mechanical or vacuum secondries

[daman02]

I'll start off by tellin what i have.  I got a 350 .060 over flat top pistons, 480 lift cam 284 adv. duration int/exh, vortec heads, air gap intake.  Now, i currently have a street avenger 670 w/ vacuum secondaries on it but i was told by a very well respected engine builder that for my application i should get rid of that carb and get a mechanical secondary barry grant demon carburetor.  The truck does get driven regularly but i want the most performance i can get.  All input will be appreciated.

[DnStClr]

Just a guess, but I think he's referring to the mech. secondaries ability to open the throttle plates more efficiently than a vaccum operated secondaries, dont you think? Those Demon carbs are pricey, but when you're building power like your engine does, you don't want the carb to be the weak link in puttin the torque to the ground...  

Don St.Clair
Culleoka Tn

[1976Scottsdale]

The Mechanical secondary carb is nice because the engine does not regulate the secondaries by vacuum.  I run a Q-jet(V secondaries I think) and it is pretty nice, but I have done away with most of the linkage and the secondaries open pretty much whenever I want them to, that is nice in engines like ours because they require more fuel.  Get the mech carb.

[daman02]

well i'm gettin a speed demon so my street avenger is for sale now

[RSBAD454]

Well, if you have an auto tranny....a Vacuum secondary is recommened. Vacuum secondaries are great for heavier vehicles with auto trannies. I have a holley 780 vacuum secondary and it works great. You might hurt your performance by using a mechanical....vauum secondaries only open upon demand of the motor.

Toys are my game

[joesgarage71]

I agree with RSBad454, I have a stout 454 in a heavy Automatic car and wouldn't use anything but a vac carb.I use a Holley on the car and have Quadrajets on my trucks.When there tuned right there awesome.Alot less gas useage.
Steve

[Leadfoot]

 

Edited by: Leadfoot at: 10/24/06 5:07 pm

[roundedline]

Ya'll realize this post is about 4 months old right?

Chris Lucas
www.73-87chevytrucks.com
www.captkaoscustoms.com
Project Su
Jimmy 2WD Project

[Leadfoot]

Aaarghhh..  

Edited by: Leadfoot at: 10/24/06 5:06 pm

[joesgarage71]

Oh Well!

[daman02]

wow since i seen that this post is revived i'll tell you that i will have 3.73 gears with a 2500 stall.  and i am looking for more performance than gas useage.

[joesgarage71]

If you can barrow a 750 vac or double pumper holley from a friend and try it for a day you will like it.Your 670 is alittle small for the engine you have.
Steve

[stepside454]

670 cfm is enough cfm for that motor to about 6500 RPMs , especially with the large plenum on that airgap intake. I woulda kept it on there myself.

[SUX2BU99]

^ Yeah, overcarbing it can lead to more performance disappointments, and mech. secondaries even more so. You might find your throttle response is lacking and too soft on the low-end.  Do you like it to feel responsive and torquey around town or boggy and then it tear up the road when the revs are high?

[joesgarage71]

And I thought that Chevrolet put 750 Quadrajets on 350's from the factory,Humm