Ignition Timing

[Tom H]

Good point , Todd, But I've checked it both ways. Using a standard timing light and looking at the 5 deg marks on the pulley, but also using one with adjustable firing and reading the deg from the digital display. Either way I need to set the idle (or 1000 RPM) at about 20-24 depending on low RPM to get it run smoothly.


Well I checked TDC using plastic feeler gauges made of round plastic rods. Tested using a 1/8" rod and a 3/16" rod, both times at BTDC and ATDC, and conclude the timimg marks are on target within +/- 2 deg. Probably dead on. Then I measured the oil pump drive at TDC. It seems that where I should have an angle of 48 +/- 1 Deg, I have an angle about 37 Deg. It's really hard to "read" the angle by eye. I still swear that my photo shows it greater than 45. But careful use of a ruler, pencil, and trigonometry actually measuring on the car says it's about 37. After pencil work, even the eyeball says "less than 45". Mis-installation of the oil pump would have a larger error than that. So that seems to say the cam is misaligned with the crank, by one cam tooth (too far advanced), I think. I think the cam sprocket has 40 teeth, so 9 deg camshaft / oil pump rotation per tooth. This would be then 18 deg crank rotation. And I'm guessing that the "best" ignition firing point may be about half way between 'normal" timing to match piston position and 18 Deg "extra advanced" to match the cam timing.

But the car has run fine for 8000 miles, getting 28 MPG, and feeling fine and peppy. Is this a reasonable result with a cam 9 deg (cam not crank angle) advanced? Remember it' a KB grind , so has longer dwells.

I cannot find the KB specs. Does anyone out there have them, so I can check the valve timing? Or I can call Delta on Monday.

Tom

 

[RootesRacer]

heavier cams like to have more static ignition timing, but a lesser advance curve.

An example for a 280 degree cam would be something like 20 degrees timing at 1000rpm idle and 32 degrees at 3500rpm wide open throttle.

This would correlate with only 12 degrees mechanical advance across the entire mechanical advance range.

Such a motor "likes" 20 degrees at idle because the valve overlap causes a much lower volumetric efficiency at and off idle that you need more timing to get the flame front to cause peak combustion pressures at optimal crank angle.

Compared to a stock engine whose mechanical advance is 24 or 26 crank degrees from 800 to 3500rpm and whose static timing is around 6 to 8 degrees BTDC at 800rpm.

In EACH case, you will want to make sure that your MAX timing (when the mechanical advance hits its stops) is 32 to NEVER more than 34 degrees BTDC. Any higher advance timing WILL result in pinging unless you are running a high test fuel (96+ octane).

In short, the MAX timing figure is how to set the timing and then setup the advance curve to give what the engine LIKES at lower RPM.
Hotter cams again like more low RPM advance since the lower combustion pressures have a slower flame front.


HTH

 

[Tom H]

Jarrid, it helps a little. But what do you think of running with the KB CAM advanced about 9 deg? I will check the cam timing once I get the specs. But right now it looks like I have it 1 tooth advanced. Am I OK as long as I keep spark advance at 34 or less?

Tom

 

[RootesRacer]

Jarrid, it helps a little. But what do you think of running with the KB CAM advanced about 9 deg? I will check the cam timing once I get the specs. But right now it looks like I have it 1 tooth advanced. Am I OK as long as I keep spark advance at 34 or less?

Tom

Having the cam advanced or retarded wouldnt change the ignition requirements, at least not that much.

Having the cam advanced helps high RPM operation, though having it that far advanced would probably hurt so much more at the low end than it would help at high RPMs.

I guess what I am saying is that I dont think your cam is off by a tooth, and even if it was it wouldnt effect your ignition requirements that much.

Ignition timing is ALL about cylinder filling (VE) and combustion chamber dynamics (material, shape and squish). Cam effects VE, but having an advanced or retarded cam timing doesnt correlate to an offset in ignition timing as 9 degrees there doesnt effect idle VE enough to necessitate a 9 degree shift in ignition timing. A 9 degree shift in ignition timing need at idle would be in the order of a 40% change in VE, which the cam could not be responsible for via just a 9 degree cam offset.

Yes, if you keep your ignition limited to 34 (better at 32 if your compression is above 9/1) you will be fine.
If you havent modified your timing curve then you are going to find either your mechanica advance is broken or way short on its advance curve or that you have been running WAY over advanced timing for some time.
I hope for the former for you


Please tell us how you arrived at 20 degrees being where you set the idle timing. Is that where it made the most WOT power, or where you got the best idle?

Also do tell what the max timing shows on your timing light with the timing set to how it is RIGHT now. This will tell us everything that needs to be known about if the engine has been abused or if you have a bad dizzy.

 

[beamdream]

Good point , Todd, But I've checked it both ways. Using a standard timing light and looking at the 5 deg marks on the pulley, but also using one with adjustable firing and reading the deg from the digital display. Either way I need to set the idle (or 1000 RPM) at about 20-24 depending on low RPM to get it run smoothly.


Well I checked TDC using plastic feeler gauges made of round plastic rods. Tested using a 1/8" rod and a 3/16" rod, both times at BTDC and ATDC, and conclude the timimg marks are on target within +/- 2 deg. Probably dead on. Then I measured the oil pump drive at TDC. It seems that where I should have an angle of 48 +/- 1 Deg, I have an angle about 37 Deg. It's really hard to "read" the angle by eye. I still swear that my photo shows it greater than 45. But careful use of a ruler, pencil, and trigonometry actually measuring on the car says it's about 37. After pencil work, even the eyeball says "less than 45". Mis-installation of the oil pump would have a larger error than that. So that seems to say the cam is misaligned with the crank, by one cam tooth (too far advanced), I think. I think the cam sprocket has 40 teeth, so 9 deg camshaft / oil pump rotation per tooth. This would be then 18 deg crank rotation. And I'm guessing that the "best" ignition firing point may be about half way between 'normal" timing to match piston position and 18 Deg "extra advanced" to match the cam timing.

But the car has run fine for 8000 miles, getting 28 MPG, and feeling fine and peppy. Is this a reasonable result with a cam 9 deg (cam not crank angle) advanced? Remember it' a KB grind , so has longer dwells.

I cannot find the KB specs. Does anyone out there have them, so I can check the valve timing? Or I can call Delta on Monday.

Tom

Others may be bored but I, like you, am keen to see the solution.

My biggest concern, if the cam were out by one tooth, would be the prospect of the valves kissing the piston, but after 8000 miles I think that one is ruled out.

I have always found that the behaviour of a vacuum guage can be enlightening, particularly where valve and ignition problems arise. The only concern here of course is that the modified cam profile may confuse things.

If you do unearth the problem, perhaps there is even more performance yet to be unleashed ??

 

[Bill Blue]

Tom, it seems everything is okay except for the amount of ignition advance. Excuse me for getting so basic, but tell us about your timing light. Is there any chance it is one of those fancy things that magically does all the thinking? I have a one time experience with those. The owner of the light asked me how much advance I wanted. I told him 12 degrees. He ran the light and I twisted the dizzy (Pinto engine, opposite sides of the block). I got 24.

Could something like that be the issue?

Bill

 

[Tom H]

Update: Oh the insanity of it all!

First, Bill, thanks for the thoughts. But this was essentially the same question Todd asked. I measured the advance using an old fashioned timing light and also one of those new digital ones that I borrowed from Geo Farrell at the Invasion. That's where I first dsicovered the apparent timing "problem"

Jarred, Yes, I've been adjusting the tiiming for good idle. not exactly Best idle, but as low as I could get it with decent idle. Below 20or so it would nearly stall.

Now the update:

1) First I realize that the 37 deg angle I see on the oil pump (instead of 48) means the cam may be retarded one tooth, not advanced.

2) I disassembled the dizzy and all seem OK, Nothing sticking or broken

3) So I reassembled and reinstalled the dizzy and checked the timing again. The setting was still at around 22, but I was easily able to adjust it down to 10-12 at 700 RPM with nice idle! So WTF???

4) I set it to 13 at 700, goes to 15 at 1000 and maxes out at 30 at 3000 RPM.

5) After I get the specs for te KB grind from Delta , I'll take make some valve timing steps to see if I have it off one tooth or not.

6) Good thing about this exercise - I discovered two things that needed attention: A) I found the red and black wires inside the dizzy that go to the Pertronix module have been rubbing against the magnet "cam" and had already worn thru the insulation and partly thru the wire. Fixed that with Silicone seal and repositioned the wires inside. B) I found I had no vaccuum advance because the vacuum hose was blocked- apparently since day one.

Maybe I need to get back on the road. I think I had better results there than in the garage.

Next Update after valve timing measurements. Thanks to all

Tom