Holley ultra double pumper???'s

[dickeymoore]

Im running a Holley ultra street avenger 670 carburetor on my sbc 406 daily driver and was wondering would it be better to install a Holley ultra 650 double pumper with electri choke on my daily driver I know I might be getting less fuel mileage from the double pumper but what about daily driver performance over the vacuum secondary Holley ultra street avenger?Thanks

 

[1320chevy]

Im running a Holley ultra street avenger 670 carburetor on my sbc 406 daily driver and was wondering would it be better to install a Holley ultra 650 double pumper with electri choke on my daily driver I know I might be getting less fuel mileage from the double pumper but what about daily driver performance over the vacuum secondary Holley ultra street avenger?Thanks

A 670 carb is fine on that but a lot depends upon your total package (cam, heads/valve size, compression, intake and exhaust manifolds etc. It's easy to under carb. You just don't have the top end performance you could with the right one. MPG is a product of everything I listed and also rear gearing/tires ignition curve, etc, not to mention your driving style.

 

[bracketchev1221]

If the vacuum secondary is tuned right, the car will have no more performance either way.

 

[dickeymoore]

Carb is tuned right I just don't have the topend power guess I'll just stick with the vacuum secondary carb by it being a daily driver

 

[1320chevy]

Carb is tuned right I just don't have the topend power guess I'll just stick with the vacuum secondary carb by it being a daily driver

With a smaller carb, you won't have a lot of top end power. Engine needs to breathe. Small carb is like breathing through a straw. Too large is worse though. Most I'd go would be a 750, dp or not is your choice.

 

[78Delta88]

This is why I like the Spread Bore Vac Secondary on daily drivers. Small primaries for basic driving and large secondaries to move air when your foot is in it.

 

[ELCAM]

I would try tuning the secondarys on your existing carburetor before upgrading.

Holley 20-13 Secondary Diaphragm Spring Kit

Allows changing the rate of the seondary operating ranges

www.holley.com

 

[dickeymoore]

ok Thanks

 

[stew86MCSS396]

I was always told if you're producing vacuum on your WOT pulls, go bigger.

 

[bracketchev1221]

Back when I was young and thought I knew more than my dad who had raced for 20 years before I could drive, I ran a 750 vs on my street car with the lightest diaphragm spring in it. I believed the double pumper had to be faster. So I put a 700 dp my dad had used with the choke horn milled off and jet extensions and ran low 10’s on his car. My car ran back to back exactly the same at the track.