have gone through the Holley 830 Annular carburetor and found nothing. I reset the float height with no benefit. I have cleaned the fuel cell, installed a new filter (100 micron) between the cell and pump; again no better. I replaced all the braided fuel lines with new lines, no help. I replaced the pump and regulator, no help. I tested the volume of fuel and the pump can provide one gallon of fuel every 19 seconds. I have played with various fuel pressure staying close to about 6.5-7psi, no help. I have been running the same setup for years, an Edlebrock headed 340 with a .557 MP camshaft and for the last three weeks I have had this problem. I have gone from the 11.40s to 11.60s and 114mph to 111-112mph. The entire fuel system has been replaced except the Holley 830. I have gone through the MSD distributor, checking the pickup and it was good. I replaced the cap, rotor, plug wires, and plugs, no benefit. I used another ballast and MP Chrome box to see if the Dart would pick up and that did not work. I have changed the actual fuel I use (93 octane). I did a compression test and it was 75psi on the first puff and 175psi after five puffs (cylinder 6 was only 170psi). I did leak down testing and every cylinder was 3% or less. Any ideas? I am running out of them.

Thanks,

Chris

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Valve springs..?? How old?