Vacuum Secondary Spring

goodnigh

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Around seven months ago we installed a rebuilt never fired 351C 4V

quench long block purchased from Don of OMS. We had all the parts

including the original iron intake and a Holley 80670 with vacuum

secondaries. The only difference between the old block (cracked)

and the new block is a cam we measured at 0.58 lift. That is

not stock. My Holley came with three springs; black, silver and

yellow. Silver is installed for "most" applications with black being

used when you want the secondaries to come off later for better

gas mileage. The yellow spring is soft producing better acceleration

at lower RPM. My mechanic says...... if there is a noticeable increase

in performance using the softer spring, I need a bigger carb.

mike

 

MeZapU

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My Holley 780 in the Mach 1 is using a yellow secondary spring. My 82 F-250 with a 302 liked a brown spring. It's not the fact that it needs a bigger carb. It has to do more with gearing and how fast the secondaries need to open to keep in synch with the engines acceleration through the gears. The spring is more of a timing thing from my experience. Every car and engine combination is different so there is no set answer to which spring is best.

-If the secondaries open too fast/early, the engine will usually bog as if its got tall gears and/or the engine doesn't have enough power to get up in rpm's fast enough.

-If the secondaries open to slowly/late, the engine could potentially be making more horsepower as the slow secondary actuation is acting as a restriction.

You just need to have a play and see which one works best for your car. A quick change spring kit helps a bunch as those secondary diaphragms can be a pain to R&R and can tear at the screw holes after messing with them over and over.

 

droptop73

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Your 670 carb should be plenty for a street car. Like Zap said, use the springs to adjust the opening rate.

 

goodnigh

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Your 670 carb should be plenty for a street car. Like Zap said, use the springs to adjust the opening rate.
Holleys come with a full set of springs. The silver is installed by the

factory. As you know, Holleys are wet flow tested at the factory and

adjusted for "most" applications out of the box. It is designed to

work well with any generic engine. Problem being the Cleveland is

far from generic. My other issue is whoever did the rebuild job put

a cam in it. Ford spec for valve lift in a stock Cleveland is ~0.44 but

we measured the valve lift on my engine at 0.58. That Has to change

the equation.

mike

 

MotoArts

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(copied from another site)

Holley Vacuum Spring Chart

(Rated from weakest to strongest spring rate)

....................................Holley

Spring............................Part

Color__________________Number

White_________________ 38R-1195

Yellow_________________38R-585

Red___________________38R-552

Purple_________________38R-597

Pink___________________38R-1331

Green_________________38R-515

Orange________________38R-825

Plain (stock)____________38R-464

Brown_________________38R-477

Black__________________38R-684

The "bog" is often mistaken for the secondaries opening and giving a "boost" feel.

True for the orange engine guys, not true for anyone else (hehe).

The transition should be seamless and will result in a better ET. Go lighter till you feel the bog, then step back to the next heavier.

Do not "strech" springs in thoughts of modifying their rate (another orange block misconception).

If your diaphragm housing requires a check ball, do not remove it.

From my experience there is no rule for the final spring choice in a carb that I know of, it's trial and error.

 
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hyena429

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Around seven months ago we installed a rebuilt never fired 351C 4V

quench long block purchased from Don of OMS. We had all the parts

including the original iron intake and a Holley 80670 with vacuum

secondaries. The only difference between the old block (cracked)

and the new block is a cam we measured at 0.58 lift. That is

not stock. My Holley came with three springs; black, silver and

yellow. Silver is installed for "most" applications with black being

used when you want the secondaries to come off later for better

gas mileage. The yellow spring is soft producing better acceleration

at lower RPM. My mechanic says...... if there is a noticeable increase

in performance using the softer spring, I need a bigger carb.

mike
how much lift you runing on your cam? And do you have the cam specs?...Clevelands do love a big carb thou...I got a 5.25 lift cam im installing on my motor...and i had to step up too a holley 750 with vac secondaires..Got to remmeber even the stock ford carb 4300d was a 716cfm i think...I heard up too 750 on the boss..But its the same carb....She mite need a bit bigger one....Can you get some bigger jets for it? You defenatly dont wanna lean out your new motor...Thats way worse than runing too rich.

 

Totalled

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Generally, the purple spring works well on most street applications. Buy the kit and play around with it.

 

goodnigh

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how much lift you runing on your cam? And do you have the cam specs?...Clevelands do love a big carb thou...I got a 5.25 lift cam im installing on my motor...and i had to step up too a holley 750 with vac secondaires..Got to remmeber even the stock ford carb 4300d was a 716cfm i think...I heard up too 750 on the boss..But its the same carb....She mite need a bit bigger one....Can you get some bigger jets for it? You defenatly dont wanna lean out your new motor...Thats way worse than runing too rich.
We measured the lift at 0.58 which is near enough to the 0.600 lift recommended for the Cleveland's intake ports. That is assuming you

are driving the car around a NASCAR 500 mile circuit at 7000 rpm all

day and not just to church on Sundays. It is a tough call.

mike

 

Darkhorse71

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When I used a vacuum secondary for a little while, my hot little 408w needed a heavy spring to keep from bogging when it was opening. I know holley advertises it as a gas mileage gig, which I think is kinda stupid. You can start heavy, with black or brown, and keep moving up until you get a bog when you go WOT, then go back one spring. Or, of course, work the other way and start light and keep going heavy until the bog at WOT goes away.

 

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