Choosing a Distributor

[SilveradoDude]

I have an 85 Silverado, 305 (w/ the "computer"), but I am not using the on board ignition computer. Also I got a tuneup kit for a distributor that doesn't use the computer and it comes with a two pronged ignition control module, similar to this:

http://www.partsamerica.com/ProductD...pe=194&PTSet=A


mine has a three pronged like this:

http://www.partsamerica.com/ProductD...pe=194&PTSet=A

I was thinking maybe I could just get a an earlier distributor like for an 84 with the two pronged module, would that work?

[jchav62]

That will work. My old '83 had the same setup you are talking about when I got it and I just switched to an older type HEI. Very simple.

[SilveradoDude]

Originally Posted by jchav62

That will work. My old '83 had the same setup you are talking about when I got it and I just switched to an older type HEI. Very simple.

Wait are you saying I can use my existing dizzy and just switch to older HEI? And how? Also, I accidentally broke one of those two pegs that the center weight is clipped to. Is there any way to buy and replace these pegs?

[SilveradoDude]

Would this work:

http://store.summitracing.com/partde...=1#Application

Here is my dizzy:

Can I get a replacement pin?
http://i85.photobucket.com/albums/k6...to/dizzy_1.jpg

[Slonaker]

Originally Posted by SilveradoDude

Would this work:

http://store.summitracing.com/partde...=1#Application

Here is my dizzy:

Can I get a replacement pin?
http://i85.photobucket.com/albums/k6...to/dizzy_1.jpg

That summit one will work. I replaced mine with a Mallory.

Slonaker

[85SBC400]

i have an accel hei in my 85 and it works great.

[SilveradoDude]

I ordered a MSD Street Fire dizzy. So I'm assuming just drop it in? What to I do with the green, brown, black white ESC connector?

[Slonaker]

Originally Posted by SilveradoDude

I ordered a MSD Street Fire dizzy. So I'm assuming just drop it in? What to I do with the green, brown, black white ESC connector?

Leave it disconnected. I just taped mine up and let it dangle.

Slonaker

[SilveradoDude]

Anyone?

[SilveradoDude]

Can someone help explain this MSD Street Fire adjustable vacuum advance:
http://www.msdignition.com/pdf/2005/frm26905_8362sf.pdf

If I want to optimize it for 4 degrees BTDC do I first tuen it all the way in then out 4 turns?

[87Bob]

Originally Posted by SilveradoDude

Can someone help explain this MSD Street Fire adjustable vacuum advance:
http://www.msdignition.com/pdf/2005/frm26905_8362sf.pdf

If I want to optimize it for 4 degrees BTDC do I first tuen it all the way in then out 4 turns?

I found this for you check it out:
Initial timing is that setting you make while your engine is idling with a timing light. This is typically between 4° ATDC (After Top Dead Center) to 16° BTDC (Before Top Dead Center). For performance applications "in most cases" you want as much initial timing as the starter can handle (the more timing the more cylinder pressure that the starter must overcome to crank the engine). Too much initial timing, besides the starter load, can also run the HC (Hydrocarbon) emission levels beyond legal or breathable levels <hint to the smog machine as a tuning tool above>.

Total timing is the calculation of the combined initial and mechanical advance timing settings (max). This "can" also include your vacuum advance though, I like to describe it as "total timing plus vacuum advance". Since vacuum advance is a nearly inconsistent value I like to use it after I have set up the correct mechanical values in the distributor. At times I must use the vacuum advance to generate the timing values I require, but I try to only use it as an "economy" tool to give a street driven vehicle more efficiency and throttle response by this addition.



How Do I Change the Mechanical and Vacuum Advance Settings?
Mechanical advance (also called centrifugal advance) as stated above, is adjusted by change the springs that control the weights and in many distributors you can also adjust or modify the advance "stop point". The stop point is where the mechanical advance no longer continues. On a Mallory distributor there is a wrench you use to adjust the stop point (in degrees). On other OEM and aftermarket distributors you need to change the weights by going to a different weight or modifying the weights to control the stop position.

This is a job that can be done by just about anyone, but it takes the correct tools and some trial and error. In most all cases, aftermarket distributors are good for your engine right out of the box, but when change needs to be made you will need assorted springs, a distributor machine, fully degreed balancer, or an advance style timing light.

You start the engine and write down each timing number at 100, or 500 RPM intervals. This means you write down the timing at idle, then raise the engine speed in 100 or 500 RPM increments (whatever you decide), and write down each one of the timing readings. To make the rate faster (more timing advance sooner), you install lighter combination of springs. To make the rate slower (less timing advance), you install a combination of stiffer springs. NOTE: Too much timing too soon can cause detonation problems, having the timing come on too slow can adversely affect performance and efficiency.

With adjusting the vacuum advance it is on the same principle, except you are now adjusting the pressure on the diaphragm in the vacuum advance can. NOTE: Only those vacuum cans with the octagon body near the nipple can be adjusted. If you are working with an OEM style distributor you must either change to an adjustable can or change cans to one with a different rating. (Most ALL aftermarket vacuum advance distributors are adjustable) On the adjustable vacuum advance cans you simply insert a 3/32" Allen Wrench in through the vacuum line nipple on the can. Turning the Allen Wrench one way or the other will add or subtract the preload pressure on the vacuum diaphragm. Lower pressure offers more vacuum advance, higher pressure lowers the amount of added vacuum.

It is our recommendation that when you are using vacuum advance distributors, that you connect the vacuum advance to "full manifold vacuum". There are two schools on where to connect the vacuum advance line. On older applications the connection point was to "ported" vacuum. Ported vacuum means the port is drawing vacuum "above" the throttle blades in the carburetor. This means that as RPM increases, vacuum increases and in turn, vacuum advance increases. This was fine on older applications with high lead fuel and other ancient engine designs. Using this set up today can cause detonation problems, overheating, and other grief.

With our suggestion of using the vacuum connection to full manifold vacuum, the port will be drawing vacuum below the throttle blades. A good running street engine will have a measured vacuum at idle between 14"-20" of manifold vacuum. Now, this will give you a ton of advance at idle, but as load increases (vacuum drops) you will take timing away. This is excellent for the faster burning fuels offered today as well as in the fact that when you put your foot into the throttle and get the RPM building, you DO NOT need or want additional timing. On a RV or tow vehicle, when you put your foot into the throttle and downshift to climb a grade, you DO NOT want added timing that will slow the vehicle and add heat. You want the added timing for subtle throttle response, and low load engine efficiency. So, when you are cruising at freeway speeds or in town traffic, you have the added timing to save fuel, add throttle response, and overall give you a better feel.

[LONGHAIR]

By those directions (which IMO are not good at all) you need to know your actual vacuum reading at idle, to make the adjustement.
I hope that there is more to the actual directions that came with this unit though. That does not give you any indication of how much timing you need, or how you would find that out? It might tell you how to get there, but no idea of where to go.
How much centrifugal advance is built into that distributor? Somewhere around 20-24 degrees?
As a generic recommendation, the approximate goal is:
10-12 degrees initial (turning the distributor body w/timing light)
20-24 centrifugal (some are fairly easy to adjust/limit)
10 degrees vacuum
For a total of about 40-44...of course there are other factors like compression, fuel octane, etc. that might force you to modify this some.

[LONGHAIR]

There are two schools on where to connect the vacuum advance line. On older applications the connection point was to "ported" vacuum. Ported vacuum means the port is drawing vacuum "above" the throttle blades in the carburetor. This means that as RPM increases, vacuum increases and in turn, vacuum advance increases. This was fine on older applications with high lead fuel and other ancient engine designs. Using this set up today can cause detonation problems, overheating, and other grief.

They are right about using the "Full vacuum" connection........but for the wrong reason. This statement that the vacuum increases with the RPM is wrong! Ported vacuum does NOT act opposite of "full". The only difference is that ported vacuum does nothing at idle, then as you begin to open the throttle is works exactly the same as "full" vacuum. Not to make light of this minor difference....You really should run you distributor on "Full vacuum".
The next statement is wrong too. "Ported vacuum" was not used in the "ancient times" of leaded gas. It was an emissions gimmick of the late 70s and early 80s. That was the era of "late" timing and generally crummy performance.

Interestingly though, those worthless directions also recommend "ported vacuum" ..........along with many of the directions that come with new carburetors? Why? I don't know? But I would bet that this is the very reason that many of them are called "junk" and replaced soon after installation.
There seems to be a lot of "mystery-voodoo" about this...prepetuated by this kind of thing.

[SilveradoDude]

OK, this is really starting to aggravate me. So I got the MSD dizzy dropped in and everything appeared to be running find and then I heard a knocking noise. Apparently the holding plate had come loose and the dizzy was hoping around so now i am not sure that the distributor is in it's correct position.

What is the procedure for getting the distributor back in sync?

[SilveradoDude]

bump.

[LONGHAIR]

1)Disconnect the cap and set it out of the way.
2)Pull the distributor out of the hole, after un-plugging the electrical connections of course.
3)Pull out the number 1 sparkplug.
4)Put your finger over the sparkplug hole and turn the engine over. You can have someone "bump the starter", use a "remote starter switch" or do it "by hand" with a socket and ratchet.
5)When the piston is coming up on the compression stroke, you will feel and hear, the air pushing past your finger. Now turn the engine (by hand is best at this point) until the timing mark comes around to the tab on the cover.
6)Now determine which terminal of your distributor cap has the #1 plug wire and which way it sits on the distributor body. Point the rotor toward that plugwire terminal and stab it back in.
7)It may not "seat" all of the way down...don't worry, it should go with-in about 1/4" or so. Just turn the engine a little bit more and it will drop right down. The distributor will rotate with the engine and when it gets lined-up with the oil pump shaft, it falls right over it.
8)Put your hold-down clamp back in place and finger tighten it.
9) Cap and wires back on, and you are right back where you started. Don't forget that #1 sparkplug, you won't believe the sound that this makes.
10)Break-out your timing light and you are good-to-go.

[SilveradoDude]

Originally Posted by LONGHAIR

1)Disconnect the cap and set it out of the way.
2)Pull the distributor out of the hole, after un-plugging the electrical connections of course.
3)Pull out the number 1 sparkplug.
4)Put your finger over the sparkplug hole and turn the engine over. You can have someone "bump the starter", use a "remote starter switch" or do it "by hand" with a socket and ratchet.
5)When the piston is coming up on the compression stroke, you will feel and hear, the air pushing past your finger. Now turn the engine (by hand is best at this point) until the timing mark comes around to the tab on the cover.
6)Now determine which terminal of your distributor cap has the #1 plug wire and which way it sits on the distributor body. Point the rotor toward that plugwire terminal and stab it back in.
7)It may not "seat" all of the way down...don't worry, it should go with-in about 1/4" or so. Just turn the engine a little bit more and it will drop right down. The distributor will rotate with the engine and when it gets lined-up with the oil pump shaft, it falls right over it.
8)Put your hold-down clamp back in place and finger tighten it.
9) Cap and wires back on, and you are right back where you started. Don't forget that #1 sparkplug, you won't believe the sound that this makes.
10)Break-out your timing light and you are good-to-go.

Great write up.

a couple of questions.

#5 "comes around to the tab on the cover" do you mean turn the harmonic balancer until the timing mark is on the ZERO mark?
#6 Is the rotor cap "keyed" the the distributor to only fit one way?
#7 This is where I got into trouble today. It didn't re-seat where it was suppose to. I sat the dizzy down pointing to #1 spark plug but it still had a bout 1/2 inch to go. By the time I finished turning it and re-seating it was no where near #1.
So you are saying turn the HB? Clockwise?

I appreciate all of your help.

[Pyrotechnic]

I actually run a Streetfire HEI on ported vacuum with no issues. 14 degrees initial, 34 total, plus whatever the vacuum can is set to out of the box. I'm running a Edelbrock Performer / Melling MTC-1 / Summit 1102 cam.

This is with an Edelbrock AFB. I have done a comparison using two gauges while driving and reading ported vacuum and manifold vacuum. Ported vacuum is non existent at idle but starts to climb when the throttle is cracked open and is EQUAL to manifold vacuum at ~1800 RPM. This means that the only difference is really at idle. The truck runs very good with this combo.

Here's a video example: http://www.67-72chevytrucks.com/vboa...5&postcount=21

I know ported was used for emissions purposes and generally made for some awful running vehicles, but those distributors also had an awful timing curve as well. The also ran barely any advance at idle, or even a few degrees retarded at idle. It's no wonder they ran bad.

[LONGHAIR]

Great write up.

a couple of questions.

#5 "comes around to the tab on the cover" do you mean turn the harmonic balancer until the timing mark is on the ZERO mark?
#6 Is the rotor cap "keyed" the the distributor to only fit one way?
#7 This is where I got into trouble today. It didn't re-seat where it was suppose to. I sat the dizzy down pointing to #1 spark plug but it still had a bout 1/2 inch to go. By the time I finished turning it and re-seating it was no where near #1.
So you are saying turn the HB? Clockwise?

I appreciate all of your help.

#5 Yes
#6 Yes, there is a tab on the cap that only fits the distributor body one way
#7 When the distributor is "nearly" down, it has already engaged the gear teeth of the cam, so your "alignment" is set and ok at that point. Now, when you turn the engine (by the crank bolt) the distributor turns with it, so the alignment stays. Yes, it has moved, but so has everything else.
Always turn clockwise, that is the way the engine turns when running. That way every bit of "slack" from any moving parts is all pulled the right way too.

[85SBC400]

and it never did this before correct?

grab your multimeter, and check the ohm's from that wire to a ground and see if you have a short or not.

[SilveradoDude]

Originally Posted by 85SBC400

and it never did this before correct?

grab your multimeter, and check the ohm's from that wire to a ground and see if you have a short or not.

No never. I pulled the entire wire it had no cracks or frays whatsoever.
The ALTERNATOR was getting red hot and transferring the heat thru the wire. I pulled the alternator and will have it tested tomorrow but other than that I am lost.

[SilveradoDude]

I put on a reman alternator and a new thicker gauge (10) alternator wire just to double check and it would still overheat after a minute. I checked the pink ignition wire and didn't see any fraying or cracking. Again the distributor is the only difference in the equation here.

[COMP]

i have no clue

[85SBC400]

the alt. itself might grounding internally......good chance thats it i recon. too bad you dont have a buddy same alt. you could try out.

[SilveradoDude]

Well the alternator tested "fine" it put out more than enough amps. Still wondering about any voltage regulator inside though.

Tell me, the current wiring setup that I had on my truck for the alternator was the main alternator red wire, the primary ignition wire from the fuse block and a red wire from the junction block all joined by a connector.