77 zz4

I found and fixed a vacuum leak last week. But now my timing seems to be off. I thought it was @ 36 total, but now its at 26* at 3300 rpm. This was all checked with the vacuum canister plugged.

1. Did the vacuum problem cause this?

2. Will I increase my total if I increase my initial?(now at 11*)

3. What if I connect the vacuum can and then set the initial timing? Will this help me get *36 total?

4. What springs do I need for the dist. to get 36* total?

BarryK

1. probably

2. yes, but that's not the correct way to set total. check and set total by chaecking total and setting total when it's all in, not by setting initial and just hoping for the best

3. not the correct way of doing it! diconnect vacuum hose off can and plug hose. set total timing for 36º. do NOT try to set 36º total with the vacuum can hooked up or your timing will be off by the amount of the advance your can is spec'd for.

4. it will vary depending on the curve you need. it's mainly trial and error to get the mechanical advance to come in soon enough (between 2500-2800rpm) but not too soon. Too stiff of a spring and it will come in too late, too loose of a spring it will come in too early. All you can do is try a number of springs and see what it requires.

BTW, did you read John Hinckley's tech article called MAPPING ADVANCE.pdf on my website that I referred you to last week in your other thread? He will take he step by step on setting up your distributor properly and when you are done it will be correct.

77 zz4

Thank you for the info. I will read it this weekend. As far as the springs are concerned, is it possible for someone to automatically know which springs I need if they know my engine (zz4 with stock HEI)? Or is it on a case by case basis?

Kalway

Simple way to do your timing.

Get an HEI recurve kit from NAPA, install the softest springs it comes with. Rev your engine to 2500 rpms and twist it till you get 36 degrees with the vacuum disconnected from the distributor. Lock it down and hook up the vacuum and see what you're at with it idling. It'll probably be like 16 degrees or so.

Simple as that. Don't install the weights that come with the kit. It's easiest to do with a timing light with a dial so you just dial it to 36 and twist till the little mark hits the center of the V.

Generally it's trial and error on the springs, but most of the time you just need the 2 softest ones. That's what mine took and it's a Procomp HEI that's under a year old.

BarryK

yes, that's the simplest way, but it leaves way too much margin for error. just setting the motor at 2500 and than setting total at 36º isn't allowing you to see just WHERE the timing is coming all in by. What if with the softest springs the timing is coming in way too soon, say by 1500 or 2000rpm? Having it all in too eary can cause detonation problems. Also, if the springs are too soft than the mechanical advance can start to come in even at idle speed which is not wanted.
Also, by omly taking the motor to 2500rpm you are also not checking to see if the timing is still coming in more at a higher engine speed which means you are setting for 36º before it's all in so it will be too high at total once it IS all in - again risking detonation problems.

sorry, there is usually the simple way or the correct way to do things and personally I'd rather take the extra few minutes and make sure things like timing are done correctly. Timing is critical to make sure that the car runs right plus if it's off the risk of detonation that can destroy pistons is too great.

77 zz4

How about this as a solution? I posted a similar question regarding my zz4 on a zz4 related board to a zz4 engine builder. This was his reply:

Andre,
Set your base ignition timing at 12º with the vacuum advance disconnected. Set your idle to about 700RPM. I wouldn't run the vacuum advance pod that comes on your ZZ4's HEI distributor. It gives you 20º of additional advance, and has a very light spring in it, so it starts coming early, and fast. Purchase either an adjustable unit, such as the Crane or Moroso unit, or a GM HD unit P/N1973681. This is a 10º pod, and has a heavy spring. Make sure that your vacuum advance is hooked up to ported vacuum. If your car is primarily a street rod, and you don't do a lot of highway driving, I would recommend not using a vacuum advance at all. If you choose to go this route, set your timing at 36º total, which usually is about 15º initial timing.

What do you think?

BarryK

First, if he actually replied that he recommends not using a vacuum advance at all on a street driven car, than he has NO concept or understanding of what the vacuum system does or how it works and has no business being an engine builder.
People don't run vacuum advance on race motors because race motors are typically almost always at WOT and the vacuum advance is useless but on a STREET driven car there are many, many benefits to the vacuum system. Believe me, GM didn't design the system and install it just because they got a good deal on vacuum cans one year.....

Second, if he also recommended hooking the vacuum advance upto a ported vacuum source rather than a full manifold vacuum sounce than yet again he is showing that he does not understand how the vacuum system operates.
Ported vacuum was designed for one reason and one reason only - emissions requirements. The car companies were required to lower the hydrocarbon emissions and one way they did it was to retard spark advance at idle hence the reason for ported vacuum.
Ported vacuum is good for lowering emissions but it's lousy for performance. It also has the added disadvantages of poor idle characteristics, reduced throttle response, hotter operating temps, and lower fuel economy.

now, based on this, why would anyone that actually understands the way the vacuun system works recommend not running a vacuum advance system and if you are running one recommend using a ported vacuum source?

I wouldn't listen to a word of advice this guy gave you.

I'll say it once again.......... read John Hinckley's tech articles on timing and mapping advance and read Lars timing paper and vac adv spec paper and you will learn the CORRECT information.
Getting responses by idiots like that ZZ4 engine builder is worst than useless, it's downright wrong information and is doing nothing more than confusing the issue.

77 zz4

Can you believe he is the "lars" for that website. People treat him with the respect that we treat Lar's on this forum. How could he be so off?

Kalway

Ok I left a few parts out. Usually with the softest springs it'll be all in by 2500 rpms, and your initial will usually land around 16 degrees. This is just my experience. I had my timing set by the Corvette shop a week ago, just so I could see it done by a professional with my own two eyes before I do it myself next time.

77 zz4

So, NAPA will know what I'm talking about? Just ask for the re-curve kit, right?

swensonm

not trying to highjack the tread but....I am lost I am a shadetree novice.
I always just unhook the vac advance and set timing to what ever the book lists (8 degree) engine idle 800-1000. What am I missing..I realize that you guys are Perfomance type guys ....just trying to learn...
Mike

BarryK

they should know, or a good local speed shop.

If you can't get it at either place local try Summit or JEGS

BarryK

Mike

what you are setting is the initial timing. That will work IF, and only IF you know as a definite fact that your distrivutor is set up perfect, the mechanical advance is coming in when you want it to, for as much as and not more than you want it to, and that the vacuum can is adding the correct amount.
If you don't know positively all these things than by only setting initial timing you are letting the total timing fall where it may and that can cause you anything from lack of performance to downright risk if the total timing is too high. Timing too high (too advanced) is the cause of detonation and detonation will destroy pistons.

Many people like to take a simpler route to timing and many times it works just fine but it's actually the reverse of what you are doing.
Unhook the vacuum line off the vacuun can and plug it but rather than setting initial timing you want to set TOTAL timing.
Bring the rpm's of the motor up until the timing is all in and set it for 36º. Instead of setting initial and letting total timing fall where it may now you are setting total timing and letting initial timing fall where it may.
In it's most basic, easiest form that's all you need to do although I'd recommend going through the entire timing process if you haven't done so recently or ever to see exactly what your distributor is doing and whar mechanical advance, initial timing, curve, etc that you really have.

Also, you do have points or an HEI distributor? If you have points, have you checked and set your dwell recently also? Always recommended do before setting timing.

Lars paper on timing is an excellent paper to read and he usually goes by the method of "setting total and letting initial fall where it may". Again, if you already know as a fact just what exactly your distribtor is doing and how it's set up it's an excellent method and will get your car running correctly in a few short minutes.

If you haven't gone through your distributor in a while or never, than an even more detailed paper that will take you step by step to mapping your distributor is one by John Hinckley.

also Lars has the best paper i've run across on explaining the vacuum advance and selecting the best one for your car along with a list of the different vacuum cans and their specs.

John also has probably the best tech paper on just explaining the basics of timing and what it really is, how and why it changes at different rpm's and loads on the motor, and explaining all the terms, etc.

If you are interested in reading them they are on my website tech articles page here:
http://69.253.166.197/page1/page65/page65.html

the articles you should download and read are these 4 especially but you are welcome to any of the articles on my site of course:

Timing101Article.pdf by John Hinckley
MAPPING ADVANCE.pdf by John Hinckley
Lars timing .pdf by Lars Grimsrud
Vac Adv Spec.pdf by Lars Grimsrud

swensonm

I wont bother this tread any more but....
Is it advisable to switch a points ignition to pointless with one of the kits you can get at auto zone or ecklers?
Mike
Again thanks for the great info

BarryK

you will get varying opinions on this.
In my opinion NO, it's not worth it.
Others will disagree and claim they benefitted from the electronic conversion.

My point of view is this:
By changing out from points to an electronic conversion kit the only thing you are doing is swapping out a switch from an electro-mechanical switch (points) to an electronic switch (the new breakerless kit). You do not gain any additional spark activity or increase the power of the spark in any way. The ONLY beneifit you really gain is that you no longer need to adjust dwell any longer but personally I find that takes me all of 2 minutes once a year during "tune-up" time. I refuse to spend $160 to save myself 2 minutes of labor a year.
Keep in mind that 99.5% od people running a points style distributor NEVER do any maintainace on it ever. They may change points now and than and may set timing but other than that as long as the car runs the distributor is a "forgotten" item in the car. GM never even specified any maintainace requirements on it at all!
Many, many cars are still driving around with the original distributor in them that has never been touch, rebuilt, serviced or anything in 40 years and yet it still works. Although it may still work and runs the car, that doesn't mean it can't use a little attentiuon every now and than.

Than what happens is that the car starts to run a little rough so people think about the distributor and figure if they put in a Breakerless electronic conversion kit it will help the car run better and in many cases it does. Why? well, one thing that happens os that as the distributor is used and gets worn the tolences get looser than spec. endplay on the main shaft causes dwell to flucuate and when dwell flucuates so does timing. If the timing flucuates than the car doesn't run as well as it should. Follow me so far?
By installing an electonic conversion kit there is no longer any dwell to flucuate and so yes, the car probably will run better with the kit BUT if they just took the time to service the distributor properly, shim it up to correct tolerances and installed new points and condenser guess what? Yep, it would also run better - the same amount that the kit just achieved and instead of $160 for a kit you only spend $10-$20 on new points and condenser.
I'd wager good money that the vast majority of people that claim better performance or a smoother running car once they installed the kit would have seen the identicle improvement had they simply serviced their distributor to correct specs and working order and still stayed with points. Basically the kits can mask a problem on a distributor that needs service, but overall the problem is still there.....

also, while many people can run these kits for years with no problem I've also seen many threads of people having failures with them. I'm very convinced that of the percentage installed, there is a much higher failure rated of the conversion kits than there are with points.
Points usage dates back to when the points ignition system was first invented in 1912 and first used on Cadillacs. Points are VERY reliable and time tested.

Last point is that IF you ever had a failure with a set of points most people keep aspare set in the car and can change them out in a few minutes and get on their way. If the electronic kit fails you are stranded waiting for a flatbed unless you plan on keeping a spare $160 kit in the car with you or at least a spare set of points. Now THAT would be classic and ironic - having a electronic kit fail and having to swap it out with "old" points to get driving again. Would make you wonder why you bothers in the first place huh?

The electronic kit fans and users can start flaming me now.......