Macadoo

Hey guys,
I finally got my dial-back timing light from HF so I checked my numbers.

Back when I refreshed this motor (with the TH350 and 2.56 gears) I was running about 14* initial, limited the HEI to....uhhhh....was it 12*?, and had about 36* all in.
After getting the 200-4r in and the 3.73 gears, I started playing with timing, without a light. I just kept bumping it up until it started poorly and backed it off. I put the lightest springs in the HEI from the MSD kit on the "stock" weights (that came with the new HEI (eBay).
The car is running great and smoking the tires with not a hint of ping (I run premium fuel mostly from Mobile).

However, here are the numbers I'm reading with the dial-back light. Maybe I'm not using it correctly. I'm just turning the dial until the hash mark on the balancer lines up with zero on the stock gauge.

Idle: 700 RPM: vac can disconnected and line plugged = 28*
Idle: 700 RPM: vac can hooked up = 42*
Vac can hooked up: all in (3500 ish RPM) = 60*

These numbers can't be right, can they? As I said, she's running smooth and strong without any pinging.

Macadoo

I forgot to mention: the timing is jumping a little at idle, like 2*. Caused by the light springs I expect.

Fun71

Right now don't worry about how much the vacuum advance adds. Some vacuum cans have as much as 24º advance, so added to 36º total (initial + mechanical)= 60º (initial + mechanical + vacuum).

Do the checks with the vacuum can disconnected. Check initial (you already have that) and the total MECHANICAL advance at ~3600 RPM.

After you know these, you can check to see how much vacuum advance your canister adds. You can make a limiter for it if needed - mine had 24º so I made two different limiters (one is 10º advance and another is 16º advance).

I will caution you that when I had the two lightest springs from a Moroso HEI kit in my car, it was giving quite a bit of mechanical advance at idle RPM. So much so that when I turned the AC on, the idle dropped, which caused the mechanical advance to drop, which caused the idle to drop - you get the idea. The engine eventually idled down and died. I had to remove one light spring and install a medium spring to correct this issue.

I discovered the mechanical advance was coming in at idle by checking the initial, swapping the lightest springs for the heaviest ones, then checking the initial again. Seems like I remember it was getting nearly 10º advance at idle!

Macadoo

Will do. I'll be honest, I can't see my tach so I'm doing it by ear. SHould I run it up that high using the idle screw?

Macadoo

Should have mentioned: I am on the #1 wire with arrow on light pointing towards spark plug.

Fun71

I used an external tach whenI was doing this.

I don't think you can get the RPM that high with the idle screw alone, but you can stick a screwdriver or similar object in there to help.

Macadoo

I'll just wait for the wife to help. But she ain't gonna' want to go out in the 110* garage.
Thanks Ken.

oldcutlass

Put a lite and medium spring on your distributor. Doing the math, 42-18=14 degrees of vacuum advance from your canister. Drop your initial back to 18+14=32 at idle with vacuum. Using your original numbers of 60-42=18 degrees of mechanical advance, so 18+18=36 degrees all in of mechanical + initial. Then add your 14 of vacuum puts you at a total with vacuum advance of 50. You can ad a few more degrees to these settings if your engine will tolerate it.

olds 307 and 403

I find the Olds V8 love a lot of part throttle timing. I found the same thing on my 260, I have 30 at 700 rpm and 36 at 1000 rpm. I have never had an HEI advance this quick, my Mallory Breakerless can be all by 1500 rpm. My other 4 HEI's all took to 3000 rpm to be all in, no matter what springs. I just put one light and medium spring in and a tune up, nothing else. My low compression Olds V8's like around 60 degrees part throttle. You need less timing only if pinging, hard starting or running at the track, otherwise run it as is.

Macadoo

I've been thinking I should change one of the springs to a medium. And I might back the timing off a tad; I've read it can cause overheating. We're going to need AC more than speed the next few weeks.

Fun71

In my experience retarded timing will cause overheating whereas advanced timing will make the engine run cooler (think of the TCS setup on factory engines). I think if the timing is greatly over-advanced the engine will overheat but you would probably notice something wrong with how it runs at that point.

Macadoo

Yeah, i was just reading that over-advanced timing will detonate and be hard to start before it has a chance to overheat. Spring change and I'm good to go.

I should have mentioned that I'm lucky if I have 8.5:1 compression.

olds 307 and 403

With your larger than stock cam and shim head gaskets, making your quench ideal, you should absolutely no issues with that much timing even on regular. I found my Olds V8's ran better at 38 total, even though 36 is always where they run the fastest at the track. I ran that and the full 30 degrees of vacuum advance, helped them feel stronger at part throttle. I can hardly wait swap out this Performer cam I am running and put in a bigger cam to allow more timing. It was crisper when it wasn't pinging with more timing.

Lee_A

For me, the timing "numbers" are ONLY for reference. I find what works best for a motor, record the value, and use it for future reference. Whether that turns out to be 25-BTDC or 5-ATDC (some Buicks) initial, if the motor likes it, I go with it.


I recently was hired to time an early 70's Camaro, which had been running deep 11's. With it running that well, I figured this would be a quick & easy tune job - WRONG! I was getting some crazy timing numbers. Turned out that the outer ring of the Summit Racing SFI-approved damper (balancer) had slipped.


When I build a motor, I always make reference marks on the inner and outer parts of the damper, so there is quick and obvious proof of slippage. Slippage isn't frequent, but I've seen it happen a few times in my life. Big slippage is obvious, but a little might just through your timing numbers off by a few numbers.

jpc647

Why not use both light springs, to get more part throttle timing? Just curious.

olds 307 and 403

Supposedly two light springs can cause erratic timing. I actually think he will be fine as is. I ran my 8 to 1 compression Olds 350 with the timing all in by 1500 rpm didn't hurt it at all. I actually preferred manifold vacuum for the vacuum advance, gave about 50 degrees at idle.

Fun71

From one of my posts above:

Macadoo

I swapped in a medium spring this morning, making it one light and one medium. Still feels strong at part throttle but did smooth things out at idle a bit. It's not jumping around anymore.
Ken, I wouldn't have thought about that. I'm pretty sure I was getting a bit of mechanical at idle and with running the air, that can really pull the idle down. Seems better now.
But right now, with the car running, the garage is around 115* with 85% humidity so since it's running and feeling strong, I'm calling it done until it cools off some.
It's definitely possible that the balancer slipped but it would have done that before I freshened the motor. If that's the case, last summer I was running maybe 4* btdc instead of the 14* I thought I had. If I had a piston stop in #1, I would be able to tell yes? #1 at tdc, timing mark should be at zero?

Fun71

Only if the piston stop contacted the piston at the very, very top of its travel.

I used the piston stop in conjunction with a degree wheel. Rotate the engine one direction until the piston contacts the stop, note the reading on the degree wheel, rotate the engine the other direction until it stops, and note that reading. TDC is then halfway between the two readings.

oldcutlass

I highly doubt you were running 4* or 14 * initial with an HEI. Yes with the piston stop at tdc your timing mark will be at 0. It will be easier to do what Kenneth suggests only mark where it sops and then move the engine backwards until it stops and divide the length of the marks on the balancer by 2, that will be 0.

Macadoo

Makes sense. I'll give ti a try asap.

distributorguy

Did you change the weights and springs or just the springs? Factory weights are heavier, and they give more consistent timing BUT they require very, very heavy springs. You don't get those springs in any recurve kit. If that's the case, use both of the heaviest springs in the kit. Besides needing more initial advance, you likely need more total timing as well so speeding up the advance curve is not a cure. Advancing the timing is. By installing two different advance springs you don't get a "stepped" advance curve in a Delco, unless your strong secondary spring fits loose at idle. You're just making the stronger of the two springs stretch out faster by not running a matched pair.
Keep in mind I do this multiple times a day, every day, for the last decade+.

And it would be no surprise if your base timing was set at 20 degrees+. Put it wherever it runs best. The advice above is correct - retarded timing causes overheating. As long as you don't hear pinging and there is no sign of detonation on your spark plugs (white with metal transfer to the electrode) you're likely safe.

Greg Rogers

My 71 Cutlass also has 8.5 to 1 compression at best. I also have found it runs best with a lot of timing. I believe mine is set at about 20-22 degrees at idle with vacuum advance disconnected and plugged. This causes the total advance at aprx 2500 to be close to 60 degrees. If I set it back to be about 12 degrees at idle w/o vac advance and it runs terrible with a stumble off idle. So I left it at 20 degrees. But now when car is cold on high idle step the whole car shakes from engine rocking back and forth. I assume the engine is also doing this going down the highway but you cant feel it when in high gear. But going aprx 30 mph if car is still in 2nd gear you can feel it. It feels like a miss. I am thinking about having the dist recurved to lower the total timing. I have the stock points style dist with a Pertronix conversion. I used to have a newer ( maybe 75-80) HEI dist and It did the same. What do you guys think? I cant believe that this rocking around is good even if its not noticeable. I wonder if that is what's causing my motor mount problems? They don't last long and sag. Thanks, Greg

distributorguy

The increased torque is destroying your mounts. You may want to buy better ones - like red poly versions instead of rubber.
Yes a recurve will help. A stock HEI distributor will come with a pretty close advance curve to what you need. Roughly 18 degrees advance plus 22 at idle. Works well. If you run ported heads, you can use less overall timing because an improved combustion chamber unshrouds the valves and lets a lower timing figure burns the same fuel in less time.

Fun71

A Pertronix conversion should not change the advance curve of the original points distributor. A factory '71 points distributor will have ~10*initial and ~24* mechanical advance. If you are setting the initial to 20* and there is 24* mechanical then you are getting WAY too much total advance (not counting vacuum advance). You definitely need to sort this out.

distributorguy

Pertronix does have some affect on timing, but not on purpose. As you decelerate, the module is slow to decrease timing - it will holds 2-4 degrees of advance for an extra 2 seconds or so. Not a problem unless you get off the gas and back on it again quickly. Then its likely to ping unless you drop a few degrees of base timing across the board. Not good for performance. Pertronix also picks up noise from your spark plug wires. It senses that EMI (electro-magnetic) as a signal from the magnets in the trigger wheel and will randomly discharge the coil at the improper time. The next time you need a spark, the result will be a randomly weak spark from an undercharged coil. The lobe sensing modules are far worse than the magnetic ones. Optical sensors are more influenced by RFI noise, which has the exact same effect. No spark plug wire on the market can eliminate this noise issue, but an externally shielded and grounded set of mil-spec wires might do the trick. I have yet to test this theory. Sleeving wires in braided stainless mesh and tying each individual wire to ground doesn't sound appealing to me.

Macadoo

THanks for the advice and welcome to the forum I have the whole recurve kit from MSD including the weights but I have to get my carb issue ironed out before I come back at the dizzy. The weights that are in there look much heavier than the MSD weights and center plate.
But carb first.

distributorguy

Ignition first!!! You always tune your carb to the ignition, not vice-versa! A timing change will require a fuel change.

jpc647

maybe I missed it, but are you connected to ported or manifold vacuum?

Macadoo

Normally I would agree but this carb is spewing gas out of the accelerator pump. I at least want to get a carb that functions properly. (Okay, "spewing" is a little overstated but it's a pretty hefty leak).

I've tried both but it runs better on manifold. I've read plenty of debates about this online, lol.

jpc647

Interesting. Mines the opposite. ha.

Macadoo

Curious, isn't it?

coppercutlass

depends on what the engine likes. I have had combinations like both ported and non for tuning reasons one worked better than the other due to certain parameters of the combinations.

Greg Rogers

I don't understand this. I understood that the pertronix is basically just a hall effect switch that takes the place of the points. I assume that the advance function comes from the centrifugal weights and the vacuum advance as it was with the points.. I don't have any module that I know of.

Greg Rogers

I bought some poly mounts for a dodge I had and it was just like having solid mounts... Shake, rattle and roll !!! I know the rubber mounts made now are cheap. I noticed one day that my convertible engine sat crooked. The air cleaner surface was actually lower on one side. I looked underneath and the mount had sagged to where the oil pan was rubbing on the crossmember. I replaced the mounts w/ ones from Auto Zone or one of those places. On the Dodge I put new generic mounts on it when I changed the engine. The headers were hitting on the center link I blamed the header manufacturer but found out later it was the new, cheap mounts. When I bought my Vista beater I noticed it had a aftermarket flex fan on it. I put back on the original clutch fan and it hit on the lower part of the fan shroud... Yep. Sagged motor mounts. Meanwhile after 2 years or so the convertible mounts have sagged. I looked hard for higher Quality mounts but I think I got the same ones from a local small town auto parts store, I just paid more !! I really don't have any increased torque as it is all stock. I was figuring if the engine rocks around due to too much timing maybe that is the reason for such short mount life.....

jpc647

just noticed something while re-reading, do you have an adjustable vacuum advance canister? Mine only gives me about 18* vacuum advance, so if you get better results at 30*, maybe the OP and myself, would beneft from a canister that provides more.

The other factor is the bushing. Doesn't that control the amount of total timing the dist. will give? For example, I'm sure my bushing is the basic black one, and could be changed for one of the others, and it'd' have more total mechanical timing. But It'd bet the adjustable vacuum canister is better. Didn't that TCS retard the timing at highway speeds? You know, that tree thing that was on the factory intakes.

oldcutlass

These are very informative links to timing and vacuum advance settings and parts:
Vacuum advance internet articles and opinions, good reads.
http://65corvette.nonethewiser.net/t...um_advance.pdf
http://www.lbfun.com/warehouse/tech_...ance_Specs.pdf

Greg Rogers

Good stuff Eric. Thanks.

Macadoo

Yeah, thanks dude. I need to figure out what I limited my vacuum advance to. My canister isn't adjustable so I put in a limiter.

oldcutlass

Just do a reading with your timing light to see what your timing is with and without vacuum at idle. Subtract one from the other and that's what its limited to.