Ignition Advance

[Jyrki]

Alleycat and others - how much spark advance have you found to give the best performance with these engines?

I bet with todays fuels, you can run way more advance and get away with it. The combustion chamber isn't particularly efficient, so I would figure something in the neighborhood of 38 degrees total might be close?

I'm finding it hard to adjust initial spark advance, as the factory sentrifugal system starts advancing from very low RPM. Maybe I should just check the total advance at around 3500 RPM and ignore initial advance?

[rcull]

Jyrki,

How would the intial advance behave if you were to lighten the weights. Would it be more stable? I would think that when using 3500 for a full advance that there must be a way of stabilizing the initial being as most of the time performance is asking for full advance as early as 2500.

[alleycat]

About 10 years ago, I started to notice that that ALL the engines in all my cars/bikes/trucks were running decidedly, progressivly worse. Some engines were well run, some not. I've always tended to run my engines with as much advance as I could get away with. And, indeed, I found that I could crank in more advance than I ever could, say, 30 years ago. Up to a point. But there was still something wrong. About 2 years ago I started a ignition expierment, to find out just how much advance engines running on todays gas can take, or more accuratly, what kind of advance it takes to burn this fuel we are stuck with and not have it going out the exhaust still burning and get some power. And believe me, it's the fuel and nothing but the fuel.

What I found is that: if the engine is set to original ignition specs, not only is it wasting fuel but it is throwing power away as well. And it'll be slow. The original specs don't work. I found that the centrifugal advance is almost worthless. It can't respond quick enough. The intial advance is critical, and believe it or not, 20-25 degrees intial is a good place to start. How good or not the cumbustion chamber is is the determining factor. In the case of our str8's, it's bad. In one of my engines with a very good chamber, I have the centrifugal totaly locked out and all the advance in intial. And I think it can take more. As for total, 34-8 might be ok, with a good chamber. I have around 50 in my BBC. My problem with actual total or intial, is that I've run clean off the end of the timing marks. I never thought I'd need fully degreed damper or flywheel. Then there's the vacume advance. It's needed, it's the only thing thats instantly variable. So, do this: dig into the distributor. Lock out the centrifugal. Leave the vac advance hooked up, direct, not ported. start cranking in the advance. What we are looking for is max advance without preignition/detonation and still have the engine start hot easy. With the vac working, it should pull back under load and when starting. This should work well in the rpm range the str8 runs in, but then there is the higher rpm range. When I ran at the drags, I found that as rpm's went up, less advance was needed. What very well may be needed here is a progressive ingnition retard. Tough to get out of our distributors. I'm still working on this. alleycat

[Jyrki]

This is exactly what I wanted to hear! Back in 2004 in the initial runs, the engine pulled strong with a "bark" around 2700 RPM. Later I checked the advance with a strobo, and pulled back the advance to factory specs. Needless to say, it didn't run that well anymore. I have tried to correct the off-idle bog by increasing accelerator pump squirt, but maybe the ignition advance has something to do with it. The difficulty in setting the initial advance with a strobo light, is that the idle RPM should only be some 350 RPM (according to factory specs), while my idle is around 800 RPM, so the centrifugal advance has already come in. My distributor is otherwise stock, except for the Pertronix Ignitor module and coil.

So what I'm hearing, is to run as much advance as I can get away with!
The gas in the US is different from the gas here in Finland. People who have purchased engines from the US, that were dyno-tuned, have to be retuned here with local gas. If I remember correctly, they ran a little rich before retuning, as you have a more oxygenates like alcohol or methanol, in your gas. This is not a fact, it's what I've been told.

[alleycat]

jyrki, you are trying to set the timing just like I use to, and it wont work. Trouble is, there is so much intial advance needed with todays gas that when added to the centrifugal, it'll be to much. And, the centrifugal is rpm controled, so it go's in and stays in. With as much intial as possiable and the centrifugal locked out, you will find the off-idle bog will disappear and drivability will be much better, but it may 'ping' and even the vac advance may not be able to get the spark back fast enough. MSD has a advance retard unit. I don't know how it works but this may be the answer. By pulling off a few degrees/rpm at the top and having it all in intial may be the trick. Having a fully degreed flywheel and shooting it with a light, you'll know where the engine likes it, otherwise this is a "seat-the-pants" operation. alleycat

[beaverman]

I have a `37 320ci model 90,running rebuilt carb,fuel pump and distributor.There is a Pertronix Ignitor fitted(with matching Pertronix coil),silicon leads and new plugs.The timing is set at standard factory settings.
The problem i have is the motor cutting out at low speed when slowing down for a junction,not every time but more often than not,and i have started to `heel and toe`so as to keep the motor revving whilst breaking.Under acceleration the car pulls like a train,and when cruising at aconstant speed it runs fine,it is just this cutting out when your foot is off the gas i find baffling.The car starts first time, everytime(even when laid up for 3 months)
Is it a fuel problem,as suggested by alleycat,with today`s fuels not being compatible with 1930`s ignition settings? or could it be it be something else,anyone got any ideas?

[alleycat]

This sounds like pretty much what was happining to my engines a while back. It's not running enough ignition advance. The stock settings are almost no advance at all. Won't work, or at least, not well. So, with the engine warmed up, loosen the hold down bolt and crank in some advance, like 10-15 degrees, don't be timid, turning it "just a smidge" won't do it. If you have a good ear, you can have the engine running, and you can hear the engine "get happy" as the ignition approches the right spot. The idle will speed up, you'll have to back the idle down. Give it a try, it won't hurt anything, and you'll likely be way happy with the way it runs. alleycat

[presten]

Alley Cat: Having just finished building my 320, (you can see some pictures of it in other posts) I am now running it on the test stand. It seems like I am having the same basic problems you are talking about. To get it to run smoothly at 2000 or so (now this is with no load), it takes quite a bit of advance to make it work. Now with this setting, it is really tough to start...even with 12 volts to the 6 volt starter you can tell there is just too much initial advance. If I back down on the initial, then the engine cranks over nice and smooth but that is not nearly enough for the higher rpm's. Now that sounds to me like I need more mechanical advance...what gives? I have the vacuum advance connected to the ported tap as recommended by the carb literature.

[alleycat]

Presten, you are indeed having very much the same issues I ve found. Annoying. When you have the advance cranked up and its hard to start, is the starter, sort of, running into the advance and wanting to stop? If so, thats not all that bad. It indicates that things are happining in the cumbustion chamber fairly quick. But this is a fresh engine, things could change. Back off the initial just enough to get started, even if the starter gets "bumped" slightly. Don't port the vac advance, go direct. The engine likely could take more in the mech advance, but the springs in there are big and don't allow much advance. You will probably have to dig in there and put in light springs. However, at this point in time, getting the timing perfect on the stand may be a moot point, as you pointed out, no load. In the car is the place where it needs to be right. Are you still running 6 volt? A 6 volt ignition just won't provide enough spunk to ignite this junk gas we have to use. Gas has strange, diesel like, ignition similarities. A MSD 6A ignition box will ignite nearly anything, you can jet the carb down, smooths the engine out and is worth real power that can be felt in the drivers seat. It is, however, 12 volt.....alleycat

[39CENT]

well sounds like we may have to look at some combustion chamber work. Maybe a little quench welded into it? I,m thinking along those lines, and using 37 flat pistons? should have better flame travel too? didnt realize the gas problem as my 39 hasnt run in quiet awhile. I have seen a straight 8 with a MSD dist. that might be the way to go.