MSD Centrifugal Advance For Big Blocks

[wedg2go]

This is something I probably should had done BEFORE I tweeked my carburetors for this altitude (+7000 asl). Especially, knowing that everything under the hood of my 70 Challenger was either freshened up or new. Including the new MSD distributor and ignition controls.

So, I timed it yesterday, to determine total timing.
BTW - I know it needs to be set at 36 to 38 degrees total timing at and around 3000 rpms.
Needless to say, I believe it is setup as is from the factory (I'll be popping the cap today to confirm, now that I have their instructions).
Which brings me to my point - The instruction, I downloaded, is just loaded with graphs and options out the ying-yang. It also states to choose the best selection over all the different springs and bushings. My question is, What is everybody else running out of all the springs and bushings that MSD offers in their kit? I know there are factors that might require tweeking on my part (Altitude, fuel quality, compression ratio, etc-etc)
I just need a suggested baseline as to where I need to start.

 

[Dodgeboy]

Mine was orginally set up with the purple bushing and one light & one med. spring. Timing was set at 39° total. (msd bullit disszy for 383)
20 years later I rebuild it and used the blue bushing (I had a opened kit and didn't have the purple bushing), set timing at 21° idle for 39° total. I had read somewhere that using different weight springs can unbalance the dist. and if your engine revs up quickly that the light springs can bounce back a bit when they first stretch out (if that makes sense) so I just used the med. springs. So far its working for me.

 

[Chryco Psycho]

I typically set for an 18 * curve 18 initial & 36 total , you can reset to 20 -21 if it pings at low RPM

 

[wedg2go]

I torn into the distributor, yesterday, and much to my surprise it had one light and one heavy spring. The bushing was a little difficult to see - I didn't go that far into it, - but I believe it was silver. Looking at the MSD graph, with this combo, it would need 4000 RPMs to bring up the centrifugal advance 25 degrees. Initial is at 10 degrees...for now.

Here's the thing. It pulls down the road like it late for a fire. No lag. No you can really feel it by the butt dyno after it hits a certain RPM. It just runs as expected. Yet, I'll research here and there - FBBO for example - and read time after time that someone will have their initial timing set at 18 degrees with their centrifugal running 18 degrees. Most with one heavy spring and one light spring on a black bushing. Hmmmm?
Bottom line: I can't help thinking that I'm missing out on the full potential of this professionally build 440 and that I can pull a little better than 7" at idle vacuum. Admittedly, this engine does have one monster lift cam that can affect vacuum.

I'll play with her and see what I can come up with now that I have something to go with along with some great advice.

Thanks Dodgeboy!

 

[wedg2go]

I typically set for an 18 * curve 18 initial & 36 total , you can reset to 20 -21 if it pings at low RPM

The same setup per the gang over at FBBO within my last reply Chryco?

 

[Dodgeboy]

For what its worth I only get 6 inchs vacuum.
(I checked my notes so heres kinda a repeat)
For the first couple of years I only ran 15° intial timing (starter coudn't handle anymore) then it gradually creeped up (by fluke), then one day I checked it and it was at 26°. I don't drive the car much so I lucked out not blowing up the motor as the advance (18°) stayed the same (44°total, ouch).
My timing is:
Idle-1300rpm 20°,
1500rpm =26°,
1800rpm = 32°,
2000rpm= 32°,
2500rpm = 34°,
2800rpm= 38°
Like I said in my earlier post I will be adding 1° at idle for 39° total. Blue bushing with light blue springs