carb selection

i have a friend here that works for barry grant, he is getting me a speed demon for $150, i have a bored 352 with a fairly large cam, a dual plane edelbrock intake and a full msd ignition system. i was looking a the 575cfm and the 650cfm, i think that the 650 may be a little big for my motor and the 575 might be a little on the small side, i have a 600 holley on it now which works fine but im 18 and basically for $150 i have to have a carb that says demon on the front of it, that how us teenagers are haha. anyway i was wondering if you would go with the 650 or the 575 and also i was looking and they offer both of them in mechanical and vacuum secondaries, will mechanical ones get a lot worse gas milege or do they do alright. i am only making 10mpg as of no so i dont want it to get any worse, i have only owned vacuum operated secondaries so i dont really have any experience with mechanical ones.
thank you
Tyler

Bigger carb manual secondaries ,gas mialage will drop ,unless you keep your foot out of it and it has smaller primaries than your current carb.

A friend that hooks you up with a speed demon for $150 is a good friend to have. That said, depending how high you wind your motor, I think 650cfm is a bit on the low side.... but should be adequate. Mech sec. are better for race applications and/or light-weight cars.... vac usually better for street and bigger cars.... there will be other (better?) opinions.

2 cents,

Chris

yah i figure if i can get a demon for $150 then i should go for it. here is the formula for carb cfm, carb cfm = rpm x displacement / 3456 x 0.85 now my motor is bored .60 over and totals 362cid if i do the formula and use 5500 for my total rpms i come up with about 490cfm this seems way on the low side for my motor. i would have guessed that it would need alot more carb than that this just doesnt make sense, i saw this and thought that i would go with the 575cfm carb but but i was also thinking that well the 650cfm is only 50cfm more but after using this formula im not sure what to think.

that's the right formula though I'm curious how you figured 85% VE. If you only plan to spin it 5500 max rpm, the 575 will be big enough even with 100%VE.

My shortcut of cid*2 I use for a motor spinning to 6900 (~3456*2,VE=100%) I use this for extra slop so I'm sure I won't be starving at high revs.... at 5500 you'll be fine with the 575.

If this is going in the Galaxie I might tend towards a vacuum secondary carb due to the car's mass. Otherwise, IMO the 650 is just about right ...........

Kitz

i figure the 85% VE from the formula i found online i relize that my motor by no means have a volumetric effecency of 85% but it was what they recommended for a street car, im guessing that i have about 60-70% VE without doing any math yes it is going in the galaxie

i just hear tons of diffrent people telling me tons of diffrent things. i was leaning towards the 650 the motor could turn 6000 but why? i never take it over 5500 its just not nessecary

yah that makes sense im just gonna go with the 650, but for a few months here you guys are gonna be my only connection to the car world.......report cards just came out so it looks like i wont be getting this carb for a few weeks ohh well ill just have to get my grades up