Vacuum or mechanical secondary

[Scott Engelhardt]

I have never used a mechanical secondary carburetor on a vehicle with an automatic transmission. I have a vacuum secondary Holley street avenger now, I bought a new Edlebrock from a friend . I have just been thinking how a mechanical secondary carb would work. The car runs good, but always thinking things could be better?
430HP 490 torque 440 We drive the wheels off this car would think about fuel injection but worry about issues on the road.
Just interested in what experiences you guys have tried.
Thanks

 

[33 IMP]

I have used 800-850 double pumpers on all my "fast cars" for years. Even ones with auto trans.
But mine have around 500 hp, 3.91, 4.10, or 4.57 gear, 5000 converters, and mileage means nothing.
You could experiment with a 750dp, but I think you'll be happier with what you have now.

 

[WileE]

Stock converter ? Stock valve body ? Rear gear ratio ?

 

[Scott Engelhardt]

Stock, stock, 323

 

[RJRENTON]

I have never used a mechanical secondary carburetor on a vehicle with an automatic transmission. I have a vacuum secondary Edlebrock now. I have just been thinking how a mechanical secondary carb would work. The car runs good, but always thinking things could be better?
430HP 490 torque 440 We drive the wheels off this car would think about fuel injection but worry about issues on the road.
Just interested in what experiences you guys have tried.
Thanks

Leave well enough alone.....if the car runs and performs like you want.....D.N.F.W.....why spend the extra $$$ for an experiment.....just my opinion.....
BOB RENTON

 

[BSB67]

Stock, stock, 323

430 hp is nice street hp set up, IMO.

What carb specifically do you have now? What cam and what intake?

For a comparable cfm rating, the one that will run better will more likely be the one you do the best job tuning on.

 

[Scott Engelhardt]

I think having only one car makes me want to tinker. Also I am very curious by nature, that is why I asked for opinions and experience for you guys. I appreciate all reply’s. This forum is one of the best sources of information available

 

[BSB67]

I get it. I have 18 carbs. If you were closer you could borrow a 750, 800, or 850.

I ran the 800 on a something similar to yours. 410 hp, factory intake, 3.23 gear, factory 12” converter in a 4200 lb car. It ran very well.

 

[RemCharger]

I'm a fan of the 800 holleys at that point. They're good. But a new quick fuel is good too.

 

[Geoff 2]

If you have an Edel AFB or AVS, then you already have a mech sec carb.........because when you go to WOT, all 4 barrels are fully open. You already have a great card, no need to change it.......

 

[71Beeper]

I had a 600 Holley double pumper on this 318 engine in this car.

1971 318 engine with a 340 cam and headers that's it.
4 speed with 3:23's out back.
I had a vacuum secondary Holley 600 on it prior to changing to the double pumper.
Night and day difference.

 

[Bee1971]

Read Post #10


With that said what is the Model # of your Edelbrock Carb

 

[Scott Engelhardt]

If you have an Edel AFB or AVS, then you already have a mech sec carb.........because when you go to WOT, all 4 barrels are fully open. You already have a great card, no need to change it.......

Sorry I should check myself before posting. The bluetooth keyboard on my ipad will sometimes delete full sentences. I really need to get rid of that keyboard. I have a Holley street avenger with vacuum secondary. I bought a new Edelbrock from a friend. It is a 1411
Sorry for all the confusion.

 

[Scott Engelhardt]

I corrected the original post

 

[68 Sport Satellite]

I have used 800-850 double pumpers on all my "fast cars" for years. Even ones with auto trans.
But mine have around 500 hp, 3.91, 4.10, or 4.57 gear, 5000 converters, and mileage means nothing.
You could experiment with a 750dp, but I think you'll be happier with what you have now.

just to clarify for us rookies - "double pumper" = mechanical secondary carb, correct?

I also have an auto trans 727 and am running a vacuum secondary holley type Quick Fuel carb. A few of my mopar friends run mechanical secondary carbs with their automatic 440's and tell me after trying them that they would never go back to a vacuum secondary carb. However, most other advice I've always heard from Quickfuel and "experts" is to stick with a vacuum secondary carb with my automatic heavy car b-body, but like the OP, I also feel the urge to try a different carb that is mechanical secondary for that more instant throttle response.

@33 IMP, your post may push me over the edge - although I know you're a racer - what do you think about a double-pumper for the street if we want fast, but also a long lasting motor?

 

[33 IMP]

just to clarify for us rookies - "double pumper" = mechanical secondary carb, correct?

I also have an auto trans 727 and am running a vacuum secondary holley type Quick Fuel carb. A few of my mopar friends run mechanical secondary carbs with their automatic 440's and tell me after trying them that they would never go back to a vacuum secondary carb. However, most other advice I've always heard from Quickfuel and "experts" is to stick with a vacuum secondary carb with my automatic heavy car b-body, but like the OP, I also feel the urge to try a different carb that is mechanical secondary for that more instant throttle response.

@33 IMP, your post may push me over the edge - although I know you're a racer - what do you think about a double-pumper for the street if we want fast, but also a long lasting motor?

"Double pumper" refers to a holley style carb (LOTS of companies make em now) with mechanical secondaries, and an accelerator pump on both bowls. (NOT merely a dual inlet carb). Slightly more of a race-style carb than a vacuum secondary version.
There are tuning options galore for vacuum carbs too. (Lighter springs to tune the secondary opening, for example)

 

[33 IMP]

just to clarify for us rookies - "double pumper" = mechanical secondary carb, correct?

I also have an auto trans 727 and am running a vacuum secondary holley type Quick Fuel carb. A few of my mopar friends run mechanical secondary carbs with their automatic 440's and tell me after trying them that they would never go back to a vacuum secondary carb. However, most other advice I've always heard from Quickfuel and "experts" is to stick with a vacuum secondary carb with my automatic heavy car b-body, but like the OP, I also feel the urge to try a different carb that is mechanical secondary for that more instant throttle response.

@33 IMP, your post may push me over the edge - although I know you're a racer - what do you think about a double-pumper for the street if we want fast, but also a long lasting motor?

You can get away with a too-big carb, or a dp, easier with a car with a stick, or a stiff rear gear. And having a light car certainly helps too.
I run an 850 dp on a small block..... but I have 4.57s, a 5000 torque converter, and 2300 lbs.

If you are gonna try a double pumper, I would recommend being a little conservative on carb size (cfm). Maybe one size smaller than the vacuum sec you have now.

 

[R/T Boy 67]

The AFB type carbs act just like a vacuum secondary holley. They use airflow / vacuum to open the secondaries even though the throttle blades are open.

 

[RJRENTON]

The AFB type carbs act just like a vacuum secondary holley. They use airflow / vacuum to open the secondaries even though the throttle blades are open.

AFB carbs operate on the principle of VELOCITY CONTROLED secondary butterfly valves, located above the secondary throttle valves. AVS carbs operate on the similar principle, but use an SECONDARY AIR VALVE, hence the name, to control air flow buffered by an adjustable spring on the air valves shaft to control opening rate....similar concept as the AFB design, but controlled differently....but where VELOCITY is the controlling factor. Just my opinion......
BOB RENTON

 

[Kern Dog]

just to clarify for us rookies - "double pumper" = mechanical secondary carb, correct?

I also have an auto trans 727 and am running a vacuum secondary holley type Quick Fuel carb. A few of my mopar friends run mechanical secondary carbs with their automatic 440's and tell me after trying them that they would never go back to a vacuum secondary carb. However, most other advice I've always heard from Quickfuel and "experts" is to stick with a vacuum secondary carb with my automatic heavy car b-body, but like the OP, I also feel the urge to try a different carb that is mechanical secondary for that more instant throttle response.

@33 IMP, your post may push me over the edge - although I know you're a racer - what do you think about a double-pumper for the street if we want fast, but also a long lasting motor?

I would not run a mechanical secondary or double pumper carburetor on an engine in a car that I drive a lot on the street. They push a lot of fuel through the engine and the low speed operation we go through can result in plug fouling, increased cylinder wear due to fuel washing oil off the cylinders, etc.
Sure, if your car is primarily for race or track use, occasional use on the street shouldn't hurt anything.