Holley 670 street avenger

[gunmetal]

If I purchase a secondary spring kit will it help increase performance very much by just changing the springs?  Would the difference even be noticable?

[MEK-Dangerfield]

Replacing the spring with a stiffer version will help gas mileage. Replacing it with a softer spring will get the secondaries involved sooner, so better performance. I believe the spring installed from the factory is more towards the gas mileage side.

I guess it depends on what you want. Is the carb working well for you otherwise?

[gunmetal]

Brand new rebuild with about 450 miles on the motor, carb was new out of the box.  I was hoping for noticible performance increase for $26. I've been told that changing the spring will allow the four barrels to open up wider allowing for better performance.

[dodge freak 2]

This is true so long as the motor needs the extra A/F--like if its big cubic inches or has a steep gear, 3.55, 3.91, 4.10....maybe even 3.23.

You keep putting in lighter springs until you get a bog on WOT, you then put the next heavier spring back in and if it never bogs then that is the spring to use.

[moper]

It's not really that you get a performance boost from the spring... but rather from getting the carb closer to what your engine wants. What I would suggest is to remove the cover and see what spring is in it, and simply go and buy the next spring lighter. There are color charts online or from Holley... But... Did you buy the carb new? There should have been a couple springs in the box with it. The 870 has them...

[matt63]

I doubt that a different spring would make a huge difference.  At least it didn't for me.  I would definitely check out the distributor timing and total advance.