Anybody out there running more than 18 deg. initial timing ? We got my motor running last night with the new closed chmber heads on (see Lackluster Performance from a month ago) and the motor seems to want lots of initial timing - we drove it with 18 deg. idled well, but power was flat. We ran out of time to keep playing, so we have not checked total yet, although we changed the springs before and timing was all in by 3000 rpm (before the head swap).

We now have about 10.2 to 1 according to compression calculator- pistons are 21 cc domes. and we have verified the cam lift at 0.525" with a dial indicator, actual duration is unknown. Could there be any other factors at work here, carburator ? We are not using any vacumm advance.

Any input is appreciated as always!!

I run anywhere from 18-20* base/38-40* total in my 454..its all in by 3K..the motor is very,very responsive.I have closed chambered heads as well,and have 10.5 to 1 compression

I run 16-18 base/37-39 total all in by 2600. Vac adv adds 6 at idle (11 in HG) and adds 16 at 3000 (19 in HG). 396 + .060, closed chamber, 10.25:1. Runs great!
Jim

I have just been through this. The first thing I had to figure out was the curve of my current weights and springs vs what I need. Then after that I ended up changing the curve to meet my cam and idle needs which was 900-3000 curve. I added a mr.gasket 929g kit. My timing indicator above my balancer seems to be a degree or two off so my base is 18-20 and total was 34-36 with a grand total including vacuum of 45. The car idles at 900-1000 with ease now and has never ran better. I thought 18 was to much but we had to twist the distributor that far to get the base idle to work so apparently the motor likes it that way. I ended up using the vacuum advance hooked to the manifold instead of ported.

Does mechanical advance always add 20 deg. or does this vary ?

Originally posted by BigBlockBeaumont:
Does mechanical advance always add 20 deg. or does this vary ? I've seen anywhere from 10-20* mechanical

Ok, what variables affect the amount of mech advance ? Weights ?

This is hypothetical, but if I was only getting 15 deg from mechanical, would there be a problem to start with 23 deg initial ? Assuming the car idled fine with that much initial.

Thank guys!

I think that is right. If you shoot for ex. 36 for full advance without vacuum and then subtract 15 from it ex. 36-15= 21 for you base. I could be wrong but I really have read up and posted allot on this subject over the past few weeks. It depends on the distributor for ex. accel give 24 advance from the factory on all there models or so there tech site says.

I run 18-20 36 total 2 stage mech advance all in by 3000

Originally posted by BigBlockBeaumont:
Does mechanical advance always add 20 deg. or does this vary ? Yes.

Get yourself a dial back timing light.
Now set your total timing(the point where the advance stops coming in with increased RPM) with the vacuum advance disconnected.

Set this total advance to 36 degrees.
Now let it idle at about 700rpm.
Write down how much advance you see.

Now do the math.

If you set the total timing at 36 and you saw that the initial advance ended up at 10 degrees this means you have 26 degrees mechanical advance.

36-subtract 10=26 total.

If you need more initial advance to get good responce you need to change the mechanical advance.This is done through replacing the advance stop bushing in a points type distributor and the MSD distributors.
MSD's new HEI distributor requires something different.

Mallory distributors require you to bend a piece of metal that controlls the mechanical advance.

GM HEI'S require you to get a different advance cam that is between the two advance weights.
This is pretty much not going to happen as GM didn't make any good ones,that is unless you have a very mild cam.
You can get these cams through companies like Mr. Gasket or Moroso but they are made of an inferior metal and they wear quickly.Not to mention they have a tone of advance,probably way too much for your engine.

This is why many people replace their HEI's with aftermarket distributors.I'm not nocking HEI's they are good distributors.It's just their lack of advustability that does them in.

Keep it in mind that changing the advance springs does not change your mechanical advance a bit.They mearly change the rate or RPM in which your advance comes in at.

Three things need to be changed to dial an engine in.

1. The advance rate(controlled by the springs)
2. The mechanical advance(controlled by bushings,stops,or cams)
3. The initial advance(controlled by how much you add by turning the housing)

This is why the MSD distributor is very Very popular.

Ok, we found the problem. We shredded the alternator belt (long story) and tried to make use of what was left to get the car set up - well it seemed it was slipping and the alt. wasn't providing enough juice to the ignition & the low voltage must have had an effect on the timing gun also. After the belts were replaced the car ran better already, hooked up the timing gun and it was now only showing 10 deg.-----wierd, so we brought it up to 18 deg. then checked total, which was 38 deg. at 3,000 rpm.

Took the car for a drive and presto, lots of power!!!

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38 degrees total.Might try 36.

I run 29deg at idle, 34deg total in by 3k in my 350.

Originally posted by Twilightoptics:
I run 29deg at idle, 34deg total in by 3k in my 350. Ya might just lock it out.
Ever tried that?