Having fun with timing

[TheContractorDude]

Late bloomer finally understanding timing in general and enjoying tuning. Wish I took the time to learn to tune 20 years ago. I have to thank everyone here on the forum for the information provided and YouTuber's for the extremely informative information on advancing timing and timing curves. This was very intimidating for me at first but now I am enjoying the process because of understanding the basics of how timing works. I now have a base line that I can further tune from. I loved pulling the distributor and taking it apart seeing how they actually work. Getting that clip out of the shaft to remove the weight limiter was difficult for a minute but easy now. I currently have my mechanical (centrifugal) advance so it max's out at 16 degrees and I used the lightest springs FBO provided, maybe I should try even lighter springs. The MP electronic distributor only had one spring installed and from what I can tell from the spacing on the weight limiter slot it may only advance about 20 degrees mechanically possibly a bit more. The slot is not much larger than the 18 degree slot on the FBO disk. My base timing is currently 20 degrees w/o vacuum. If I adjust the vacuum canister screw all the way clockwise it will add 16 degrees max. I ran my engine with this 36 degrees for a bit and it ran pretty good. btw I have not run into any pinging yet, I am taking it slow with the adjustments. I backed off the vacuum advance a bit to 10 degrees so now I am at 30 degrees and it is more responsive. My total timing of 40 degrees comes in at 3200 RPM's somehow the math doesn't add up off by 4 degrees but the car runs much better and I can tell it is not running as rich as it was before. The exhaust stank before nasty stuff. I will be checking the sparkplugs after I drive it for a bit to see what is happening in the chambers. My 383 Barracuda is much happier as I am as well. It has a purple shaft cam 280/474 lift I believe, can't remember it has been so long and running the factory four barrel carb with stock exhaust. The exhaust system is 2.5" all the way to the tips. Just thought I would share my experience. Thanks!

 

[TheMopars]

This is something I need to learn as well. Did it on my motorcycles but my cars were all
modern with electronic ignition. I'd much prefer to do this myseld than take it to someone.

 

[TheContractorDude]

This is something I need to learn as well. Did it on my motorcycles but my cars were all
modern with electronic ignition. I'd much prefer to do this myseld than take it to someone.

Yes it is intimidating at first but can be very rewarding.

 

[Newbomb Turk]

You said you have the mechanical at 16 degrees locked out. Do you mean that that's the most it will advanced or is it locked out?

At any rate, without any specs on the engine no one can say what you should have for a curve.

We need to use the same terms so we can understand what we are talking about.

Locked out means you have the mechanical advance inoperative and your total timing is whatever you set it at.

That would be 35 degrees or something. That is almost always a no no.

With that said, keep on learning. You are on the right track.

 

[AJ/FormS]

For best fuel economy
Have you considered that the Cruise timing, depending on rpm, will want to be mid 50s., say 56* @2600 rpm ( say 61mph with 3.23s and a modest stall TorqueFlite)
To get that much timing, your V-can may need to be modified. the factory Mopar one can be modified to in the range of 22>24.
***************************
In this discussion, I will be talking only about fuel economy, with an automatic transmission..

Your Secondary curve points to 16* ending at 3200, but does not state when it begins. If I assume it begins at ~1000rpm; thus the curve is 16* per 2200rpm, therefore .727* per 100rpm,
Therefore, by the math, at 2600, this would add
11.6* to the 20*@ idle= 31.6 to which your VA can add up to 16 at cruise
for a total of 31.6 + 16 =~48 ; That's only getting close to 56, but 8* more would put it darn close.

The problem is this;
cruising at 30mph in Second gear at 1750 rpm with, 20+5.5+16=41.5 degrees which may be/probably is, not enough. You opted to take the Va down to 10*, so you should be getting 35.5, which is not nearly enough.
IMHO, what you should be considering;
is taking Idle-timing out,
keeping the all-in Power-timing near the same,
Plus modding the Vcan to 22/24*;
and in this exercise, that 280 Purple should IMO, not be saddled with anything less than a 2800 and 3.91s.

Ok so, with 3.91s now, 30 mph in Second is now 2100, and the Cruise timing will be
14* idle
plus mechanical timing will be .846* per 100, so is 9.6 .
plus up to say 22 in the can Which now totals 45.6. But when you stomp it, the VA comes out, leaving you with ~24total, but the Convertor is jumping up to 2800 where the Total is 14* plus 15 =29, and in the blink of an eye will be 36*@ 3200. If it detonates at 3200, delay it. Maybe at 3400 it will be fine IDK.

Now; 65mph with 3.91s will be around 3200 depending on slip. At this rpm, your timing could be;
14 Idle +19 mechanical +say22VA= 55* Cruise-Timing so now, yur really in the ball-park.
Plus the low speed off-idle circuit will love you for it, with your Mixture screws back where they belong.

As to idle fueling; What you need to know, is that at Idle, your engine is getting whatever fuel it needs from the combination of Transfer slot fuel plus Mixture screws.
The mixture screws cannot provide ALL the idle fuel, but with the timing cranked up, almost. You can therefore set the idle timing to whatever you want, until the mixture screws run out.
The trouble is, now the Transfers are as good as shut off, and the engine is pulling in nothing but air from the Idle-wells, and so, when you tip the throttle in, those transfers take time to wake up again. This usually causes a Tip-In Hesitatation, maybe even a stall if yur not careful.
But it doesn't stop there. As soon as the low-speed circuit wakes up, it goes very rich because the mixture screws are cranked wide open. So then, about 100% of the time, that you are cruising on the transfers, the mixture will be overly-rich, and you blame it on the cam.
Well, truthfully, that cam does suck gas alrighty, especially so on a low pressure engine, which makes it all the more important to be able to run the mixture screws lean! not rich.
The trick is to run the mixture screws a hair lean, and have the transfers supply the rest of the Idle-fuel, then control the Idle-speed with idle-timing. It the exhaust starts to burn your eyes, you add bypass air.
Now, I can tell you that when I was running the 292/292/108 cam It would idle down to 550rpm @5* advance, and still take throttle! So, don't let anybody bully you into telling you that you need to have a certain amount of Idle timing.

Here is the shortcut.
Run your rpm up to 2000 and fix it there.
Now twiddle the mixture screws to best lean running.
Next advance the chit out of the timing, a little at a time until additional timing does not produce any more rpm.
Reduce the idle speed back to 2000.
Twiddle the mixture screws again to see if you can go leaner.
Now, read your timing.
This is the exact setting that your engine wants, to cruise at no-load, at 2000 rpm. You cannot make it any better, now the rest of the bad fuel economy is on the cam, lol.
Idle it back to ~750. and take out 3 degrees for anticipated load at 2000. again read the timing.
Whatever number you get at idle, is, at this point, fall out.
Now, Without changing the timing, and with the VA defeated; rev the engine up to, whatever rpm gets you the most amount of timing, and make a note of the amount and rpm it takes to get there. If this number is less than 34* at more than 3400rpm, You may want to change that. The trick is to create an advance curve that runs from the previously established cruize-timing at 2000, and to approximately 34*@3400.
What it then arrives at, at idle, is again fall-out.
The only way I know of to change that idle-timing, is with a two-stage timing curve. and that is a lot of trial and error.
But, honestly, with a 2800 convertor, Your engine doesn't hardly care about idle timing. The first time it cares is at stall.

Thus, really, you have only three data points to hit;
Cruize-timing,
Stall-timing, and
Power-timing.
Let idle-timing be what it will be.
So keep after it, I know yur having fun, and you're closing in on the home stretch.
Happy HotRodding
PS
Now if you have a manual transmission, it's a whole different ballgame.

 

[TheContractorDude]

You said you have the mechanical at 16 degrees locked out. Do you mean that that's the most it will advanced or is it locked out?

At any rate, without any specs on the engine no one can say what you should have for a curve.

We need to use the same terms so we can understand what we are talking about.

Locked out means you have the mechanical advance inoperative and your total timing is whatever you set it at.

That would be 35 degrees or something. That is almost always a no no.

With that said, keep on learning. You are on the right track.

Yes sorry not "locked out", correct that is the most it will advance.

 

[TheContractorDude]

For best fuel economy
Have you considered that the Cruise timing, depending on rpm, will want to be mid 50s., say 56* @2600 rpm ( say 61mph with 3.23s and a modest stall TorqueFlite)
To get that much timing, your V-can may need to be modified. the factory Mopar one can be modified to in the range of 22>24.
***************************
In this discussion, I will be talking only about fuel economy, with an automatic transmission..

Your Secondary curve points to 16* ending at 3200, but does not state when it begins. If I assume it begins at ~1000rpm; thus the curve is 16* per 2200rpm, therefore .727* per 100rpm,
Therefore, by the math, at 2600, this would add
11.6* to the 20*@ idle= 31.6 to which your VA can add up to 16 at cruise
for a total of 31.6 + 16 =~48 ; That's only getting close to 56, but 8* more would put it darn close.

The problem is this;
cruising at 30mph in Second gear at 1750 rpm with, 20+5.5+16=41.5 degrees which may be/probably is, not enough. You opted to take the Va down to 10*, so you should be getting 35.5, which is not nearly enough.
IMHO, what you should be considering;
is taking Idle-timing out,
keeping the all-in Power-timing near the same,
Plus modding the Vcan to 22/24*;
and in this exercise, that 280 Purple should IMO, not be saddled with anything less than a 2800 and 3.91s.

Ok so, with 3.91s now, 30 mph in Second is now 2100, and the Cruise timing will be
14* idle
plus mechanical timing will be .846* per 100, so is 9.6 .
plus up to say 22 in the can Which now totals 45.6. But when you stomp it, the VA comes out, leaving you with ~24total, but the Convertor is jumping up to 2800 where the Total is 14* plus 15 =29, and in the blink of an eye will be 36*@ 3200. If it detonates at 3200, delay it. Maybe at 3400 it will be fine IDK.

Now; 65mph with 3.91s will be around 3200 depending on slip. At this rpm, your timing could be;
14 Idle +19 mechanical +say22VA= 55* Cruise-Timing so now, yur really in the ball-park.
Plus the low speed off-idle circuit will love you for it, with your Mixture screws back where they belong.

As to idle fueling; What you need to know, is that at Idle, your engine is getting whatever fuel it needs from the combination of Transfer slot fuel plus Mixture screws.
The mixture screws cannot provide ALL the idle fuel, but with the timing cranked up, almost. You can therefore set the idle timing to whatever you want, until the mixture screws run out.
The trouble is, now the Transfers are as good as shut off, and the engine is pulling in nothing but air from the Idle-wells, and so, when you tip the throttle in, those transfers take time to wake up again. This usually causes a Tip-In Hesitatation, maybe even a stall if yur not careful.
But it doesn't stop there. As soon as the low-speed circuit wakes up, it goes very rich because the mixture screws are cranked wide open. So then, about 100% of the time, that you are cruising on the transfers, the mixture will be overly-rich, and you blame it on the cam.
Well, truthfully, that cam does suck gas alrighty, especially so on a low pressure engine, which makes it all the more important to be able to run the mixture screws lean! not rich.
The trick is to run the mixture screws a hair lean, and have the transfers supply the rest of the Idle-fuel, then control the Idle-speed with idle-timing. It the exhaust starts to burn your eyes, you add bypass air.
Now, I can tell you that when I was running the 292/292/108 cam It would idle down to 550rpm @5* advance, and still take throttle! So, don't let anybody bully you into telling you that you need to have a certain amount of Idle timing.

Here is the shortcut.
Run your rpm up to 2000 and fix it there.
Now twiddle the mixture screws to best lean running.
Next advance the chit out of the timing, a little at a time until additional timing does not produce any more rpm.
Reduce the idle speed back to 2000.
Twiddle the mixture screws again to see if you can go leaner.
Now, read your timing.
This is the exact setting that your engine wants, to cruise at no-load, at 2000 rpm. You cannot make it any better, now the rest of the bad fuel economy is on the cam, lol.
Idle it back to ~750. and take out 3 degrees for anticipated load at 2000. again read the timing.
Whatever number you get at idle, is, at this point, fall out.
Now, Without changing the timing, and with the VA defeated; rev the engine up to, whatever rpm gets you the most amount of timing, and make a note of the amount and rpm it takes to get there. If this number is less than 34* at more than 3400rpm, You may want to change that. The trick is to create an advance curve that runs from the previously established cruize-timing at 2000, and to approximately 34*@3400.
What it then arrives at, at idle, is again fall-out.
The only way I know of to change that idle-timing, is with a two-stage timing curve. and that is a lot of trial and error.
But, honestly, with a 2800 convertor, Your engine doesn't hardly care about idle timing. The first time it cares is at stall.

Thus, really, you have only three data points to hit;
Cruize-timing,
Stall-timing, and
Power-timing.
Let idle-timing be what it will be.
So keep after it, I know yur having fun, and you're closing in on the home stretch.
Happy HotRodding
PS
Now if you have a manual transmission, it's a whole different ballgame.

Wow thanks for the break down. I am running an automatic 727 with stock convertor and 3:55 gears. Ya I am still playing around with finding the sweet spots with timing advance.

 

[Newbomb Turk]

Wow thanks for the break down. I am running an automatic 727 with stock convertor and 3:55 gears. Ya I am still playing around with finding the sweet spots with timing advance.

Remember that these engines generally want less timing at peak torque and more timing at peak power.

How you get that done is the job.

If you know your engine peaks power at say 6k then you can reasonably figure peak torque is 1500-1800 rpm less than peak power.

So peak torque should be (in this example, yours could be different) in the 4200-4500 range.

Knowing that, you can now work to get the timing correct to peak torque. I’m not sure what heads you have or the particulars of your engine. You have to sort that out.

Having done this stuff for a bit I can say that unless you are turning 7500 plus your engine probably won’t need more than 35 total.

That means you should have 35 at 6k in my example.

I also know that it probably won’t want much more than 26-28 at peak torque.

Your job as the tuner is to figure out how to get the curve slow enough to get from say 20 initial at 1k idle to 26 by 4500.

Then you have to figure out how to get from 26 at 4500 to 35 at 6k.

It can be done but it’s easier if you have a distributor machine. And a day on a dyno would speed things up.

Also of note is the ignition you are using. Unless you are running points, every electronic ignition WILL retard with rpm.

Where it retards and how much is only a guess until you measure for it.

You have to account for this retard or you’ll never know what your actual timing is at any point in the rpm curve.

 

[Mattax]

. The MP electronic distributor only had one spring installed and from what I can tell from the spacing on the weight limiter slot it may only advance about 20 degrees mechanically possibly a bit more. The slot is not much larger than the 18 degree slot on the FBO disk.

Too bad someone messed with it.
The older Chrysler built DC and MP distributors came with very good curves in them for their specific purposes.
Both could be tweaked by adjusted the spring perches but all this seems to have been a secret (or been forgotten)
There should be a primary spring and a secondary spring. The primary spring has tension on it even when the distributor isn't spinning. The tension force determines the rpm when the advance weights will begin to move out.
The secondary spring engages when after the weights have moved the advance governer (slotted plate) X number of degrees.

The 'tach drive' units were set up for easy starting and winning drag races, stock eliminator type racing. A bit more initial tension will make a more consistant idle. Tach drive Race Distributor
The street/strip units (with vac advance) seem to get best idle with a close to factory high performance cam. Over 220 @ 50 duration the curve should be shifted a little so a higher initial is obtained for stability at idle.

Here's some examples of guys adjusting the curve on Chrysler built distributors.
Here as Rick as he works through and posts the effects of his changes
And an example of how that changes a bit with different combustion characteristics for later engine
I spill the beans on shaping the curve here

Earlier in that same thread are links to videos illustrating why the heavy secondary spring is important with electronic ignition.

 

[TheContractorDude]

Remember that these engines generally want less timing at peak torque and more timing at peak power.

How you get that done is the job.

If you know your engine peaks power at say 6k then you can reasonably figure peak torque is 1500-1800 rpm less than peak power.

So peak torque should be (in this example, yours could be different) in the 4200-4500 range.

Knowing that, you can now work to get the timing correct to peak torque. I’m not sure what heads you have or the particulars of your engine. You have to sort that out.

Having done this stuff for a bit I can say that unless you are turning 7500 plus your engine probably won’t need more than 35 total.

That means you should have 35 at 6k in my example.

I also know that it probably won’t want much more than 26-28 at peak torque.

Your job as the tuner is to figure out how to get the curve slow enough to get from say 20 initial at 1k idle to 26 by 4500.

Then you have to figure out how to get from 26 at 4500 to 35 at 6k.

It can be done but it’s easier if you have a distributor machine. And a day on a dyno would speed things up.

Also of note is the ignition you are using. Unless you are running points, every electronic ignition WILL retard with rpm.

Where it retards and how much is only a guess until you measure for it.

You have to account for this retard or you’ll never know what your actual timing is at any point in the rpm curve.

Too bad someone messed with it.
The older Chrysler built DC and MP distributors came with very good curves in them for their specific purposes.
Both could be tweaked by adjusted the spring perches but all this seems to have been a secret (or been forgotten)
There should be a primary spring and a secondary spring. The primary spring has tension on it even when the distributor isn't spinning. The tension force determines the rpm when the advance weights will begin to move out.
The secondary spring engages when after the weights have moved the advance governer (slotted plate) X number of degrees.

The 'tach drive' units were set up for easy starting and winning drag races, stock eliminator type racing. A bit more initial tension will make a more consistant idle. Tach drive Race Distributor
The street/strip units (with vac advance) seem to get best idle with a close to factory high performance cam. Over 220 @ 50 duration the curve should be shifted a little so a higher initial is obtained for stability at idle.

Here's some examples of guys adjusting the curve on Chrysler built distributors.
Here as Rick as he works through and posts the effects of his changes
And an example of how that changes a bit with different combustion characteristics for later engine
I spill the beans on shaping the curve here

Earlier in that same thread are links to videos illustrating why the heavy secondary spring is important with electronic ignition.

Interesting thanks for the information. Looking forward to checking out the links and learning more. My 383 is 60 over with a mild cam, looking forward to getting it dialed in. Here on Maui we have a beautiful 1/4 mile track with a lot of history. There is also a circle track here so in that regard we are very lucky considering how remote the Hawaiian islands are. There are a ton of enthusiasts here as well. Last time at the track there was a dragster than ran a 6.8 @ 198 mph.