11 replies to this topic

[croc7]

The HIF44 red spring is rated at 4.5 ounces, the yellow spring at 8 ounces. Wouldn’t replacing a red spring with a yellow spring have the same effect as using a thicker damper oil?

[ACDodd]

No, because it increases the static load on the piston which increases the depression over the jet at any given height at steady state running.

Ac

[PoolGuy]

No, think of it in the same way that suspension springs and dampers work. The spring supports the weight of the vehicle and the damper controls (damps)  the movement of the spring. So a yellow spring will produce more force on the dashpot causing it to rise less than it would with a red spring. The oil affects the speed at which the dashpot rises, and to a lesser degree how fast it falls.

[croc7]

My question should have been; given identical conditions using the same damper oil and needle, and the piston subject to more static force if using the yellow spring, would the fuel mixture/throttle response tend to be leaner compared to using a red spring?

Or to put it more simply, if I switch my red spring for a yellow spring, what would be the result?

Edited by croc7, 17 May 2022 - 05:26 AM.

[sonscar]

I think the question should be"I am trying to achieve XXX,how can I do it?"Steve..

[croc7]

I think the question should be"I am trying to achieve XXX,how can I do it?"Steve..

Always looking for improvement. Needle tested over the years went from BCE to BDK to BEU to BFC. Not a lot of rolling roads with a wall full of needles here in the colonies.

[timmy850]

Given the only change being the spring:
Heavier spring will make the damper sit lower
For a given load, the same amount of air through a smaller opening will cause a higher velocity airspeed and will draw more fuel from the jet and run richer

[PoolGuy]

OP, do you have an AFR meter?

[croc7]

OP, do you have an AFR meter?

Yes. Tomorrow will install the AFR hardware and yellow spring . Should be interesting.

[Pigeonto]

Try it !! I have.

Yes the piston will run lower with a stronger spring and in theory increase the venturi effect pulling more fuel but the needle is larger there so less fuel.

I've had varying results.Depends on the manifold pressure according to the cam, allsorts.

Worth a go

[sonscar]

For ultimate results you will have to revisit the timing as you change the mixture.Steve..

[croc7]

Try it !! I have.
Yes the piston will run lower with a stronger spring and in theory increase the venturi effect pulling more fuel but the needle is larger there so less fuel.
I've had varying results.Depends on the manifold pressure according to the cam, allsorts.
Worth a go

Replaced the red spring (checked to be about 4.5 ounces) with a verified yellow spring and the AFR dropped about a full point across the range of throttle settings. Mid 13’s at idle to 12’s, same for around town and cruise. Interestingly wide open throttle was slightly leaner.

With the modifications to my engine, the BFC needle is the best that I’ve found.