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Holley Vacuum Secondaries opening
#1
Hi,

today I've checked if the vacuum secodaries of my Holley 600 cfm 1460 do open. What I found is that during a test run in fourth gear up to 4000 rpm (~90 mph), they opened half way.

Is this what I should expect from a correctly tuned carburetor or should I go for a lighter spring (higher opening rate)?

My engine is a basically stock 351C-4V with a 4 speed toploader.

Thank you, Manfred.
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#2
how did you determine they are opening half way?
Did you ever get the motor to it's max RPM?


'Mike'
73 Convertible - 351C/4V CC heads/4bolt/forged flat tops/comp 270/rhodes/mallory unilite/tri-power/hookers/glasspacks/c6/3.50 limited slip/Gear Vendors/Global West sub frames, strut rods and shelby style traction bars/ Rear sway bar/tilt steering (not original)

Pics of modifications included in:
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#3
will e;25484 Wrote:how did you determine they are opening half way?
Did you ever get the motor to it's max RPM?

I put a paper clip on the shaft coming out of the vacuum secondary housing up against the housing. The clip was moved downwards on the shaft when the secondaries partly opened. By observing the position of the clip after driving I could determine how far they opened.

And no, I didn't dare accellerating it to may rpm in 4th gear on that road ;-) Only up to 4000 rpm.

regards, Manfred
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#4
Ok, that's good way to confirm how far they open.

What about 1st, 2nd or 3rd, did you run it up to your highest RPM?

'Mike'
73 Convertible - 351C/4V CC heads/4bolt/forged flat tops/comp 270/rhodes/mallory unilite/tri-power/hookers/glasspacks/c6/3.50 limited slip/Gear Vendors/Global West sub frames, strut rods and shelby style traction bars/ Rear sway bar/tilt steering (not original)

Pics of modifications included in:
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#5
I know the first test is to lock the secondaries closed and go for a drive and see if its worse or better. if you feel the bog is worse then you know the secondaries are at least doing something.

but you said your secondaries are opening a little so first check the diaphragm and gaskets for damage and clean the vacuum ports.
make sure the mechanics of the secondaries can open fully and nothing is jamming them. they should have free motion to open all the way.

Keep in mind that they may not open if the carb is too large for the engine or if the spring is too stiff.

To increase the secondary opening speed install a lighter spring. the common spring kit (20-13) will include 7 springs the following list is from heavy to light.
Black,
Brown,
Plain,
purple,
yellow,
short yellow,
and white.

I recommend starting with the black spring and working your way down. When you can feel the secondary come in (kick) go back to the previous spring.

Granted i don't know what setup you have as far as CFM on the carb.
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#6
72HCODE;25501 Wrote:I know the first test is to lock the secondaries closed and go for a drive and see if its worse or better. if you feel the bog is worse then you know the secondaries are at least doing something.

but you said your secondaries are opening a little so first check the diaphragm and gaskets for damage and clean the vacuum ports.
make sure the mechanics of the secondaries can open fully and nothing is jamming them. they should have free motion to open all the way.

Keep in mind that they may not open if the carb is too large for the engine or if the spring is too stiff.

To increase the secondary opening speed install a lighter spring. the common spring kit (20-13) will include 7 springs the following list is from heavy to light.
Black,
Brown,
Plain,
purple,
yellow,
short yellow,
and white.

I recommend starting with the black spring and working your way down. When you can feel the secondary come in (kick) go back to the previous spring.

Granted i don't know what setup you have as far as CFM on the carb.

I don't think he is chasing a bog. I think he is just trying to confirm the secondaries are fully opening under load.

However, I don't think the test the OP described applies sufficient load on the engine to result in full secondary opening.

73 conv. 460, D0VE large valve heads, Performer RPM manifold, Voodoo 227/233 cam, Holley 950 HP carb, C6 trans, 3.25 trak-loc.
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#7
The different springs control not only when but 'how fast'.

I don't understand your logic in picking a spring. If you started with the heaviest and went lighter until you 'feel' the secondaries open and then went back to the heavier, wouldn't you cause them to not open? I am not trying to flame or nit-pick, I just don't understand.

On my setup I can feel the secondaries 'kick in' as I go past the 2500 or so RPM range, I assumed I would want a lighter spring or one that kicks in earlier.


And I still would like OP to clarify if he has run it up to max RPM in 1st, 2nd or 3rd gear.

'Mike'
73 Convertible - 351C/4V CC heads/4bolt/forged flat tops/comp 270/rhodes/mallory unilite/tri-power/hookers/glasspacks/c6/3.50 limited slip/Gear Vendors/Global West sub frames, strut rods and shelby style traction bars/ Rear sway bar/tilt steering (not original)

Pics of modifications included in:
  Reply
#8
will e;25499 Wrote:Ok, that's good way to confirm how far they open.

What about 1st, 2nd or 3rd, did you run it up to your highest RPM?

Looks like reving it up all the way to 6000 rpm in the lower gears is something I will have to try today. It may be silly, but I hate the idea of reving it that high after all the work that has gone into it in the last years (I told you I'm silly ;-)

BTW: I couldn't find a redline value for the '71 351C-4V in my documentation. Would 6000 rpm be safe?


Regards, Manfred
  Reply
#9
will e;25522 Wrote:The different springs control not only when but 'how fast'.

I don't understand your logic in picking a spring. If you started with the heaviest and went lighter until you 'feel' the secondaries open and then went back to the heavier, wouldn't you cause them to not open? I am not trying to flame or nit-pick, I just don't understand.

On my setup I can feel the secondaries 'kick in' as I go past the 2500 or so RPM range, I assumed I would want a lighter spring or one that kicks in earlier.


And I still would like OP to clarify if he has run it up to max RPM in 1st, 2nd or 3rd gear.

Generally you don't want to "feel" the secondaries kick in. You want a seamless increase in power. The method 72HCODE suggests will determine the correct spring for that. The "kick" you feel from the secondaries is actually recovery from a hesitation which may be caused by using the incorrect spring and results in a slower car.

73 conv. 460, D0VE large valve heads, Performer RPM manifold, Voodoo 227/233 cam, Holley 950 HP carb, C6 trans, 3.25 trak-loc.
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#10
On my '71 quench head M-code the vacuum secondaries open around 2500 RPM, If Needed. There is no "kick" but you can feel and hear it. A NIB Holley should not need any adjustment assuming it is the correct Holley for the engine. I think the question is are the secondaries capable of opening all the way. You would need to ask Holley how to determine that. If they are not opening, As Needed, it could be an obstruction or vacuum leak. My carb is a Holley 670 CFM Street Avenger (4150 series). Holley was one of the four factory choices that came with all '71 Fords.

mike

[Image: 1_11_11_13_11_50_27.png]
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