pav8427

I have a stock 79 H/o that I would like to try to improve the timing curve on.
I am looking at just playing with advance springs.
My timing light is not a dial back and I dont have a degreed balancer.

Stock timing specs call for 20*@ 1100.

After swapping springs, would setting the initial back to stock be the best way to 'baseline' for any changes/improvements?

Since this is a street driven stocker, where am I most likely to feel any
changes I make?

Thanks, Doug

Fun71

Yes, verify the initial timing is correct after swapping the springs.

Changing the springs should not cause the initial timing or the total timing to change; it should just change how fast the mechanical timing comes in.

oldcutlass

If you do not have a dial back timing light leave it alone. Before you can make it better you need to know where you are. You need the right tools to do the job.

z11375ss

I curved my MSD billet without a light. Silver donut under the weights with one silver spring, one light blue spring on top. This combo is supposed to get it all in by 3300(?), with a total of about 37 degrees all in. Had a timing tape and couldn't read it at 3000 rpm. It kept jumping around. Set it to about 12 to 14 BTDC initial. Got in the car and ran it hard. No ping. Advanced it, still no ping. Advanced it until the car had a hard time starting and backed it off a tad to where it would start well. The car really woke up. It had the feeling it was laying over when you whacked it. Not anymore. Instant throttle response. We got back to the house and I wanted to read the timing tape to see where the timing was at initial. The tape had flown off! We LOLED!
The funny thing is that I went back to my roots as a Hot Rodder and used the seat of the pants method to set the timing and it still works. I say, mess with it. What do you have to lose? You have knowledge to gain. It was a fun hour or so with a good friend I wouldn't have had if I hadn't tried. Get a dial back before you jump in though. Just in case. Oldcutlass has wisdom.

Intragration

I would recommend going the full aftermarket weights/springs/center plate route, along with reducing vacuum advance. You can get maximum mechanical advance in more quickly with lighter springs and factory weights, but you really want to be shooting for around 35 degrees maximum for best performance. A worst-case scenario would be using factory weights that don't allow a high enough maximum, and then springs that are too light and allowing some advance at idle, in which case all you'd be doing is more quickly getting to a greatly reduced maximum advance.

First of all, if you're a DIYer, you can make your own degree markings on the balancer. My suggestion is to do this based on the actual dimensions of the balancer, as opposed to using the existing tab as a template, the markings on mine were way off from actual.

The ideal setup for mechanical advance is around 35 degrees total mechanical at about 3k RPM, letting initial advance fall where it may. (You might be able to go a little higher with a low-CR motor. Beware of detonation, and dial back a little if you encounter it.) The aftermarket weights and center plate will allow you to get to this, but you'll also want to use stiff enough aftermarket springs (still lighter than factory) to not be into advance at idle. While you're at it, make sure everything advances and returns smoothly. Decades of neglect usually leads to gummed up components which need to be cleaned and lubed to work properly again. You might need to remove the distributor to do this correctly. This applies to factory OR aftermarket weights and center plate.

When increasing your maximum mechanical advance, you also want to restrict your vacuum advance to no more than 10-12 degrees, you can do this with an aftermarket vacuum advance solenoid, or you can make a restrictor for the stock one out of a small piece of aluminum.

Doing all this on my motor led to a very noticeable improvement under pretty much all circumstances.

Fun71

I agree with all you posted except this:

My experience with an HEI distributor off a 78-79 403 was the factory weights and center bar, coupled with aftermarket springs, allowed ~18º initial advance and 36º total advance, which my engine really liked. The aftermarket Moroso HEI Advance Curve Kit had wieghts and center bar that gave 24º mechanical advance (same as the factory points distributor) which left the initial at ~12º that didn't work well with my engine. The idle vacuum was a bit low and bouncy and idle speed dropped when the AC was turned on. The higher initial with the factory HEI center bar/weights had higher vacuum and idle speed and the idle RPM didn't drop with AC on.

Intragration

You're right Fun71, thanks for pointing it out. I had forgotten that there was a specific reason I needed to go with the aftermarket weights and center plate. The factory ones didn't provide a wide enough range for me. With 35 degrees total and at around 10:1 CR and a factory starter, initial ended up too high to allow easy hot starts. I needed the aftermarket ones to maintain 35 degrees total and still have an initial setting below 15 degrees. I should have said "The ideal setup for mechanical advance is around 35 degrees total mechanical at about 3k RPM, letting initial advance fall where it may, provided it is in a range that works. If initial is too high, THEN you might need to consider a different weight/center plate setup that allows for a wider disparity between initial and max".

You still need to make sure the springs are strong enough to prevent mechanical advance at idle though. Otherwise you're wasting mechanical advance range, and either your initial will end up too high, or you will have a hard time attaining 35 degrees max.

Fun71

Good point about the light springs allowing mechanical advance at idle. I ran into that when I was experimenting - when I turned the AC on, the idle RPM decreased, which caused the mechanical advance to decrease, which in turn caused the idle RPM to drop more, and eventually the engine would die. Simply swapping one light spring for a medium spring fixed it.

olds 307 and 403

Since we are dealing with an approximately 8 to 1 350, run a lot of timing. I found, no matter what springs were used, total timing wouldn't come in before 3000 rpm. Try 20 base with one medium and light spring with whatever your vacuum advance puts out for timing. Low compression Olds V8's love a lot of timing.

pav8427

Since this is still all stock and high geared(2.56) I figured some more timing wouldnt hurt as long as it doesnt come in to soon and detonates. Re-marking the balancer would help a lot and if I can get at it I will. I have read if I time it at say 10*, shut it off and turn it over by hand to the 10* mark, I could re mark it at 24* using the timing tab. That would give a reference mark at 34*
Anyone ever try this method?

olds 307 and 403

Your car should have 2.73 gears, not much better. Other have marked the damper accordingly, dial back last light is easier. I can tell you, if you rev over 4000 rpm, the stock HEI, especially with lighter springs will add timing. This won't hurt since your vacuum advance won't be coming into play. Pinging shouldn't be a problem with one light and medium spring and be more responsive.

Intragration

Theoretically, IF the timing tab had markings accurate to your balancer, you could put the timing mark on 10 degrees, and mark the balancer where the zero mark is. You could then move this zero mark to the 10 degree mark on the tab, and mark another mark at zero degrees, "stacking" 10+10+10 etc. from the timing tab marks. I measured my balancer and marked off a true 45 degrees based on it's circumference. I compared this with the markings on the timing tab, and the timing tab was off. I believe 10 degrees on my factory tab is more like 12 degrees on my balancer. This means that if I had used this stacking method (mark, move, mark, move, etc.) that by the time I got to say 40 degrees, the mark I was making on the balancer for 40 degrees would more closely represent 48 degrees. I don't recommend this method, as you don't know if your timing tab is accurate to your balancer or not. It would be good enough for setting 10 or 12 degrees initial timing on a factory motor, but when you're trying to achieve 35 degrees total at 3,000 RPM, you should mark it manually or use a timing tape to be accurate. Or use a dial-back timing light.

pav8427

Sounds like the easiest route would be to borrow a dial back.
This is a California car and does have 2.56 gears.
Does the 35* by 3000 still apply?
I would imagine that no matter what, the car will like what it likes.

Intragration

It should, my car liked it with 2.41s, likes it even better with 3.42s. And the actual number may be a degree or two higher or lower. I'm guessing with low-compression, you could go a little higher. Just watch for detonation. And make sure you limit the vacuum advance.

rustyroger

Getting the advance to come in early surely isn't ideal?.
At any given speed there will be an optimum timing, with factors such as fuel grade, throttle opening, atmospheric pressure, even air temperature to be considered.
If all the timing comes in early the motor would ping at lower revs or not have enough advance at high revs.
In a perfect world the timing would always be just before pinging occurred but that's never going to happen with a mechanical distributor and vacuum advance.
On a modern engine the timing will be all over the place as the computers take information from all kinds of sensors and tell the ignition when to spark each plug.
Such engines are beyond the scope of home tuners, on the other hand they can squeeze a remarkable amount of clean energy from a gallon of fuel, certainly in comparison to our favorite ohv V8 they can.

Roger.

Intragration

I agree that it would be difficult to get the timing curve just perfect, meaning, so that at every RPM level, the timing is exactly, scientifically where it needs to be, not a degree too high or low. But once you get the right combination, meaning the correct max advance that comes on around 3k RPM, a workable initial setting that allows the car to start in all scenarios, and no mechanical advance at idle, the archaic system of spinning mechanical weights and springs does a pretty marvelous job of acting like it's doing what it's supposed to be doing.

You account for temperature by either adjusting your timing depending on the temperatures you're going to encounter, or by setting it so that it's low enough for any temperature you might encounter. In this case, you are leaving some advance and some power on the table on a cool day, so that you don't encounter detonation on a hot day. Essentially, you do the same thing with fuel quality. Hopefully you tune it using fuel of the same octane that you will always use, and hopefully the fuel you get is always of the same octane level, as there's no knock sensor to make adjustments on the fly, if you happen to get a bad tank of gas.

In the end, it's all part of the fun of these old cars, getting them set up just right for the range of situations you might encounter, and then turning the key and going. On the upside, as long as there's gas in the tank, power for spark, and your ignition system is working, you won't encounter a million little gremlins as a result of computer or sensor problems. My daily driver was out of commission for a week earlier this year, as I hunted to find the sensor that was out of spec, but not reporting that it was out of spec.

coppercutlass

fWIW on my dad's 77 pontiac boneville with a mild 350 ( previous combo in my car ) it had 2.41 gears and i found that the timing coming in faster actually made the engine want to stall out. Engine wanted to go but the dog assed gears held it back so i slowied the timing down considerably and the off the line performance improved. now that we have installed 3.08 gears You can literaly feel the timing starting to advance at about 15 mph the car really comes to life. I have yet to re curve the dist. But thats another thing to be careful about when messing with the timing curve.

olds 307 and 403

Disagree on the vacuum advance, my 8 to 1 Olds liked nearly 60 degrees total, part throttle. I ran max vacuum advance and went from 36 to 38 total and the car felt faster. It was slower at the track but seat of the pants was better. Now my 9.5 to 1 350 ran awful with 30 degrees vacuum advance.

Intragration

What it sounds like you're saying is, if you have 8:1 CR and you want the car to be slower, then run 30 degrees of vacuum advance, but if you have higher CR, or you want the car to be faster, then less vacuum advance. Are you sure your vacuum advance solenoid was operational at the time? The fact is, vacuum advance doesn't come into play at the track or other times when vacuum is low. But when you're cruising along at speed with high vacuum and 30 degrees of vacuum advance, and you get into the throttle and the mechanical advance starts to ramp up towards 35 degrees before vacuum advance has tapered down, you're going to have detonation, unless you're at some extremely low CR or you're running racing gas. Or your vacuum advance solenoid is broken. In general, I would not recommend running 30 degrees vacuum advance and 38 degrees mechanical advance unless you're planning an engine swap in the immediate future.

coppercutlass

Vacuum advance is only for economy not power . I don't run a vaccum advance on my hei . No need to and the power is there. At. W.o.t there is no vaccum so vac. Adv. Is pointless for all out pulls.

Intragration

I tried with and without, I found there's a certain immediate response going from high- to low-vacuum situations that I like. Certainly not necessary for racing, and I guess ditching it simplifies tuning.

coppercutlass

I spend alot of time on the throttle so my main focus is w.o.t from a stand still and on the upper rpm range. The only thing i found the vac. adv. good for is to help idle characteristics atleast in my experience. As far as response on the street between high vaccum and low vac. situations i never felt a loss with or with out but then again my main focus is w.o.t. On the street it is what it is as long as it runs good . That is not to say i will sacrifice street perfromance becasue last weekend i put over 100 miles in 1 night of crusing . i can see where in down shift situations the vac. adv. will help but again i have a 3000 stall and manually have to downshift so i usually hit the gas as i downshift and its gitty up and haul *** .

olds 307 and 403

No I am saying with miserable low compression, part throttle is actually improved with more timing. My 350 with 9.5 to 1, small Performer cam, even with the vacuum advance dialed back detonates on regular. I wouldn't doubt my 350 would detonate on premium with the vacuum advance putting out 30 degrees.