Mr. Gasket 928G distributor spring kit

[Duke W.]

A member recently took the following measurements for the springs in the Mr. Gasket 928G distributor spring kit:

Color----- no.of coils --- wire diameter, inches


gold ------- 9--------- .0275


silver------- 9 -------- .0265


black ------ 7 -------- .025

For a given number of coils, the smaller the wire diamter, the weaker the spring (and for a given wire diameter the greater the number of coils, the weaker the spring), so it looks like the silver are the weakest. He currently has the gold installed and will install the silver set and check to see what difference it makes in the centrifugal curve.

Duke

[Donald O.]

Re: Mr. Gasket 928G distributor spring kit

What are the same measurements of an original spring?
What is the actual spring rates, in lbs/in (or any other format) for the Mr Gasket springs and the OE springs?

DonO

[Duke W.]

Re: Mr. Gasket 928G distributor spring kit

There are many original spring part numbers, and I only have data on a couple. Though the wire diameter and other measureable data can be used to calculate the rate, it's primarily an academic exercise, but anyone else is free to do so. Weights, football shape, and cam assembly also affect the curve, so there are scores of combinations. The best thing to do is measure the current baseline with a dial-back timing light and go from there.

On the particular distributor in question, the two installed springs were different, their origin unknown, and produced a poor curve that started at 1300 and wasn't all in until over 4000. The new curve with the gold springs starts at 900 and is all in at 3200.

In the vast majority of cases the silver and gold springs from the 928G kit will create a more aggressive detonation-free centrifugal curve, which is highly desireable for reasons that I have stated countless times.

The one exception is the OE centrifugal curve of the 365/375 HP 327s. That one is ideal from GM.

In order to optimize the spark advance map one needs to test and record the current baseline, which may not necessarily meet OE specs due to the fact that changing the centrifugal curve has been a known way to optimize output across the entire rev range for over 50 years, so many have been changed in the past, but not always for the better.

Also, engine modifications such as installation of high overlap camshaft in place of a low overlap camshaft calls for a different map.

Once a baseline is established, one can use the guidance in my San Diego presentation to optimize their specific engine configuration spark advance map using readily available springs and VACs.

One thing to be aware of is spring rate is a function of the fourth power of wire diameter, so, given the same free length, number of coils, and OD, a small change in wire diameter can have a significant effect on rate, and the silver spring's rate should be about 14 percent less than the gold.

Duke