"Not sure what's considered 'significant' horsepower, but have heard some say in personal testing that 20-30hp ranges have been seen."
I've done some testing in that area and it's true. When you go up with the intake and stick the carb closer to the hood often a drop base air cleaner is required. Nothing at all wrong with that except you MUST have a minimum of 3" from the flange where the air cleaner base sits to the bottom of the lid or there will be a performance loss.
Even worse I've ran into scenarios where the engine would stumble/hesitate or even "puke" all over itself going quickly to full throttle even if it pulled pretty decent after it got thru all that. Remove the lid completely and they were fine.
It's an area where few folks do any testing much past "seat of the pants" so they never know how much power they lost adding a spacer, high rise intake, or both when it required moving the air cleaner lid closer to the carb to get the hood closed......FWIW....
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73 Ventura, SOLD 455, 3740lbs, 11.30's at 120mph, 1977 Pontiac Q-jet, HO intake, HEI, 10" converter, 3.42 gears, DOT's, 7.20's at 96mph and still WAY under the roll bar rule. Best ET to date 7.18 at 97MPH (1/8th mile),
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