Locked dizzy with 6AL2 digital

[boosted79]

For you guys running a 6AL2 digital, how much advance are you locked at? Looking at the shop manual I see the spec for the 1979 California cars was 31* +- 4* BTDC @ 4000 (no boost) so that tells me I can run 35* BTDC and not worry about cross firing, correct? I have a '79 rest of the usa car and spec is 26+-4 so that would say 30* no problem but they are the same dizzy physically right? I'm just talking rotor phasing here, not about advance from a det standpoint, that is a whole other subject. For now I am just running with the stock dizzy set up until I get the engine run-in this week but am planning for the future..

[356911930]

boosted79,

I believe you set your timing at idle to 0* and mark the spot on 13mm distributor slot. Pull the distributor, lock it at full advance, and disable the vacuum lines at the pot. You can remove the pot and cover the hole with very thin sheet metal...some have used a cut section of beer can.

Reinstall distributor and align with the mark you made for 0* at idle. This should give you full advance at idle but be 6AL2 will pull out timing (retards up to 25*) per your setting retarding it to 10* BTDC or whatever works for you.

I'm sure there are other ways of doing this but this is how I understand it. Others will probably chime in.

Rahl

[copbait73]

Originally Posted by boosted79

For you guys running a 6AL2 digital, how much advance are you locked at? Looking at the shop manual I see the spec for the 1979 California cars was 31* +- 4* BTDC @ 4000 (no boost) so that tells me I can run 35* BTDC and not worry about cross firing, correct? I have a '79 rest of the usa car and spec is 26+-4 so that would say 30* no problem but they are the same dizzy physically right? I'm just talking rotor phasing here, not about advance from a det standpoint, that is a whole other subject. For now I am just running with the stock dizzy set up until I get the engine run-in this week but am planning for the future..

Just a word of warning. I'm running the MSD 6AL BT with black blaster coil. If you are using this coil the socket for the coil wire is extra deep. After extreme effort chasing midrange misfire with the CIS check, fuel pressures , delivery, new pump, new filter, intake full pressure check with removal and reseal all visible soap leaks, cylinder leakdown, new plugs - found the coil wire (newer premium set) was not deep into the coil and was arcing. Showed visible soot after repeat roadtests. Pull the wire out of the boot and compare with coil to make sure you are good to go.

[boosted79]

Thanks for the responses but I'm talking about misfire due to incorrect phasing between the rotor and the tower terminal after timing is pulled with the msd box. It depends if the dizzy is firing on the leading edge or the trailing edge of the rotor. If the dizzy fires on the trailing edge of the rotor at what you have it locked at (say 35*) then when the box pulls timing as boost comes up the rotor is going to be even further away from the tower terminal. That can lead to misfires because of the increased gap between the rotor and the tower. With forced induction you want your hottest spark at max boost. So that means you want the rotor terminal directly across from the tower terminal (minimum distance) when the MAP is seeing max boost. On the big Detroit caps you can drill a hole right next to the #1 tower and put a timing light on it to see where the rotor is firing in relation to the tower. Since these boxes can only pull timing you want your phasing so it fires on the leading edge of the rotor then when it pulls timing at max boost you want it to fire when both the rotor and tower are lined up, that means minimum distance and hottest spark. But you need an adjustable rotor to change phasing, not sure any are available for these? I'm a ways from getting into this on mine but when I do I'll buy a new cap and see if I can cut a window in it to see what's going on. There may be a way to either adjust rotor or cap if necessary.

[356911930]

Others have checked phasing issues with a cut cap and have found no issues.

Rahl

[boosted79]

OK, that's good to know. I think I will put a window in one anyway just to see where it's firing both off and on boost.

[Jonny H]

No problems using a locked SC dizzy with our CDI+ ignition. Rotor is at end of post at idle and comes back to centre at high revs.

MSD uses higher voltage than standard making arcing more likely.

[Jonny H]

Forgot to say, if you do need to adjust phase, file the locating tabs in the cap so you can turn it, then build tab up with epoxy. Much easier than messing with the rotor.

[boosted79]

Great info, thanks!

[1979-930]

^^^ I hope you get this all figured out by winter.

Because I'm just going to copy you..

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