OK I think I am on the same page now. It gets a bit confusing when some numbers are half and others whole degrees.
I understand that anything over 12 deg initial will make idling difficult. And if you HEI is 20 mechanical I guess getting it to 38-40 degrees total is going to be difficult.
I await with interest your conclusions and remedies, please keep us all informed.
Steve. How's it going? I think I have this figured out. 1,535,643 websites and forums late. Now, I'll tweak it tomorrow, but this is what I've discovered.
1st; TOTAL advance is very important for a properly running car. Newer cars have computers and do max out the advance, but that's not what we are working with. So we have to do it manually. Here's what I've found out. At least for the 289. For total advance, based on compression. The higher the compression of the engine, the lower the max total advance can be. Plus, the higher the compression, the higher the octane in gasoline should be. But that's a different topic. Here's the total advance numbers for a 289. If you have the 302 or 351 the numbers will be slightly different. I haven't looked them up.
9:1 - 9.5:1 = 38-42 total advance
9.6:1-10.5:1 = 35-38 total advance
>10.6:1 = 31-34 total advance
Being the haynes says my car is at 9.3 compression, I will split the difference on the total advance, and say 40 for mine. (Plus it's an easy number to work with)
1) Set static initial timing
2) Know what the mechanical/centrifugal timing of the distributor is. I have found that about 90% of all HEI distributors are fixed at 20 degrees of advance. The paper I have is generic so it may not be accurate when it said 23 degrees. I am going to assume 20. It's actually easy to check. After plugging vacuum line to vacuum advance, and setting static timing, check timing at high RPM when it reaches max advance and doesn't go higher even with higher rpm. The difference between highest advance and static is the mechanical. Assuming mechanical/centrifugal is pretty much fixed, it doesn't really matter.
3) Hook back up vacume line and check advance at high rpm again to see max. You want it, in my case, 38-42 degrees.
Here's where the adjustments come in. Assuming I set my static to 6 btdc like the book says, add the 20 for the mechanical (I tested it and it came out to about 26 btdc so it is probably close to 20 degrees). If vacuum isn't bringing it up to 38-42, then I can adjust my vacuum advance up or down as needed. It just uses a small allan wrench in the vacuum tube hole where the vacuum line went.
Of course, you could make up the difference with changing the static. But we know that we can't go too high because the engine doesn't like that at idle. PLUS, this is somewhat important, to ACCURATELY set static/idle timing, we should connect a vacuum gauge to the manifold vacuum port. The one that goes to the PCV valve. Then, adjust the static/initial timing for MAXIMUM vacuum. Then, whatever that is, plus the mechanical, plus the vaccum advance on the distributor, should be in the 38-42 degree range. If it's too high or low, adjust the vaccum advance on the distributor with the allan wrench accordingly.
The only caviat would be if the vaccum advance on the distributor wasn't adjustable, OR you didn't have a vaccum advance. (Some don't). In these cases, you could make up the difference eith with static/initial timing, or changing the weights in the distributor.
Even though I am using an HEI distributor, timing is still timing and is the same even for an original dizzy. I wouldn't even worry about mechanical unless you didn't have an adjustable vaccum advance on the distributor. Then you would need to know.
Swapping/Adjusting the springs will just bring up the advance of the mechanical at a lower or higher RPM depending on how stiff the springs are.
So, tomorrow, until I can get a vacuum guage, I will probably split the difference on base static/initial timing, and set it for 8 btdc. I will then check the total advance with the vaccum on and adjust the vacuum advance on the distributor to give me my 40 degrees btdc that I am looking for.
If I am in left field, please let me know. Also, this method, assuming you have an adjustable vacuum advance, allows two place to peak/tweak the engine and compensate for predetonation/pinging. I.e. Idles fine but pings at high RPM, don't adjust static/initial timing, adjust down the vacuum advance so there's not as much advance at higher RPM. If it idles poorly but runs fin at higher rpm, adjust static/initial, and readjust vaccum advance higher or lower to bring back total.
The only thing I still find weird is the vacuum line issue. With a lot of the chevy's they mention the manifold vacuum (The one out the back going to the PCV valve). Some people in the ford community is also mentioning using that. I don't quite understand that, because the vacuum is only there during idle. At higher RPMs, the vacuum eventually reaches 0. Most people say to use the ported vacuum that increases vacuum as rpm's go up. The one on the passenger's side of the carb next to the choke. Metal tube. Use the manifold for the PCV.
Anyway, that's what I've found out. I think I understand it and agree with it in principle. That explains why there's only 20 degrees of advance on the mechanical. On a distributor without vacuum advance, you'd probably find 15L or 18L weights. Times 2 would be 30-36 degrees of advance. Plus the original 6 for static/initial would be 36-42. Anyway, let me know what you think. I am going to go to checkerauto tomorrow and see if they loan vacuum gauges or if there's one for not too much money. Then I can set my static/initial off of the manifold vacuum and set the vaccum advance on the distributor up or down as needed to max out at 40 degrees. Thanks for all the help and getting me thinking. Later... Mike....
It's going fine down here apart from the fact that it has rained every weekend since May and I am starting to get cabin fever.
As far as using the vacuum advance to compensate for a lack of total advance I think this is off in the wrong direction.
For maximum fuel efficiency the vacuum advance should be connected to the timed port on the carb, this port provides no vacuum at idle but comes in not far after.
The vacuum advance is not a constant value, and is designed with fuel efficiency in mind, the way I like to think of it is as a load dependant device. When the motor is working, perhaps towing or driving up a hill the vacuum advance kicks in. The function also works in the lower rev range for general acceleration for max fuel efficiency. These examples are when the motor is providing large amounts of vacuum.
Shelby took the thing off his HIPO cars as he didn’t care for the fuel efficiency, and as a high performance car lives in the higher part of the rev range I guess it was almost irrelevant.
As the engine climbs through the rev range and plateaus the vacuum provided by the motor to the vacuum "can" is not enough to have an effect on the unit and therefore does not have any impact on "total advance" at this point.
I think the direction I would be off in is to look for a kit for the dizzy to change the total advance to get closer to what you are looking for.
I tried to use the Vacuum advance to compensate for timing issues I was having with the old 289 motor, but it is like trying to catch eels with your bare hands.
Hey steve. Yea, I'm not too sure on the vacuum. I still think there is something there, but I just can't figure it out. It appears that just about all HEI distributors have a mechanical advance of about 20 degrees and a vacuum advance can. If not counting the vacuum advance, you'd need almost 18 degrees of static advance to get to the 38 degree total. This is obviously too much initial advance. Back in the day, there was no HEI and vacuum advance wasn't really adjustable. So, applying what's available now to then might be off base a little.
I used a vacuum guage to set my static/initial timing. (I found a gauge in all my crap). I adjust static for max vacuum, then backed it off about 2 degrees. While I was at it, I readjusted my air/fuel mixture for max vacuume. So much easier than with a tach. Anyway, after backing off 2 degrees from max vacuum, my static/initial timing is right at about 10 degrees btdc. That would give me a total, just static and mechanical, of about 30 degrees. With just about every article and post mentioning the HEI mechanical of only being around 20, there has to be something with the vacuum advance can on the HEI. Without vacuum, I've checked total timing at RPM, and it is indeed about 30 btdc.
Now, the ported vacuum line definitely hold vacuum even at high RPM. Of course, this is without a load. I thought that adjust the vacuum advance can all the way CCW was suppose to turn OFF vacuum advance, and the more CW you turned it, the more vacuum it would provide. All the way CCW still allows the vacuum advance on the distributor to advance. With the distributor cap off, I adjusted the vacuum advance full CCW and using the "Suck on the Hose" method (Don't go there) LOL!, I was able to watch the distributor advance. However, with the vacuum guage in line, it definitely takes a lot more vacuum to initiate the advance when turned fully CCW compared to say 5 full turn CW. I.e. about 8 hg of vacuum required to BEGIN advance when full CCW and only about 4 hg when turned in about 5 turns CW. My vacuum advance holds vacuum fine, so I guess that part is Ok.
So, that is where I'm at. If 90% of modern HEI distributors have 20 degrees of mechanical advance, then there's got to be something with vacuum to make up the rest. Even though I haven't tested the vacuum under load, I have to believe that there is still some vacuum even at higher RPM. The only way to tell is to put a vacuum gauge in line with the ported vacuum line to the distributor and check it while driving. Without a load, the vacuum line connected along with mechanical and static will yield in the 45-50 of total advance. I'm sure that under load and the vacuum pressure lower, it will be in the 38-42 area. Adjusting the vacuum advance accurately is the issue. By default factor settings, my vacuum advance can was set about 5 turns from full CCW. That's where I returned it to. About 4 1/2 turns.
Obviously I'd like to see the timing while driving so the vacuum would be under load and not as high. I'm thinking that there is something else with the total advance timing, or it's a little different using a newer style HEI distributor with vacuum advanced included. We'll keep experimenting. Thx... Mike....
You are digging deeper than i have and teaching me that some of my assumptions may be off the mark, all the reasearch i have done to date was for the points style dizzy.
I would be interested to see the result of the driving test, i don't have a vacume gauge in my car so i can't try this myself.
The link i posted earlier has this to say about vacume advance;
"In other words this is an engine-load dependent advance. This would be a typical situation when climbing a steep hill, or driving at low rpms, light throttle, conditions. In these conditions there is high engine vacuum, so the vacuum signal applied to the diaphragm in the canister, via the hose, will cause a 'pull' effect on the arm, which moves the breaker plate and results in a timing advance. During full throttle conditions there is very little engine vacuum, and thus the vacuum advance does not contribute to total advance.
Vacuum advance is tricky to tune because there is no direct measurement like total. In fact, the reason you must measure initial and total timing with the vacuum hose disconnected is because when the engine is in neutral there is no load, thus the vacuum is high, and if the hose were connected you'd see as high as 60 degrees advance and think something is really wrong! The only way to tune vacuum advance is on the road, by feel, and AFTER the initial and total are adjusted.
In short, vacuum advance was developed to optimize fuel economy and reduce emissions. It is not a bad thing to have on a car which sees a lot of street driving, and in such conditions the engine will perform better with it properly adjusted. However many factory and aftermarket performance distributors do not even come with a vacuum advance. The reason is simply because race cars do not spend much time at part throttle.
You could be correct about the HEI depending more on the vacume to gain a different "total" but the inner workings of the can have not changed as far as i know.
excellent possibility on the octane issue. I've always known that with the higher compression ratio's, that higher octane was needed to eliminate dieseling and predetonation. The lower octane and the addition of ethanol may be a factor. Still, there seems to be a large difference between a stock distributor being recommended to have an optimum advance total of 38-42 and an HEI distributor that even pushing the envelope on the static/initial of around 12-14, only being able to max out total advance of around 32-34. And that's pushing it. Decent range of 6-10 btdc would yield total advance of 26-30. Definitely vacuum advance has to come into play here. There's only 3 ways to advance timing. Past 12 on the static; the car doesn't like it. The majority of ne HEI are stoc with 20 degrees and I haven't really seen any kits for changing the weights. Older dizzy's is common to change weights. There's already 2 different ones built into it just by flipping the weights around. That only leaves vacuum left.
I definitely think that my next thing to try, might be to run a T-connection to my port vacuum line and run my vacuum gauge inside the car and check the type of vacuum available while driving. Obviously this isn't a major important project here. But, understanding "WHY" has always been important to me. I can't just accept things because that's the way it is. I need to know why. So, if vacuum goes low when cruising, then total advance is pretty much static and mechanical. In which case it's only about 30 degrees for me. So, how are we suppose to get to 38-42 with an HEI distributor? I'm also going to start searching for curve kits for HEI. I've seen the dyno tests. Our cars definitely don't seem to get enough advance. The newer computer controlled cars DO GET ENOUGH advance. The computer hold it at the curve. Thanks for working with me here and keeping me thinking. Later... Mike....
Excellent info on different weights for the distributor. And also modifying the stock 20 degrees. Interesting. So, just like with traditional dizzy's and weights, replacing the weights seem to be the answer for getting to the premium advance for your particular motor. I'n still curious about how much vacuum is actually available when driving. I know it says that WOT (Wide open throttle) that there is NO vacuum from the ported timed vacuum tube on the carb. BUT, in reality, we are not racing our cars and therefor almost never run at WIDE OPEN THROTTLE. So, how much vacuum is actually there; and how much of this vacuum is advancing our timing? Things that make you go hmmmmmmmmm!!! Later... Mike....
Just got back after a nice rain free day and a drive into the city with my wife in the old rattlebox.
I put the light on mine, I think I am getting around 20deg of mech' plus the 12 = 32 @ 9.0:1 compression (approx(it is very hard to tell as the numbers are not clear and are on the wrong side of the ballancer)).
My dizzy is a pro-comp brand apparently; I talked to the shop where I bought it and was assured that it's mech' advance is 28 deg’, obviously not so.
It has to be said that this car runs sweet.
But:
I don't know how the tuning guy set it up, did he do as you say tune the vacuum to compensate for this... I have no idea. He had a rolling road type dyno, he certainly had a kit for the carb (600CFM (1405) Edelbrock 4 barrel) but we didn't even get to chatting about the dizzy.
I read something else along the lines of what you were talking about with calculating the total including the vacuum on an HEI but with a variable vacuum environment this must be difficult (slippery eels).
Steve; I got it figured out. I have to admit, I cheated a little and CALLED the company that sold me the distributor. Which also happens to be a speed shop and works on every car known to mankind. "Mostly Ford and Chevy".
Anyway, everything depends on where you get your vacuum. Just about all carbs and such have manifold vacuum of course. That is high vacuum at idle and decreases to nothing (almost nothing) at high RPM. There's also some carbs that have a similar vacuum port on the side for the distributor. Pretty much no vacuum at high rpm's. In these cases, if that's what you use, then you want to go with the combination of weights and static/initial timing to get to your desired "Total Advance". In my case around 38 degrees BTDC. The guy told me all the different weights I can get, along with springs, to do what I want. In this configuration, vacuum gets the advance to the 38 that I'm looking for, BUT as rpm goes up and vacuum decreases, the centrifugal is kicking in and keeping it around the 38. By the time you are at no vacuum, the weights and static timing are doing all the work. BUT, unless you are racing, no one is at full weights and no vacuum. So, it's a continual combination of the two. However, there isn't much vacuum even at cruising, so it's trickier. But you get some full horsepower if done correctly.
If however you want to be more economical and are going for more fuel efficiency, then using a vacuum advance that is progressive as RPM's go up, is indeed a better way. The vacuum port on my carb is that way. It gradually increases vacuum. Not sure of what RPM it maxes out, put the vacuum increases to a point and holds there. In this scenario, the guy told me with the 19-20 degrees that the mechanical in the HEI distributor gives; (He verified my suspicion); and the 10 degrees of static/initial I have; (He verified that too); he said I need to adjust the vacuum advance can, (Being I'm using the progressive vacuum that increases), to give a max of about 8-10 degrees. He said that after adjusting the static, (He recommended doing what I did with using a vacuum gauge to set static/initial and then backing off about 2 degrees. Then reconnect the vacuum advance, and at high rpm (Where timing doesn't go any higher), adjust the vacuum to get the 38 that I'm looking for.
The way it was before, the vacuum advance was pushing me up around 45-50 degrees. So, using the progressive vacuum line (Timed, ported, or whatever it's called. The one where vacuum increases with RPM up to it's max vacuum and holds there); I did the following:
1)Put vacuum gauge on manifold vacuum. (The one that is to the PCV and is HIGH at idle)
2) Adjusted static/initial timing to MAX vacuum. (Distributor vacuum line disconnected and plugged). Result was about 12 degrees.
3) Backed off static/initial timing by about 2 degrees. Result to about 10 degrees BTDC.
4) Replaced manifold vacuum line to pcv valve.
5) With vacuum line to distributor still disconnected, checked timing at high rpm. Mechanical combined with static was about 27-28 degrees.
6) Reconnected vacuum line to vacuum advance can
7) At high RPM checked timing. It was about 45-48 degrees
8) Adjust vacuum advance can CLOCKWISE (Some have less vacuum if screwed in clockwise, so less vacuum counter clockwise. Mine reduces if screwed in clockwise).
9) Adjusting is trickie because the can is spring loaded and you have to push in on the spring with the allan wrench after turning to find the lock spots where the springs stays IN. If it pops out of it's groove, you get full vacuum. Easy once you do it. Different vacuum advance cans can be different.
10) Went back and forth adjusting, putting vacuum back on can, checking timing, etc... Until I got to around 38 degrees at high rpm.
After doing that, I IMMEDIATELY noticed that the throttle response on the carb went from "This is good" to "OH MY GOD" mode. Quick!!! Took it out for a quick 10 mile drive. I definitely had to watch my foot on the pedal. I also noticed THAT MY ENGINE IS RUNNING COOLER!!! That was another issue. I still need to get a shroud, but on the way home from work today, it was getting a little warm like it always does. Between the "M" and "P" in the word TEMP. After this vacuum timing adjustment; on the same road to and from work, it NEVER got past the letter "M". For me, it's noticable.
I probably need to tweak a little bit to get the timing exact where I want it, but I was so excited I wanted to get in and post this. This is not a plecbo effect. I've worked on a lot of cars. Just never had a vacuum advance that was adjustable. Plus, using manifold vacuum on other cars made the vacuum advance not much of an issue at cruising altitude speeds. I can honestly say that the car runs smoother cruising 50-70 mph. Didn't hit the interstate or I would have tried faster. The response from a stop is MUCH quicker and smoother. Shifting (Automatic) from 2nd to 3rd seemed smoother. (That could be plecebo). Temperature was cooler. (That's an issue I was very noticeable of and that is not plecebo). And I'm sure that I will probably get better gas mileage. (One of the main reasons).
Timing is indeed everything. Someone may think what I wrote here is wrong. I don't think it is. The vacuum line I use is the one on the side of the carb that increases vacuum as the rpm increases, until full vacuum pressure. That must play into affect on the total timing. The MAX advance the adjustable vacuum advance can provide (At least the one I have) is about 24 degrees. I'm assuming the FIXED vacuum advance on stock distributors are probably set for around 8-10. That would make sense with a traditional 6 BTDC static, 2 10's of weight, and the 8-10 vacuum bringing it to about 34-36. Switching the weights around to 13 on the older dizzy would bring advance to 40-42.
Anyway, this is what I found. The techs at the shop I bought the distributor from explained it all to me. It sounds right. I did it their way and it runs so much nicer. Obviously there are a couple of caviats with different HEI distributors. Different size weights, static timing, clockwise/counterclockwise vacuum advance port, which vacuum line you use. So, this is where i'm at, and I seem pretty happy. AT LEAST TODAY. LOL!!! Mike....
An absolute inspiration to us all Mike, they'll probably give you a sticky for your hard work or a medal.
I’ll be taking a look at mine on the weekend to see how the vacuum has been set to see if there is anything I can to do to get a little extra “Oh my god”.
I am glad for all of us that you took the time to figure out and ask “why”.
Thanks Steve. But a lot of this couldn't have happened if you weren't involved. You asked me questions and forced me to experiment. When I came up with a theory, you made me question it and validate it. Without your feedback, I probably would have gone off on a wild good chase. Even calling the techs at the distributorship where I bought the distributor, I probably would have been confused and slightly frustrated had I called them prior to you and I brainstorming back and forth. I'm an electronic engineer by trade, and you helped me understand this the same way I would have attacked and electronics/telecom/data issue. Thanks....
With the older original dizzys that come in these cars, it's much simpler. Even with the stock vacuum advance and distributor, you are close with timing if you adjust static/initial by the book. You'd have a total of 34-36. Tweaking with static or weights could get you another 4-6 degrees and improve performance. That's why the majority of dizzys have the 10-13L weights in them with a vacuum advance. The tech said that without a vacuum advance, you normall have 15 or 18L weights in the dizzy. Again, getting you 36 to 42 degrees. Again, what you're wanting.
Only when it comes to the newer distributors; especially the HEI and others that have adjustable vacuum advance that you start having issues. These distributors are built for a variety of different cars. The shaft/gear assemply is about the only thing that makes it car specific. I can go and buy replacement parts for any GM HEI distributor from the traditional 1974-1986 design period. That means the weights and vacuum advance had to be such that it could work on many different cars. Including chevy's that like 12-18 degrees of static timing. Hence the reason for an adjustable vacuum advance that can do up to 24 degrees of advance. Not knowing about TOTAL TIMING, I was idling fine and running "OK", but I was doing it at about 45-50 degrees of TOTAL ADVANCE TIMING. Some of the chevy specs I looked at showed this to be normal for them. Supposedly not so for my ford. Dyno tests show 38-42 to be optimum. Even a little less.
Fortunately, since putting on this distributor, I haven't driven more than maybe 100 miles. Not much at very high speeds. Doubt anything bad would have happened with the engine, but running it 10 degrees too advanced is probably not the healthiest. Again, it was your questions, feedback, and encouragement that helped me understand and research. Like I said, I might be off on explaining part of the "Details"; but the how and why I understand. So, thanks again. Hopefully anyone using a newer HEI, or even those using a traditional points distributor; whether they have adjustable or fixed vacuum advance, can be helped by this explanation and can tweak their ford better. I'm pretty sure that all the standard fords of the time; 289,302, or 351 lived with the same total timing. Of course, compression and fuel play a part in it. As does all mods like a new cam or such. In those cases, I have absolutely no idea what TOTAL TIMING ADVANCE should be. But once you research and know what your total advance in timing should be, the rest is easy. Points, HEI, adjustable, or fixed vacuum advance. Thanks again.... Later... Mike....
It pretty much says what was told to me and what I am now doing. I guess there are pros and cons to the manifold vacuum method, and therefor would require different adjustments. Plus, cruising speed would be difficult because unless racing, you are never at a WOT with no vacuum.
The important parts (And this is for a dizzys in general) are;
.....At idle, there should be no vacuum to the vacuum advance because the throttle plates are closed. Vacuum-advance units get ported vacuum, which means only when the throttle opens. As the throttle opens, a working vacuum advance begins to get ported vacuum, which enables it to move (advance) the breaker plate. Theoretically, as engine rpm increases, the vacuum advance should hand off its job to the mechanical advance, which is affected by increased engine speed. .......
......To get it right, dial in mechanical advance first, then fine-tune the vacuum-advance unit's rate of advance......
.....Aftermarket vacuum-advance units typically employ an Allen screw inside to control advance rate. Turn the screw clockwise to slow the advance rate; turn it counterclockwise to quicken advance rate. To understand the effect this tuning has, use a timing light and watch the timing mark as you open the throttle....
.....Ignition timing needs to be checked and tuned at least two different ways. First, static ignition timing should be checked with the vacuum-advance hose disconnected. Follow factory specifications for initial timing. Small-block Fords are typically anywhere from 6-12 degrees before top dead center (BTDC). Six-cylinder engines are 5-6 degrees BTDC....
.....With the vacuum advance reconnected, check total timing, which can be done two ways. Total timing is checked at 3,500 rpm with the vacuum advance connected. Ideally, push for the maximum number of degrees before BTDC without detonation (pinging or spark knock). In most circumstances, total advance should be 34-36 degrees BTDC........
(Of course, this number depends on engine compression ratio, grade of fuel, etc... Depending, it could be 34 to 42) See my chart in the previous posts.
Adjust the initial timing to what you engine likes, then simply recurve the distiributor to get the total. Vacuum advance does not count, it should be plugged when checking. Add only initial and mechanical advance.
Now, I'll tweak it tomorrow, but this is what I've discovered.
