A friend of mine has a 64 Impala SS with a mild 350 in it.
He purchased a new HEI distributor for it.
We can't seem to get all of the advance out of the distributor we want.
It seems like the most we can get out of it is around 20 degrees no matter what springs we use.
Does a HEI distributor limit you to a certian amount of mechanical advance?
If so how do you get more mechanical advance out of one?

 

May be a stupid response, but are you turning the distrib. to get your initial advance around 12-16 first, then checking the full advance?

 

From what I know ...

 

You may have to change the stop bushing...
Thanks,
Joe

 

Yip.
We put around 12 degrees of base timing into it and then check total timing by reving the engine up with the vac canister disconnected and we end up with around 32 degrees total timing. So we are only getting about 20 degrees of mechanical advance out of it. Tell me about stop bushings and what they do please. I take it they control how far out the advance wieghts can go which also limits mechanical advance?

 

Your problem is that you have the blue bushing in there, which is 21 degrees of advance, and then your initial timing is set to 12, which equals 33, or in your case 32.

This is what I would do (you may want to check with Lars, he is the expert):
Put in the lightest springs and the largest bushing (remove the vacuum advance).
Rev the engine until it is fully advanced.
Set that total advance to 36 degrees, (start by setting the intial timing to 18, because with 18 of cent. advance, it should make total equal to 36, but it may be slightly off).
The goal is to get the total to equal 36 degrees.
and you're done.
total should be 36 and that would make initial about 18.

Here is a section directly from the manual about the bushing:

“Three different advance stop bushings are
supplied in the distributor kit. The distributor
comes with a Blue (21°) bushing already
installed. If a different amount of centrifugal
advance is desired, follow the next procedure
to change the bushings. The chart in Figure 5
gives the size and approximate degrees for the
corresponding bushings.”

Here is how to change them:

“CHANGING THE ADVANCE STOP
BUSHINGS
1. Remove the distributor cap and rotor.
2. Remove the locknut and washer on the
bottom of the advance assembly (Figure 6).
3. Remove the bushing and install the new one.
Install the washer and locknut. Do not over
tighten.
LOCKING OUT THE CENTRIFUGAL
ADVANCE
1. Remove the advance components including
the springs, weights and the advance stop
bushing from the advance assembly.
2. Remove the roll-pin from the drive gear and
remove the gear from the shaft.
3. Slide the shaft two inches out of the housing.
4. Rotate the shaft 180° and insert the advance
stop bushing pin into the small hole on the
advance plate (Figure 7).
5. Install the locknut and washer to the advance
stop bushing pin. This locks the advance in
place. Do not over tighten.
6. Install the drive gear and roll-pin.”
Red =28 degrees
Silver = 25 degrees
Blue =21 degrees
Black = 18 degrees

Thanks,
Joe

 

Simple answer, you need more initial timing. 20 degrees mechanical advance is plenty. Unless you're running into detonation issues, there's no reason to run the factory-mandated 12* initial. This is straight from what I learned from Lars in NoVA a few weeks ago


Chris

 

There is no need to be obsessed with initial timing unless you have smog testing issues...