Speed Demon Carbs

[TonyMadrid]

Hey Guys,

I need some info on carbs. I'm building a 351W and I am thinking about going with a Speed Demon 650. What is the difference between using vacuum or mechanical secondaries. What are the pros & cons of each?

Thanks,

Tony

[Roscoe]

Tony,
All I know is that many people have had problems with Demon Vacuum carbs. I have a 650 mechanical and love it. Never had a problem.
Roscoe

[TAB]

I run a 750 SD with mechanical secondaries, had some problems with the venturies and had some work done to them to open them up a little but overall even before the work was done ran pretty good.
Todd

[Jack21]

Similar setup. 351W, TFS heads, Comp hydraulic roller cam. Replaced Holley with Speed Demon 650 DP and it runs great. Demons worth extra $$ over Holley.

Rule of thumb for vacuum secondaries vs mechanical: Heavy car, small engine, auto trans, tall rear gears (under 3.00), use vacuum. Light car, large engine, manual trans, short rear gears (over 3.00) use mechanical secondaries.

The only Cobra I could imagine using a vacuum secondary carb would be a 302, auto trans, 2.88 rear gears.

[viking]

I run a 750 SD w/vacumn secondaries on my 427 FE , I have gone from 850 holley mechanical to 750 SD mechanical to 750 SD vacumn, Berry Grant finished what holley started, the vacumn carb has no problems at all, it starts fine, a little to much foot still lites the tires , hard 1st to second shifts still raises the left tire off the ground a bit , you still DON'T nail it in the turns, and while crusing I'm getting 4 more mpg, in short other than the mpg I don't notice any difference. Don

[Great Asp]

750 Race demon, mech secondaries, no problems.

I wait for the water temp to come up a little before I drive the car anyway. As a matter of fact, I don't rev past 3000 till I get some oil temp.

Eric