[Sun Tuned]

Well I see Darby beat me to it.

I pretty much agree with that. Here's what I found...

Took a customers dist that had just been sent in, unworked and crusty, pickup coil worked, nothing was cleaned and the pins very slightly worn and I mean very slightly, removed all the ancillary stuff and peeled this onion, put on a set of 139 weights as thats what it had to start with and got 12 dist degrees( 24 crank degrees), pulled the 139's off and replaced with some 053 weights so we could talk apples and rudabegas, got 10.75 distributor degrees (21.5 crank degrees)with that, so being nothing had been cleaned and lubed and worn parts flapping, I'd say that was pretty much on the money with Rocky considering the crud and non lubed parts I was working with. But certainly good enough for what we needed to know.

I will say, make damn sure you don't use a rotor that binds the weights when doing this as the weights will not return (snap) back to their at rest position like they normally do. They do come back but not with the authority they do stock. This is not really a big deal as they do return and they return repeatably,they just don't fully return all the way back touching each other as in the oem position. Just make sure as you should always do that the rotor moves through it's full range of motion and returns "freely".

[grandville455]

Just trying to help Bob

[Sun Tuned]

And man you did a good job of it, you did!!

Was wanting Rocky in on this, but he's probably writing another new article for us to read in the next issue, and is busy with life in general so the foot soldiers gotta get the job done in the interim.

When you gonna make prints of that avatar.... I want one! A big one like 1/2 scale. What a barge!!

[Kenth]

Just adding:
#1112930 was used on 1975/76 455 A/T.
Advance start @800rpm 0-2 degrees, @1000rpm 2-5 degrees, max @2200rpm 4-6 degrees.
Vacuum advance #1973493 starts @6-8 in/hg, full advance 12 degrees @16-17 in/hg.
All rpm´s & degrees are at distributor, double these numbers for crank specs.

[Murf'sDad]

Originally Posted by grandville455

I have his one article and with a 399 center plate is 25 degrees with 139 weights or 045... 23 with the 053 weights..

I've got the article as well. Nicely done. Except Rocky did all his tests with the center plate in the "numbers up" position. My factory distributor was "numbers down". Not that I disagree with Rocky's way, but you have to know which way the numbers were derived to be able to make comparisons.

I've got a 381 center plate and 045 weights which give me 16* max, numbers down. Unfortunately Rocky didn't check the 381 plate so I can't compare. I'm talking to Sun Tuned in another thread and we'll see what we can find out.

Stewart

[grandville455]

Stewart I had my dist originally setup by Bob...Numbers down on center plate. and it has ran perfect for 5 years!.. But with this roller i needed more initial and less mechanical,,but same total so i used Rocky's chart and that is also right on!.. either way works

[Murf'sDad]

Originally Posted by grandville455

Stewart I had my dist originally setup by Bob...Numbers down on center plate. and it has ran perfect for 5 years!.. But with this roller i needed more initial and less mechanical,,but same total so i used Rocky's chart and that is also right on!.. either way works

I figured the way the plate was installed wouldn't FUBAR things.

I'm hoping my 381 plate will give me about 24*, when flopped over. I never liked running a lot of initial and with the 381 in stock position I'd have to run 16* - 18* maybe even 20* initial to get me in the ballpark of a proper total.

Stewart

[grandville455]

Hell the plate I had in mine before would do that.. think it was 11 -12.. for 22-24 degrees!... i think it was a 370? this is Bobs chart below...

Centerplate=======Weights=======Dist.Degrees
368=================139=============10======
406=================139=============12======
349=================139=============15+=====
371=================139==============9======
489=================139==============14=====
375=================139==============13+====
364=================139==============12=====
397=================139==============12=====
370=================139==============12=====
346=================139==============11=====
396=================139==============11.5===
398=================139==============10.25==
383=================139==============12=====

[Murf'sDad]

I just got off the phone with Bob. He's sending me some bits and pieces that he figures I can use to sort out what I need, including a 12* center plate. Bob's the best.

Stewart

[Schoust]

Can someone send me a copy of that artical please? So what do you guy's recamend here? My car is a stick......

[Sun Tuned]

Waaait for ittt. Just close your eyes and relax.

[Rocky Rotella]

The particular HPP article in question isn't found online anywhere. I'll have to locate my copy of that issue, scan the article, and post it here, but I know it isn’t easily accessible. Probably just as good as anything is the chart I created using my findings at that time. You can see two columns; one shows the center plate with its numbers facing up and the other with its number facing down.

The center plate installation, as designed by GM was with its numbers facing down. So many of them didn’t yield enough advance for performance applications when installed in this manner. Others continued advancing at high RPM adding several degrees, which could be detrimental to an engine.

One day while tinkering in the garage, I found that some center plates, which might otherwise be useless to hobbyists, could be usable if installed “backwards,” or with the numbers up. Not only do some yield desirable amounts of centrifugal advance, but the flat edge is a natural stop, which prevents the distributor from advancing further.

Sun Tuned and I have discussed the subject at length and I believe we’re in agreement that some installed numbers up are not as desirable as others simply because they can add too much advance too quickly, also not allowing the weights to fully retract at idle. If you are testing your distributor on an engine and find a center plate that doesn’t retract fully, simply try another center plate or flip it so the numbers are down.

I have used center plates on my own distributors installed in either direction. My concern is the rate and amount of advance it provides regardless of shape. With such a large assortment of them in my collection of them, I can usually find one that works suitably installed numbers down, but I occasionally have to use one installed with its numbers up to achieve a specific number. As long as you’re aware of what’s going on in your distributor and carefully listen for detonation while under heavy acceleration, I doubt you’ll injure the engine while trying to find the advance curve that works best.

Hope this helps!

[Rocky Rotella]

Originally Posted by Murf'sDad

I've got a 381 center plate and 045 weights which give me 16* max, numbers down. Unfortunately Rocky didn't check the 381 plate so I can't compare. I'm talking to Sun Tuned in another thread and we'll see what we can find out.

Stewart, I spun all the center plates that I had available at that time and unfortunately, 381 wasn't among them. I did acquire one at a later date, however, and did take the opportunity to spin it. If you look at the hand-written notes on the right on the attachment in the above post, you see "381/139". That combination yields 15 degrees or damn close to the 16 you found. If you look on the left, you see that its followed by "15" there too. I doubt that the 381 center plate will provide the amount you need. It sounds like Sun Tuned has you headed in the right directon, however.

[Murf'sDad]

Originally Posted by Rocky Rotella

Stewart, I spun all the center plates that I had available at that time and unfortunately, 381 wasn't among them. I did acquire one at a later date, however, and did take the opportunity to spin it. If you look at the hand-written notes on the right on the attachment in the above post, you see "381/139". That combination yields 15 degrees or damn close to the 16 you found. If you look on the left, you see that its followed by "15" there too. I doubt that the 381 center plate will provide the amount you need. It sounds like Sun Tuned has you headed in the right directon, however.

Thanx for jumping in with the chart Rocky. Great article BTW. Looks like the 381 is a dud, no matter numbers down or up.

I'm just waiting to see what all Bob sends me. The 12* plate should allow me to run 8* - 10* of initial. With my 9.75:1 CR that should work out very well with my Q-Jet dialed in per Cliff's recommendations and parts.

Stewart

[Sun Tuned]

I know one thing about all this for sure....

The Chebby boards could but only dream about the organized abundance of knowledge we have channeled into the Pontiac message boards.

Thanks Rocky for the input, now we got the whole trip around the yard covered... front and back top and bottom. Crystal clear.

[Sun Tuned]

One other thing I forgot to mention Rock,

Some cams work pretty damn well, bottom side up, advance wise with the factory "hood springs" installed, Now I gotta use for that big bag of perviously thought un-useable shiny new GM hood springs. Look out buddy, Santa may visit ya a touch early this year.

Ya reckon a 6 pound sack of those springs, will work a few distributors or so???

[Rocky Rotella]

Sun Tuned, you bring up and excellent point I forgot to mention!

Yes, when installing the center plates bottom-side-up, they do require heavy-tension springs to properly control the advance curve. Light tension springs allows the advance to come in too quickly, and then won't allow it to retract.

Got a few pounds worth of hood springs, Bob? I may be interested in some just to have around for a rainy day project!

[Rick Jones]

Suntuned and Rocky:

are the weights the same for a points distributor? I have a '71 Formula I am building and trying to keep it as close to stock as possible and would like to recurve the original distributor.

Thanks, Rick

[Rocky Rotella]

Rick, no they're not the same. Points-type weights are shaped differently and can severely restrict the amount of centrifugal advance when used with an HEI.

[Schoust]

Ok Guy's I finnally got it running with the HEI and it does sound a tad rough? Here is a Link to the engine at idle. Let me know what you all think.
Thanks Ralph
http://www.youtube.com/watch?v=mg1z26lmgMM