[danmayo]

Just installed a msd-6 box. Engine set-up is a 455 pontiac with 64 heads, 230 @ .050 dur. .480 lift cam. 750 holley with vac. seconarys, edelbrock performer intake, hooker comp headers, HEI dist., Car is a 1980 firebird mainly street cuising. What I need to know is how and what my timing should be? Also would like to know if going to a mechinacal advance would be better than the vacuum advance? When timing I am having a problem getting a good reading with the multi spark system.

[danmayo]

Just installed a msd-6 box. Engine set-up is a 455 pontiac with 64 heads, 230 @ .050 dur. .480 lift cam. 750 holley with vac. seconarys, edelbrock performer intake, hooker comp headers, HEI dist., Car is a 1980 firebird mainly street cuising. What I need to know is how and what my timing should be? Also would like to know if going to a mechinacal advance would be better than the vacuum advance? When timing I am having a problem getting a good reading with the multi spark system.

[David Holmberg]

I would start with 12 initial and 32 to 34 total. Only testing for performance and what the fuel will allow before pinging will tell you the exact timing. I have a MSD 6 box on my TA and it does not affect the timing light at all. If it's jumping around you may have a problem inside your dist. Also when you check the timing, you do have the vacuum advance line off...Right?

[Half-Inch Stud]

Just finished rebuilding/re-phasing/re-timing my HEI..just closed the hood 20 minutes ago.

Running lots of spark:
One thing you may want to do: Check the rotor-to-cap phasing. Get a spare HEI cap, cut a rectangular hole right below the #6 post. Install spare coil into cap...
Install this inspection cap onto your engine.

Put timing light on #6 plug wire and point timing light at #6 window. See if your rotor is phased to the post...

All you know-it-alls should know the answer..it's not phased well at idle with the Vacuum-advance connected.

Well, disconnect the Vacuum-advance hose and recheck rotor-to-cap phasing. The rotor beter show up in-line with the post, and steady vs RPM ranges. If the rotor is not then I suggest the following:

With the Vac-Advance hose disconnnected:
If rotor is to the left of the #6 post [Unlikely this will be the case]:
RE-phase rotor to post by slotting the 2 Vac-advance mounting holes so it can be pushed into the distributor cup by about .1"

If rotor is to the right of the #6 post:
RE-phase rotor to post by adding an S bend to the Vac-advance rod by using pliers and 8"Cresent wrench to bend the rod to make it shorter. I did just that tonight.

When you re-install the Vac-advance hose [to ported vacuum] the rotor will phase out by going to the left of the #6 post AT IDLE.

Rest assured that when you hit the gas pedal, the ported vacuum goes away quickly, the rotor phasing becomes optimal, and your timing advance becomes what you set it for.

I'm sure you know to check you total timing advance with some good RPM like 2600, 3000 or so [like Holmberg said 34 degrees total].

Then verify you have sufficient timing at idle like 800 RPM [like Holmberg said 12 degrees initial].

Reconnect the ported vacuum advance hose and watch the timing go up up and away. Improves idle with the big cam. If you have pings during part-throttle driving then more and better timing surgery is needed. Most folks are correct to say "leave the Vac-Advance hose off" because it is tiresome to get it to play just right.

One trick to avoiding the pings here is to use a fast-response Vac-Advance pot: mine shows the number 30. That was faster then the numbers 25 and 20 Vacuum pots, which I also evaluated tonight. GM stamped these numbers into the stamped steel bracket. You'd be surpirsed how fast it respondes compared to the moter response. So try to find a high number [like 30] in the bone yards.

Let's go under the Rotor:
My other trick to avoiding the pings here is to limit the mechanical advance by adding a ball-bearing in each 'pocket' under the weights. If your phasing was 'way-out' without the vacuum advance then the two ball bearings gives you a chance to rephase the rotor without much fuss, while limiting the total mechanical advance capability. I forgot where I got the ball bearings..not from TH400 check balls as they are too big.
I probably got them from some valve lifters.

Tip to avoid frustration, some proper wording: rather easier to limit the mechanical retarding ability with the ball bearings in the pockets. If you stare at the advance weights long enough you'll see that they receive torque from the cam gear, and transfer torque to the Rotor mount. Then as RPM goes up they fly out a bit -giving the rotor/magnet-trip mount a push ahead [mech advance]

THUS: thin wire springs to have mech advance come in early, ball bearings in a retard-limiting position. The result will be that the advance weights will have the best lever force on the Rotor mount. you will see a 'brick wall' for the total timing advance with RPM, rather than some flakey soft advance/ inconsistent advance vs RPM.

By the way did you get the MSD-6 to fix some sort of HEI problem [img]/infopop/emoticons/icon_smile.gif[/img]

If you are OK with all this, the MSD-6 may be fairly evaluated.



[This message has been edited by Half-Inch Stud (edited 08-08-2000).]