[Hotrodjohn71]

I have a 1965 Pontiac 326 engine basically stock.

I have it running on manifold vacuum for the spark advance but I have a question.

When Pontiac went to ported vac advance in the late 60s, did the design of the vacuum canister change? Would it be safe to assume that a new off-the-shelf distributor vacuum canister will function the same as an early 60s Pontiac vacuum canister did?

The distributor I have is a new HEI style clone distributor. The vacuum advance canister does have an adjustment whereby you use an allen wrench to adjust the vacuum advance on the canister itself (through the vacuumport)..

Being that this is a new distributor I'm wondering if there is a different kind of canister required for the manifold vacuum style set-up since manifold and ported work a little differently.

I'm 'assuming' that this distributor canister is designed for ported vacuum since that seems to be the norm since the late 60s., but I don't know if there is a difference between the two

I

[Cliff R]

If you still have it and it's in good shape I'd go back to the factory distributor. That's just my opinion based on what I've seen with the offshore billet HEI's they are selling at rock bottom prices.

If you really want to use it I suppose it could be made to work OK, but in order to get optimum performance from the HEI you bought, or anything else it needs to be set up to do the same thing as the OEM distributor.

This means that it needs to provide the same mechanical spark curve and add the same amount with the vacuum advance.

It would be a lottery ticket if what you bought is doing the same thing that the factory points distributor did. With the aftermarket HEI's is difficult to alter the advance curve with them. Although they use similar parts as the OEM HEI's I haven't seen one yet that was easy to work with and provided a nice steady spark advance as it should starting right off idle and smooth and steady till all-in when it should be. Most have too much leverage in the mechanism as they are designed to get ALL the timing in quick and early, and by the time you put strong enough springs on them to keep some of the advance out at idle they don't advance well as RPM's increase.

The vacuum units are OK, and easy to modify. Most only change spring tension when you adjust them, or when (inches of vacuum required) they add timing. To change how much typically requires modifying them for the correct amount of travel when they apply.

I really don't see any of the offshore HEI's any sort of upgrade from a stock distributor. I've also yanked a few out of pretty "fresh" engine builds brought here with very low miles on them only to find the gear worn down to "knife" edges and about to fail. So they need to start finding better car bumpers to melt down to make those gears from over in China......IMHO.......Cliff

[steve25]

Does a HEI even fit well with the pre 67 intake Manifold?

[Hotrodjohn71]

Yes. In my car it's a perfect fit. (Not done with the spark plug wires)

[Schurkey]

Originally Posted by Hotrodjohn71

Being that this is a new distributor I'm wondering if there is a different kind of canister required for the manifold vacuum style set-up since manifold and ported work a little differently.

I'm 'assuming' that this distributor canister is designed for ported vacuum since that seems to be the norm since the late 60s., but I don't know if there is a difference between the two

The canister doesn't know if it's getting manifold vacuum or ported vacuum. For practical purposes, ported vacuum is just manifold vacuum that's shut off at idle.

The canister has a designed-in amount of travel which equates to the amount of vacuum advance in degrees.

The canister has a designed-in spring tension, that equates to the amount of vacuum needed to provide that advance.

Aftermarket canisters may have some amount of adjustment for the amount of degrees, or the amount of spring tension, or both. In that case,it's up to you to "adjust" it for optimum performance on YOUR vehicle.

[Hotrodjohn71]

Thank you. That was the information I'm looking for. I suppose I over-thought the complexity of the vacuum canister concerning the two different sources of vacuum for its activation.