I have a 1968 455, Engine is a stock rebuild with a Rochester 2 GC. I put in a HEI distributor and wondering if my only option is to run full manifold vacumn to it. I dont see any port Vacumn nipples on the carb.

Also what would be a good timing number for this also.

Thanks in advance
George

 

I run manifold vacuum, the car will idle better and get better gas milage. Manifold vacuum was used for 40-50 years, then ported vacuum was introduced when they started making cars have a cleaner exhaust emission.
Try it you may like it.

 

x2

As far as your base timing, is there an emissions sticker under the hood? If not, any repair manual should have the spec, if you can't find it online. I'll check my chilton and get back to you.

 

Mines not stock, but I prefer manifold vacume also.

 

As for the timing, unless you are planning to change out the center bar and weights you should set the initial to the specs for the engine it came out of, which is probably around 20º BTDC. This will ensure the total timing is correct. The way to really know it's right is to use a dial back timing light and set the total advance to the value you desire and then let the initial be whatever it ends up at.

Remember: total advance = initial advance + mechanical advance

Mechanical advance is usually ~34º, so: initial advance = total advance - mechanical advance

Points distributors have around 24º mechanical advance, which means the initial is set around 10º to achieve the 34º total.

HEI distributors have around 14º mechanical advance, so the initial is set to ~20º to achieve the 34º total.

So unless you alter the mechanical advance some way (recurve kit or whatever) you will end up with way too little total advance if you set the initial to the same value that was used with the points distributor.

I tried a Moroso HIE Advance Curve Kit since its center bar and weights give 24º mechanical advance. This allowed me to keep the factory 10º initial setting, but later I swapped back to the factory HEI parts as the higher initial advance gives a smoother idle and higher vacuum.