MP distributor....changing advance springs.

[Harlow]

I need to slow down the timing curve on my MP distributor. Its all coming in at about 1700 rpm. I have an old distributor that came out of the car and it looks like it had a stronger spring put in it. If I take this heavier spring out of the old distributor will I be able to put it in the MP distributor? I think the MP distributor is a stock distributor with the electronic stuff put in, so I'm thinking this would work. What do you think? Heres a picture of the spring. Also, when I punch it from a dead stop it seems like the engine has trouble until about the 1-2 shift (its going pretty slow for how many rpms its turning) and then after that shift it makes really good power. You think this is due to the advance coming in too early?

[aifilaw]

I'll attempt to post my old article in here...

How to recurve a Mopar BB Electronic distributer


Here I will go over how to recurve a mopar electronic distributer for performance or otherwise applications. Below I will list various other sources of information on the subject, and I will also list information given to me during my trials in performing this operation. Read it all and I hope this helps someone as I went through a great deal of trouble learning this information the hard way.

Ok lets begin.....

I'm going to assume you are going through absolute hell here, because if you aren't then you probably just bought a brand new distributer, or have the dyno and air/fuel monitor to do the job correctly, most of us however are short the several hundred dollars to invest in something so trivial, I'm also going to assume that while you need to recurve your distributer you don't have a timing tape, or even a timing light.

First of all we will cover the basics, like lets say your curve is fine and you just need to set the timing, then I'll cover vacuum advance, then lastly we will get into the nitty gritty and go over the recurving of the distributer springs.

Well first of all lets say you bought a brand new distributer and you just want your car to run, or you would like to make sure its tuned correctly, there are several ways to go about this. First you have to know where your distributer is and how to adjust it. the distributer would be that big thing with 9 posts, 8 around the outer edge, and one in the center going to your coil with wires coming out of each one. That is referred to as the distributer cap. You don't need to mess with that at this point, just look for how the whole unit is held down, this is done by a metal plate about 4 inches below the bottom of the cam held down by a skrew, its just a pressure hold and by loosening that one bolt on the plate the distributer should move freely, easy killer moving that distributer one millimeter in either direction is about 2 degree's and that can make a BIG difference in your performance.

[aifilaw]

Ways to set your timing are:

A. bust out a timing light with an adjustable dial, set it at 38 degree's, have someone keep the car running at exactly 2500 RPM or slightly above, with that bolt loose move the distributer counter clockwise to retard, or clockwise to advance your timing until the timing light on the marker reads 0 degree's, that's 38 degree's, you should be good to go, if your not, then A. you installed the distributer backwards (there are only two ways so your either 180 degree's off or not), or your timing mark, or tape, or harmonic balancer is off, but never fear, we will get to other ways of setting the timing.

B. Shut the car off, now advance the timing about 3 millimeters or so, now start the car twice, giving it about 10 seconds between starting and stopping and stopping and starting at least, if it has trouble starting (knocking) then its too far advanced, back it off a tad and try again, once she starts perfectly you should have it perfect (this is of course assuming its curved correctly) Note: on performance engines with high compression or not will require much less advance to crank the engine over, but will be a dog once its started at low RPM's, either deal with it or use some other method for distribution like a programmable system

C. run it at 2500 RPM's, advance the timing till you hear the exhaust popping and it runs rough, back it off till it runs smooth and the RPM's start dropping as you retard the timing, set it right there and tighten it down, your done.



READ THROUGH FIRST THEN BEGIN!!! I can't stress this enough

Now we will go over the vacuum advance, for those of you with very high duration cams like myself never fear, the vacuum advance still provides a crucial role and is needed, its hard to get perfect timing once removed, and you won't like the backfiring you get without it on as you decel from RPM's. This is the hexagon shaped peice attached to the side of the distributer, its on the top left of the screen in this picture...

[aifilaw]

See that "10L" written on the side, that means it produces 10 degree's of advance at most. Now as you can see in this following picture it hooks into the bottom of the rusty plate, thus moving the rusty plate and that magnetic pickup forward decreasing the time it takes the points on that center peice to hit the magnetic pickup, hence increasing the timing. see picture below...  Now how do you adjust it? Answer is simple, get yourself an allan wrench as seen in the very top left of that first picture, I believe its 5/32nds or the one slightly larger than that one. stick it down the hole where the vacuum line attaches from the carb, by tightening (counter-clockwise)(yes is bass ackwards), you will restrict its ability to create advance, in other words if you have exactly 8 turns from all the way tight to all the way loose and you turn it 4 turns then it will only provide 5 degree's of advance once it receives enough vacuum from the carb to pull it that far. and if you turned it 2 turns from the far clockwise position it would probably provide about 7.5 degree's of advance, you can figure out the rest.



ALLLLRIGHTY THEN, now for the fun part, recurving.... let's start from the beginning, unhook your magnetic pickup, that's the red and black wires going to the funny black plastic connector from the side of your distributer. Now unhook the two snaps on either side of the distributer cap holding the cap on, they are metal and they have tabs so they unsnap easily. Good now pull the cap off and push it to the side, best not to disturb all those wires on the posts as they break easily. now you should see a white plastic thingy with a metal piece across the to, that is the thing that distributer is supposed to be moving, makes you sick doesn't it? below I'll post a picture of it, its the white piece you can barely see at the top left by the skrewdriver.

Ok then, before you start unscrewing things willy nilly like the 4 skrews on the outside of the distributer, two holding the advance unit on and two holding the main unit on you need to get a pair of skinny needlenosed pliars and dig the snap ring out from the center, its down inside the hole that the white piece was on top of (by the way at this point you should have unskrewed the bolt holding down your distributer to the engine block and pulled the distributer OUT and taken it inside. ok underneath that white piece take out the snap ring, NOW unscrew the vacuum advance unit, after its unscrewed use a flathead and pry the rusty peice up from the second picture off of the non-rusty piece beneath it (they are attached but flexible) and pull down and away on the vacuum advance unit, this should remove it from its little hole and you should be able to pull it out off the distributer. Now unscrew the other two skrews holding down the nice metal piece, after doing this you should be able to gran ahold of the 8 point pickup and pull that whole unit off (2nd picture middle, or 1st or 3rd picture right side), this is what you should see...

[aifilaw]

     
How to recurve a Mopar BB Electronic distributer


Here I will go over how to recurve a mopar electronic distributer for performance or otherwise applications. Below I will list various other sources of information on the subject, and I will also list information given to me during my trials in performing this operation. Read it all and I hope this helps someone as I went through a great deal of trouble learning this information the hard way.

Ok lets begin.....

I'm going to assume you are going through absolute hell here, because if you aren't then you probably just bought a brand new distributer, or have the dyno and air/fuel monitor to do the job correctly, most of us however are short the several hundred dollars to invest in something so trivial, I'm also going to assume that while you need to recurve your distributer you don't have a timing tape, or even a timing light.

First of all we will cover the basics, like lets say your curve is fine and you just need to set the timing, then I'll cover vacuum advance, then lastly we will get into the nitty gritty and go over the recurving of the distributer springs.

Well first of all lets say you bought a brand new distributer and you just want your car to run, or you would like to make sure its tuned correctly, there are several ways to go about this. First you have to know where your distributer is and how to adjust it. the distributer would be that big thing with 9 posts, 8 around the outer edge, and one in the center going to your coil with wires coming out of each one. That is referred to as the distributer cap. You don't need to mess with that at this point, just look for how the whole unit is held down, this is done by a metal plate about 4 inches below the bottom of the cam held down by a skrew, its just a pressure hold and by loosening that one bolt on the plate the distributer should move freely, easy killer moving that distributer one millimeter in either direction is about 2 degree's and that can make a BIG difference in your performance.

Ways to set your timing are:

A. bust out a timing light with an adjustable dial, set it at 38 degree's, have someone keep the car running at exactly 2500 RPM or slightly above, with that bolt loose move the distributer counter clockwise to retard, or clockwise to advance your timing until the timing light on the marker reads 0 degree's, that's 38 degree's, you should be good to go, if your not, then A. you installed the distributer backwards (there are only two ways so your either 180 degree's off or not), or your timing mark, or tape, or harmonic balancer is off, but never fear, we will get to other ways of setting the timing.

B. Shut the car off, now advance the timing about 3 millimeters or so, now start the car twice, giving it about 10 seconds between starting and stopping and stopping and starting at least, if it has trouble starting (knocking) then its too far advanced, back it off a tad and try again, once she starts perfectly you should have it perfect (this is of course assuming its curved correctly) Note: on performance engines with high compression or not will require much less advance to crank the engine over, but will be a dog once its started at low RPM's, either deal with it or use some other method for distribution like a programmable system

C. run it at 2500 RPM's, advance the timing till you hear the exhaust popping and it runs rough, back it off till it runs smooth and the RPM's start dropping as you retard the timing, set it right there and tighten it down, your done.



READ THROUGH FIRST THEN BEGIN!!! I can't stress this enough

Now we will go over the vacuum advance, for those of you with very high duration cams like myself never fear, the vacuum advance still provides a crucial role and is needed, its hard to get perfect timing once removed, and you won't like the backfiring you get without it on as you decel from RPM's. This is the hexagon shaped peice attached to the side of the distributer, its on the top left of the screen in this picture...

See that "10L" written on the side, that means it produces 10 degree's of advance at most. Now as you can see in this following picture it hooks into the bottom of the rusty plate, thus moving the rusty plate and that magnetic pickup forward decreasing the time it takes the points on that center peice to hit the magnetic pickup, hence increasing the timing. see picture below... Now how do you adjust it? Answer is simple, get yourself an allan wrench as seen in the very top left of that first picture, I believe its 5/32nds or the one slightly larger than that one. stick it down the hole where the vacuum line attaches from the carb, by tightening (counter-clockwise)(yes is bass ackwards), you will restrict its ability to create advance, in other words if you have exactly 8 turns from all the way tight to all the way loose and you turn it 4 turns then it will only provide 5 degree's of advance once it receives enough vacuum from the carb to pull it that far. and if you turned it 2 turns from the far clockwise position it would probably provide about 7.5 degree's of advance, you can figure out the rest.



ALLLLRIGHTY THEN, now for the fun part, recurving.... let's start from the beginning, unhook your magnetic pickup, that's the red and black wires going to the funny black plastic connector from the side of your distributer. Now unhook the two snaps on either side of the distributer cap holding the cap on, they are metal and they have tabs so they unsnap easily. Good now pull the cap off and push it to the side, best not to disturb all those wires on the posts as they break easily. now you should see a white plastic thingy with a metal piece across the to, that is the thing that distributer is supposed to be moving, makes you sick doesn't it? below I'll post a picture of it, its the white piece you can barely see at the top left by the skrewdriver.

Ok then, before you start unscrewing things willy nilly like the 4 skrews on the outside of the distributer, two holding the advance unit on and two holding the main unit on you need to get a pair of skinny needlenosed pliars and dig the snap ring out from the center, its down inside the hole that the white piece was on top of (by the way at this point you should have unskrewed the bolt holding down your distributer to the engine block and pulled the distributer OUT and taken it inside. ok underneath that white piece take out the snap ring, NOW unscrew the vacuum advance unit, after its unscrewed use a flathead and pry the rusty peice up from the second picture off of the non-rusty piece beneath it (they are attached but flexible) and pull down and away on the vacuum advance unit, this should remove it from its little hole and you should be able to pull it out off the distributer. Now unscrew the other two skrews holding down the nice metal piece, after doing this you should be able to gran ahold of the 8 point pickup and pull that whole unit off (2nd picture middle, or 1st or 3rd picture right side), this is what you should see...

That's the snap ring in front of the distributer by the way.

Ok see those springs, those are the rusty stock springs from before that were in there, one is elongated eye and impossible to pull on, also seen in bottom of picture #1. Pull on the springs and don't vary too far from stock, chances are in high perforamance applications you are going to need a bit more advance on the low end and lesson the top end, so lighten up the other spring a little and put in a spring of the same toughness but not immovable and alongated into the elongated section, but now I'm telling people what to try and that's BAD.

[aifilaw]

That's the snap ring in front of the distributer by the way.

Ok see those springs, those are the rusty stock springs from before that were in there, one is elongated eye and impossible to pull on, also seen in bottom of picture #1. Pull on the springs and don't vary too far from stock, chances are in high perforamance applications you are going to need a bit more advance on the low end and lesson the top end, so lighten up the other spring a little and put in a spring of the same toughness but not immovable and alongated into the elongated section, but now I'm telling people what to try and that's BAD.

I'm hoping you were smart and read this section first before you did anything, now I'm going to tell you which springs to choose. First of all with your car in operating condition tighten your vacuum advance ALL THE WAY clockwise, this will eliminate weird things from happening, now do the starting and stopping test to detirming best timing on the low end, now take your car for a spin and slm the gas in the 1000-2500 RPM range, try power braking, or lighting the tires, that's who I discovered perfect timing, now advance it a little, see if it knocks, or if your engine/exhaust is so loud you couldn't hear it knocking if you wanted to (like mine) try it by seat of the pants, its very easy when dealing with this RPM range. once you got it advanced and retarded and have a little rubber on the road and feel confident you have the low end set correctly take a color chalk and mark a line on the distributer to the engine block to mark low end. good now try in the 2500-3700 RPM range, you will most likely need a stopwatch for this and carb tuning/vacuum secondaries can trick you big time here, I usually do this is second gear, running it up to 2500 and stomping on it and counting seconds till it hits 4 grand. There we go, now repeat the process for the high end, 4000RPM till whenever you wish to redline.

[aifilaw]

If after you complete this process and change springs and its still needing a bit more advance at the top end, get a drill and drill out the holes in the plate shown in picture #1 on the right side, elongate those slightly, then try again, if it needs less advance at the beginning, then elongate them slightly on the inside. You shouldn't need to shorten them, you can do this with heavier springs, and I don't encourage welding on this piece.

By the way that "13" on the bottom of above mentioned plate means double that is the amount of advance it can provide, so at maximum length those weights provide 26 degree's of advance.

http://www.zhome.com/ZCMnL/PICS/detonation/detonation.html

http://www.centuryperformance.com/timing.htm

[aifilaw]

Basics?

Basics. Initial advance could be anywhere from 6 deg. BTDC to 14 at idle. Add in mechanical advance from 1,000 rpm up to 2,500 - 3,000 rpm of let says 20 degrees. With initial of 14 that equals your full mechanical advance of 34 at, say, 2,700 rpm. Vacuum advance can kick in another 18 or so degrees at cruise, so you may have total advance of 52 during cruise.

Tuning overview. Before you change anything, make a graph of your initial and mechanical advance curve by rpm. Now with stopwatch in hand, time your car's acceleration through an rpm range of your choice, say from 3,000 to 4,500, and then another one from 4,500 to 6,000. Or any increment you wish that you can put a reasonably accurate time on. NOW alter your timing by 2 degrees at a time, both above and below your current settings. Take all those same stopwatch recordings of the same rpm ranges. You will eventually see what timing advance your engine likes best in which rpm ranges by looking for the lowest elapsed times. Determine what the TRUE timing advance was for each of those points and plot that on your graph. That is your engine's desired perfect curve. The only problem now is trying to match it with different springs, filing or welding the advance plate, etc.
When you take off the cap from either a points or an electronic (non-Lean Burn) distributor, you will see the rotor and the vacuum advance plate. On that vaccum advance plate are either the points and a rubbing block or the electronic pickup and a reluctor wheel. Those things signal the spark. If you remove that plate, underneath you will find the mechanical advance weights, springs, and limiter plate. This looks the same for a points distrib. or electronic, but not a Lean Burn. You can get different strength springs to adjust the RATE of the advance curve, the weights can also be different, and the limiter plate can also allow for different amounts of advance. The length of the "slots" in that plate govern the amount of mechanical advance. Weaker springs allow the advance to come in quickly. Longer slots give more mechanical advance. A spring with an elongated spring 'ear' allows for a faster initial rate and then a slower rate after a certain rpm.

[aifilaw]

Don't forget that most factory smog engines used one strong spring with an elongated spring eye on one end. This would create a fast initial advance, then it would slow down the rate considerably once the elongated eye spring 'caught' it's pin. This might be what you need - check the junkyard for mid '70's 318 & 360s.

As the weights swing out under centrifugal force, it causes the timing to advance. Heavier springs slow the rate of advance. You do not want any mechanical advance below your idle speed, whatever that is for your engine. You can mix and match the springs, or only use one spring if that's all you need. The plate with the two rectangular slots is what controls the amount of mechanical advance that can be added. You can weld it shorter or file it longer.

Reduce initial advance if you're having problems starting.



Once I get the curve correct, or buy a new distributer what's a good set timing I don't want to recurve?:
Get a timing light with an adjustable curve dial indicator, set it to 38 degree's... now have someone sit on the throttle to keep the engine at 2500 RPM's, good now move the distributer until it lines up at exactly 38 degree's at 2500 RPM's, that should be good enough.

[aifilaw]

All about spark plug gapping and ignition:
Plug Gap....

Typically, .035-.045" is recommended for electronic ignitions, .022" for points.


That said...

Spark plugs are gauged generally due to two things, the power your outputting to them, and the compression ratio in the environment they will be firing. Once you detirmine how much voltage is going across the gap, you need to detirmine the other half of the equation, compression ratio. The gap is a spark plug is generally increased when you have lower compression. This is done because of the molecules are less strictly compressed between the gap and you can get a good even spark with maximum coverage to ignite as much fuel as possible. This of course comes into effect when running a slightly richer air-fuel mixture, the gap should be changed to reflect that. So if your gunna run nitrous (craploads of more compression due to more oxygen added to cylinder) you should tighten the gap on the plugs before a run at the strip, it will not run perfectly however you will feel the difference between a perfectly set gap and not, especially when running nitrous. Forced induction is normal because you will be able to use a compression tester and find the total compression, whereas I'm pretty sure most people do not shoot nitrous while tuning. There are many other things to consider, such as humidity when gapping(lowers compression).

[aifilaw]

To sum..
High compression engines require plugs that have smaller spark gaps. A smaller gap will create a more predictable spark. A spark that takes too long to cross the gap will be more likely not to make it, or to make the gap at the wrong time. This means you get timing problems that can easily lead to detonation. For a high compression engine you may want to experiment with smaller gaps (on the order of .028 to .025) until you get no misfires at any RPM. The gapping is very subjective and needs a lot of trial and error before you get it right. Of course you don't want to gap down to much less than .025 or short out the plug as this could ruin your coil. Just keep in mind - high compression means short spark.

I wish I could find the site with a huge table listing all the compression ratio's and voltage and retarded timing schemes etc where you could easily use the stats from your distributer or ignition, and compression tester, and gap your plugs perfectly, perhaps someone else can provide this?

Compression Calculator if you don't have a compression tester..
http://www.race-cars.net/calculators/compression_calculator.html

I will continue to search for the formula for calculating spark plug gap exactly from compression and spark. If I can't find it I will spend some time gathering stock specs and create one from scratch.

However if your hoping to get the absolute perfect spark gap for your engien and increase your potential efficiancy to 100% as opposed to the 97% your prolly getting with a barely mis-adjusted plug, I would suggest you get a plug wrench, a pair of jumper cables, a spare vehicle, and just start it, run it shut it down over and over and inspect the plug. There are numerous sites on the net showing pictoral detail on how to detirmine if you need more or less gap.

[Ghoste]

That is a fantastic read.  That with Chryco's Holley tuning guide are two things everyone should know. 

[aifilaw]

somewhere I still have the pictures detailing all the things mentioned....

[darrin75]

post those pics

[firefighter3931]

One medium and one light spring usually does the trick. With pump gas compression a spark gap of .035-.040 is fine with a stock style MP ECU. With a MSD box you can open up the gap to .050.

The rate of advance seems to be coming in too slow from what you are describing. The base timing probably needs to be increased as well. How much timing do you have at idle ?

Map out the timing curve in 200 rpm increments and post the results.


Here's a good read on tuning a 383 ignition/carb for best performance :


http://1970chargerregistry.com/70messageboard/viewtopic.php?t=1207




Ron