Im new to the site guys i have a 67 ss 4spd car with 4:10s .I just picked up my zz502 and it comes with a 850 vac sec does anyone have one. Does it work ok or would you go with a double pumper.

While it may not be a max effort combo, I don't believe GM would have supplied it with the engine if it didn't work. Give it a try and if you think you need more then I would start experimenting. Congrats on the new engine and good luck smile.gif

The vast majority of 60's and 70's Chevy performance cars all came equipped with vacuum secondary carbs. The exception being the 1969 L88 and ZL1 which had a holley 4296 850cfm double pumper. When set up properly, a vacuum secondary carb is a much better choice "drivability wise" than a DP especially on an automatic equipped car. JMHO smile.gif

I have one, and have a 825 race demon on it, once tuned, makes more power and has decent driveability, the vac secondary works ok, but there are better choices, IMHO.

Thanks for the input any idea of what trans i should put in

Umm, correct me if i am wrong, but i believe that a vacuum secondary carb can also be a double pumper. IF it has 2 inlets it is a double pumper. The difference would be if it was mechanical secondaries or vacuum secondaries. I believe you have a double pumper with vacuum secondaries. Vacuum works best on automatic cars as a rule of thumb, but if you have a higher stall and a bunch of power mechanical secondaries work just fine on an auto. I say try it out and get an HP950 later if you don't like it.

Originally posted by cody:
Umm, correct me if i am wrong, but i believe that a vacuum secondary carb can also be a double pumper. IF it has 2 inlets it is a double pumper. The difference would be if it was mechanical secondaries or vacuum secondaries. I believe you have a double pumper with vacuum secondaries. Vacuum works best on automatic cars as a rule of thumb, but if you have a higher stall and a bunch of power mechanical secondaries work just fine on an auto. I say try it out and get an HP950 later if you don't like it. A vacuum secondary carb can have duel feed inlet bowls, but that doesn't make it a double pumper.

A double pumper is also the same as a mechanical secondary. The double pump term comes from the fact that it has two accelerator pumps. One on the primary, one on the secondary. Each pump feeds a squirter. On a vacuum secondary carb there is only a primary pump and squirter. The secondary side does not have a pump or squirter.

Normally on a car equiped with a manual transmission a mechanical secondary carburetor will give you better throttle response, and driver control.

I'm running a 850 vacuum secondary Speed Demon and a 4-speed with 3.31:1 gears. The car is a blast to drive and is downright scary! The ZZ502 is stock.

What are your intentions for your car? If your after the best time while racing, then IMHO I would go with the double pumper, if its a street cruiser I would keep the one supplied. Thats my .02 worth!