total timing advance

[ed cougar]

Hi, I'm still messing with that dual diaphragm distribtor on my scj. Check this out, I can set my initial timing (vac. lines disconnected and plugged) to way up there around 18* then hook up manifold vacuume to retard (inner) port and the timing comes right back to about 12* at idle, thing is my total timing retains the high numbers say 42* and it all comes in around 3000 RPM. It really woke up this 428. Now I tried to lose the retard side of the advance but without it I have to run the initial to about 18* to get the 42 total so right now it seems to be my advantage to have it. The mechanical stop on the advance slot makes it impossible to achieve 42* unless I set initial to 18* whitch I think is too advanced off idle. thats where the retard comes in and pulls it back to 12*, there's nothing aftermarket on my engine and I'm trying to get the most out of whats there. Any opinions and expertise with distributors please reply for I feel that I may be missing something here, thanks.

[NROTOXIN]

Total is what is important along with rate of advance. If it starts at 18 (hot)I would not worry about it.

curtis

[6T5 Cbra]

On my 428 I run 18° initial, 38° advanced, and all in by 3000. From my understanding (and as curtis mentioned), unless you have a starting problem at 18° initial, the advanced timing and curve are the only things you need to worry about.

6T5

[scottj]

I like to keep it simple and know where the timing is at all times. Mine is locked at 35* adv. If starting was a problem I could install an MSD start-retard box, but on the street engine it wasn't needed.
Scott

[Nantucket427]

I read the intial timing spec. on the cam (15) and ended up calling the Master Bill Parham at Southern Automotive. He said to run the engine up to 3000 and set the timing between 36 - 38 forget about the intial setting. I actually found 38 at about 3200 but the engine starts and runs good.
It doesn't like to run to long under 3000 but that is another story for another tread.

[coyled]

Initial timing does not matter much as long as the car starts. Total should be all in just off idle as long as it does not ping. My cranking is at 12 degrees,30 degrees once it starts which is also the total. EFI, another advantage. Scott

[ed cougar]

Thanks alot, you guys make this a great forum, I learned alot about total timing and I'm now setting it for 38* at 3000 and the initial is what ever it ends up being in my case about 18* no ping starts fine great throttle response. I cant advance much more before the dist. vacuum can touches the waterpump bypass hose clamps. I wonder if the engine will overheat at idle with this much advance it was borderline to start with? The days are cooling off now and so far all is cool.

[Excaliber]

For what it's worth department:

In the old days (points and vacuum advance) "racers" would move the vacuum advance hose from the carb port to an intake manifold port. Theory being that the signal was a little stronger and came on a little faster, thus improving performance.

In some cases "idle speed" will be dramatically affected due to high advance as soon as the car starts, adjust idle speed accordingly.

I never heard of anybody using the "retard" vacuum part of the distributor for any purpose, so that is an interesting variation.

Ernie