Re: bog
Bill, I've been flogging Q-Jets for 23 years in my SS car and I still learn new stuff all the time! Your bog problem is most likely too much fuel during the launch. I see it a lot in EGT traces. When the mixture is just right the EGT's continuously climb during the run and the RPM stays flat at the stall speed and then increases to the 1-2 shift point. When it is too rich the EGT's go down or stay flat after the launch and then go up--RPM sags at that point (bog).
First: you need the right jets and secondary rods for max power from dyno testing (you would be surprised how many Q-Jets don't even work on the dyno).
Second: tune them for the track. "G" loads and wheel stands totally change Q-Jet metering. Generally the secondary rods should be leaner than the dyno rods and primary jets should be OK plus or minus 1 size. Idle and driveability are another problem which you can address later.
Finnaly: once you are close FLOG THE HANGER and the SHAPE OF THE RODS; they control the A/F ratio during the opening of the air valve where the bog typically happens. The air valve should be fairly tight; too loose and you get a lean bog and it is hard to tell the difference without instrumentation. Another common problem is that many racers think the more open the air valve the more power. This is only partially true for very high powered engines. An air valve that is too far open will definately lean out the fuel curve at low RPM. Most engines benifit from closing the air valve and it will help make sense of your test data. The choke pull-off should take about 1 second.
All of the above assumes your fuel system is adequate and all testing is done on the same day! Weather, especially humidity, has a big effect on metering requirements depending on your application.
Also I've found that no two Q-Jets are the same!
Like I said I've been doing this 23 years. I am almost there!
Good Luck! Vic Santos
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