StDomingos

So I've spent weeks reading articles on this forum (and others) about setting ignition timing for performance.

Special thanks to Lars and BarryK for their previous great posts and papers on the subject .

I have never done this type of thing before but I'm doing my best to learn more about these cars and do more stuff myself. I was hoping some of the more experienced members on here would look at my settings and comment on whether it looks good or if it could be improved.

To start with, I have a de-smoged, de-computered '81 with a distributor and carb from a '78 L82. The engine is otherwise stock I believe (I'm not certain about the cam, but if it's been changed it sounds pretty mild).

I run 91 octane gas and live at about 3000' above sea level.

When I swapped out the springs in the distributor I noticed that the bushings seemed quite worn and that the weights really flopped around (I assume they are not supposed to) so I ended up using the weights and bushings in my recurve kit (Mr Gasket 929G).

Once I got everything dialed in this is what I ended up with;

Initial timing of 16* at 625 RPM (idle)
Total timing of 34* "all in" at 2500 RPM (so 18* mechanical advance).
Vacuum advance of 16* (so 50* is the maximum possible advance).

I took readings at various speeds and got the following curve;

625 RPM - 16*
1000 RPM - 20* (4* advanced)
1500 RPM - 25* (9* advanced)
2000 RPM - 29* (13* advanced)
2500 RPM - 34* (16* advanced)
3000 RPM - 34* (16* advanced)

I did notice an immediate improvement in throttle response and power. The car seemed to start with no difficulties (though it has only been about 65 Fahrenheit here) and idled as well as it did with the original timing.

I guess my big concerns are;
1) Should I be concerned about my initial timing being high? Are there problems that could arise from that?
2) I'm terrified of detonation but I don't really know what I'm listening for. I've spent hours watching Youtube videos and reading descriptions. I've heard it described as a pinging sound, as sounding like "you are dragging a chain", and as the sound of "shaking rocks in a coffee can" which are all pretty different sounds. I don't think I'm hearing any of those noises, but the exhaust note is fairly loud and I'm not confident of my assessment. Because of this I chickened out a bit and stopped a few degrees short of the "magic number" of 36* total.

Should I compromise and dial back the timing 2 or 4 degrees for a more conservative set up? Does this look pretty safe considering my low compression, high altitude and high octane?

Thanks in advance for your feedback.

resdoggie

That looks fine. Does the car run smooth from idle to wot? If so, leave well enough alone. If you start getting some ping at cruise, reduce the vacuum advance with an adjustable canister. You can check for ping also by disconnecting the vacuum can and go for a drive. If you get any ping, reduce your initial by a degree or two until the ping is gone but I think you'll be ok with the curve you have. My engine is modified and I'm running 22* initial, 10* mech'l and 8* vacuum advance. Car runs way better than the factory recommended timing with 12* initial. Now you go to the next step and fine tune the carb!

cooper9811

I agree with Resdoggie. That curve looks pretty good.

flyeri

I think the "rocks in a can" description is pretty accurate. I can no longer hear it but my daughter and my wife can. Take a female for a ride and ask them to listen for it. Their ears are better able to hear that range than ours.

REELAV8R

You should be fine with that timing, altitude and octane combo. The L-82 has flat top pistons and pretty close to a .040" quench, two things that will help avoid detonation.
Engine temperature, intake temperature and how rich or lean it is are also considerations.
I have heard detonation sound like many different things depending on the engine and the load. In a 6 cylinder chevy pickup it sounded like a metalic rattling sound. In a two stroke dirt bike it sounded like a sharp snapping sound to a hammer on metal sound. In my corvette it sounded like rocks in a can at WOT in the stock motor.
You can also check the plugs for signs of detonation. If they have shiney specs on white insulator you are detonating. Or if the tips appear corroded away. Some times black specks on the white insulation.
With the L-82 forged pistons they will tolerate quite a bit of detonation before severe damage begins to occur.

bluedawg

Your numbers look good to me, don't know if your running a larger cam, but the more duration you have, the more advance you need to burn that fuel, I'm running 24* initial on my 400" that has 236* @ .050 " to burn the fuel at idle. To check your timing, take your car out, first if it's an auto, power brake it, but try an go as high as you can with out spinning the tires and listen to see if it pings, second is high gear climb a tall hilly to see if pings, after each one if these activities pull the plugs and look for gray to black specs. Some times detonation is quite if it's barely happening, forcing it can cause it to happen sooner in the cycle which would help it be more audible. Remeber that fuel quality and ratio can cause detonation as can engine temp and carbon build up on the pistons. 34* is a good total with out vaccum, you might try 36* and 32* to see if you notice it running any better and even if it don't detonate at say 34* doesn't mean that 34* is were it will run best. Good luck with your project.

BKbroiler

I agree with everyone above. Nice work on that distributor and nice work reporting the results.

StDomingos

Thanks to all of you for your feedback on this and your suggestions. I did take the wife, whose sense of hearing (and smell for some reason) is better than mine out for a drive and she could not hear anything that sounded like rocks being shaken in a can either.

I tried backing the timing off two degrees and didn't notice any changes for the better, so I put it back up. I have decided to leave well enough alone for now and we'll see what happens.

I am amazed how much I've learned doing this and I love the satisfaction that comes from improving the car on my own (the assistance of the forum notwithstanding).

What's next?

cooper9811

For stock heads, 34 degrees might even be slightly conservative. Not sure if you have stock or aftermarket, but I agree you are in a good place. I doubt you will notice a degree either way.

I would look at the carb tune next if you are just trying to refine your setup. You may find it doesn't need much done. Search on carb tuning, lots of good posts here that will give you some things to think about.

resdoggie

A new carb!!!!

jnb5101

I believe that Lars recommends NOT using the weights from the kits. I'm not sure why, but my comparing them to originals shows them to be of inferior shape and weight.

7T1vette

The shape of the flyweights changes the shape of the plotted timing curve. Depending on the shape, it can bring in timing earlier or later, but still keep the same total timing. But, for a steet vehicle, weight shape is a very minor detail.

StDomingos

Jnb5101,

I had seen Lar's recommendation about the weights too. I didn't feel I could use the factory weights because the bushings were so worn. The bushings in my kit were too big to fit in the factory weights as well. I couldn't seem to find a simple way to get factory bushings in good condition so I was forced to use the weights from the kit.

Thankfully I seemed to be able to get them to work ok and the curve (when I graphed it ) seems pretty linear.

StDomingos

That's a shiny Holley there resdoggie

I think I'm going to try to get the qjet sorted next though. I did adjust the idle mixture screws after the recurve, but that's it.

I think the carb needs a rebuild and will probably try to tackle it myself during the winter. I bought Ruggles book with that in mind. Looks like an awful lot of levers and tiny screws

7T1vette

Just be aware that most "carb" problems are due to ignition problems and/or vacuum leakage somewhere in the system. Do what you can to make sure your vacuum systems are not leaking. If you have significant vacuum leaks, NO CARB will work well on the engine.

REELAV8R

That is a good book. I used it to alter my Q-jet years ago and it has ran excellent ever since.