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post #1 of 4 (permalink) Old 07-15-2015, 11:18 AM Thread Starter
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timing my Judge

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My '69 Judge ( RA III, 4sp, 3.55 ) has all orig running gear. Points dist and q-jet. This engine has 34* total timing, but requires 15* initial to aquire it. I also use 2-3 gallons of Sunoco 112 leaded in each full tank of fuel ( Chev 91) car runs nice and no startability probs. I want more performance. I would like to get 36-38* total while at same time backing off initial . Can someone give me some pointers on how to do this? A tech friend said my distributor and carb are excellent, but that someone in past put an advance curve kit in distributor. He cannot get more than 34* total.( while at 15* initial ) engine has stock RA III cam ( 068 ) and no a/c ...thoughts? Thanks very much
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post #2 of 4 (permalink) Old 07-15-2015, 02:07 PM
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Your questions tell me that you need some basic explanations of how this all works.

I'm going to ignore vacuum advance because you seem to be concerned with performance, and under "performance" (wide open throttle) operations the vacuum advance mechanism is inoperative and is doing nothing.

Inside your distributor there is a system of weights and springs. As rpm increases, the weights pull against the spring tension and rotate the spark triggering mechanism inside the distributor to occur earlier and earlier. There are mechanical limits to this process - a starting point for the weights (engine off) and an ending point (weights have moved as far as they can). This total range of weight movement is what determines how much advance (called mechanical advance or centrifugal advance) your distributor is capable of providing. In your case, your distributor is capable of providing 19 degrees of advance. Coupled with 15 degrees initial, that's how you get to 34 degrees total" 15+19=34.
If you want more total (38) without having to add more initial, then you will have to modify your distributor internally so that it has more range of movement for the weights.

Now some answers to questions you didn't ask.

Why do you think you want 38 degrees total? If your engine is a real RA III and has RA III heads, 38 degrees total is very likely to give you LESS performance than what you have now, not more. RA III heads are open chamber design and as such have very nice flame propagation characteristics and good combustion efficiency. They don't require as much "lead time" (advance) to develop maximum effective cylinder pressure (torque) as other heads (for example the 1967 '670' heads) do. By lighting the fire earlier than necessary, you're building cylinder pressure while the piston is still on it's way UP in the bore and you're essentially trying to make the engine run the other direction. This is not how you make power

If you want to dial your car in for max performance by playing with ignition timing, there are only two ways to do it. 1) On a dyno 2) at the drag strip with a set of accurate timing clocks. Start with a setting that you know is lower than what you need (in your case, I'd start around 32 degrees total). And then start dialing in more advance 1 or 2 degrees at a time, taking fresh measurements after each change (another dyno pull or several quarter-mile passes) until you find the point that makes the best power / produces the quickest times. Generally this means finding the peak and going past it some (where performance starts to fall off again). That peak point will be the best setting for YOUR engine.

Why are you concerned about running 15 degrees initial? As long as the car starts easily and doesn't overheat, the initial timing setting is of very little consequence. What matters is the total.

Ignition advance is NOT a case of "more is better". Best results come when the setting is optimized for the combustion characteristics of your particular engine. Lighting the fire too early is just as bad (if not worse) than lighting it too late.


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post #3 of 4 (permalink) Old 07-15-2015, 06:37 PM Thread Starter
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Thank-you Bear. I really appreciate your reply. Owned this Judge 25 years. Yes, RA III w/48 heads. Car is underpowered and sluggish. We will get in there again and tinker. I readon this forum that 24* + 12 initial is good for my setup. Gonna keep at it til it runs right. Dyno tune is great idea. I do not track my ride..thanks again. Taking under advisement!
Cliff Ruggles built my orig Q-jet (28273 ). I think I am close to dialing in the tune.
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post #4 of 4 (permalink) Old 07-15-2015, 08:42 PM
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MJ: "Car is underpowered and sluggish."

x2 on everything Bear has said. That said, underpowered and sluggish has the sound of a fuel/carb problem. Have you played around with the secondary air flap adjustment on the Q-jet. If the spring for the flap is too tight, the secondary air flap won't "pop" open soon enough to give you that good snapping boost of power and the engine will seem under powered or sluggish until it does. The same thing can happen if it opens too quickly and takes a big gulp of air and your car stumbles or even back fires through the carb. A 4-speed can sometime compensate for this, but you will feel it "nose over" and then pick up and accelerate as the secondaries open. If your Q-jet still has the choke pull-off/vacuum diaphram on the linkage for the secondary opening, this can be tailored to open/respond faster as well. Personally, I have never messed with the diaphram and disconnected them. I relied solely upon the spring adjustment for the secondary air flap found on the side, which is secured by a hex lock screw underneath the small set screw seen on the side. I would adjust the tension on the spring until the carb secondaries would not open too soon and bog the engine. Adjust 1/8" at a time. Cliff recommends using the choke pull-off rather then remove it. Who knew? Seemed to work OK for me 30 years ago without it.

I assume you have Cliff Ruggles book, it is all explained in there. So, I think I would look into fine tuning that Q-jet at this point.

Also assume your engine has either been rebuilt or your timing chain/gears have been replaced at some point as a sloppy/worn chain/gears can affect performance if they have not.
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