A 750 Vac. sec. will work well on a 400, especially if you have a mild cam. My 406 has ported no.48's, a Crane 284H (284 dur., 228 dur @ .050, .480 lift), 750 vac. sec. on an e-performer, Hooker comps and 2 1/2" duals, TH-350 w/ 2200 conv., 3.08 posi and my 'Bird runs consistent 13.0x's.
The DP's are good for competition but will kill you on the mpg- the vac.sec. is much better suited for the street, as your engine will tell the carb when it wants more fuel and open the secondaries.
Ehh, I ran a 4500 stall with 850 DP on the street daily. It was ok for me. It's only when I went with a .630 lift and 270 280 duration @ .050 that it wasn't that much fun anymore to putt around in.
I 2nd the 650dp. Another consideration would be a Qjet modified by Cliff, do a search over on Performance Years forums. Plenty of performance, great economy.
I'm running a full race 750dp on my 383 Pontiac, but mine has all the tricks and it's running on E85, so I needed the volume to go with the increased appetite for the go juice. I don't know what I get 'exactly' for mileage, but I top it off every 100miles...the factory gas gauge works like crap even with a new sender.
Brian Hobaugh SCCA National Tour June 2014
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