Holley 3310 vacuum secondary spring selections (pic) - Chevelle Tech
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post #1 of 16 (permalink) Old Jun 21st, 08, 12:07 AM Thread Starter
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Question Holley 3310 vacuum secondary spring selections (pic)

I have done some searches and have some questions (for the sake of discussion, limited to n/a engines in a street Chevelle):

I know that I can simply try all the springs in a given kit and find the one that works best. I would like to see if I can be a little less random about it with your help. Not only does this help me understand why a spring works, but helps me understand which way to change during future modifications like a cam swap, gear swap or whatever.



Left to Right (lightest to heaviest springs):
White, Yellow, cut Yellow (upsidedown), Purple, plain, Brown, Black.

Based on the picture, do I have that right? The brown and black were hard for me to to tell which was which.
Despite the differences in spring free height, the wire diameter and coil pitch are more particularly what drives the spring rate as I understand it.

So the real questions here:
Is there a generic rule about where to start with spring selection (such as heavy cars start with black and work backward)? Or are there too many factors to make some generic rules?

Some guiding questions to help answer the above question:
I would assume cam selection makes a big difference for vacuum signal, right? Lower engine vacuum needs a lighter spring?
All else equal (manifold vacuum, gearing etc.), does engine displacement affect the needed spring?
I understand that rear gearing can impact the needed pump shot on the secondaries of a double pumper. Does gearing impact vac secondaries?
Changing from a stock snorkel/paper filter to a open element K&N or equiv filter would impact the signal too I think, which way (confusing posts in the search on this)?

I am happy to hear your experience, particularily if you can tell me why something worked, so I understand better.

Thanks for your time,
Ron

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post #2 of 16 (permalink) Old Jun 21st, 08, 1:03 AM
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Re: Holley 3310 vacuum secondary spring selections (pic)

Based on the picture, do I have that right? - Yes

I would assume cam selection makes a big difference for vacuum signal, right? - No, no vacuum under WOT LOAD is what opens the secondaries.

All else equal (manifold vacuum, gearing etc.), does engine displacement affect the needed spring? Yes, more cubic inches, more airflow, more spring to keep it closed.

I understand that rear gearing can impact the needed pump shot on the secondaries of a double pumper. Does gearing impact vac secondaries? Just that the engine can get into the RPMS quicker

Changing from a stock snorkel/paper filter to a open element K&N or equiv filter would impact the signal too - YES

I would start with the Purple or Cut Yellow first. Then go weaker till you get a bog, then go back up one.

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post #3 of 16 (permalink) Old Jun 21st, 08, 1:11 AM Thread Starter
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Re: Holley 3310 vacuum secondary spring selections (pic)

Thanks Walter, of course, that makes sense. As load increases, the secondaries open - I should have thought of that

So it is really all about air flow through the carb then? Then the 'signal' for the secondaries is above the throttle blades?

(edit, nice car BTW!)

Are there other factors to consider? Or am I over thinking this as usual?
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post #4 of 16 (permalink) Old Jun 21st, 08, 1:27 AM
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Re: Holley 3310 vacuum secondary spring selections (pic)

Hey Ron
I have had the best luck running the purple spring. You can try the yellow spring , but I have found they usually bog.

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post #5 of 16 (permalink) Old Jun 21st, 08, 2:04 AM
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Re: Holley 3310 vacuum secondary spring selections (pic)

I've found the Black spring to work the best for Me. Just seem's to really make the car snap.

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post #6 of 16 (permalink) Old Jun 21st, 08, 3:44 AM
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Re: Holley 3310 vacuum secondary spring selections (pic)

it's really not vacuum as normally understood that opens the secs. It's air velocity through the primaries, which creates venturi vacuum, which acts on the diaphragm against the spring. So even though there's no manifold vacuum because of WOT there's still air velocity through the primarys which opens the secs. To fiddle with tuning the secs you really need the pod with the opening lid, makes changing the spring a snap.

I also have had the best results overall with the plain or black spring. The light springs usually produce a bog by letting the secs open too fast leaning out the mix as air velocity thru the venturiis drops off. Big engine, light car, steep gears all allow a softer spring and faster opening.

Tom
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post #7 of 16 (permalink) Old Jun 21st, 08, 1:48 PM Thread Starter
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Re: Holley 3310 vacuum secondary spring selections (pic)

Thanks Dave & Dave & Tom.

In reading some other posts, I see the purple spring recommended by several people. I will likely try several, just making sure I comprehend what changes will impact this choice in the future.


I did get a quick change kit. I think I am beginning to see what you mean Tom, thanks. If it is about air flow, would that mean that in tuning I am going to get a different secondaries reactions depend on what RPM I am at when mash the pedal? What I mean is, how should I be checking for bog - do I cruise in 4th at 2000 rpm and mat it? OR do I need to row up through the gears? Or should I only be tuning in the RPM range of where my cam 'comes in'?

thanks again...
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post #8 of 16 (permalink) Old Jun 21st, 08, 2:59 PM
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Re: Holley 3310 vacuum secondary spring selections (pic)

When enough airflow is going through the primaries the venturi effect will pull enough vacume on the secondary circuit to open the secondaries-(spring tension permitting). If you pull the carb off and trace the vacume circuit from the vacume pod you'll see it goes to the right front primary bore just below the booster and when enough air is rushing past this hole it will pull vacume on the channel. Smaller carbs will flow faster air sooner than one with larger primaries so spring selection will be different between the two carbs. Do yourself a favor and start with the heaviest spring and launch the car from a dead stop running it through two gears-should pull smooth but may be lacking power if the secondaries aren't opening all the way or slow. Then install the lightest spring you have and check out the performance difference-if they open too soon you'll feel a hesitation and hear the bog at the same time. Then it's just a matter of finding the spring in between than opens fast enough without bog. Spark curve, A/F mixture, gearing, and PV selection also plays in heavy to the total combination. Example:A heavy car with poor gears is under a lot more load than a light car with good gears so the spring selection would be totally different between the two. Test and tune.
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post #9 of 16 (permalink) Old Jun 21st, 08, 3:07 PM
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Re: Holley 3310 vacuum secondary spring selections (pic)

shortest yellow works the best for me...and I have the timeslips to prove it
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post #10 of 16 (permalink) Old Jun 21st, 08, 3:24 PM
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Re: Holley 3310 vacuum secondary spring selections (pic)

i play with those all the time in my combos and i have found ad much as 1.5 mph gain in a single spring change, most of the time yellow gives me best times but causes bog on the street. the bog usually shows up right at kick down ( passing gear) on automatic tranny.

another little trick to do just to make sure your secondary's are opening, use a paper clip of some form and put it on the secondary rod, make sure you shove it up to the bottom of the pod, when the secondary's open the rod will go up in the pod and paper clip will slide. when the rod returns to normal the paper clip will be moved down the rod. this shows you how much the secondary's opened.

start with a black spring the most stiff, then go test drive the car, rolling 20 mph or so. then go home and change to the weakest, you will feel the bog and you will now know what your feeling for.

now find the one that suits you. remember just taking off from a dead stop and rolling thru the gears usually will not show the bog as much, rolling from 20 or 30 will give you the better feel and at highway speeds when you go to pass someone.

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post #11 of 16 (permalink) Old Jun 21st, 08, 3:40 PM
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Re: Holley 3310 vacuum secondary spring selections (pic)

The white spring appeared the give me the beat results, even with ET Streets dead hooking at the track. Couldnt get the thing to bog at all. It all depends - all engines are different. This was with a 770 vac sec carb on my last combo. Now with an 870 carb, the secondaries dont seem to work as good as the 770 did no matter what spring I try...just seem to hit too late. I guess the 770 had a stronger venturi effect making the secondaries come in nicely.

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post #12 of 16 (permalink) Old Jun 22nd, 08, 12:09 AM Thread Starter
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Re: Holley 3310 vacuum secondary spring selections (pic)

Bob, Chris, Dennis, Vince,
thanks for the additional insights. I think I have as much as I need now - just need to finish assembling the carb and try it!

Thanks to all for your input.
Ron
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post #13 of 16 (permalink) Old Oct 7th, 08, 12:35 PM
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Re: Holley 3310 vacuum secondary spring selections (pic)

I'm sorry to jump in late, but I have a follow-up question related to spring selection for my 4160 carb. Here's the trick (and I know this is a Chevelle forum), but it's for my ski boat. Sorry in advance.

I have an 88' Ford 351, with the 4160 and the secondaries appear to be opening too early from the load. There is a large flat spot in acceleration, then a wham-o, a big surge from what appears to be the air catching up with the fuel.

This all happens around 3200 RPM. Now maybe I'm wrong and the secondaries are opening late and hard, but I think they are early for the application I need. What do you guys think? This is all just speculation at this point, but it sounds like a stiffer spring is the answer.

The reason this is a problem is when pulling the skier, the secondaries open hard and then skier's get's pulled way out of position. Here's another idea: for this application, would just disconnecting them be all that bad? Would that damage the carb or motor? Thank you.
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post #14 of 16 (permalink) Old Oct 7th, 08, 4:10 PM
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Re: Holley 3310 vacuum secondary spring selections (pic)

Quote:
Originally Posted by psm View Post
I have an 88' Ford 351, with the 4160 and the secondaries appear to be opening too early from the load. There is a large flat spot in acceleration, then a wham-o, a big surge from what appears to be the air catching up with the fuel.

This all happens around 3200 RPM. Now maybe I'm wrong and the secondaries are opening late and hard, but I think they are early for the application I need. What do you guys think? This is all just speculation at this point, but it sounds like a stiffer spring is the answer.

Here's another idea: for this application, would just disconnecting them be all that bad? Would that damage the carb or motor? Thank you.
Sounds like you are on the right track about the secondaries opening too quickly. Before changing springs I would check to make sure the secondaries are opening smoothly and are not bound up or sticking.
I would not disconnect them to band aid what appears to be a simple issue.

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post #15 of 16 (permalink) Old Oct 8th, 08, 12:05 AM
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Re: Holley 3310 vacuum secondary spring selections (pic)

Tall Yellow one is the one I like the best.
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