Setting initial ignition timing

[Mr Lee]

Ok, so I'm a newbie to understanding ignition timing.  Have read a few articles and have a basic understanding and looking to learn more so I can tune my motor.
I have a freshly rebuilt 383 Magnum in my '70 Challenger. Bored .030 over, mild cam, but otherwise a stock rebuild.  Pertronix ignitor electronic distributor conversion.

So my question is, how do i know where to set my initial timing?  I understand I'm supposed to disconnect the vacuum tube from the distributor to check initial.  Do I need to plug the vacuum line, or cover the inlet on the distributor when setting initial timing?

Before I get into mechanical and vacuum advance, any tips on where to start with initial?  Do I go by sound and feel?  I'm at 13 now and it seems to want a little more.  How much is too much?
Thanks in advance.


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[Chryco Psycho]

I hope you have a timing light , but I threw mine out years ago .
Basically the most important setting is the timing at 3000 RPM so bring the engine up to that rpm area & adjust the timing , you can hear by ear where it runs best . So advance the timing until the RPM quits rising then turn it back where it just starts to drop RPM again , you can put a light on it & see where it is , now do the same thing at idle , advance the timing at idle to where it runs best , so these are the 2 most important settings . Now the the advance curve needs to be adjusted so you have the same initial & total timing curve .
I Never use vacuum advance , Ever .

[Mr Lee]

I hope you have a timing light , but I threw mine out years ago .
Basically the most important setting is the timing at 3000 RPM so bring the engine up to that rpm area & adjust the timing , you can hear by ear where it runs best . So advance the timing until the RPM quits rising then turn it back where it just starts to drop RPM again , you can put a light on it & see where it is , now do the same thing at idle , advance the timing at idle to where it runs best , so these are the 2 most important settings . Now the the advance curve needs to be adjusted so you have the same initial & total timing curve .
I Never use vacuum advance , Ever .

OK, question.  You said "Now the the advance curve needs to be adjusted so you have the same initial & total timing curve"   I'm not sure what you mean by adjusting so they have the "same curve".  I do understand that the curve can be adjusted with different springs and adjusting the slots in the dist, etc but don't understand the second part.

So you plug the vacuum advance on the dist?

[71383bee]

You only need to plug the port at the carburetor. It provides the vacuum for the dizzy.

What CP is referring to is the mathematical difference between the initial and total is called the mechanical advance.  It can only be adjusted by lengthening or shortening the advance plate slots in the distributor. 

You need a dial advance timing light or a degreed balancer to help figure these points out. 

My preference on initial setup is similar to CP. Have a partner rev the car up to 3k or so. With the dial advance light set at 34 adjust timing to hit 0 on the balancer. Idle it down and dial the timing down on the gun to see where initial timing is at in idle. Most cars this is higher than previous but not always. Anyways when it hits zero look at the number on the gun and that is your current initial timing.

To properly set initial you adjust the distributor as CP said in idle for optimum rpm and vacuum.  To test it shut the car down and start it up. If the starter kicks or lags then back down the timing a degree or two. Figure out what setting works best and that is your ideal initial.

To adjust the curve you are targeting the mathematical difference between these two points. Let's say your car likes 18 initial and 36 total. That means that you need 18 degrees of mechanical advance in the plates. The size of the plate determines the amount.

For you 13 is a good start for initial but it likely wants more.  16-18 is typical.  For now I would rev it up and set total and see where initial is after idling it down.

Keep in mind though that if you have to add initial to get it to run better AFTER setting total I recommend NOT to drive it as you added total as well. Let's say you bumped it 5 degrees to get 18 initial you also moved total 5 degrees which could lead to detonation.  Finding ideal initial is a target for distributor recurving if you have to add a lot. I would reset to where initial was after setting total if your going to drive it.   It's safer to be a little lower on initial then to be to far on total.

Hope this makes sense.  If you were nearby I'd swing out with my light and spend an afternoon with you dialing it in!  I love doing this part.


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[Skdmark]

The port on the distributor vacuum can does not need to be plugged.
Just port the vacuum source it was connected to.

To limit total mechanical advance you can install an advance plate in your distributor.
http://4secondsflat.com/Mopar%20Mechanical%20timing%20limiter%20plate.htm

My 383 is at 16 to start and 34 total. Mild cam, 10.5:1 compression, 93 ethanol free. I use both a timing light and vacuum gauge.
Set timing, tweak carb, recheck timing.

[Chryco Psycho]

If you total timing likes 36* & at idle it likes 18* then you need to have a 18* advance curve .
I never connect the vacuum advance at all you can leave the hose in place & dial back the the screw inside the vacuum canister with an allen wrench counterclockwise so it cannot advance the timing if you prefer .

[kawahonda]

I disagree with any notion to disable the vacuum advance indefinitely, but you should plug up vacuum advance until you are finished tuning. Treat it like an accessory that gets dialed in at the very end that adds timing to your cruise RPM only.

There are great, cheap, vacuum advance canisters available today that can offer as little as 8 advance when adjusted a little bit with an Allen wrench. It helps with drivability and MPG. There's no reason to not use one in a street engine. I could understand someone "giving up" on one because they're stuck with a crappy 18 degree stock one that causes the engine to ping, but there's no reason to not use one in the end for a street vehicle.

You really need to get a timing light (get a digital one) and start jotting down notes on where you are at and what you have.

[71383bee]

I disagree with any notion to disable the vacuum advance indefinitely, but you should plug up vacuum advance until you are finished tuning. Treat it like an accessory that gets dialed in at the very end that adds timing to your cruise RPM only.

There are great, cheap, vacuum advance canisters available today that can offer as little as 8 advance when adjusted a little bit with an Allen wrench. It helps with drivability and MPG. There's no reason to not use one in a street engine. I could understand someone "giving up" on one because they're stuck with a crappy 18 degree stock one that causes the engine to ping, but there's no reason to not use one in the end for a street vehicle.

You really need to get a timing light (get a digital one) and start jotting down notes on where you are at and what you have.

I agree with you there on that.  The VA can actually help cruise and mid range if dialed in right.  You can get along without it but I don't see the harm in it if it operates properly. 

BTW...I was going to suggest that Mr. Lee read your tuning thread which is a ton of good info on dialing a motor in for both timing and carb tuning.  For a few of of my earlier cars I've been of the mindset to just set total and initial lands where it is (which usually was a decent improvement) adjust idle and be on my way.  Your AVS tuning thread has motivated me to dig deeper to get the timing exactly where it likes it and crack into the carb to get the most out of it.  Its a must read I feel...very cool! 

[Daveh]

I agree with Neil not to use the vacuum advance.  If I can't turn it back not to function like Neil said then I will put a ball bearing in the line to disable it.  I've done this on a few old cars and it seems to work just fine. Good Luck

[Mr Lee]

I appreciate all the help. Sounds like a lot of good info and I'm eager to try it out. It's a lot to take in, but I think I get it. Gonna have to read through this again while I'm doing it and I think it will make more sense. 

I do have a digital timing light that has up and down arrows that let you advance or retard the light to your desired setting.  Am looking forward to getting into this and will take some notes.  Thanks for the link for those plates. 

I'd be interested in reading that tuning thread that was mentioned.  Where might I find that?

Thanks


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[RUNCHARGER]

I always optimise the vacuum advance as well. I believe it helps fuel economy for one thing. Whatever works for an individual though.
On a mild 383 with a slight cam I would start with a shorter advance plate and aim for 16 initial and 36 total to start with.

[chargerdon]

On my 408 stroker with Lunati 703 cam ...i use VA on the Full not ported side.   Why?  simple... Adjusting the intial as stated by CP for best rpm and vacuum will have my initial at around 24 degrees...but...at 24 degrees it will kick back when starting..to eliminate kickback it has to be no higher than 18.     

So, to get the 24 at idle and eliminate kickback i allow the VA to add at idle and low load another 6-8 degrees.  gives me 18 while starting and then 24-26 at idle and slow speed driving...    On mopar Vaccum cans you can dial back its normal 10-12 degrees with allen wrench to the 6-8.  Then i limit the mechanical to around another 16.    This brings the full to around 34 when under load (vacuum goes away under heavy throttle) or as much as 40 without load.   Just make sure you are on the full not ported side of carb.    No pinging at all on 93 octane fuel.   

[71383bee]

Don't sweat it mr lee!  For the amount of wrenching you have done on that car this is a piece of cake.

It's sounds like you have the right kind of light. Once your ready hook it all up, start it, and get a feel for how it works. A lot of the newer lights can switch from rpm to degrees. Play with the buttons and have a notebook handy.  Figure out your current baseline for initial and then rev it up to see where total is.  From there you can map out what you need. 34-36 for total is typically ideal. Set it and see where initial lands.

Chargerdon that sounds like a good use of VA using manifold.   There are a lot of schools of thought on ported vs Manifold.  Generally I feel that cars that like a lot of initial like yours work better on manifold as you discovered. It's all part of the process of getting a good tune.   For now I use ported.

Mopar Connections magazine Did a great write up as well on tuning the distributor. It was on a slant 6 dart and is in there tech archives.  They curved it and dialed in the VA for maximum economy.   The concept is no different between the /6 and a hemi so it's totally relevant to your 383. It's a good read.

https://moparconnectionmagazine.com/more-power-for-your-leaning-tower-add-14-horsepower-to-your-slant-six/


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