MSD distributor tuning

[gliderider06]

God morning all!
My 87 Ramcharger has a MSD ready to run distributor in it. It's a stock 318 other than dual exhaust and 4bbl.
I just cant get more than 30* Mechanical advance out of it. Initial is at 15* and with vacuum it go to 50*. I changed the stop bushing from 21 to 25*. The springs I run is 1 heavy and 1 light silver springs. I feel the heavy silver is limiting my advance. If I take out the heavy for a lighter, it will ping. (Heavy truck)
I was thinking about trying to opening the C-C distance of a heavy spring, a few thousands to hopefully give me some more. Any other suggestions besides doing this? I also toy with the idea of using a factory Mopar spring with the elongated end (smog limit spring?)
This truck needs more timing and responded well to the 25* bushing. I will probably go with the 28* after I get more Mechanical out of it.
Your thoughts?

 

[Newbomb Turk]

I’m not a fan of using two different springs on a GM style advance. It causes wear and it makes things wonky.

I’m not a big fan of using real heavy springs either.

I’d get the initial up to 20 and it might take 24. That means you’d only need 10-15 degrees of mechanical advance to get 34-35 total.

If you get that much initial, you have to bring the curve in pretty slowly. If not, it will rattle. To get there, you either need big honking heavy springs, or you can shorten the advance weights. Then it’s a matter of getting the right springs with the shortened weights.

All engines want a timing curve. All of them. Most engines want less timing at peak torque and more timing at peak power. So if you start out with 20-24 initial, you need to make sure the timing doesn’t start moving until 2k rpm or close to it. If you don’t delay the start of the curve, you’ll have too much timing at peak torque and it will kill torque and power.

 

[gliderider06]

I forgot to mention as well.
Anything over 15* initial the thing will ping when hot when giving it a slight push on the throttle. I'm using autolite 64 plugs. It helps reduce the detonation.
I recently changed from a 1406 Edelbrock to a 650 Holley spreadbore. Just by doing that I was able to go from 10* to the 15* before the thing started pinging.
At this point, I think I'm maxed out on my initial timing and need to get the total closer to 36* before adding the vacuum advance.
Thanks!

 

[Mattax]

. I feel the heavy silver is limiting my advance. If I take out the heavy for a lighter, it will ping. (Heavy truck)

There's a clue, isn't it. Figure out the timing, rpm and vacuum when it pings. Mark that in red on your timing vs rpm chart, and whether it was moderate load or heavy.

I also toy with the idea of using a factory Mopar spring with the elongated end (smog limit spring?)

That's a bunch of nonsense repeated by the comic books and entertainment shows. Nothing to do with smog. The secondary spring is used to slow advance because combustion efficiency improves once the engine is over 1600 rpm or so. On a 318 its probably a little earlier (lower rpm) unless its been hot rodded.

This truck needs more timing and responded well to the 25* bushing. I will probably go with the 28* after I get more Mechanical out of it

it seems the truck may be telling you otherwise.

You should look to the factory curve for that engine. Thats the baseline of what the truck wants. And if you can find a pre '79 truck 4 bbl 318 curve, that will be basically pre-smog version. The diffence between 2 bbl and 4 bbl is the 2 bbl is a bit more efficient at idle and off idle and the 4 bbl combustion is more efficient at mid to high rpm. So after 2000 to 3000 rpm the 4 bbl timing will advance much more slowly than the 2 bbl

 

[Mattax]

Anything over 15* initial the thing will ping when hot when giving it a slight push on the throttle. I'm using autolite 64 plugs. It helps reduce the detonation.

And there is another clue. Measure and plot that timing curve. Mark it in red starting the rpm it will ping with light throttle if that was done without vacuum advance. Mark it in orange something like that if it was with vacuum advance. Then go check vacuum advance so you know the actual timing when the pinging occured.

As far as the carb, it mostly will change the AFR. AFR and Timing are related. Leaner less dense conditions need more advance because the burns tend to be slower.

Generally best to set timing, then work on fuel mixtures. Repeat until you can't get closer or don't care to get closer for all conditions.

Timing has to be set for hot engine conditions - unless you are drag racing only

 

[Newbomb Turk]

I forgot to mention as well.
Anything over 15* initial the thing will ping when hot when giving it a slight push on the throttle. I'm using autolite 64 plugs. It helps reduce the detonation.
I recently changed from a 1406 Edelbrock to a 650 Holley spreadbore. Just by doing that I was able to go from 10* to the 15* before the thing started pinging.
At this point, I think I'm maxed out on my initial timing and need to get the total closer to 36* before adding the vacuum advance.
Thanks!

That’s why I said to delay any timing with the initial that high. If you have that much initial and the curve starts right away it will rattle.

 

[TT5.9mag]

With 15 initial, why do you need 30 more in mechanical? That’s 45 degrees all in. Way too much. The reason you can’t get more mechanical is the MSD is limited to the bushing size available and the smallest bushing, red (most mechanical advance) is 28 degrees.

 

[TT5.9mag]

You need the blue bushing for 21 degrees. With 15 initial, plus 21 that puts you at 36 all in. Then tailor the curve with springs to your combo. Big tires, heavy truck, small engine, means a long slow curve probably not all in till 4000. Probably one heavy and one medium spring. Then bring vacuum advance in for cruise.

 

[Mattax]

15 Initial is a lot for stock 318, depending on the rpm of course.
Running idle leaner than the old days, then it should be OK as long as the idle rpm is somewhat high.
That might be best if its got cats. Rich idles aren't good for cats.

 

[gliderider06]

With 15 initial, why do you need 30 more in mechanical? That’s 45 degrees all in. Way too much. The reason you can’t get more mechanical is the MSD is limited to the bushing size available and the smallest bushing, red (most mechanical advance) is 28 degrees.
View attachment 1716207772

No I have 15 initial and another 15 Mechanical. 30* total. Will not go higher until vacuum is applied then goes to 50*. I replaced the blue bushing with the silver and I got more total timing now, from 44* with vacuum advance. This is why I think the heavy spring may be holding me back.

 

[gliderider06]

You need the blue bushing for 21 degrees. With 15 initial, plus 21 that puts you at 36 all in. Then tailor the curve with springs to your combo. Big tires, heavy truck, small engine, means a long slow curve probably not all in till 4000. Probably one heavy and one medium spring. Then bring vacuum advance in for cruise.

I was thinking this with the springs. I tried this before with the edelbrock and the valves pinged badly and I put the heavily spring back in. With the new Holley, I think I will be able to get away with it. Actually, it would ping at 10* when I ran the edelbrock carb. One of the many reasons why I switched it out.

 

[TT5.9mag]

No I have 15 initial and another 15 Mechanical. 30* total. Will not go higher until vacuum is applied then goes to 50*. I replaced the blue bushing with the silver and I got more total timing now, from 44* with vacuum advance. This is why I think the heavy spring may be holding me back.

Get rid of the vacuum advance, for now. Plug it off. Get the initial and mechanical figured out. Then add the VA after that is done.

 

[TT5.9mag]

With the sliver bushing you should have a 25 degree swing. So 15 initial plus 25 mechanical would be 40 all in. You might have a weight hung up. Or something is up with the timing light or balancer. Could be you are not revving it high enough to see all the mechanical come in.

 

[gliderider06]

With the sliver bushing you should have a 25 degree swing. So 15 initial plus 25 mechanical would be 40 all in. You might have a weight hung up. Or something is up with the timing light or balancer. Could be you are not revving it high enough to see all the mechanical come in.

So, I had both weights off when I changed the bushing and they move freely. I bought a new adjustable timing light for this to check against my old, non-adjustable one and both read the same. I revved the motor pretty high and would not go past 30* . The distributor is relatively new <5000 miles on it. I think it
Is the springs, but I do have a set of weights that I can swap if needed if changing to lighter springs do not help.

 

[TT5.9mag]

I revved the motor pretty high and would not go past 30* .

How high? And what springs were in it when you did it?

 

[RustyRatRod]

I believe you need to try bumping the initial to "around" 20 and limiting the total to like 35 using medium to heavy springs and see what happens.

 

[TT5.9mag]

So, I had both weights off when I changed the bushing and they move freely. I bought a new adjustable timing light for this to check against my old, non-adjustable one and both read the same. I revved the motor pretty high and would not go past 30* . The distributor is relatively new <5000 miles on it. I think it
Is the springs, but I do have a set of weights that I can swap if needed if changing to lighter springs do not help.

The 8388 RTR distributor is shipped with 2 heavy silver springs. That is the slowest curve possible. The engine would likely have to go to 4000 rpm with the blue bushing.

 

[gliderider06]

How high? And what springs were in it when you did it?

One silver heavy, and one silver light. Revved it well above anything that I would ever be driving it. I dont have a tach, but it was screaming. Guessing well over 3000. My dial back timing light never went past 30*
I think I need to go to the light saver and blue springs and hope the timing gets closer to 36*

 

[Mattax]

The 8388 RTR distributor is shipped with 2 heavy silver springs. That is the slowest curve possible. The engine would likely have to go to 4000 rpm with the blue bushing.

View attachment 1716208018

Unlike a real GM distributor, with the MSD going to have to see what RPM the advance begins. heavier springs will delay the start even though they may be the what is really needed from 1600 rpm up. So these need to be tweaked like @midnight340 did
But without a tach its all a wild goosechase.