Quote:
Originally Posted by Captainfab
The 3310-1 was the only one that came from Holley with a secondary metering block and power valve. The 3310-2 and subsequent releases came with the metering plates. Also the 3310-1 was rated at 780cfm and had downleg boosters and the rest were 750cfm with straight leg boosters.
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John,
You pretty much nailed it. The universal 3310 that we know today was actually modeled after an original GM carb that came on the Z-16 396 Chevelle back in '65. It was a list 3310-1 and did have a rear metering BLOCK as did all the factory GM 4150 series carbs. That was the only way they could power valve up the rear of the carb. Holley decided to release the 3310 as a universal carb to the public as a 3310-2 and above.
You generally have 3 styles of boosters. To keep it simple, we'll just talk about the difference between the straight leg, and the downleg, or sometimes called the dogleg. It refers to how it comes off the rear hole in the main body. the straight leg comes off straight over the venturi. The downleg steps down into the venturi. The link you referenced goes into really good detail but to keep it simple, the closer the booster is to the smallest part of the venturi, the greater/quicker the signal. The high velocity/low pressure is the physics needed to start the siphon effect from the booster. The 3310-2 and above all have straight leg boosters to slow down the start up of the main circuit and make it a little more of a forgiving carb. Since the straight leg will flow slightly less, they give it the 750 rating where as the quicker downleg boosters that GM used all got 780 cfm ratings. Ford even took it one step further and had Holley install straight legs on the primaries and downleg on the secondaries.
The picture below shows the high velocity-low pressure part of the venturi which creates the strongest signal. It is the smallest part. This is why little 650 double pumpers will have a much snappier throttle response than perhaps a 750 and yet the 750 will outflow the 650 way up in the rpms because of the less restrictions.
I'm getting really tired........I need to stop so my info doesn't start drifting.....lol