AJ's guide to Ballparking Idle Timing

[AJ/FormS]

AJs Quick guide to selecting an initial timing number;
Basic is 12*
add; +1* per 5*of cam timing larger than 220@050, and, -1* per 5* under 220@050
So, basic plus;
a 220 cam needs (220 -220)/5 = plus 0*, So 12*, and
a 250*cam needs (250-220)/5 = plus 6*, So 18*, and
a 200* wants (200-220)/5 = minus 4*, So 8*
That will get your T-port sync pretty close. Fine tune from there.

 

[bobscuda67]

Ah! Good info to have. Since I really don't understand timing curves.
That's just where Don at FBO set my dist. up at. With the 230 cam is set at 16* initial. But he recommends that you use manifold vacuum instead of ported vacuum. It did help to close up the transfer slot where it's supposed to be, and I have idle control with the mixture screws.

 

[AJ/FormS]

I wouldn't use full manifold vacuum on a 230 cam, unless you have a very small Vcan. To do so, is to invite ping under light throttle acceleration. The biggest can I have seen is 22*, so 16 + 22=38 would be excessive. But a 9*(the smallest I have seen) can , totals 25* at idle, much more sane, and certainly smoother than 16. Unfortunately 9* is not gonna do much for your fuel mileage. And depending on your Dcr, ping is an ever-present possibility, when running a fast curve and a big can. However, here is the deal, if your combo runs without detonation of any kind and at every load and rpm setting, then there is nothing wrong with running it as you are.

 

[bobscuda67]

I have no pinging at all. It's setup at 16 initial with the vacuum timing at 14* at 14" and the mechanical at 18* at 3400 rpm.
I seem to remember seeing a 8.5 stamped on the vacuum advance arm, it's been a while since I had it apart.

 

[AJ/FormS]

I'm guessing the mechanical 18* is added to the initial of16* to total 34*
I shorthand this to; 16/34@3400 plus 14 full time.
And I'm guessing you are idling at 16 plus 14 = 30?

 

[bobscuda67]

Yep, 18 mechanical and it's around 25* at idle right now. It would be 30* but it has a vacuum leak.
I had 12 inches of vacuum when I checked it today as it was idling like crap. Should be 15 inches. Pulled out #3 plug and it had oil on it, no oil smoke out of the exhaust though.
After having my intake angled milled .004 looks like it wasn't enough to seal the intake port.