anybody making big power with vacuum secondaries? - Hot Rod Forum : Hotrodders Bulletin Board
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Old 08-07-2006, 08:11 PM
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anybody making big power with vacuum secondaries?

hey guys, with the motor that i just built i would like to get two carbs, one primarily tuned for racing, and the other for excellent street performance and drivability. i know that with my cam im not exactly going to pulling much vacuum, but im not running power brakes or anything. i was given a holley 3310 -2 from a good friend at work and am wondering how well it will work for me with not too much vacuum. is there anybody on this site who is running a big block chevy with a pretty big cam and vacuum secondaries and still making good power and throttle response?

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Old 08-07-2006, 11:12 PM
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Sorry don't have one, but I can say, it is all in the tuning and adjustments..... somebody good can make them work...... most people just screw them up so dump them for an air valve secondary or a double pumper.
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Old 08-08-2006, 05:20 AM
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I'm more a fan of the Q-Jet and don't currently have a 3310 on anything but over the years I've known scores of people that have used the 3310 with great success on everything from a wild 283 to a very healthy 454. Now you can buy an adjustable secondary diaghram setup from the aftermarket that allows almost infinite adjustment of the secondary opening point and rate so vaccume shouldn't be a real issue. Assuming the baseplate isn't warped or the throttle shaft bores worn out it should be a good carb to start with. I try to keep a couple good 3310 cores on the shelf "just in case".
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Old 08-09-2006, 11:17 AM
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I'll add some to the flames too.

I was running a 750 vac sec on my 406 SBC, which did pretty well I thought.

I am now running a borrowed 850 demon double pumper. For my combination, the double pumper provides much better throttle response, but then the car is a 6spd, so you have a little lag for the secondaries to open every time you shift. Have every color spring HOlley offers and no matter what, it just takes a split second for the secondaries to open. On an automatic car, it probably wouldn't make any difference, since you always stay on the throttle.

On the street a vac sec carb is very forgiving - so that's worth something as well. It seems you can pick them up cheap on eBay cause everyone wants a double pumper for EVERYTHING. I dunno why.

have fun. jer
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Old 08-09-2006, 11:41 AM
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Vacuum secondaries is actually a big misnomer. Your idle vacuum or lack there of had little influence on your secondary action.

You have a vacuum actualted based on the signal running down the primary bore. On the pass bore you will see a small hole for the signal to the vacuum pot. There is a smaller hole, or at least used to be, in the secondary bore to assist in the signal to the pot to help pull it in when you want it.

I was shown once that you can use a small BB or bearing to plug the hole to the secondary thus making the primary hole the only influence on the action of the secondary. I have not done this to any carb.

Additionally if you get the holley "YELLOW" colored spring, cut off the largest coil, or the end NOT painted you will get supprisingly fast secondary action. I used to keep a pot with the cut yellow spring and put it on friends 3310's to show them just how fast it can open. A buddy would actually pull the "C" clip off and not use the secondaries for street driving in his sbc's. When he went to the races, he would connect it. It was faster than changing pots or springs. With the easy access tops to change springs you can take some time and dial it in and get decent performance and mileage. Using a double pumper will usually allow a bit more performance and bragging you have a double pumper is worth about 50 to 70 mental horse power IMO.

The amount the secondaries open on a 3310 or equivalent "vacuum secondary" carb is usually directly proportional to the level of lead in ones foot.
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Old 08-09-2006, 12:14 PM
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Thanks Larry,
will that cut coil be outrageous on the street, generally speaking?


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Old 08-09-2006, 01:25 PM
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Don't know what you consider "big power", but have 3,600 lb street car 400 sbc, 3310 Holley vacuum secondaries. Has gone best of 10.69 & 123.77 MPH quarter mile.

You could get much more power than this I'm sure, with more motor and a higher flowing vaccum carb like a "950 HP Holley", etc. Come to think of it my carb has "non-dowleg boosters" so there is more flow and HP there.

NHRA superstock chevys run *stock* OEM Holley 3310-type vacuum carbs and even Quadrajets and go into the 9's.
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Old 08-09-2006, 02:59 PM
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Quote:
Originally Posted by xntrik
Thanks Larry,
will that cut coil be outrageous on the street, generally speaking?


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You are welcome and the secondaries with "THE SPRING" as I likes to call it, will not affect stop and go driving.

However, when you pedal to the metal, hang on.

BTW, the 950 cfm Holley 3 barrels were vacuum secondary.

Like novajohnb said, the factory chevy HP engines wore the infamous vacuum secondary 780. That includes the 302 to the 425hp 427. Chevy had a special mod done so they could cal each carb to the size engine it would end up on. This cal was an adjustable idle bleed.
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