MSD Timing Curve - questions

[Beach_Dude]

Getting ready to install the MSD 8519 to work in conjunction with the MSD 6AL and the TFI coil on my 1977 AMC 360.

I plan on running a little advanced, 11* since my idle seems to run best with ridiculous vacuum around 10-12*.

The 79 setup seems to be 0* @ 900 RPM and 19* @ 4,400 RPM. The vacuum advance starts at 3" @ 0* and peaks at 27* @ 11" in acuum.

MSD states the vacuum advance is maximum 10* at 15" of vacuum, which I assume is distributor advance, not crank? I'll call support and get an answer for you guys.

Here's the stock curve for the 1979 Duraspark ignition



Here are the curve options for the MSD distributor



I'm tied between the extremes.... graph A is stock for the unit and has the longest curve but put the limiter on at 18* since I'm running 2* more advanced to begin with.

Graph F has the lowest starting advance at around 800 RPM, but seems rather aggressive?

Anyone have input and knowledge of timing curves or MSD billet distributor setups?

[wiley-moeracing]

Its been awhile since I did mine, (many years ago), You have to know what your came specs are, carb your running, torque convertor lock up is, gear ratio/ tire size combo, weight and then start to dial it in with the correct curve. When you change the curve you will find you will need to change the carb jetting to compliment the curve.

[Beach_Dude]

Everything is stock, carb, cams, TC, etc. except for the fact that I'm running 33s instead of factory spec tires, which were 31.4".

I have been thinking about uping my diffs, but doing this for now. Iirc the diffs are at 3.54.

[wiley-moeracing]

The gear ratio is hurting you, causing you to rely on very low torque curve/ low power curve. If and when you change gears you will end up having to recurve again. Change your gears out to 4:10's and your truck will come to life and the stock curve will be good. With the stock cam/ carb etc. you want the power to come on around 800 and slowly go up, not aggressive. Only get more aggressive if and when you add higher compression and a more aggressive cam profile and a 4 bbl carb and intake otherwise it is all for nothing. The "B" curve looks to be your starting point, your motor will never see 6000 rpm and you want a slow rise on the curve with stock compression and torque.

[Beach_Dude]

Thanks for that!

Just got off the phone with support and they said the vacuum of 10* is actually crank degrees, not distributor. Seems super low, but hey, why not. With that much spark, it should be more than enough.

I was going to do 3.73 to keep it closer to stock since I'm running 33s, not 35s, and won't go to 35s. This is a road car with light trail use, like once every ten years.

[wiley-moeracing]

I would still think at least the 4:10's would be better than 3:73.

[Beach_Dude]

I'd go higher than 3.73 if there weren't so many freeways in the area.

[Beach_Dude]

So, anyone else familiar with setting the timing curves for the MSD distributor?

Ready-Run or not, they're all the same timing curves.

[johnsonic]

It 100% depends on your setup. I'd start by trying to match the curve from the factory for your year (it's in the TSM). From there you can tweak it.

I have mine starting @ 19 degrees with the stop bushing limiting advance at 36 degrees at 3000 RPM. But I'm also running manifold vacuum and replaced the vacuum can with an adjustable one.

There really isn't a right answer here.

[FSJunkie]

Some years used a lower base timing setting like 0* with a high mechanical advance like 35* and other years used a higher base timing setting like 15* with a low mechanical advance like 20*.

The net result driving down the road at engine speeds above idle is the same. The only difference is one idles with more advanced timing than the other.

The base timing that you choose largely depends on what the mechanical advance curve looks like. More specifically, the maximum limit on the mechanical advance.

Generally, ideal timing for most AMC V8 is 5-10 degrees at idle and 30-35 degrees at 4000 RPM.

[Beach_Dude]

My biggest issue is that my other cars are zippy m series bmw and a daily driver 328i.

The torque feels great, but it almost always has... I feel like I'm missing some top end HP though.

Everyone says play with it till it feels right. Also, set it till detonation, then back off... i don't know why, but this goes against logic for me.

I ended up going with diagram C's timing curve since it matches the 10* mechanical advance at the same 2000 RPM, with the black bushing capped at 18* and 13* initial advance.

Should I try swapping swings and/or bushing to see what happens or should I call it a day and be happy?

[babywag]

No harm in trying different springs.
Running manifold vacuum vs. ported will give a snappier throttle response.
Due to the vacuum unit being fully advanced @idle on manifold vacuum.
If on ported there is no vacuum advance @idle.
Age old debate/argument on that one though...
Easy to test and see what you/your engine prefers.

When I ran carb(s) I found initial in ~13* range to be best but honestly, it really depends on the engine.
They're all a little different and what works for one doesn't always work for another.

[Beach_Dude]

I ended up with Diagram C, and then did the 19* bushing. Runs great, but not a single knock or ping! I even pushed the baseline to 15*.

Still no knock or ping.

I've even turned the dizzy over enough to get the idle to roughen out, and still no pinging that I could hear!

I just don't want some detonation occurring that I'm not picking up, go on a long drive and blow out my engine.

Ideas?

[Mikel]

I ended up with Diagram C, and then did the 19* bushing. Runs great, but not a single knock or ping! I even pushed the baseline to 15*.

Still no knock or ping.

I've even turned the dizzy over enough to get the idle to roughen out, and still no pinging that I could hear!

I just don't want some detonation occurring that I'm not picking up, go on a long drive and blow out my engine.

Ideas?

How's the performance?

[Beach_Dude]

Runs great... 22" vacuum, smooth idle, again, perf is great.