[Kevin]

Hi everyone,

I'm looking to get some help setting up the timing curve for a new engine and would like to get the input of the more experienced members here to hopefully get it close on start up. What I have is a 461 with an old set of the original E-heads with the cast chambers, 9.9:1 CR, OF HR cam, FI Tech and a TH400. I have read that these chambers like/need more advance than the newer heads, 12-14 degrees of initial advance and up around 40 degrees of total advance. Is that accurate or am I off?

The distributor that I have is the Summit SUM-850084 billet distributor with vacuum advance. The vacuum advance on this distributor starts at 6 degrees and is all in at 18 degrees, with a max of 10 degrees. I'm assuming that for a street driven car with a TH400 it is likely to run the best with the vacuum advance? If so, would manifold or ported vacuum be preferred?

Thanks for any help or input,
Kevin

[25stevem]

Without knowing what you have for rear gears, for idle vacuum level and at part throttle at lets say 3000 rpm, then it’s a guessing game as to what type of vacuum take off point will work best for you.

In answer to you’d assumption, any car when cruising at part throttle will run better, run cooler and provide better gas mileage with some level of vacuum advance.

[Kenth]

The only difference between ported or constant vacuum for the ignition vacuum advance is at idle speeds, foot off the pedal.
If the vacuum signal at idle is too low to fully activate the vacuum advance, then use a ported source.
You might need to adjust the idle circuit, idle tubes, down channels, idle needle holes and idle bypass air due to the weaker vacuum signal using a ported source.

[Kevin]

Thanks guys and Happy Easter to everyone!

The car has 3.23 gears in it.

So it sounds like, yes, use the vacuum advance and start with a manifold vacuum source?

As far as setting up the distributor for initial startup, it has a 21 degree advance bushing in it now with a set of medium springs that are all in at 4000 RPM. The vacuum advance adds in 5-7 degrees of advance, so lets call it 6.

14 degrees initial + 21 degrees mechanical + 6 degrees vacuum = 41 degrees total advance, all in at 4000 RPM. Does that sound like a reasonable starting place or does something need adjusted?

Thanks again.

[Kenth]

I think you´ll be good with the initial+centrifugal advance total 35° @ 4000 rpm´s.
6° vacuum advance seems low if crank degrees, i would add 10° for 16° crank degrees.

[Kevin]

Yes, the vacuum advance is in crank degrees, I can adjust that up.

[25stevem]

Did that 850084 come with a Allen wrench to go in the vacuum port to set the limit on the amount of vacuum advance?

[Kevin]

Yep