Holley double pumper vs vac secondary?

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hux340

hux340

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Hi All,
When I bought my 71 Dodge Demon 340 it had a holley double pumper on it. Was pretty bad on fuel but when you nailed it you were instantly gone, loved it. But like I mentioned was bad on fuel. So I replaced it with a brand new Holley 680 street avenger. Was obviously better on fuel but you always get that slight delay every time you gave it some.
My question is, if you drove the car exactly the same to compare both carbys what would be the % increase with the double pumper over the vac secondary.
My reason I ask this is I'm thinking of putting the double pumper back on. I liked it that much. I put 98 octane fuel in it here in Aust. (which is the highest you can get at your local bowser). The car is only a sunny sunday driver which probably only does approx. 5,000 miles a year.
Cheers,
Glenn.
 
on a holley double pumper...the secondary do not begin to open until the primaries are at 40 degrees...so your foot controls the opening of the secondaries and the gas mileage....
Now if the jettng is incorrect then the carb be too rich ...or if the idle circuit is too rich...or has the wrong power value or it is blown from a backfire....
 
70aarcuda said:
on a holley double pumper...the secondary do not begin to open until the primaries are at 40 degrees...so your foot controls the opening of the secondaries and the gas mileage....
Now if the jettng is incorrect then the carb be too rich ...or if the idle circuit is too rich...or has the wrong power value or it is blown from a backfire....
Click to expand...
I was just getting ready to type this ^^^^^^^^^^^^^^ So instead, I'll say "Amen"
 
hux340 said:
Hi All,
When I bought my 71 Dodge Demon 340 it had a holley double pumper on it. Was pretty bad on fuel but when you nailed it you were instantly gone, loved it. But like I mentioned was bad on fuel. So I replaced it with a brand new Holley 680 street avenger. Was obviously better on fuel but you always get that slight delay every time you gave it some.
My question is, if you drove the car exactly the same to compare both carbys what would be the % increase with the double pumper over the vac secondary.
My reason I ask this is I'm thinking of putting the double pumper back on. I liked it that much. I put 98 octane fuel in it here in Aust. (which is the highest you can get at your local bowser). The car is only a sunny sunday driver which probably only does approx. 5,000 miles a year.
Cheers,
Glenn.
Click to expand...

Try changing the spring in the vacuum pod for the vacuum secondaries to the short yellow spring (second lightest) to get the secondaries to open sooner. It will wake up the vacuum secondary carb.
 
Last edited:
You can make either carb work better with tuning.
Its impossible to know the reasons for the different responses from each without knowing where in the throttle position, rpm and loading these things occur. You can experiment changing springs and pump shots to discover which ones may help or you can systematicly test the circuits, each in turn. Really depends how deep into it you want to go.
 
The vacuum secondary carburetor is more for street cars while the double pumper is more for hot street/race.

Gas mileage=Prius
 
RustyRatRod said:
The vacuum secondary carburetor is more for street cars while the double pumper is more for hot street/race.

Gas mileage=Prius
Click to expand...

Yeah but I remember before I put the vac secondary carb on, the double pumper made the car more responsive. I'm putting the double pumper back on, it made the car more fun to drive.
 
Check this out .. No spring b.s. adjustment.. , and gas mileage..


quickfuel.gif

QUICK FUEL 63-12QFT...
A adjustable vacuum secondary setup...
 
With any of these carbs, learn how to tune them with things other than main jets, accel pumps/nozzles and power valves.

There is a huge difference in getting one well tuned from the factory metering specs for IAB. IFR, PVCR, Emulsions, IFR location.
 
crackedback said:
With any of these carbs, learn how to tune them with things other than main jets, accel pumps/nozzles and power valves.

There is a huge difference in getting one well tuned from the factory metering specs for IAB. IFR, PVCR, Emulsions, IFR location.
Click to expand...

Agree! That's what I was hinting at up there. :)
 
I have built/tuned many many Holleys over the years. I have raced with both VS and DP Holleys. If you are running a mild converter I think the VS is a better choice and will not bog with the correct spring in it. I always switch over to the plastic quick change kit on my customer's builds. Now, if you are running a 4-speed with some gear or an automatic with a decent converter than the DP is the way to go. I love the HP series, especially the 950. Excellent tuneability. I also build Demon carbs but they do not work well out of the box and are definitely more finicky than a Holley.
 
70aarcuda said:
on a holley double pumper...the secondary do not begin to open until the primaries are at 40 degrees...so your foot controls the opening of the secondaries and the gas mileage....
Now if the jettng is incorrect then the carb be too rich ...or if the idle circuit is too rich...or has the wrong power value or it is blown from a backfire....
Click to expand...

That would depend on the linkage. Mine are 1:1 on my blower car.
 
With a stick-car
the DP is the way to go.
And the reason is because the crank is married to the tires. There is no help in the TC (no slip/no TM), and no kickdown,and the 3.23s keep the engine in a pretty low rpm handicap zone until over 3200rpm/30 mph. So if the tires don't spin, then you're slogging up to where the power starts, up past 4000/37.5mph
The DP opens the secondaries instantly, and kicks in a few extra footpounds right when you need it; NOW! Dog-gone it!
I tried the 600/750 vacuum secondaries, and the TQ, and finally bolted the 750DP back on, cuz it's just so much more fun. And it stayed on since around 2004.
____________________________________________
With the 2.66low in the A833,the 3.55s would bring 4000rpm down to 34.1mph, and 3.73s to 32.5, and 3.91s to 31. So if you follow the progression, from 3.23s; 37.5-34.1-32.5-31, you can see a point of diminishing returns.
So what about a lower first gear?
You might see that a 3.09 low gear would be cool. The new numbers are;32.2-29.4-27.9-26.6;some 5mph sooner in each ratio. And I just gotta say, that for a streeter,the 3.09 low is awesome. It is plus 16.2% stronger. To match it, the rear gear would need to jump from 3.23 to 3.75.
Now remember, either the 3.75s or the 3.09 low, will increase your on-road-torque all through low gear at every speed and rpm,by that 16.2% .
Whereas headers would be most effective over a narrow range of about 1500 to 2000 rpm, say from 4000 to 5500 or from 37 to 52 mph with the 3.23x 2.66 combo. This is why gears make such a huge difference in a stick-car; no help from the TC.
 
Thanks AJ,
Demon is 4 speed with 3.23 gears.
Cheers,
Glenn.
AJ/FormS said:
With a stick-car
the DP is the way to go.
And the reason is because the crank is married to the tires. There is no help in the TC (no slip/no TM), and no kickdown,and the 3.23s keep the engine in a pretty low rpm handicap zone until over 3200rpm/30 mph. So if the tires don't spin, then you're slogging up to where the power starts, up past 4000/37.5mph
The DP opens the secondaries instantly, and kicks in a few extra footpounds right when you need it; NOW! Dog-gone it!
I tried the 600/750 vacuum secondaries, and the TQ, and finally bolted the 750DP back on, cuz it's just so much more fun. And it stayed on since around 2004.
____________________________________________
With the 2.66low in the A833,the 3.55s would bring 4000rpm down to 34.1mph, and 3.73s to 32.5, and 3.91s to 31. So if you follow the progression, from 3.23s; 37.5-34.1-32.5-31, you can see a point of diminishing returns.
So what about a lower first gear?
You might see that a 3.09 low gear would be cool. The new numbers are;32.2-29.4-27.9-26.6;some 5mph sooner in each ratio. And I just gotta say, that for a streeter,the 3.09 low is awesome. It is plus 16.2% stronger. To match it, the rear gear would need to jump from 3.23 to 3.75.
Now remember, either the 3.75s or the 3.09 low, will increase your on-road-torque all through low gear at every speed and rpm,by that 16.2% .
Whereas headers would be most effective over a narrow range of about 1500 to 2000 rpm, say from 4000 to 5500 or from 37 to 52 mph with the 3.23x 2.66 combo. This is why gears make such a huge difference in a stick-car; no help from the TC.
Click to expand...
AJ/FormS said:
With a stick-car
the DP is the way to go.
And the reason is because the crank is married to the tires. There is no help in the TC (no slip/no TM), and no kickdown,and the 3.23s keep the engine in a pretty low rpm handicap zone until over 3200rpm/30 mph. So if the tires don't spin, then you're slogging up to where the power starts, up past 4000/37.5mph
The DP opens the secondaries instantly, and kicks in a few extra footpounds right when you need it; NOW! Dog-gone it!
I tried the 600/750 vacuum secondaries, and the TQ, and finally bolted the 750DP back on, cuz it's just so much more fun. And it stayed on since around 2004.
____________________________________________
With the 2.66low in the A833,the 3.55s would bring 4000rpm down to 34.1mph, and 3.73s to 32.5, and 3.91s to 31. So if you follow the progression, from 3.23s; 37.5-34.1-32.5-31, you can see a point of diminishing returns.
So what about a lower first gear?
You might see that a 3.09 low gear would be cool. The new numbers are;32.2-29.4-27.9-26.6;some 5mph sooner in each ratio. And I just gotta say, that for a streeter,the 3.09 low is awesome. It is plus 16.2% stronger. To match it, the rear gear would need to jump from 3.23 to 3.75.
Now remember, either the 3.75s or the 3.09 low, will increase your on-road-torque all through low gear at every speed and rpm,by that 16.2% .
Whereas headers would be most effective over a narrow range of about 1500 to 2000 rpm, say from 4000 to 5500 or from 37 to 52 mph with the 3.23x 2.66 combo. This is why gears make such a huge difference in a stick-car; no help from the TC.
Click to expand...
 
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