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: Holley 650 DP or 750 Vac Sec DEEBOO Dec 28th, 03, 11:31 PM I talk to my engine builder and he thinks I should run a Holley 650 DP Mec Sec rather than my plan to use the 750 Vac Sec. He dont think that I will have enough vacuum to operate the vac sec of the Holley 750. However I think my combo is calling for the 750 Vac Sec. UDHarold said he did not have a problem with this cam running power brakes in a 406. RatONaStick Dec 29th, 03, 12:06 AM Vacuum secondaries dont actually rely on engine vacuum for operation. there are actually 2 small orifices in the venturies of the carb, when sufficient airflow passes through the venturies over these orifices it will create a vacuum in the vacuum secondary pod. which pulls the diaphram open. i think a 750cfm vacuum secondary carb would work well for you. 6D9 Dec 29th, 03, 12:31 AM With your cubic inches and 3000 stall I would go for the 750DP. I ran a 650 DP on my 350 and it was great but I am sure it would be too small for a 406. Purs Dec 29th, 03, 1:18 AM I started with a 750 Vac Sec on my 408 Big block and it ran pretty well but my dad pulled his 650 Double Pumper and I thought what the heck I'll give it a try. What a difference! Not just a little but ALOT! It pulls much better on the bottom and midrange and as good or better up to 6500.... I wouldn't have believed it in a million years.... graemlins/clonk.gif mr 4 speed Dec 29th, 03, 6:54 AM Go with the 750 vacuum sec. if you already have it... JUNK YARD DOG Dec 29th, 03, 8:04 AM the 650 dp will out perform the 750 vs but if your going to buy a carb get the 750 dp to start with you will be alot happier BLK64SS Dec 29th, 03, 8:51 AM I ran a 850 DP on my car, tried a 750 VS on it and as far as " seat of the pants" feel there wasnt any difference, the track showed it was a bit slower andlost some MPH. If this is a street driven car, I myself would use the 750 VS. thrasher Jan 1st, 04, 1:38 AM My thoughts... http://www.holley.com/HiOctn/ProdLine/Products/FMS/FMSC/0-80528-1.html mr 4 speed Jan 1st, 04, 7:46 AM ...don't be fooled by seat of the pants with a double pumper vs. a vacuum secondary carb..this is the biggest mistake anyone will make..since you don't "feel" the secondaries open on a vacuum carb,people mistake that for the car being slower.A timeslip is the only way to tell Sure,a DP might feel "better" at part throttle when you snap them open,but there isn't any part throttle condtions at the track-only on the launch. | ||