Need Help With Selecting Carb Size
 

Guys, I need help selecting a carb for a 396 stroker sb. The question I have is would you guys gomwith a new 750 Holley ultra dp or an 870 sa. The build is as follows: 4.030x 3.875, dart platinums, custom ground 292 .630 int dual pattern but can't remember ex 106 centerline, 1.5 rockers, 9.5cr. Fully forged bottom end. Was told that with a 106 centerline to go with a tci breakaway ( with anti baloon plate). The gears will be changed but are 2.73 for now. 350 th. My engine builder told me to use mechanical secondaries is why i am Leary of the sa, but would like to hear opinions. Holley says vacuum on street with auto trans so I have conflicting info as my builder has been building for over 40 years and has built many race engines and street engines for my father who used to race. Thanks for all input

I would go with vac secondaries... also, 870 seems a bit big to me.

I'm a bit curious about how the builder calculated that 8500 rpm ceiling too, while still having everything hold together. I have a 393 stroker, with all balanced internals, and the builder recommended keeping the limit in the 6k range. Maybe he's being "safe", but still. Because of the long stroke, these engines are more for torque than rpm. The way mine is built, my max torque levels off in the 5k rpm range, so winding it much past that isn't necessary anyway. I will tell you that with the engine balanced as it is, it reaches 6k in the blink of an eye, which is quite nice. And to get to 8500, is he using solid lifters? Generally, hydraulic lifters can't go nearly that high. If rpm goes past the lifters limit, they'll "pump up" and cause valve float. Even ones that are "anti-pump up" tend to be limited to the 7k rpm range. Solid lifters is how the 1st gen Z/28 302 was able to hit those kind of rpm numbers, that and having a much shorter stroke.

I can't imagine any long stroke motor going 8500 rpm at any time! That's extremely high even for a short stroke motor with all the right components. Amazing if it will do it, but I'd sure be leary fo making more than one trip in the 8500 rpm range!