Im trying to figure out the best demon carb for my engine im building i dont have much exp. with demon's and im wondering what would be best for my engine that i listed below

355
142 weind supercharger 8 pounds of boost 6 for street
23 degree trick flow heads intake flows 256 exh 186
cam int:234 exh:244 at 50 int:lift 488 exh:510
21 cc dcup forged pistons h beam connecting rods
headers with 3 inch exhaust
msd 6 ingition with supercoil
holley blue fuel pump

Also does any one know where i can get a good free desktop dyno or if your good at guessing post what you think this engine will make

 

I would recommend the Speed Demon 750 with mechanical secondaries.

 

I am running a 750 Demon on my 408. I am not a demon expert but I have been told that Demon carbs are tested with a wet flow process, where Holley uses a dry, flow. I am not exactly sure what it means but I am assuming it is amount of air flow with a fuel flowing through it,i.e. wet flow, Dry flow is just air flowing through it, no fuel. IF I AM WRONG PLEASE CORRECT ME. Thus a 750 demon will dry flow close to 800.
Hopefully I have helped.
John

 

A 750 Demon dry flows 810 to be exact according to Demon when I asked this same question after hearing of this when I bought my Demon.You are correct.

 

whats the difference between a race demon and a speed demon carb is it worth the extra $300?

 

A Race Demon has removable venturi's (to change CFM ratings of the carb),different boosters more suited to racing(obviously),I beleive-no power valve which will kill any fuel economy on the street,among many other features.For what you are after I would recommend the Speed Demon 750 still,you will not need a Race Demon even with your planned combo,it would be overkill,and the $300 extra dollars will be better spent elsewhere on the car.

 

Demon just rates thier carbs differently so they can say that a "750" Demon outperforms a Holley 750. Just cheating in the name of on paper advertising. Demon is still a good carb and all..but that gets on my nerves. In practice when choosing a carb..it doesn't make that big a difference. The extra 5% or so flow just isn't that significant.

To answer the original question, either one would probably work quite well. I'd get an 850 to be safe...that engine will move some air.