i'm wonderdering about spark plugs i.e. warmer or colder and gaps.
engine is a 1968 455 2bbl. and bone stock.
btw. got a reman. carb that'll gone on simultaniously
idea is to "msd" it later along with some other performance enhancements

HEI was designed, and used, for emissions purposes, on '74 and later GM engines. Use your '68 specs, including plugs and gaps.

Make sure you change the power source to 12v switched.

Because the advance curve is different in the HEI, you will need to set your total mechanical advance to the same setting as the original dist, or you can use 34° @ 3500 RPM. The difference in advance curves will increase your initial setting, which will cause a power increase at lower RPM. If it's hard to start when it's warm, retard it a couple of degrees.

As a "performance enhancement", MSD is a waste of money.

Norm

If i set set the mechanical advance to 34, what abaout initial timing?
that would be anything from 4 to 14, and the vacuum? I've learned not to use portet but only true vacum?
i'm learning, old dog and new tricks
I can feel the potential but it just don't wanna burn the rubber

It should take care of itself.

If you do not have your original '68 specs, 34° is a good substitute. Either way, it might need a 1° or 2° "tweak".

After you are happy with the way it runs, use your own light to mark the initial setting. That will be your new spec.

If you are not happy with it, let us know. We can go from there.


My guess is, 8° to 12° with your existing dist, and 18° to 22° with the HEI.

Using 20° initial, as an example, the points dist would work fine at WOT,from idle up to 2000 RPM or so, but any higher, the automatic advance to 46°, would make the engine very unhappy. 10° less dist advance in the HEI would keep the total at 34°, where it should be.


Separate issue. You'll need to get the centrifugal "dialed in" first.


A manifold port should never be used for vacuum advance. But that is a different topic, and we will deal with it later.

Norm

sorry, i haven't been back on your fantastic and informative reply, but in between 6day/12hour shifts, (in the midlle of the so called summer (weather has been terrible around here)) i haven't had much time, "forking" around my Old's. But one last qustion before:
To fully recognize the "hopefully improvements" should i replace the carb. or the ignition first.
I'm experiencing "bog" when i'm putting the pedal down?

We have to work, so we can play.


No need to replace the carb unless it cannot be repaired/adjusted. Or unless, you will be changing to a Q-jet.

No need to replace the ignition. HEI will not make it run any better than points.


Is the vacuum advance hooked to the manifold?

Does it run OK, otherwise? Do you see strong squirts from the accelerator pump? If the vacuum advance is connected to the carb port, is it working?

Are the plugs/points/condenser/wires/cap/rotor/fuel & air filter in good shape?

Do you have that dial back timing light yet?

Norm