Jeff Smith: Wow, there's a lot going on here. My first recommendation is to go back to the original combination with the Q-jet and the way the car was set up and evaluate the e.t., speed, and 60-foot times. When a car slows down, it can be from multiple factors. Let's first look at what happened when you removed the Q-jet and went with the big 830-cfm Holley carb. Right away, you experienced a hesitation that you addressed with a larger 50cc rear accelerator pump. That may not have been totally the carburetor's fault. I have a buddy who used to run a small-block Chevy bracket car and discovered that his mild engine didn't like uncovering all four barrels of a large Holley carburetor on the starting line. His car actually would 60-foot quicker with a same-size vacuum-secondary Holley, because there was higher velocity through the primaries alone for the first few feet off the line until the secondaries started to open. Your 403ci Olds sounds like a relatively mild engine. Did you know that your original Q-jet is rated between 750 and 800 cfm? The Q-jet uses huge mechanical secondaries but tempers this with a velocity-sensitive air-valve door. The door opens only when a sufficient volume of air is traveling through the primaries. Once there is sufficient velocity, the air begins to push on the door, whose opening point is controlled by a small, adjustable spring. Loosening the spring tension allows the door to open sooner. This is very similar in operation to a vacuum-secondary Holley carb.
'CC Quickies
Butler Power
This is the engine that is in the GeeTO Tiger drag race GTO in the Wangers collection. The 467ci Pontiac is blessed with a stout cam, Edelbrock aluminum heads, and an Edelbrock Victor single-plane intake.>>>
Now with the big Holley and its mechanical secondary, it kills the velocity when you dump all four throttle blades open on the starting line, especially if the torque converter has a low-stall rpm. The hesitation you experienced with the out-of-the-box Holley carb is likely due to very low air velocity through the carb at low rpm. Your solution was to cover up that lean sag with a giant accelerator-pump squirt. The problem with adding the 50cc pump is that the engine probably didn't need that much accelerator-pump volume. When you add the larger capacity, the greater volume of fuel extends the duration of the acceleration enrichment. The duration of the accelerator-pump squirt is determined by the size of the discharge nozzle. It's possible that you could remove the larger rear pump and have just added the more aggressive cam you mentioned and that might have Band-Aided the problem, but it is still not corrected. You lost 0.30 second with all this most likely because the air/fuel ratio went dead rich for the first 60 feet and that's what hurt your e.t.
You also mentioned that you plugged the power valve on the front (primary side) and added jet. This made the air/fuel ratio go richer right off idle, because the power valve is designed to remain closed until the manifold vacuum drops below its rated level, where the engine demands more fuel. This allows the primary circuit to run at a leaner air/fuel ratio at part-throttle where it's happier-somewhere around 13.5:1 to 14:1. The most common power valve is rated at 6.5 inches of manifold vacuum, which means the fuel is not added to the primary main metering circuit until load (throttle opening) achieves 6.5 inches of manifold vacuum level or lower. By plugging the power valve, you're now running around at part-throttle with a much richer air/fuel ratio in the primaries. That's why the spark plugs are black.