I started trying to write an explanation but gave up.
We have discussed spark advance curves countless times on here. If you didn't get the gist of it then you won't now.
But basically fit the bush that limitis the advance in the dizzy as much as possible. The black one if I remember right?
Then fit the springs that give you total advance by 3000rppm and about half of it at 2200rpm. This should leave you with an initial advance of 16 degrees or so.
The basic theory is that you want as much spark as possible at each rpm up to 3000. You fuel and compression will dictate that. The lower the rpm the less spark advance your engine will like so it has to increase with rpm.
Re curve dizzy
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Dave-R
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Let me try again.
I will tell you what my curve is with the same dizzy. Refer to the graphs that MSD give you.
I am using 1-silver (heavy) & 1-silver (light) springs which is the third graph down on the left hand side.
I am also using the black bushing.
See on the graph that the line for that bush stops at 3000rpm and at a timing level of about 17 degrees?
Now I know my car likes 35 degrees total advance. So if I set my total advance at 35 that is 18 degrees inital. Yes? 18 Initial plus the 17 in the dizzy = 35 degrees.
Now you want about half of the dizzy advance in by just over 2000rpm. So I am looking for about 8.5 degrees around there. In fact the chart shows 8.5 degrees comes in at or just below 2000rpm.
Probably close enough.
Because I have made changes to my engine, when I get the car on the road I need to see how much advance my engine will take at 2000, 2500 and 3000rpm without pinking under load. Then adjust the springs to suit.
I hope that is more helpful.
I will tell you what my curve is with the same dizzy. Refer to the graphs that MSD give you.
I am using 1-silver (heavy) & 1-silver (light) springs which is the third graph down on the left hand side.
I am also using the black bushing.
See on the graph that the line for that bush stops at 3000rpm and at a timing level of about 17 degrees?
Now I know my car likes 35 degrees total advance. So if I set my total advance at 35 that is 18 degrees inital. Yes? 18 Initial plus the 17 in the dizzy = 35 degrees.
Now you want about half of the dizzy advance in by just over 2000rpm. So I am looking for about 8.5 degrees around there. In fact the chart shows 8.5 degrees comes in at or just below 2000rpm.
Probably close enough.
Because I have made changes to my engine, when I get the car on the road I need to see how much advance my engine will take at 2000, 2500 and 3000rpm without pinking under load. Then adjust the springs to suit.
I hope that is more helpful.
Let me just give you some real basic timing info Pete, I think it will help. Initial timing is what you set at tick over. Total, is what ever you set the initial at, + what the distributor adds as revs increase. That bit that the distributor adds is what you are adjusting with the springs and stops. The heavier the spring the further up the rev range the timing will start to advance and the longer it will take to reach full advance. A light spring will do the opposite. The thicker the stop the fewer degrees of timing will be added.
OK, lets get a bit more technical, you need only a certain amount of total timing, lets say 35 degrees. To allow you to increase the initial timing you use the stops to prevent the distributor from adding too much more and going over that 35 degrees.
The rate at which the distributor adds timing is called the curve, a fast curve would start at say 1500 rpm and have all the timing in by 2500rpm. A slow curve might not start till 2000rpm and not be all in until 4000rpm.
The springs are what control this rate of advance.
For best performance you want all the timing in as fast as possible, the engine spec dictates how fast that should be, weather a slow or fast curve is best. Sluggish performance or detonation will be the result of the wrong curve.
With the sort of engine you are building, I would start off with 15 degrees initial, 35 degrees total and have it all in by 2500rpm. That will get you in the ballpark. You can then fine tune it at the track, increasing the initial until you find what the engine wants, same with the curve and same with the total.
An engine kickback test will tell you how much initial the engine wants, your 60ft times can be a gauge for the advance curve, and your total timing will affect your mph so increase it a bit or back it off until you get the best terminal speed.
Hope that's written in brickie language!
OK, lets get a bit more technical, you need only a certain amount of total timing, lets say 35 degrees. To allow you to increase the initial timing you use the stops to prevent the distributor from adding too much more and going over that 35 degrees.
The rate at which the distributor adds timing is called the curve, a fast curve would start at say 1500 rpm and have all the timing in by 2500rpm. A slow curve might not start till 2000rpm and not be all in until 4000rpm.
The springs are what control this rate of advance.
For best performance you want all the timing in as fast as possible, the engine spec dictates how fast that should be, weather a slow or fast curve is best. Sluggish performance or detonation will be the result of the wrong curve.
With the sort of engine you are building, I would start off with 15 degrees initial, 35 degrees total and have it all in by 2500rpm. That will get you in the ballpark. You can then fine tune it at the track, increasing the initial until you find what the engine wants, same with the curve and same with the total.
An engine kickback test will tell you how much initial the engine wants, your 60ft times can be a gauge for the advance curve, and your total timing will affect your mph so increase it a bit or back it off until you get the best terminal speed.
Hope that's written in brickie language!
“It’s good enough for Nancy”
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Anonymous
Great info guys. 
If it were me setting the ignition timing up i would lock it out & fit a switch (kickback) , reason being is the car will never see the street & will be well over 3000 rpm anyhow.
Pete , if you turn the distributor through 180* , you can lock it out & do away with the advance bushings.
If it were me setting the ignition timing up i would lock it out & fit a switch (kickback) , reason being is the car will never see the street & will be well over 3000 rpm anyhow.
Pete , if you turn the distributor through 180* , you can lock it out & do away with the advance bushings.
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Trigger_Andy
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forget the springs.-
Dave-R
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I think there comes a point where no matter how fast you rev the engine you don't get any more gain from advance. Maybe because fuel burns at a constant rate no matter what the rpm?
Plus of course if you have too much advance the wrong cylinder is firing so there is a limit to how much advance you can actually give.
Another point. The higher the octane of the fuel, the more advance you usually need because it burns slower.
Plus of course if you have too much advance the wrong cylinder is firing so there is a limit to how much advance you can actually give.
Another point. The higher the octane of the fuel, the more advance you usually need because it burns slower.
The answer to that Pete, is a complete can of worms! Static compression, quench, head material, cam profile, fuel octane and temperature all play a part in whether a particular combo will detonate on pump gas or not. You can not simply say something like, 9.5-1 won't detonate but 10.5-1 will, either might or might not, depending on those other factors.
“It’s good enough for Nancy”