Smokehouse69

I got a chance to try out my new Sears Advance timing light today, it verified what I had seen with my old timing light, I have 12 degrees advance at an idle of 650 with the vacuum advance disconnected and plugged. Reving the car up to 2500-3000 rpm the advance light showed that the mechanical advance took the timing to only 28 degrees. With the vacuum advance hooked up at idle the advance stayed the same but at 2500-3000 rpm the total advance both mechanical and vacuum was about 47 degrees.
It looks to me that I don't have the best advance curve with the HEI distributor that came with my ZZ4.
Anyone have any ideas on what I need to do it get more advance into my distributor? I was looking for a total mechanical advance of around 36 degrees at 2500-3000 rpm. Am I looking at something wrong?

Smokehouse69

I found Lar's articles on setting your timing and discovered that the problem is with the stock springs in the distributor, who sells lighter springs for the HEI distributor? It seems like I have seen them in parts stores, but since I wasn't actually looking for them I don't know if I imagined it or not.

Pedro'74

Steve,

You can find a Mr. Gasket kit at Autozone or other chain stores, in the "performance" (="chrome dress-up" :D) section.

-Pedro

Smokehouse69

Thanks Pedro! I knew I'd seen them somewhere.

Gordonm

To check and see how much total timing the distributor will allow take the springs off totally. Start the car and just rev it a little. This will tell you how much total timing the dist will allow. The timing will not return back due to no springs but then shut it off and put the springs back on. It does not matter how light the springs are if the dist. does not allow the advance cam to rotate far enough. This allows you to check total timing without having to rev the motor up.

Smokehouse69

Thanks GOrdon, after reading all of the Lars tech papers I was going to do that. I know that "fastburn" and Vortec headed engines perform best with a little less total mechanical advance than other heads, but I don't think the L98 aluminum heads on a ZZ4 falls into that category, so I'm still shooting for 36 degrees total mechanical advance.

Vetterodder

Your distributor may not be reaching full centrifugal advance until well over 3000 rpm. I'm not sure of what a ZZ4 dist is set at but many stock HEI's don't reach full advance until well past 4,000 rpm. Readings taken before the distributor has fully advanced will be bogus because the distributor hasn't stopped advancing yet. I think 36º @ 2800 would be a good starting point for your timing but it will probably require a spring change to get full advance at that rpm.

theandies

I don't run the stock ZZ4 HEI unit, I have a MSD tach drive distributor on my ZZ4. I am running 10 degrees at Idle with the vacuum advance disconnected (connected to ported vacuum source so I have no vacuum advance at Idle or WOT). My total mechanical advance is 34 degrees with a very aggressive curve. Total advance is in by 2600 RPM. I have played with different spring and have found this to be the best performing combanation. If I advance my total avance any more then my engine starts to ping. You will know when you hit the best timing for you individual engine because it will definitly wake it up some.
John

Smokehouse69

It appears that the stock ZZ-4 HEI distributor will not allow more than 28 degrees mechanical advance, no matter what springs or weights you have. With my springs off, the mechanical advance would only go to 28 degrees. A Buddy of mine had a Mr. Gasket spring and weight set which we tried, I told him it would do no good, but it is a nice day and he wanted to get out of the house, so we tried it. They behaved exactly like my stock weights and springs, and the only thing we accomplished was to loose one of the the clips that hold the weights down. Now I have to go searching for one of those little blastards.
Anyone heard from Lars lately? Or does anyone have any ideas on how to recurve an HEI that limits mechanical advance? I might be going back to my old distributor and the Pertronix if I can't find a solution pretty quick.

Gordonm

Not sure on a HEI but on mine there is a pin on the dist. shaft that fits in a slot on the plate the weights are on. If you are not getting enough advance the slot is not big enough. I was getting to much advance because the slot had elongated. They welded up the slot and adjusted to get the proper advance. It might be as easy as taking a file to the slot and making it longer. The problem is it is trial and error so it might take a few times to get it right. The HEI should be similar but I'm not sure.

Vetterodder

As Gordon posted, the springs don't affect the total amount of advance, only how fast it comes in. Distributors have a set amount of mechanical advance but, as Gordon said, the amount can be changed. The procedure varies among different types of distributors but I'm sure that Lars will be abe to advise you on yours. If you are only getting 28º total with 12º initial, your distributor is only allowing 16º mechanical advance, which seems pretty low to me. Did you check to make sure that you were reving it high enough for all the advance to be in? As I mentioned previously, most stock type distributors don't reach full advance until well over 3,000 rpm, some well over 4,000 rpm. I've set up my MSD with 25º mechanical, 12º initial, for a total of 37º by 2500 rpm and it works great.

Smokehouse69

No, I started it without springs and the total advance never got past 28 degrees. Maybe I'm doing something wrong, but with the adjustable timing light at idle I have the dial set at 12 degrees and the timing lines are lined up. Then at 3000 on up to 5000 it will only get to 28 degrees on the adjustment dial. As the engine revs up it is like the timing advance hits a brick wall at 28 degrees. I'm assuming that the slots in the mechanical advance won't allow the unit to go up past 28 degrees. I'm going to try and get a hold of Lars and see if he can offer any wisdom.

Vetterodder

If you have the timing light set to 12º and you get a reading of 28º, your total is 40º. With the light set at Oº, your timing marks should line up at the 12º mark at idle (assuming that it is set at 12º initial). Back your initial off to to 8º, set the light at zero, and it should read 36º once fully advanced.

page62

It's good to see you're going through this learning curve. 'Cuz when you get to S.A., you can help me install my Lars' recurve kit! :cheers:

Smokehouse69

Ok let me see if I have this straight, if I have the timing lines lined up with the dial set to 12 degrees at 650-700 rpm, then increase the rpm to 3000-4000 and increase the dial to 28 (to keep the timing marks lined up) then my total timing is 40 degrees? If that's the case I_REALLY_AM_A_DUMBASS, no wonder I was a liberal arts major, this timing stuff really is to obtuse for me. :D
Page, as one liberal arts major to another, if we both work on your car, it'll probably never run again! :lol:

Gordonm

That makes much more sense to me. Most of the time as in my case the timing gets to be more than 38 due to wear in the slot. I have never seen a dist. that has only 16 degrees of mechanical advance. Mine was giving me 12 initial with 58 degrees total before having it fixed. It only had 50K miles on it also

page62

No, you're not a d_u_m_b_a_s_s! If the timing mark is truly at TDC and your light is set to 28°, then what you see is what you get. I may have been a liberal arts major in another life in another country, but 2+2=4 no matter which side of the border you're on! :lol:

Steve, let's get JB down here. Perhaps with 3 liberal arts majors in 1 garage we can invert the equation and make everything work to our advantage! :seeya

Vetterodder

Now you have me confused :). Does your light give a readout of advance or does it just have a dial that you set to subtract initial timing? My previous response was based upon an assumption that you were using one with a digital readout. If using one with a digital readout that has been set to the amount of initial, the figure it will display is the amount of advance there is beyond what you dialed in. If the readings you posted are based upon the marks being at zero with the light set at 28º, then you are indeed getting only 28º. There's a simple way to confirm this (or to set total timing with a standard timing light). Measure the circumference of your balancer and divide that figure by 10. (The circumference is 360º so 1/10th of that is 36º). Put a mark on the balancer that distance from the zero mark (on the passenger side of the mark). With the light set at 0º and vacuum advance disconnected, rev the engine until the timing marks no longer move. Adjust the distributor until the new mark on the balancer aligns with 0º on the tab and you will be at 36º total. Let the engine idle and take a reading to see where your initial is. (On cars with a high idle speed, mechanical advance may have already started and idle rpm may have to be reduced to get an accurate reading.) The difference between the two figures will be the amount of mechanical advance you are getting.

Smokehouse, don't beat yourself up for not knowing something that most others don't know either. We only know what we learn and I don't think ignition timing has ever been a required course in school :). Much of what we do learn comes as a result of a need to know. You just haven't had a need until now but I bet you're gonna learn it real good. Down the road, you'll be helping us with what you learn.

Smokehouse69

My timing light has a dial on the back of it with the range of 0 to 60 degrees. At idle with the dial set at 0, the timing shows to be about 12 degrees advance. If I turn the dial to 12, then the mark at TDC lines up with the timing pointer. If I rev the engine to 3000 + the timing will advance, if I turn the dial from the initial 12 to 28 then the timing mark is again lined up with the TDC mark on the balancer. This is all with the vacuum advance disconnected and plugged. When it is connected to a ported vacuum source and the engine is reved up it will advance to a total of 45 degrees. I have reved the engine up to 5000 and it does not advance past 28 (on the dial) or 45 with vacuum advance connected.

bob

If the pointer and balancer are correct, the way you are doing it says 28 degrees total advance. At least it probably doesn't ping much. Either the springs are really strong or the stops need to be changed. Use the advise of others and take the springs off and see what the stops are set at for a starter.
bob