Double pumper vs Vacuum sec

[747mopar]

When I was putting my Charger together I did allot of reading before making my decisions and am having second thoughts. If you go by the carb manufactures it seems like they all agree that a heavier car (I believe it was somewhere around 3,500-3,800 lbs) should run a vacuum secondary. Reason being a heavier car can't accelerate fast enough to use the fuel being dumped in. I still have some more tinkering to do with it but so far I'm missing my double pumper so the question is what do you guys think. How many of you are running double pumpers on your heavy cars and have you tried the 2 back to back?

 

[PlumcrazyRR]

I am very interested to see the responses here. I have been going back and forth for the past month trying to make a decision on a carb for my RR. It is really the last major component left to buy for my engine. And now I am to a point where I really need to make a decision in the next week or two. Hopefully there are some good informational responses.

 

[benno440]

i was always aware vac secondary for heavy street car and DP for light racecar. Holleys website has a great carb selector for you to try out

 

[SlinktRR]

Vac secondarys generally get better economy and are better street carbs while the double pumper is better for the track. I have a 650 and an 800 AVS. The 650 is nice for cruising and can be tuned to give ridiculous gas mileage, but it falls off at 5000 rpm on a big block...had it on the dyno and the horsepower goes flat at hi rpm no matter how its jetted, the small secondarys are nice for fuel economy but choke the power.

That said, the 650 has great throttle response and the power is good at typical rpm range for a mild BBM. 800 is the performance avs but my 383 prefers the 650cfm. I'm saving the 800 for a 440 build this winter or maybe go Holley/quickfuel.

 

[383man]

Both are good carbs. Myself I run an 850 DP on my 63 and it weighs just over 3700 lbs. But I run 4.30's with a 30" tire and a Dynamic 9.5 converter that will flash about 4200 at the track but drives like a normal car. My brother has a 750 Vacum carb on his street Duster with a 360 in it and it works good on that car. Like I say both can work good but I prefer the DP as I like all four barrells open when I nail it. Ron

 

[Meep-Meep]

The DP carbs are not a street calibrated carb, so depending what your engine is like you may want to go with a true street carb with a leaner transition circuit. The performance might also depend on whether you have street tires or slicks. I ran a vac secondary on my 68 383 RR (prob 3800 lbs as raced) and there was no issue with secondaries opening, and that was with slicks.

 

[rumblefish360]

The trick to running a DP on the street is right foot control.
The vacuum secondary carb is a stomp on it and forget about it device.

 

[AMX364]

The old line was if standard transmission then DP, it also was that a DP can not get gas mileage. A DP on the highway only maintains the speed and so gas mileage can even be better then expected.

 

[67 B-body]

DP 850 Holley on my 440. Working okay,,, could use more CFM.
I have an 8" converter, and 4.10 differential with 27" Hoosier QuickTime Pro tires on lightweight aluminum wheels.

 

[black64]

I do not know if this helps but for me an eldebrock thunder series carb has good performance and secondary vac adjustment without changing springs. There is plenty to figure in on when you need the CFM like heads, exhaust, rear axle ratio, trans gearing, etc. If you are running mainly on the street Vac secondaries work for driveability. The thing you want to avoid is the big bog when you nail it.

 

[splicer]

My ride is a 64 Polara weighing 3700 with me in it, 727 auto, 2800 stall, 505 ci stroker, with 3.73 gears. The first year I had the car on the road I ran an 870 Street Avenger with vac secondaries.
The car's street manners were excellent and I had no troubles with hesitation, surging, or any other issues.
Over that winter, I researched running a double pumper and decided to buy a 950 street HP.
Sure enough, I initially had a huge flat spot punching it wide open off idle and in fact, the engine would usually quit right then and there.
After more research and a whole lot of mis-information about heavy automatic cars and double pumpers, I finally found a guy with the same carb, engine and problem but he had bought a custom carb that solved the problem.
Luckily, he was kind enough to tell me the specs on his carb so I modified mine accordingly. I was skeptical that it would work but indeed it did work.
The engine now goes from idle to wot with no bog or hesitation whether it's on street tires or dead hooking on slicks.
I also picked up 3 tenths on my ET with just that change.
Either carb type can work very well on the street even on a heavy automatic car.
Hope this helps...

Splicer

 

[bigmanjbmopar]

And you're going to leave us with no specs?> wtf is that? lol c'mon man tell us the set up on that carb!

 

[Propwash]

I have no issues with running a Quick Fuel Q950 DP on my 512 on the street. Runs good. Of course gas mileage is out the window, but i'm much more interested in the whip some *** factor anyways. Motor is Dyno tuned, and i'm sure that made a big difference in it's manners.

 

[Gpuller]

Been running a 750 DP on my Charger for years. Swapped out the vac secondary carb long ago, like the DP better. No problems on the street with a heavy car.

 

[furyus]

I'm running a 750 race Demon DP on my 64. Way faster than the vacuum 780 I tried. Have no problems going to full throttle from idle when warm. The DP just needs to be tuned to the car, just like any carb. Usually done by advancing timing and increasing squirter size or changing accelerator pump cams.

 

[747mopar]

Good to hear, I'll keep tinkering with the vacuum sec for now but really think I'll eventually get a DP, I loved the one I had on my last car.

 

[Budnicks]

1st thing is I'd highly suggest you get a few books on "How To Tune a Holley Carburetor",
especially for use on any types of Performance/Racing applications

IMHFO There's nothing wrong with a vacuum secondary style carb, especially when using a Holley style carb
{Quickfuel, ProMax, Proform, AEM, Holley/HP, many others}

The proper sized main jets will help allot too

changing the activation springs in the Secondary Vacuum Pods, to the proper style/color for your specific needs & driving style, lighter springs will activate quicker, heavier springs will slow it down, if that's what your specific combo needs...

changing your Accelerator Discharge Pump & the proper colored acell. pump cam for your specific build/needs, will help also
&/or also the Discharge "Squirters" Nozzles again must be properly sized, to get the full efficiency

also changing your front bowl metering block with an adjustable Billet Quickfuel {my preferred choice}
or ProMax {my 2nd choice}, either of them will flow much better & are much better than the factory Holley Metering Blocks, they are adjustable too, unless you have one of the new Holley HP Series carbs or one of their race carbs...
It's relatively cheap, Changing the metering blocks, mainly so you can change air bleeds & emulsion bleeds, every engine needs it's own specific settings, what works on mine even if they are very similar, may not work perfectly on yours, they are all different, depends on elevation you live & drive in, the weather & your driving style/needs etc.

& going to an adjustable rear metering plate, with removable screw in reg. Holley type main jets like from
www.quickfueltechnology.com &/or www.promaxcarbs.com I'd suggest that you can contact either of them, call them is the best way, they will actually help you & help to steer you in the proper direction, for your specific needs

also the proper sized power-valve, generally the #'s about 1/2 of what you vacuum at idle is
{if you have 10-in/hg vacuum you should run between a 4.5 - 5.5 PV}...

http://www.youtube.com/watch?v=0FFfBZ3qgv0

- - - Updated - - -

holley tech tuning
http://www.youtube.com/watch?v=gag-Bg-X8cM

 

[prplcar]

I had a speed demon 750 DP on my 440, now a 800 thunder AVS. I switched because Edelbrock recommended it to match with the top end and cam I bought from them. The car is slower in the 1/8 mile, faster overall. but I miss the instant power of DP. Fuel mileage is about the same. My car weighs 3190lbs and has a 3000stall converter.

 

[747mopar]

1st thing is I'd highly suggest you get a few books on "How To Tune a Holley Carburetor",
especially for use on any types of Performance/Racing applications

IMHFO There's nothing wrong with a vacuum secondary style carb, especially when using a Holley style carb
{Quickfuel, ProMax, Proform, AEM, Holley/HP, many others}

The proper sized main jets will help allot too

changing the activation springs in the Secondary Vacuum Pods, to the proper style/color for your specific needs & driving style, lighter springs will activate quicker, heavier springs will slow it down, if that's what your specific combo needs...

changing your Accelerator Discharge Pump & the proper colored acell. pump cam for your specific build/needs, will help also
&/or also the Discharge "Squirters" Nozzles again must be properly sized, to get the full efficiency

also changing your front bowl metering block with an adjustable Billet Quickfuel {my preferred choice}
or ProMax {my 2nd choice}, either of them will flow much better & are much better than the factory Holley Metering Blocks, they are adjustable too, unless you have one of the new Holley HP Series carbs or one of their race carbs...
It's relatively cheap, Changing the metering blocks, mainly so you can change air bleeds & emulsion bleeds, every engine needs it's own specific settings, what works on mine even if they are very similar, may not work perfectly on yours, they are all different, depends on elevation you live & drive in, the weather & your driving style/needs etc.

& going to an adjustable rear metering plate, with removable screw in reg. Holley type main jets like from
www.quickfueltechnology.com &/or www.promaxcarbs.com I'd suggest that you can contact either of them, call them is the best way, they will actually help you & help to steer you in the proper direction, for your specific needs

also the proper sized power-valve, generally the #'s about 1/2 of what you vacuum at idle is
{if you have 10-in/hg vacuum you should run between a 4.5 - 5.5 PV}...

http://www.youtube.com/watch?v=0FFfBZ3qgv0

- - - Updated - - -

holley tech tuning
http://www.youtube.com/watch?v=gag-Bg-X8cM

Thanks, I have a good book that covers everything and have already changed the power valve and primary main jets with great results. I just need to tackle the secondary's now and see what happens, I just miss the feel of the DP I had on the last one but maybe this one will come around. I actually got that Holley tuning video off of them at a Summit show not to long ago, thanks for the info I'll read it all and get back to the tuning this weekend.