340 w/ 650 double pumper ?

I have a 360 that I have had a Holley 600, Demon 725 and Holley 750 (all are vacuum secondaries). When I built the engine I had the 600 on the shelf so I put it on. The car ran great but everyone was telling me that I was leaving a lot of power on the table with the 600.

I hemmed and hawed for quite awhile between purchasing a Holley Street Avenger 670 and a BG Road Demon 725. I kind of liked the look of the Demon and enough people told me it would be a good choice I went for it. I fiddled with this carb all summer and could never get it to run well between 1200 and 1800 rpm. Once past 2000 rpm it ran a bunch harder than the 600. Since I use the Cuda as a daily driver in the nice weather and 90% of my driving is in the 1200-2000 rpm range I put the 600 back on.

I even called BG about my troubles and I was told the carb was to big for my application and I should have purchased the 650 Speed Demon vac secondary, never did get any real help to sort out the carb. I compared all the specs (BG does give you all the vital specs on there web page) and it seemed I could convert the 725 to a 650 with only a change of the main body and some jets. Couldn't get anyone at BG to tell me how to order a main body. If anyone knows where I can order a main body let me know I would like to make it a 650.

Couple of weeks ago I sold a 383 long block and took a Holley 750 vac sec (#3310-2) as part of the deal. I was comparing the 750 to the 725 and noticed the 750 had smaller butterflies than the Demon 725 so I threw a quick kit at it, verified the jets were all stock sizes and put it on the car to see how it would run. Made a couple of runs down the street and backed the secondary spring down from the black to the plain and called it good. The car runs just as hard on the top end as it did with the Demon and I am not giving up any driveability or throttle reponse in the 1200-1800 rpm range compared to the 600. Haven't checked fuel mileage or mixture yet but at this point I think I have found the carb I am going to stick with.

FWIW, the car has run a best of 13.7 sec @ 102 mph with a 2.2 sec 60' with the 600. The top end increase with the 750 is very noticable in the seat of the pants so I hope to see something on the order of 13.4s the next time I run it.