I am finding 26" of vac at idle hard to believe. Dropping down a steep grade with my foot off the gas my 360 pulls 24.5"

I had readings like that with my old gauge, It read 5" with the engine off!

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'72 Duster 198 stock cam, 3:23's

93 D350 Cummins THD Maxfuel 35mpg parts to hit 400hp+ Suncoast Cat2 A518, converter DDP Stage III injectors 62/64 HX35, 3 piece manifold, 4" Diamond Eye, Gear Venders OD. Stage I street/tow PDD head on order.

I changed from a 350 Holley to a 390 last year and I must say the 390 feels a lot more responsive off the line. I haven't really noticed much difference in fuel economy, but to be honest it's hard not to open those 2 extra barrels from time to time......just for fun.
In the last few weeks I've put in a 4.5 power valve which seems to have a helped a bit with the economy.
My vac is 9" in gear and around 14" in Neutral.
FWIW going from the 350 to the 390 I picked up 0.15 sec down the 1/4 mile. So performance wise the 2 carbs aren't streets appart, not on my engine anyway, but the 390 feels better on the street.

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62 Valiant, 225cid Slant 6/PB 904 with lots of good bits

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