just a thought to help with the tuning, use a timing tape and a fabbed marker of your choice.
as long as the engine is TDC , mount the pointer were you can see it .. then use a performance timing tape around your dampner.
you can mount it wherever it suites you.
AND you can't always assume the mark on the dampner is correct, look at the one on my 455, the yellow mark is true TDC, the factory one is at about the 8' position in the pic.. it has rotated on the hub. I will be replacing it in the near future.
I agree with rabbit. Without a timing mark you're just guessing.
You said...
"Engine runs very well from idle to WOT, however at wot, under certain conditions, pinging will occur, sometimes heavy. Problem; The initial timing was set only by ear, because I cannot get a light on my timing marks. They are buried by the PS bracket, and I cannot get enough angle to see in, due to the intrusion of my non stock rad shroud. But I feel that I'm pretty much in the ballpark with initial. Probably around 12* or so. I know, I know, you're probably shaking your head, but it is what it is, lol!"
The engine has 9.1 to 1 compression and it's pinging on 94 octane fuel. You've got to suspect that the timing is too far advanced. If that's the case, using lighter advance springs will only make it ping sooner.
IF your timing mark is right you can set it to TDC and then put a new mark on the damper and the timing cover somewhere where you can see it. You can use a timing tape on the damper or just measure and put marks where you need them, like at 36 degrees.
You can use this on line calculator to get the proper distance for the marks...
For example, if your damper is 6.75" in diameter 36 degrees would be 2.121 inches from your TDC mark. Of course, a dial back timing light will also work if you happen to have one. In that case you'd only need a visible TDC mark.
If I was in your position I would pull the vacuum hose off and plug it, then rev the engine until it hit full advance and set it at 36 degrees. It doesn't hurt anything to rev the engine to 3,000 rpm or whatever it takes but it is a little scary working on an engine that's reving that high, so if you want you can pull one advance spring off of the distributor while you set the total advance. (that way it'll reach full advance at a fairly low rpm, like about 1,500)
I think you're on the right track regarding how you'd like to set up the distributor but you're really just guessing without some timing marks to go by. You might get lucky by just setting by ear until you get the engine to run well but it's a lot easier when you can actually see what's happening by using the timing marks.
-- Edited by jim_ss409 on Friday 11th of October 2013 07:13:23 PM
Some thoughts on setting the distributor curve on a 350 SBC. Bear with me, this is how I learn...by explaining what I don't know in public!
In the quest for a better running engine, I've spent some time with my Edelbrock 1405 600 CFM carb. With some jetting, rod and spring changes, I feel I'm getting close to target. But in doing that, I'm now beginning to focus on the ignition side of the equation. My gear head Cousin laughs at me, telling me "You've got hidden power in that distributor, adjust it already!" So that's what I'm going to try to do
Engine runs very well from idle to WOT, however at wot, under certain conditions, pinging will occur, sometimes heavy. Problem; The initial timing was set only by ear, because I cannot get a light on my timing marks. They are buried by the PS bracket, and I cannot get enough angle to see in, due to the intrusion of my non stock rad shroud. But I feel that I'm pretty much in the ballpark with initial. Probably around 12* or so. I know, I know, you're probably shaking your head, but it is what it is, lol!
The Pertronix dist gives me 3 advance spring options to adjust the mech advance curve,
Copper; Start 1000 RPM, end 2000 RPM
Silver; 1500 - 3000 (in place from factory)
Bronze; 2000 - 5000.
And also gives me 3 mechanical advance degree limiting tab options,
Natural; 12 degree mech limit.
Blue dot; 16 degree
Red dot; 20 degree.
The distributor mechanical advance is said to deliver 24 degrees of max advance. So with applying different combinations of springs and limiters, one can "fine tune" the mech curve.
With my settings as is, I'll say I have an (estimated) 12 degrees initial, combined with 24 degrees of mechanical, for a total of 36 degrees all in at 3000 RPM. I'm not going to factor in the vacuum in this.
The car starts and idles well. Load at part throttle induces no pinging. But it will ping at WOT though to 5500. So where I feel I should go is to NOT retard timing, but to possibly LIMIT total advance. And then possibly QUICKEN the advance curve.
If I was getting idle to part throttle pinging, then without question, I'd retard the initial slightly...but it never pings there!
My plan is to add one copper spring to quicken the all in to around 2500.
And add the 20 degree limiter.
Check for pinging, performance gain or reduction.
Go from there.
Any thoughts on this.? Where do most low compression 350's like to be? Am I on the right track?
Is your vacuum advance hooked up? If so try running without it to see if the pinging is still there. There are two sources of vacuum advance, one below the throttle plates and one above. The one below gives max. vacuum advance at high engine vacuum, with little throttle opening, such as idle and cruise, great for fuel economy. The other, ported, gives advance with the throttle open wider, even under low vacuum, sometimes causing pinging at WOT.
just a thought to help with the tuning, use a timing tape and a fabbed marker of your choice.
as long as the engine is TDC , mount the pointer were you can see it .. then use a performance timing tape around your dampner.
you can mount it wherever it suites you.
AND you can't always assume the mark on the dampner is correct, look at the one on my 455, the yellow mark is true TDC, the factory one is at about the 8' position in the pic.. it has rotated on the hub. I will be replacing it in the near future.
Keep in mind that at Wide Open Throttle (WOT), your manifold vacuum drops to zero. So even though the vacuum advance added more advance under idle, it is removed under WOT. If it's a stock vacuum advance module, the amount of advance may be stamped just behind the cannister. You may have a model # stamped on one side, and the amount of advance on the other. Such as 305 16 The 16 is the amount of vacuum advance.
The pinging is only happening at the upper end of WOT, under big load, pulling hard. And that would be under very low manifold vacuum. The Vac advance should be of no consequence there would it?
I guess ideally, one would want to be on the threshold of detonation across all rpm's, idle to 5500. Or is that not necessarily the case?
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65 Laurentian post, 67 Grande Parisienne 4 door HT.
I just realized what engine you are working with and 36 deg. is too much advance for that engine, 32 is the recommended total. Hypereutectic pistons are very sensitive to detonation and cracking is very likely so please reduce your timing right away!!
I just realized what engine you are working with and 36 deg. is too much advance for that engine, 32 is the recommended total. Hypereutectic pistons are very sensitive to detonation and cracking is very likely so please reduce your timing right away!!
Thanks Randy
Good point. Pinging is really hard on an engine and should be avoided.
Also, in my example I used 36 degrees because that was a fairly common total timing setting for older engines like I'm used to but many newer smallblocks with their improved fast burn combustion chambers make maximum power with less timing, and of course, less timing is also safer.
Don't worry guys! When the pinging hits, I do let off...that much I know! I don't continue to push.
One thing I should mention is that I have moved the distributor into all sorts of positions. I've tried ported and non ported vacuum. Different Idle screw settings, and the way it runs now is the best compromise I could find. It runs well, but if I set the initial back, the bottom end seems to suffer. Idle becomes less smooth and it seems to be less responsive.
I'll roll the initial back a little and see what happens tomorrow.
I apologize if this thread sounds so SBC mundane.
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65 Laurentian post, 67 Grande Parisienne 4 door HT.
You're on the right track. Sounds like you need a bit more initial timing but your total sounds close. Do all your testing without the vacuum advance hooked up. You want a clean idle and crisp off idle determined by your initial advance. Then limit your total so you are a few degrees from pinging. Poor fuel quality and heat promote detonation so leave some cushion concerning total advance, eg. a few degrees away from detonation. After you have a satisfactory initial and total then it's vacuum advance time, a totally separate deal.
Put the copper springs in today. Starts advancing at 1000 now, and is all in at 2000. Was 1500 -3500 before. Feels livelier. No new pinging down low. Still some up top.
Next I'll add the 20 degree limiter, see if it stops the pinging. If it does, then perhaps I'll incrementally add just a little more initial, until I'm just at the threshold of detonation.
I can say the engine is running way better than it was last week.
It's a good feeling when you can find hidden power with some adjustments.
Thanks for the input!
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65 Laurentian post, 67 Grande Parisienne 4 door HT.
Just got back from a run, and I now detect a slight hint of pinging under load, at or above 2000 rpm. Another thing worthy of note, is that with the total coming in so fast, is the exhaust note. It's become louder down low. I don't know if I like the Blaaat much. I have Thrush welded mufflers (really just Flowmaster 40 knockoffs), and it's now just above what would be deemed obnoxious. Maybe it's time for something quieter.
When you think about it, the appearance of slight pinging down low, is really a good diagnostic tool. It confirms to me, what most logically saw as a simple case of excessive ignition advance.
Had I not installed a fast curve, I would have only ever seen detonation up high, at or above the old "all in" point of 3500. Now it appears on or after 2000.
Time to start dialing the initial back. And when there is zero detonation, I'm good! I then move onto understanding vacuum advance.
cheers'
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65 Laurentian post, 67 Grande Parisienne 4 door HT.
Tried dialing back my initial today. It felt less lively, but idled well and didn't ping. Didn't have the same snap as before. I could live with it.
But I couldn't be content, so I dialed in more initial, and put in the 20 degree limiters. No pinging, but really felt flat everywhere.
At that point I said, enough is enough. As suggested, I need to know where I am. So I got out my timing light and went to work to see if I could get a reading. Just like before..no dice. But before I had installed my engine, I had put on one of those adjustable timing pointers. It had a little pointed rod that indicated the degrees. I had also installed a timing tape on the damper, and spend some time making sure zero on the damper was actually zero. It was very close. The pointer was just hidden from view. I could see see the Zero, 10, 20 tape marks flashing in the strobe, but not the actual 1 degree graduations.
Simple solution! Extend the pointer with a little piece of vacuum hose. Trim the end to a point. Reach in and around (barely can get fingers in), and push it onto the pointer.
Crude, but it at least gives me a reading. The pointer appears to be flashing at just before the half way between the 10 and 20 degree mark. So I'll call it as good as 13 or 14 BTDC. I'll improve the pointer at some point, buy a new timing tape and mount it more outboard on the damper, so I can actually see the small increments. So at least now a have a baseline.
Had to thread my camera in to get this shot.
That done, I pulled the limiters, and added one medium tension Silver spring. Looking at the chart, I estimate it should start the curve around 1200 and be all in at 2800 or so.
Initial at 14 plus 24 = 38 total. Two copper springs give you a curve of 1000 - 2000. Probably just too quick for this motor.
Took it out for a test, good idle, no pinging and a very strong pull down low through WOT to redline. Besides a slightly richer rod change to the carb tomorrow, and a possible slight initial timing increase, I think I'm in the ballpark for a good running 330 horse HO 350!
I didn't expect this. I was on the converter and it just came to life! Sorry neighbors...
-- Edited by cdnpont on Wednesday 16th of October 2013 06:43:12 PM
