76, (and belately Muddywaters, desi, sperkins, & sixfooter)
thanks for the kind words.
i'm glad you found the post worthwile and hopefully helpful.

76, I know what you mean, sometimes it just takes a different wording on the same info to get it to "sink in". I'm very much that way myself on may technical things.
I tried to word things and explain the procedure as easily as I could because I remeber very much how difficult it was for me to initially grasp the overall concept and reasoning of the whole "timing thing".
It was Latin to me at first but once it finally sank in thru by unusually thick skull it finally clicked and all came together - especially on the vacuum advance system. I'm glad it was beneficial to you.

Now, if only I can get myself to understand the rest of the motor's operational areas I'd be in good shape!

BTW, I don't drink so you don't need to buy me a beer but you are welcome to buy one and enjoy it yourself as you set the timing on your own car!

Oh.......... one last note 76. If you read a thread on the forum and you have questions, ASK THEM! It's the only way to learn. I hesitated asking most question at first also. When I did I was somewhat embarrassed because some of my questions were so basic in nature that I felt any breathing human being over the age of 6 months should have known the anwers. The thing is I did and I knew unless I asked I would never know.
Turns out when I started to ask many basic questions I got a lot of emails and PM's from other forum members thanking me because they also didn't know the answers and had the same questions but they too had been too embarrassed to ask so were glad I did.
It also turns out that while a topic I brought up was being discussed, others who thought they knew the answers were wrong and it allowed them to find out the true answer, procedure, or whatever.
The point is, ASK. Believe me, you probably aren't the only one that may have the same questions so many will benefit and the discussion thru the thread can help many people of all experience levels.

Let us know how you make out with your new distributor and getting your timing set up. If you have any questions, post them in a new thread and ASK and i'm sure someone will be able to help you.

 

Thank you barry, very clear to me now .I printed it out and put it in my home made tech. binder and it got the clear protector treatment

 

thanks murvette, glad you found it useful

 

This was a great post i learned a lot!!! Think i will be picking up a dial back timing light this weekend and checking my car out. Where can i get the differnet springs for the centrifical advance if i need them, and how do i know which ones to get?

 

BarryK...Thanks a lot. You presented a fine, easy to understand article.
76 Sting....you will like the e-curve dist.....I have one and once you understand their instructions, it's simple.

 

IMA66
I got my dial-back light at Sears - only about $69 or so. Well worth it over a standard light.
I'm not that far from you so if you want any help let me know and i'll be glad to come over or if you didn't get the dial-back light yet you are welcome to drive over here to my place and use my light and vacuum gauge to get your car set up


David
Thank you

 

David,

Thanks. I do like the concept, but the directions are misleading. They say to include the vac adv in the total timing (mine is 38 deg). However, everyone else states to not include it and to add it in at the end. which makes sense to me. Meaning, 18 init, 20 elec, and 15 vac gives me a real total of 53 deg. just like Barry and Lars mentioned. If I do this the way they (MSD) say to do it I will likely have 8 init, 20 elec, and 10 vac. I do not think this is the right combo, but it is what MSD is telling me if I am reading this correctly.

My main reason for the concern is I just installed a brand new engine from Year one with 430 HP and 430 ft or TQ. However, I am not able to get off the line and it is hesitating a little. I would have hoped that 430 HP and TQ would have allow me to smoke those tires at will. Unfortunately, I can't even get them to chirp off the line. My thought is that my timing may be off due to me misunderstanding the instructions.

Sorry to turn this into a QA, but I am getting a little depressed that no matter how much money I seem to spend, I can't get this car off the line.

 

Great stuff
But it make my hair hurt....alot

 

76

unless MSD is doing something inside the distributor such as automatically calculating the vacuum advance based on your settings with it hooked up (perhaps it automatically disconnects the vacuum advance during timing set-up than reactivates it after setting are made?? - I have no clue since I don't know a thing about the e-curve unit) than they are way wrong. Timing settings should be made with the vacuum hose disconnected from the vac can and the line plugged while setting timing.
if you can use 38º total timing without detonation than great, but check the car carefully on a test drive to make sure - otherwise drop down to 36º. You do NOT want any detonation.
My recommendation would be to try a setting on the distributor of 36º total, with a centrifigal advance of 24º. This will than give you an initial timing of 12º. If you can run 380 without any detonation than that's fine too with the same centrifigal advance and an initial timing of 14º.
with the vac. advance than reconnected you would have another 15º advance on top of those numbers.

As for your off-the-line performance and not being able to smoke your tires, that can be somewhat from the timing settings - if they are currently wrong such as 38º INCLUDING the vacuum advance that means your total timing is only 23º which is VERY retarded ( in more ways than one ) and you are losing a ton of power.
The other issue can be the overall design and buiold of the motor.
I do NOT understand cam specs well enough to know what the number all mean compared to other cams but one thing I know well is that generally the hotter the cam the more power you get at the top end but at a sacrifice of power and torque at the low rpm end. The question isn't how much HP and torque the motor is making, but WHERE in the rpm range is it making it.
A perfect example is my '65 327/365hp motor. That motor has a stock cam called the 30-30 cam. The motor makes 365hp and can screeam and revs easily to redline and beyond. The problem is that for a factory can the 30-30 cam is pretty radical - great for a race car, lousy as a street cam. The power doesn't come on until 3500rpm. Off the line until you reach 35oorpm the car is a real dog, even with the 4.11 rear gears in am running. On the other hand, once the cam comes into the powerband at 3500 hold on tight because the car takes off hard and will scream to redline and far beyond that. At low rpms though it's like a granny car and feels like it has no power.

i'd first double check to see the correct way to setting the timing on the distributor and get the timing set correctly in the range I suggested above.
Than once that is set, than check the specs on your motor and see where the powerband is on it. if the torque and HP only come on high up in the rpm range than no matter how well the timing is set you are only going to have so much lower rpm power to work with. You motor may scream and have a lot of power up high, but if that's the case than you are going to have a lack of power down low and smoking the tires isn't going to be easy.

 

76 sting, Darin, yes, the instructions are poorly written and the tech help is no better when you call. BTW, the last two words on page 7..."timing curve"....should say "initional total timing"
To confuse me even more, the spec. that came with my gm zz383/425 says 32* max .@ 4000rpm with vac disconnected......well, with that set plus 10* vac added gives me only 42.....sounds like everybody else is shooting for 52......I don't know what to set mine to.
currently the initial is 32 with switches at 0,0 and vac plugged, then connect vac and set to 0,7 and rev limit to 6k ....runs good but I may be leaving some on the table.
Maybe someone can step in and help.

 

David
unless there is something I don't understand or aware of about your ZZ383 (which is very possible, there is a LOT I don't know or understand ) I can't figure why they say to not go above 32º total timing. Is there any other info that is related to that statement that would be relevant? What's the compression on the motor? Perhaps the compression is high on the motor and they mean don't go above 32º on regular pump gas because of detonation from low octane gas??
If no other info is supplied that explains the statement than you might want to call the vendor that you purchased the motor from and ask them.

Also, you mentioned 32º plus 10º = 42º with vacuum advance. Are you saying your vacuum can is only supplying a 10º advance? that's pretty low.

i'd shoot for a timing set up of (BEFORE vac adv) of:
34º - 38º total - all in by 2800-3000rpm (depending how much you can go without detonation)
centrifugal advance of 22º-24º

than I'd use a vacuum can that supplies 15º-16º of vacuum advance.

I'd first try to look at the instructions that came with the motor and/or call the vendor and ask about the 32º timing statement

 

Barry,

Thanks, the engine manufacture sugests the 38º, but I will try 25º (cannot select 24) with 12 init and 15 vacuum. That will put me at 52 total. However, I have read many times to try and run as much init as possible without detonation and at 18º init and 38 total (no vac) it does not detonate.

I cannot post the image of the dyno graph, can I send it to you for a quick overview? Maybe you are right and I am not making enough power early (low RPM) to get those tires to smoke?

 

David,

WOW I might actually be able to finally help someone out. Unless your compression is 10:1 or higher 32 may be a little low (I agree with Barry here). My compression is 9:5 and I can run 38* no problem and the engine vendor recomends it.
However, your current set up (switches) is set up with no vac advance. Meaning your only getting 32 total and no vac. which is low. If you want 10* of vac switch #1 needs to be on 4 and switch 2 should be on 7. This will give you a total of 42* with vac. But you may like switch #1 in the 6 position. This will give you 15* of vac and a total of 48...much closer to the 52 ideal total that we both have read.
You selected #7 with full advance to come in by 2500 RPM's, which is exactly what I have.

How far are you from flour Mound?

 

yes, a number of people like to run very high initial timing settings but I don't agree with that. Running initial timing too high can cause problems with starter drag, especially in hot weather, plus detonation problems.

The two most important aspects of timing are total timing and the centrifugal advance curve out of the distributor. Setting these thwo correctly will have the initial fall where it will, but it's important to keep an eye out on where that falls. The way I learned timing I was always told to keep initial (depending on the motor, configuration, etc) between 8º-14º. I don't too much harm in taking it to 16º. The think 18º starts to push thing sa little bit and I'd personally never consider anything higher under any circumstances although others will tell you they run 20º, 24º or even more on initial timing. Honestly, I don't even know how their motors start on some of the high initial timing settings I've read some people are running.
Pushing initial timing up higher can give you a bit more throttle response and perhaps a bit more off-the-line performance but the higher you push it the more risk you have of detonation (plus starter drag).
Additionally, to keep total timing in the 34º-38º range, the more you push the initial timing higher the shorter you need to make the centrifugal advance curve which limits the motors ability to make adjustments as needed when driving under different RPM and load conditions which is the main reason for the advance system to begin with!
There is ALWAYS a compromise to be made somewhere - some people prefer to gain every edge of performance possible while compromising on the detonation threshold. I prefer to set up the timing on the motor to give myself a nice safe medium between performance and safety on the motor so it lasts. When you set it up with safer timing settings you can push it harder under more conditions without worrying about destroying the motor.

Think about it........ how many threads and posts have you read on here about people blowing up their motors, destroying pistons, etc. Most of that is because of incorrect timing settings. It doesn't take much detonation to blow a hole in a piston - ask Lars sometimes. He carries around a destroyed piston with him on his Tuning for Beer toursto demonstrat what detonation can do to a piston.

On your motor, if you can run 18º and 38º with no detonation than go ahead but remember that once you reconnect the vacuum advance you are going to be around 33º and 53º. I'd recommend you check carefully for detonation (with a hi performance motor, and a more radical cam it's not always easy to hear. Also, as you test drive the car set it at a nice easy cruise speed in 4th gear and feel carefully for any surging, chugging, or jerking. If you get any than your vacuum advance is too high.

 

I agree fully with you here. I will try a few different combos and see what the results are.

Here is what I will try:
20* elec adv (same as centrifugal for the MSD e-curve disty)
16* init
15* Vac
total of 51*
and
25* elec adv
12* init
15* Vac
total of 52*

I will try to compare that with my current set up and see what yeilds the best results.

 

EDITED TO CORRECT ERRORS...(made adjustments in my medication)

Here are some details I get from the MSD eCurve instructions, which were somewhat confusing to me.

The Total amount of timing Change possible is 34* (25 elect. + 9 vac).

If you don't want to use the vac advance, don't plug it in. Switch settings don't turn it off or on.

All 20 of the switch combinations under Q R S and T keep timing from advancing beyond the setting you position the dist. at, but will retard this setting to make cranking easier.So,after engine reaches 600rpm, the advance will no longer be set back but rather allow you to rotate your dist. and set it to the max amount of advance you want by rotating the dist body.This adjustment will be the total amount of advance you desire your timing to be.

So, to adjust the MSD eCurve dist....

1)Set switches to any of the 20 Q R S or T settings , disconnect and plug vacuum and set initial timing to your desired setting by turning the dist. and then tightning the clamp. In my case it will be 32*.
2)Set the 2 switches to the curve you desire using figures 3 and 4. For my engine with fastburn heads MSD recomends J or K with no vacuum advance connected. They also recomend the 32* setting, same as GM does in their doc.

76 String... I live NW Fort Worth Eagle Mountain Lake. probably only 35-50 miles from Flower Mound.

Barry, We really didn't mean to take over your great thread. Thanks for creating it. It is allowing me to resolve some questions I have had for a while.

 

Barry,

First let me commend you on a fine write up (and my respect for the sheer effort it took to write all of it). This should be of great help to several members of the forum. Thanks for bringing all of this together
I have one item I'm not comfortable with. Near the beginning of your write up you state that at idle and cruising that the air fuel mixture is lean, and as the load goes up it becomes richer. This is not necessarily true. Unless one measures the exhaust gas we have no idea what side of stochiometric we are (are we lean, or are we rich), nor do we know what the carb does (A/F wise) over load/RPM. The vacuum diaphram function is to change the advance due to cylinder air density, not fuel richness. Otherwise, an engine with a carb (or fuel injection) that maintained an A/F ratio of 14.7:1 over the RPM/Load range would not require a vacuum advance to modify the timing even as the manifold vacuum or cylinder pressure changed. You are correct that leaner mixtures generally burn slower, and richer mixtures generally burn faster, but that is a secondary condition (like the timing effects of air temperature, humidity, etc) compared to the advance requirements dictated by how dense the cylinder mixture is. Engines with higher compression ratios generally require less advance than lower compression ratios, due essentially to the density of the mixture in the cylinder. This difference in timing (between a high CR and low CR engine) is similar to the changes in timing required when the throttle opens up and more air is injested into the cylinder. The "closer" the air and fuel molecules are to each other (whether by squishing the molecules closer with high compression, or adding more molecules into the cylinder by opening the throttle further), essentially the faster the flame front will travel, thereby requiring less advance.
The above is not a criticism, but just hopefully a little more explanation of the whole ignition system function. Thanks again for all your hard work on this, and please continue your good work.

 

The post was written and intended to help answer and explain the overall process of what timing is and how to set timing on your car. It was written as much as possible in "layman's terms" as to mot be too confusing for people that are new to working on their car or don't have much experience in understanding and setting timing. I know how frustrating it can be to not know this stuff and depend on others such as local mechanics for what is actually a fairly easy thing to do. It wasn't that long ago that I was in that situation myself!
On that premise I tried to make the post as easy to understand for most people as possible and in some cases went with TYPICAL or GENERAL circumstances.
Now, having said that, the following is taken straight out of John Hinkley's tech paper on Timing called "Timing101".

"Fuel/Air Mixture and “Burn Rate”: At idle and steady cruising speed, the load on the engine is
low, and the air-fuel mixture is “lean” (more air/less fuel); when accelerating, the load on the
engine is higher, and it’s fed a “rich” air-fuel mixture (more fuel/less air). These are two very
different conditions, as a lean mixture burns relatively slowly, and a rich mixture burns faster.
Remember this distinction – it’s a key factor in ignition timing.

Back in the cylinder, with the piston rising and compressing the air-fuel mixture, the idea is to fire
the spark plug at just the right moment such that the mixture is ignited (starting the “burn”, as the
flame front proceeds across the cylinder) and the rapidly-expanding gases reach peak cylinder
pressure just after the piston reaches TDC (top dead center), exerting maximum force to push the
piston down on the power stroke for maximum efficiency."

John stated directly prior to the above info in his paper that he is not getting into the gory details of combustion theory, but rather just trying to give people an idea of what's happening in the cylinder during the combustion stroke, the effects of spark timing, and different fuel mixtures. (again I'm paraphrasing).

Again speaking GENERALLY, you can assume what the mixture will be under various loads as during idle for example there is a relatively little amount of fuel going into the carb - during acceleration you are pushing down on the gas pedal, opening up the throttle blades, allowing more air in but at the same time this creates a greater amount of venturi vacuum allowing more fuel into the carb richening up the mixture.

Now, for the purposes of explaining to people that are new to setting timing to their cars lets look at a bit of what you wrote:

"Unless one measures the exhaust gas we have no idea what side of stochiometric we are (are we lean, or are we rich), nor do we know what the carb does (A/F wise) over load/RPM. The vacuum diaphram function is to change the advance due to cylinder air density, not fuel richness. Otherwise, an engine with a carb (or fuel injection) that maintained an A/F ratio of 14.7:1 over the RPM/Load range would not require a vacuum advance to modify the timing even as the manifold vacuum or cylinder pressure changed."

To be perfectly honest I don't even understand half of what that means (I did claim at the beginning I was no expert!). What in the word does stochiometric even mean?
Since I don't even understand the word (I didn't bother to look it up yet) I won't try to debate you or to say if you are right or wrong but just assuming you are correct it's still confusing for people that are not experienced in this work. If I read that before I started to learn how to do this stuff myself I may have never started!

on the other hand, The simple ideas that under little or light loads the mixture is lean therefore the timing must be advanced and under loads such as accelerating the mixture is richer therefore the spark timing needs to be less advanced generally holds true and is easier to follow and understand (at least for me because I'm thick-skulled).

I appreciate the feedback to my post and the additional information (i'll go look up that word now ) but take into consideration the overall purpose of the post. It's to give a general and working explanation of typically what's happening during the motors operation and how that effects the requirements of timing to help explain why timing must be advanced or retarded by the distributor and vacuum advance systems in addition to just the basic 1, 2, 3 steps on setting your timing.

If I cut too many corners to make the overall picture easier to understand than the mistakes are mine.
As I stated in the original post - all the information basically came from John Hinckley's and Lars papers. Everything correct is credited to them and any mistakes are mine alone.

 

Good info...thx Barry and others

 

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Quote:

Originally Posted by BarryK

The post was written and intended to help answer and explain the overall process of what timing is and how to set timing on your car.......................
Now, having said that, the following is taken straight out of John Hinkley's tech paper on Timing called "Timing101".

[I]"Fuel/Air Mixture and “Burn Rate”: At idle and steady cruising speed, the load on the engine is
low, and the air-fuel mixture is “lean” (more air/less fuel); when accelerating, the load on the
engine is higher, and it’s fed a “rich” air-fuel mixture (more fuel/less air). These are two very
different conditions, as a lean mixture burns relatively slowly, and a rich mixture burns faster.
Remember this distinction – it’s a key factor in ignition timing.

I'm not trying to assign blame. I'm just trying to correct a misperception in the function of the vacuum advance.
Concluding though, I greatly appreciate the courtesy you've shown in your correspondences. (69427)