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post #1 of (permalink) Old 05-15-2007, 10:53 AM Thread Starter
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distrubuter curve info needed.

How about a little class on advance curves?
I'm having a pinging problem with a Ford 302 in a YJ.
It has a stock 1991 block and heads
stock exhaust manifolds
Duraspark dist
T/R upgrade
Cast 2 barrel iron intake
M/C 2100 carb
Lunati Bracket Master camshaft (.488 lift, 218 degrees duration @ .050
284 degrees advertised duration)

With timing at 0 BTDC almost no pinging (what is there starts at approx 2500 RPM.) and the throttle response and low end sucks. Around 8 degrees initial timing the bottom end is strong and extremely responsive. So, time to screw with the advance.

What is a good place to start? What seems to work on small block Fords? Any tips and tricks?

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post #2 of (permalink) Old 05-15-2007, 12:52 PM
 
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What kind of plugs and wires are you using? I had that problem in my Ram because I was using 8mm wires and platinum plugs, even with 87 in the tank. Neither of those work in old engines. The electrode in the plugs are too small and with the wires being so thin, the lack of spark caused them to arc out, thereby causing pinging, especially when the motor was cold. Once I put a set of non-platinum Champion plugs and 10mm Accel shielded wires, it went away and I could use 110 again on the track and 93 on the street. The cold-start issues also disappeared, too.
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post #3 of (permalink) Old 05-15-2007, 11:15 PM
 
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WTF did that guy just say?
----------

Anyway, back to planet earth,
Your distributor for a SBF car with 4 barrel by any chance?

Quote:
"With timing at 0 BTDC almost no pinging (what is there starts at approx 2500 RPM.) and the throttle response and low end sucks. Around 8 degrees initial timing the bottom end is strong and extremely responsive. So, time to screw with the advance."[
First off, you don't have the best cam for slow off roading, so I'm assuming you are using this vehicle for street driving also?
-----------

My guess is you are getting too much mechanical advance.
You can try a couple of things,
First off, keep your initial timing at about 8° BTDC, that is a good, calm place to start.
Since you are happy with the idle and off idle performance, this is the hot ticket
Make sure your vacuum advance is unhooked and the line is plugged when you set the timing.

Secondly, move your vacuum source to a 'Spark Ported' supply.

Third, Hook up the vacuum and see how much vacuum advance you are getting at idle. We'll need to know that to do this properly.

Fourth, Unhook the vacuum and plug the line again.
Rev up the engine and see how much advance you are getting from centrifugal.

Fifth, leave the vacuum unhooked, drive it a little bit, see what it does.

Now, If your vacuum advance has 'Flats' just behind the vacuum line nipple, you have an adjustable vacuum advance from the factory.
There are two kinds, An Allen wrench type, and a flat blade screwdriver type.
The Allen wrench type is much more common...
You can limit the total vacuum advance by moving the screw in and out.
You will have to reset initial timing after you make changes.

The Centrifugal advance is somewhat harder to get at...
It's in the bottom of the distributor, under the mag trigger/advance plate and floor plate.
In this image, marked R13 & R18,


These denote the amount of advance each slot will allow. (Amount of Centrifugal Advance)
You can take some top end out of the advance by retarding or limiting the amount of travel in this slot.

You should also notice the springs.
Larger springs won't give you less advance, but it will make the advance you do have come in later (Timing of Centrifugal Advance)
If you need new springs, try Mr. Gasket part number 925D. This will give you a selection of springs so you can try different combos.

If you don't have a balancer that shows your total advance (many don't), you can solve this problem easily.
Measure the distance from the 0° mark on the timing tab to the 10° mark.
Transfer that distance to the balancer starting at the regular timing mark and moving to the left (before TDC).
Do that about 3 times and you will have 40° of timing marked, and that should be enough for a SBF.
Read your new mark on the timing tab like it was the original, but don't forget to add 10° for each mark you go past on the way to the totals...
(Example, 1 new mark plus 2° is 12 degrees total.
2 new marks plus 5° is 25° total.)

Now, here is something you need to know...
In the center of the advance head (copper part shown in picture) there is a steel shaft.
(It will be covered by a lubricating 'Felt' in a stock distributor.)
Around that steel shaft is a very small wire clip that expands to get it out.
DON'T LOOSE OR BEND THIS WIRE CLIP!
This is what holds the advance head on the distributor shaft, and without this, you are screwed! There isn't anyplace to get replacements, so be careful and use a magnet!
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post #4 of (permalink) Old 05-16-2007, 06:05 AM Thread Starter
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Quote:
Your distributor for a SBF car with 4 barrel by any chance?
It's "supposed" to be for a 2 barrel 79 Ford truck, but who knows.[/quote]



Quote:
First off, you don't have the best cam for slow off roading, so I'm assuming you are using this vehicle for street driving also?
Yes, it is a little big. Sometimes you run what you have. Actually, it is not bad at all. I can lug the idle down to 300 without killing it, not really a lopey idle at all, but you can feel it coming to life at 1500. I'm funning an Np 435, 4.56 gears and 33's so I figured I could give a little bottom end up.
-----------

Quote:
My guess is you are getting too much mechanical advance.
You can try a couple of things,
First off, keep your initial timing at about 8° BTDC, that is a good, calm place to start.
Since you are happy with the idle and off idle performance, this is the hot ticket
Any guess as to what the total advance should be?


Quote:
If you don't have a balancer that shows your total advance (many don't), you can solve this problem easily.
Measure the distance from the 0° mark on the timing tab to the 10° mark.
Transfer that distance to the balancer starting at the regular timing mark and moving to the left (before TDC).
Do that about 3 times and you will have 40° of timing marked, and that should be enough for a SBF.
Could have used that trick a while back. i bought a timing tape that did not stick and eventually (finally) had a brainstorm to measure and mark the ballancer.

Thanks JJ. Confirms a lot of what I have been hearing.

Oh, Are the 4V distributors different?

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post #5 of (permalink) Old 05-16-2007, 08:47 AM
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Or you can get an advance timing light - the kind with the knob - it's made to measure timing beyond the marks.

Ported spark vacuum - 0 or near 0 at idle - increases with R's.
There should not be any change connected or disconnected at idle.

8 initial -
Vacuum disconnected at around 1000 - 1200 timing should start to advance -
around [email protected]
It should slowly and gently advance with speed and max out about [email protected] RPM
Record the timing at a couple of points between, ie: 1200, 1500, 1800 2000 etc.
If it jumps or is erratic - weights are sticking.
That takes care of the mechanical advance - that's essentially your "power" curve.

The vacuum curve follows a curve more with more advanced timing - the "efficiency" curve - mileage.
Remember - the vacuum "adds" advance to to power curve. (The AF charge in the cylinder is less, taking more time to burn, so we light it earlier - advanced.)
Vacuum Connected it should read somewhat higher timing than it did. Take your readings again at the speeds initially recorded - it should be higher each time, slowly progressing until about 2500-3000 RPM where it should max out about 35 degrees.
Yes, it can and will run with more than 35 degrees, but much above 35 degrees it's putting a tremendous amount of wear on the rings and everything, radically shortening engine life.

Essentially mechanical adds around 15 degrees on top of initial, and vacuum adds another 15 on top of that.

As JYG suggested, try it without the vacuum - if it stops pinging mid range you are on the right track - timing.

If not - it could be fuel - or a lack of it - lean mid-range. Do a search on here for "propane trick" - it's a simple way to determine if the mix it right.
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post #6 of (permalink) Old 05-16-2007, 10:44 AM
 
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Jeeps seem to like around 35° total, and they DON'T like it to come in too fast...
Normal, heavier vehicles (Like a Ford Full size truck!) will take timing faster.
'Normal' size tires and a 3.50 to 3.70 gear is about normal in a truck, so it's going to be able to use the timing a little faster than your jeep.

I'd try limiting the vacuum to about 10° to 15° max (nothing you can do about rate of a vacuum canister).
Fast vacuum canister is a good thing for fuel milage and street/low end drivability.

If it were me, I'd start with limiting the vacuum to about 10° then I'd put two heavy springs on the centrifugal and move the advance head to the smaller slot on the limiter.
You can always creep up the vacuum a little at a time until the 'Ping' starts again, then back it off a little.

Are you running big tires?
Tall tires will kill your gear ratio, and also kill your engine tune unless you make up for them with proper gearing...
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post #7 of (permalink) Old 05-16-2007, 09:30 PM Thread Starter
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Running 33's and 4.56 gears. At the point the pinging starts (2600 RPM)I am getting 20 degrees total advance (4 initial and 16 mechanical with the vac advance unhooked) at 3000 RPM 22 degrees, and at 4000 26 degrees.

Took a look at the rotor. Looks funny. Is this a sign of a rotor phase problem?
Sorry for the bad pic.
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Last edited by jeeperjohn; 05-16-2007 at 09:33 PM.
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post #8 of (permalink) Old 05-17-2007, 02:03 AM
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Rotor phasing won't change timing - it just makes the arc between the rotor and cap terminal longer. The signs of it are the side or edge of the rotor tip burns.

That's not normally a problem on a stock distributor - as it's phased properly from the factory. At idle it's a little to one side, at speed it's to the other side. Mechanical advance doesn't change the relationship - only vacuum.

But if someone's changed the position of the pick-up coil - or you are running 7000+ R's it should be looked at.

Heavier mechanical springs will slow it down and change the stop so it's not quite so much.

What plugs are you running? Mickey Mouse plugs - like Bosch, Plats, Multis, or Splits will also cause ping - big time - use the stock plugs the head was designed around!!! Unless you've radically reshaped the combustion chambers, the original stock plugs are best.

If you have the junk ones, change them out before anything else!
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post #9 of (permalink) Old 05-19-2007, 09:24 AM
 
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Several years of Dyno testing have proven Autolite plugs do the best job off the shelf from your local discount auto parts store...

On the dyno, we found Autolite did the best horsepower wise, and Dinso (as in Nippon-Dinso) was second.

So the .99˘ each plugs actually beat the fancy, high priced plugs in the dyno room where it counts...
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post #10 of (permalink) Old 05-19-2007, 09:40 AM Thread Starter
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I have been running Autolites for ever. I have never had a problem with them.

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