Another forum member posted a thread about distributor recommendations and it got me thinking.

I wrote the numbers down off mine last year or the year before when I pulled my distributor our to replace the o-ring gasket, and it comes up as a dizzy for a 260 Oldsmobile. 1103320-78-80 was the number on it.

And I got to thinking, although it works in my 72 350, is it really the best option. It has vacuum advance, and I'm running a lot of initial timing, but would a distributor out of a 350 be better? Or say one of the new replacement ones off ebay?

What's different about the distributor in a 260 vs a 350 vs say a 455?

 

I replied in your other thread as well.

The distributor housings, pickup coils, reluctors, and modules are the same. The difference is in the weights / center bar that control the amount of mechanical advance and the "curve" profile, and the vacuum canister that controls the total amount of vacuum advance and the vacuum level that starts it moving.

 

If you don't like the way your timing is set get a re-curve kit for your distributor and call it good. That would be cheaper than getting a new distributor and would accomplish the same thing. You could also get an adjustable vacuum advance canister.

 

Gotcha. That's exactly what I was asking.

I've done that. I bought a Mr. Gasket timing recurve kit, and I think I used a light and a medium spring. I think my car could use a little more initial timing, but i'll have to restab the distributor, or change how the vacuum canister is mounted. My engine seems to like a lot of initial timing, the more initial timing, the better it seems to run off idle.

 

Just remember when you increase your initial timing it also increases your total timing by the same amount.

 

I went that route before - Moroso HEI advance curve kit that gave 24* mechanical advance so I could set the initial at 10* just like factory specs, along with 1 light and 1 medium spring. Jump forward many years and I installed a new cam and wanted more initial to smooth out the idle and give more vacuum and off-idle torque, so after much experimenting I ended up back with the factory weights and center bar that gave 18* initial. Still used the light and medium spring combo to bring the advance in earlier and I am completely happy with the end result. Just wished I had figured it out sooner.

 

I read bad things about the weights in the kits. So I used the factory weights. One medium and one light spring. Maybe I'll throw the other lights spring in, and see what happens. Bring the timing in a little sooner. Listen for ping. Hopefully won't be any.

Are you saying you wished you'd used the factory weights and bar the whole time with just the lighter springs?

 

I tried two light springs and eventually found that there was a significant amount of mechanical advance at idle. When I turned the AC on, the RPM dropped, which caused the advance to decrease, which caused the RPM to drop, which caused the advance to decrease - this led to the engine idling down until it died. Installing one medium spring along with one light spring kept the advance from coming in at idle speeds and cured that whole issue.

Yep.

 

I know, I read that was your problem somewhere else. I don't have an AC, so I don't know if it would be a problem. Was it a high lift cam in the 350? Or is this the new 355 motor?

Maybe I'll throw the light spring in and see what my timing is and if it changes at idle. I'm sort of just curious if it would make a difference off idle. It's quick and easy to try. If not, I'll end up re-stabbing the distributor to give me more initial. I've read a lot and no ones seems to have had to do that. Makes me wonder what else could be the issue.

 

The current 260 distributor with light and medium spring advances very early and quick. It is the first HEI to come all in at about 2500 rpm. Most come in about 3000 even with lighter springs. You want at least 20 base, shoot for 38 to 40 total without vacuum advance. Yes 36 worked best at the track but felt weaker on the street.

 

My current timing with vacuum advance disconnected is 30* at 2250, 34* at 2800 36* at 3100 and 40/41* at 4000k.


I'm at about 22* base timing, and the vacuum pot is just about touching the firewall, so if I want more base timing I have to restab the dizzy, remount the vacuum pot somehow else.

If you're saying all in by 2500 rpm, I might be better off with the two light springs.

 

You could try but only certain weights will allow full advance before 3000 rpm. Unless the advance plate is welded, you will always gain extra advance around 4000 rpm.

 

Gotcha. You may be right then, I may have to change the weights...

 

I put the Moroso kit in my Hei. It came with heavier weights like originals, a previous owner had put a spectre kit in and the weights were thin n light.

W two light springs, I got mechanical advance at idle w 1 lite and 1 mid spring I hit the best compromise I could get, maybe w the light weights you could run 2 lite springs