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Old 07-17-2009, 09:18 AM
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Mech Advance Dist Only, Ignition Timing

Edit: This post can be deleted. In all my research and posting on various forums, I forgot I had already posted this problem on here before.

I am having a heck of a time getting my 428 to run right. Since I first built the engine in 1996, it has been more or less fine with the non-vacuum Mallory YL distributor set up as follows:

Initial 10 Deg BTDC
Max 38 Deg BTDC

However, those numbers turn out to be all wrong for two reasons:

1/ My harmonic balancer outer ring had slipped (Close to 30 degrees), and

2/ some of the dist advance was already used up at an 850 rpm idle (5 degrees).

To make a long story, I was playing wiht the timing, set it too far advanced and broke a piston. Now, I've just finished my re-build which includes a new damper which I have triple checked to make sure it reads TDC correctly, but I have timing issues. I fire it up with intial set to 10 Deg. Engine gets hot very fast with a lot of heat from the headers and a bad bog when I give it gas. Bump the timing up to 16 (14-16 intial is recommended for my cam) and it's better, but still a bad bog when I give it gas (although a little better).

So I look at what my old timing figures would be if I corrected for the slipped damper and already slightly advanced dist mechanism.

So I set it up for 28 intial and 38 max (closer, but not quite as high as the old figures based on the slipped damper correction). Much better, bog is basically gone, maybe a tiny hiccup. Engine runs cool.

Still not the same as before I broke the piston with that "hiccup". So to correct for that, I need to advance to where I think I was before....i.e. more....maybe 30 intial and 38 max.

This seems way to high and I'm nervous about doing it.

Car weighs only 2500 lbs. Am using a Crane solid lifter cam at 294 advertised and 227 Deg @ 0.050" with a single plane 2x4 manifold. Mech dist only.

Here's a tidbit. I adjusted my engine for max vacumm and rpm at idle. Timing was at 38 Deg BTDC. I am certain once the throttle opens at 38, I will get detonation until the rpms build, so that's out.

Anyway, I am of the theorey that if an engine needs a ton of advance with no-load, and very little advance under full load, then a vacuum advance would be a terrific help. And since I don't have one yet, my car benifits from timing somewhere in-between. I just havn't figured out where yet.

Keep in mind, I only use 1/3 to 1/2 throttle zipping up through the gears, so there will be a partial vacumm to keep the ignition advanced. It's not like a heavy car or truck with an automatic transmission where you can successfully floor it..

So for now, I am trying to get this mechanical dist dialed in until I can sort out which vacuum dist I should buy (that will fit for one thing).

1/ Does anyone have any thoughts on why I need such a high initial timing?

2/ I am thinking about getting this Pertronix vacuum dist:

Does anyone know the max diameter of the cap? I need to know if it will fit as there's not much room.


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