help setting timing

[hpfiend]

Ok guys-

 

Here is the setup:

 

2700lb chassis

th350 automatic

355 small block chevy with low compression (dished pistons)

MSD billet distributor with vacuum and mechanical advance

holley hp 750 double pumper 4bbl carb

 

Pointer doesn't have numbers that I can read- is each point on the triangles a degree? With vacuum line from distributor- it reads max before tdc. Any higher and it is off the pointer. I put the vacuum line on a manifold vacuum source instead of port vacuum (where it was) and it bumped it up beyond the pointer. I drove it and it felt like a whole new car- smokes the tires at will now and it was soggy before. With the combination of a bigger shooter went from 14.0 to 13.2 both at 95.

 

Holley says I don't want port vacuum I want manifold vacuum and that I should set the base timing higher. I could not get a vacuum indication at all on the port on the side of the metering block at idle and revving in park - and why would I want vacuum advance to coincide with mechanical advance shouldn't they work at opposite parts of the spectrum?

 

The way I have it I know as the throttle goes down I lose the off idle vacuum timing and then at some rpm set by the springs the mechanical advance is supposed to kick in. so I should have the same timing across the board maybe a little more up top depending on the bushings in the distributor...

 

Do I just crank it until it pings and then bring it back or crank it on 89 and then run 93? It matters how hot/humid it is outside doesn't it? I don't hear it pinging at high rpm/wot now but it's so loud maybe I wont hear it? which raises the second question- how do you know how much mechanical advance to run or total timing you can get away with?

 

Thanks!

BTW our light does not have any numbers on it so how do you know how much you are running when you are beyond the gauge? Do they sell them with numbers or is that what an innovate is for?

[AJ]

my timing light has advanced and retard settings so i set it to the degrees i want and then line it on on zero on the timing tab.

[Cordell]

I haven't done many of these, but you use a vacuum gauge to set base timing. Max vacuum is where you want base timing, then most aftermarket dizzys allow you to make mechanical adjustments inside the dizzy to change how far it can advance, and sell you different springs to change the mechanical advance curve. Vacuum advance is there for decent economy and part throttle drivability.

 

Not sure what your question was, you may already know this, but I'm posting it anyway.

 

Edit: nevermind on the vacuum thing, I'm thinking of the carb

[Dave1647545494]

ok first things first you need to set the base timing with the vacum advance disconnected and the port plugged on the manifold......

 

can you take a picture of your balancer and pointer? I can probably help you out.