iginiton timing questions

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Mopardude

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How do you know what RPM your timing should be all in at? Is that a standard RPM or is that effected rpm range of the motor or anything? When we are talking about all in that is mechanical only not with any vac? Also for example lets say I am all in at 32 at 2600rpm for a total. So if it rev up to 4000rpm 32 degrees it should still read with out the vac plugged?
 
A lot of your questions depends on whether it's a stock dist or one that has had the advance diddled with

Some stock, expecially '72-3-6, etc, "smog" distributors, can have a loooooonggg slow advance, and be slow to "kick in." Some of those started with a VERY low initial timing, sometimes zero or on some cars, even AFTER TDC

Also, some of us set (check, recheck) our timing at a high RPM and just set it for TOTAL mechanical advance. In my own case, I don't presently use a vacuum advance.

So it depends on the "curve" that is in the distributor

So you have:

low idle speed, before there is any vacuum at the port (should be disconnected to check timing

and low enough idle that the mechanical advance is NOT activating

what you have there is known as "initial" advance. This is the figure that is specified on your engine "smog sticker" if you have one

NEXT, is "when does the mechanical advance" start to kick in? This depends on the SPRINGS that are installed.

Next, is once the mechanical advance DOES fully advance --and the RPM that happens at depends on the SPRINGS......

that is "total" advance if you have not vacuum advance, and IF you have vacuum advance, this figure will be when you have your foot planted on the floor --because ever if you run vacuum advance, there will be none under this condition.

The amount (degrees) of mechanical advance depends on the length of the slots which the mechanical weights work "in." These slots, on a stock dist, must be ground, brazed, filed, shortened (patiently) and usually by the use of a distributor machine until you "get" the advance curve you want. Many "performance" distributors, including the one I have, have screws or other methods by which you can "easily" change the amount of mechanical advance

The above, "foot on the floor" and engine at high enough RPM that the advance is "all in" is the "full power" condition, and will be the "initial" advance plus the MECHANICAL advance.

Now, in addition to the above, when you are cruising down the road at a high enough RPM to generate vacuum at the port for the advance can, AND have a light enough foot on the throttle (not going up a steep hill, passing, or just "lead footing")

The vacuum can will ADD (depending on the can) 10* or so

So the ultimate "TOTAL" advance is INITIAL + MECHANICAL + VACUUM

You can plot your dist curve yourself by either degreeing your balancer or buying the proper size "timing tape." Then use a tach and timing light to plot out what RPM gives you how much advance.

In my case, I have a performance Accel dist. that has somewhere around 22* "in the distributor" meaning the mechanical advance.

In my case, I twisted the dist, revved the engine, back and forth until I had 38* at high RPM. This means that at idle I have 38* -- the 22* in the dist, so my initial is around 16*. I don't recall offhand, how "fast" this kicks in, but it's much much quicker than a "stocker" smog dist.

Another thing you must be careful of, is that some dist. specs are specified in "distributor degrees" instead of "crank" degrees. The 22* I mentioned in my dist. are "crank degrees"
 
This should be stored somewhere here for reference!!!!! 67dart!! Thanks!!!! Nice simple explanation Sweet--Swifter
 
Yes definately good reference kinda fills in some the gaps I am fuzzy on.

After work tomorrow I need to go out and put my hands on the car put this knowledge to work cause that is the way I learn. I can read a 100 things on doing this but it doesn't snap into my brain till I have hands on. Than i will probably come back with a million questions for you. :)

Distro is stock from an 82 Ramcharger. Is there a way I can tell for sure if its a smog distro? Being an 82 I would assume it probably is? If I had a smog and was running the init timing advanced would that create a situation where I was advanced to far or would that even it out or even slightly retard it?
 
Your vehicle is not a "lean burn" thing, I hope?


Anything built from 66 onwards in the state of CA, and Federally (U.S.) from 68 onwards is some sort of "smog" application. Some of 'em just got worse and worse as the years went on.

Indeed some stock dist's can result in an over-advanced condition if all you do is bump up the initial timing.

Generally speaking, most stock (especially) smog dist's need the mechanical advance shortened for degrees of advance, and lighter springs installed for QUICKER mechanical advance.

Most stock dist's will accept an early vacuum can, so usually you can just get one that is for 66/67 and cure that EXCEPT that some "parts store" advance cans are nowhere near equivalent to stock figures. That is, they'll sell you one that fits "65-78" or some damn thing, and you hope it works OK.

If you download some of the factory manuals here:

http://www.forabodiesonly.com/mopar/showthread.php?t=132309&highlight=manual,+download

The have the specs for advance in the rear part of the electrical section to give you some idea.
 
***Update*** Well this is what I came up with, when I got this engine running initially, when I setup the init timing I did a rookie move and left the vac advanced hooked up. Car runs good now that I have the timing right on it seems and my carbueration issues are gone. Since a recomendation I seen in a lot of tuning threads on this forum is to run with out the vac advance I plugged it up as well.

This is how I have always timed a car. I dunno where I learned this from, it maybe some BS way I came up with on my own when I was a kid and its just always seemed to get me there. So feel free to pick it apart and tell me the errors of my way, because I wouldn't mind knowing how to go about doing it better. Basically I would start with some init timing from my experience with LA small block engines I have found usually starting at 15 or 16 degrees is a good place to start and go up from there. Than I tune the carb for idle. Than I would just rev it up and go by sound and feel basically till it felt right but that only usually got me so close. Than I would take it out on the road and see what it was really doing under load and just kinda played with it till it felt good.

As for my distro being a "smog" distro I kinda doubt it or someone already change the springs out to lighter ones. Keeping the timing gun going and reving the engine to maybe 2000 or so, the timing seems to advance out very quickly. So this brings me back to my original questions I started this thread with or maybe I am asking the wrong questions. We known the ini timing but we don't know the mechanical timing. How can I go about finding out how much mechanical advance I have in the distro. Also for the springs are they marked in any sort of way where we can tell if they are lighter or heavier?

On a side note to help me figure this all out. I have a 360 thats fairly built up with a FBO system. When they built it for me they took the specs of engine and car and mechanically built it for those specs and gave me a data sheet that told what to set the init timing (20) than the total (34) and it should all be in at 3100rpm. So that would mean my distro on that engine has 14 degrees of mechanical. I have no idea what the curve is but I can tell you it doesn't seem the mechanical kicks in as fast as the one on the other engine. So my question is how did they come up with these numbers? I have tested trying to squeeze more timing and either the change isn't even noticeable or you get to a point where the change starts to effect how it acts in a negative way so it seems to me they have it nailed in pretty good.
 
OK whoever gave you that data sheet either set the distributor up on a "distributor machine" or they checked the engine with an accurate timing light.

Here are some ways to determine your own curve

1 You can buy a so called "delay" or "readout" or "dial up" timing light. There's probably more slang terms. What these are, you use the light, and it has some sort of display --meter or digital--and a knob. You run the engine at some RPM and turn the knob until the marks appear to move to zero (TDC) Then your readout on the light tells you how much advance you have at that condition. I DON'T LIKE THESE because in a previous life I've run into quite a few that were just not accurate

2 You can degree your balancer

3 You can buy the correct timing tape for your balancer

To do 2 or 3, first thing you want is to verify that the balancer mark is accurate. It may or may not be. To do this, you need to buy or build a "piston stop," like this:

http://www.atlanticspeed.com/productcart/pc/catalog/comp_4795_2150_general.jpg

You can make one from an old spark plug.

Remove the no1 plug, make sure the piston is "down a ways" and unhook the battery ground for safety

You will surely have to play with the length setting. Wrench the engine around untion the piston stops at some point. You don't WANT it to stop at TDC, you want the piston "down somewhat."

At this point, make a temporary mark under TDC on the timing tab onto the balancer.

Do the same thing going counter clockwise

Now you'll have two temporary marks on the balancer. True TDC will be halfway in between, and if the factory mark is accurate, that is where it will be.

Now that you've done this, measure carefully AROUND you balancer with a small flexible tape. Do this a couple of times, to be accurate.

Now figure how many degrees per inch (360* in a circle!!) and measure off 40* with your tape, carefully. Check it at least twice, and scribe the balancer.

Now you can use a pair of dividers.

Divide the distance from TDC to 40* in half. You can make sure this is correct by checking both halves, so now you have 20 and 40

Now divide the 20 in half, and mark for every 10*

You can take this as far as you want. Once I have 10* on the dividers, I add another 10* out past the 40 marker to make 50

After checking TDC with your stop, and measuring your balancer size, you can also go to Summit or other speed outfit and buy timing tape for your balancer.


NOW that you finally have all this done, you can take a tach and your timing light, and measure the timing at different RPM to see what your curve IS.
 
Yea FBO builds all there distros on a machine.

As far as doing all those timing marks I always do this when I have the engine apart and putting it back together. That way there is no guess work later whether the marks are right or not.

After what you have told me and reading that article the only question I really still have is do you agree with always using a total of 35 @ 2500 as a baseline?
 
That's a good starting point. I'm currently running a low compression 360 with a mild cam a lot closer to 40*
 
All of my cars have been street/strip small blocks I've put the lite springs in and run 36* timing all in by 2500 RPM's that was just mechanical no vacum advance.
 
Yea this new found knowledge gives me something to tinker around with and see what I can come up with. Funny thing is I always kinda knew there was a better way to setup timing but my way worked so I never gave it to much thought. Most of the engines I have built have been mild 360's, cam, intake, and carb usually. The 1 360 I did build up for street/strip I had that FBO system so I never had to dick with it.

This particular engine I was having issues with is just a mild 318, first 318 I ever messed with and when I set up the init timing it was way off of where I thought it should be (cause of me forgetting to disconnect the vac). I thought it was weird the init was so far off what some of the 360's I have had were set at but I thought maybe that is just how 318's are. Than when I couldn't tune the carb to do much of anything everyone kept asking if I had the timing set right but me being me I just ignored them cause I thought for sure it was a carb issue. So after watching a few Youtube vids on tuning my particular carb I came to the conclusion either my carb is junk or I need to go reseach timing and see what I am missing. So if I hadn't forgotten to unplug the vac it probably wouldn't have forced me to come to learn how to do it right. LOL
 
And Thanks for the help! I hit the thanks button thinking it would give you some sort of notice but I don't think it works like that.
 
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