TFI - plug gap, has anyone actually done the advance springs?

Midrange is exactly where the extra zip should show up with lighter springs.
From off idle to about 2,500 to 3,000 is where the springs come into play, and as long as you don't have any detonation, it's free horsepower.
Kind of a pain in the butt to have to take the distributor out and take it apart, but if you really want the 'zip' the HEI guys have, that is how to get it.
Don't put the lightest springs in first, that's a bad Idea...
One factory and one medium kit spring first, then two mediums, then one med & one light.... ect...
Back up one if you get detonation or pinging while mildly accelerating.

If you detonation or pinging comes at cruse, when the throttle is steady, back your timing up a couple of degrees at a time until it stops.
DO NOT LET AN ENGINE DETONATE! Even small amounts of detonation can be VERY harmful, so keep a good ear out...
Or buy one of those detonation 'Knock Sensors' out of Summit for a few bucks, and that will tell the tail really quick...

Good luck guys,
Aaron.

If Chris Columbus "Discovered" America (with 25 million already here), Can I Go "Discover" Florida?

Hi, Chuck... long time, no talk to, etc. I posted a day or two ago about the DS mechanical advance, and I am aware that TR has posted a few times, also. In my opinion, one needs to work with the DS mechanical advance a little, if you want to feel the same performance you feel with the HEI. I agree with TR's post about one heavy and one 'medium' spring is a good place to start. I have only checked two DS distributors on the machine, so far, and based on only these two, I would suggest that TOTAL centrifugal advance needs to be looked at on the DS distributor. I found a 'pin' in a slot controls the amount of mechanical advance available, and I just took a dremel and a file to open the slot. As for the 'amount', I suggest the same amount of advance that a HEI has. TR posted his opinion for an amount, a few days ago. I would go with his experience, or just copy a HEI. I assume most people here will be working at home, with no distributor machine, so I am hoping that I can make some measurements and re-post back here on what to do. If you get a HEI and a DS both in your hands, and compare the total mechanical advance of the two, you will quickly get a rough idea of how much metal to remove from the DS 'slot'. Or if you have simple angle-measuring tools, you could do the same thing. I've just run the 83 CJ DS (CA-emissions) distributor on a distributor machine, and, it seems to have about 6 degrees distributor advance available (or, 12 degrees crankshaft). And, a HEI and a couple of old Delco points distributors, have about 10 degrees (20 crank). You can do a simple calculation to determine the amount of slot-enlargement needed to get 10 distributor degrees in the DS, about 0.090-inch material removal, for a total DS slot-travel of .217-to-.220, at a radius of 1.25 inches. Perhaps TR will post back with some 'target' numbers, as his experience might suggest that the HEI has too much advance, and maybe I am using it as a target, when I should not.
I should caution everyone that the Duraspark distributors I've looked at are from CA emissions (258), and I have no idea if 49-state distributors are the same. Please don't take my word for your 'starting-point', and just start hacking on the slot. I suggest be sure of what you are doing, or, maybe invest a little with someone that has a distributor machine. You could do your own disassembly/reassembly, and enlarging of the slot, but trust someone else to check what you've done.
Best wishes. BobH

bobH

Bob, I won't post on that...
Not because I don't want the numbers out there, but because your suggestions, although effective, require machining, and a distributor machine to verify, and can not be 'Undone' like restoring original springs or distributor cap...

I believe machining is better left to the professionals with a milling machine and distributor machine.
Just a disagreement here, not trying to start anything.

Something else you should be aware of, if you apply vacuum advance to both the GM HEI and the Motorcraft distributor while the centrifugal advance is in full, you will find the total advance is probably sufficient.
The Ford vacuum advance adds more to the total than GM, so it sort of works out in the long run.
If you use the lighter springs, the advance just comes in a little quicker...

Sense your total advance isn't changed, you should still pass emissions tail pipe tests also...
The centrifugal advance hasn't started at idle, and at cruse speed, the centrifugal advance should mostly be in anyway, so the advance rate isn't important to pass emissions tail pipe tests...

I'm trying not to get real radical here, mostly just bolt on stuff for the do it your selfer...
If you want to put your ignition on the ragged edge of maximum performance, you need to take it to someone with a dyno and the approate machine tools.
I was just trying for a little upgrade to take advantage of the technology advances in the past 20 years, not put the ignition up on the ragged edge that racing demands.
It would be too easy to make a mistake here, and do real damage.

It's a lot easier and a lot safer to add an MSD module to bring the ignition up to CDI standards, and add timing controls with a knock sensor so you don't destroy your engine.
You can use the newer MSD digital units to add any amount of advance at any time through the rpm range, and it's all at the turn of a knob...
That's how we find the best ignition curve on the dyno, and then try to make a distributor to match the curve if it's going into a street driven vehicle.

Later folks, Aaron.



If Chris Columbus "Discovered" America (with 25 million already here), Can I Go "Discover" Florida?

I agree with TR... don't try this at home.
For anyone that cares to know, after I removed .088-.090 from the slot (measured with a caliper), the distributor ran 9-9.5 degrees (18-19 crank) on the machine. With stock springs, advance started at about 575 (1150 crank), and was all in at about 1250 (2500 crank) rpm. (For anyone that is following this post, you will note that this result is almost identical to what I measured for a stock HEI, reported yesterday.) The stock vacuum advance added 10 degrees (20 crank), started at 4-in, and all in at 13-in. (Sounds to me like a good reason to not use manifold vacuum for this. Aaron?)
For information, I found that the part with the 'slot', for the mechanical advance, is VERY hard. Ordinary files would not touch it. I used a die-grinder to remove the .088-.090 material. Also, this part is made symmetrical. This means there is another, unused, slot, located opposite the slot being used. These two factory slots are not identical. One is larger, one smaller. The smaller slot was being used in the distributor that I am working with. A small amount of advance could be gained, just by switching to the larger factory slot... I'm guessing it would change from the original 6 degrees to about 8 degrees (double for crank). Something to think about, if you are looking for a few degrees, and do not want a permanent change. (Maybe 49-state Jeeps already use the larger slot ??)
I really like your MSD suggestions... I believe this is the direction I will head with one of my personal 'test-mules'.
As for this Jeep distributor (83-258), I have nothing to put it in. I will be waiting for a 'willing' customer (already identified), and I will be doing a little dyno-test, comparing the results with the factory-stock DS, the 250 Chevy HEI, and this modified DS. This person has a 86 CJ, and has already run both stock DS, and the HEI. I do not have any intention of getting near any 'ragged-edge'. I believe this would be for racing-only. On the street, there are too many atmospheric variables and fuel variables. Ain't modern computer-controlled cars great, for taking care of all the variables?
Thanks, Aaron, for your input. Best wishes. BobH

bobH

Even the bottom of the MSD CDI line, (the 6 series) makes so much of this a waste of time.
Every timing gadget MSD makes will plug right into the 6 series modules.
Timing advance at the twist of a knob and the Knock sensor are my two favorites...

Lets not forget just the Capacitive discharge alone is worth the price of admission!
I'm sure someone will invent a better ignition in the future, but right now, MSD is the way to go!

I noticed the longer slot also on the motorcraft advance head... Also noticed you can gain a little by taking the rubber stop bumper off, but that is going to cause bounce.
I know why Motorcraft put the weights down low, I just wish I didn't have to pull the distributor to change springs.

In the all out race cars, we lock out all variable advance, and set the initial timing with all the advance we are going to run.
On street driven cars, I always try to leave the vacuum and centrifugal advance in...

You make a very compelling argument for ported vacuum! There are several here that swear their GM HEI's run better on manifold vacuum. They also b*tch that they get no milage... (Well, DUH!)
I usually find I need to limit the travel on GM vacuum advances, while on a Ford, it just makes up for the difference in centrifugal advance between Ford and GM...
On the 258 I-6, you shouldn't need to limit the advance. AMC set the timing up so spongy that full advance still isn't anywhere near the upper limit, no matter what you do...
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Later folks, time for me to turn in...
Aaron.

PS, Bob, you are going to do well here!

I haven't committed a crime. What I did was fail to comply with the law...