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Discussion Starter #1
I read somewhere that the distrib. that came with california emissions (Thermactor) equipped cars was somewhat more restrictive than the reg c code distrib. Is there a good reason to switch to an aftermarket one? I already installed a pertronix II, and am running the coil to match it.

Thanks
Ted
 

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Ted,

From looking in the shop manual, it looks like the distributor for your car, 289 automatic, should be a dual advance distributor. That is for the Thermactor equipped or non Thermactor equipped car.

Some of the 66 I6's were equipped with the Load O Matic distributor, which doesnt utilize the vaccum advance, but that doesnt apply to your case. The I6 that has a Thermactor has a dual advance distributor.

I put a Pertronix in my I6 w/Thermactor (the Pertronix unit was actually special for Thermactor distributors- I believe the anchor point for the Pertronix is different in the thermactor dist, that I believe is the only difference).

I would have to guess you put in the Pertronix made for the 289 thermactor equipped engine, you shouldnt have any issues.
 

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The Pertronix is just an ignition that fires whenever the distributor tells it to, there is no Thermactor version that I know about.

The Thermactor distributors had different advance curves and the details are in the shop manual. The centrifugal portion wasn't all that different but they were not identical. Some advanced quicker and some slower depending upon auto/manual, etc. Thermactors generally had less static advance which you can easily change.

The vacuum advance portion was about the same except the max advance was more limited on the Thermactor versions. However, the centrifigal advance limits were higher by similar amounts. The vacuum advance limit as well as the vacuum limit were set with shims, etc., inside the vacuum unit so those can be changed but it may not be worth your trouble for a stock engine. I doubt an aftermarket advance curve would be any closer to an original, non-Thermactor curve than what you already have.
 

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Gary,

Thanks for filling in the technical blanks I had there- I know enough, probably just enough to keep it out of the mechanics shop on a good basis!

In regards to the pertronix units, there are in fact different ones for Thermactor vs. non Thermactor units:

Results for pertronix -

I am not totally sure of the differences myself- but did notice when I ordered one for my thermactor equipped car that there was an option. Must be some reason for it.
 

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The only difference would be Loadmatic vs Dual Advance; there may be some difference that affects fit. Thermactor itself has no affect upon how you fire a spark plug.
 

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The listing for my Pertronix was...1957-1974 All Ford V8 with single points. The other listings for Ford V8's was for dual points set up. That be from NPD. Says nothing about TE.
 

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Discussion Starter #7
Interesting that the 6 cyl. models have a thermactor option, but not the 8 cyl. I thought that my distrib advance curve might be different because @ 3500RPM, I am at more like 23 deg. I read that stock distributors should be at about 34 deg. @ 3500RPM. Perhaps I need to look over the shop manual and adjust my curve.
 

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I believe Gary is correct though, on the reason for a different Pertronix for 6 cyl w/Thermactor, the mounting is different.

In my V8, with the Dual Advance dist, the index nub of the Pertronix was in a totally different point than the Pertronix unit I bought for the I6- which also uses a 6 cyl version of the Dual Adv dist, the Thermactor one.
 

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The 6s used different distributors for TE cars, the V8s did not. The V8 TE just had different advance curves in the same unit which is how you can use the same Pertronix for 25 years.

Ted I believe you have a 289, 2V, TE, car. The attached graph shows the advance curves for EVERY V8 Mustang, Comet, Fairlane and Falcon produced in 1966 taken from the Ford shop manual. There are NONE of them that ever had more than 28 degrees centrifugal advance at 3500 RPM and the ones with the most advance are TE cars! What I plotted is the average of the advance range given at each RPM. If you take the range into account then your 23 degrees is probably at the bottom end or the range but still within spec. If you switch to a non-TE distributor you will get less advance not more. This plot easily makes a lie out of the common assumption that a TE distributor had an awful advance curve. They could be more aggressive than the others probably to make up for the retarded static timing.

Remember that the plot is in distributor RPM and distributor degrees so 3500 RPM for the engine is 1750 on the chart and that 14 degrees on the chart is 28 crankshaft degrees advance. The lines are a little hard to decipher but the two very top ones, the blue and yellow ones are for manual and automatic, 2V, TE, 289s. Their max advance stop is set at 16 degrees (32 deg crank) and they wouldn't reach that until about 4500 engine RPMs. The engines with the least amount of advance, again (light) blue and yellow lines on the bottom right corner, are the A-code and even the HiPo engines. The HiPO had no vacuum advance so that light blue curve on the very bottom is all the advance they ever got and at 3500 engine RPM that was only around 17 degrees advance. Even though the non-TE, 4V distributors had a stop set at 14 degrees the engines would have had to turn about 10K RPM (not gonna happen) to ever reach that 28 degrees of advance.

For the 4V 289s the yellow line just above the HiPo is for both manual and automatic. That non-TE line is well below the pair of 4V TE lines that are the purple/pink pair that at 1000 distributor RPM are just below the top two 2V TE lines. So any TE 289 had a more agressive centrifugal advance curve than the corresponding non-TE version.

The 'curves' that look almost like straight lines more to the bottom for most of the RPM range are the 390 cars.
 

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Discussion Starter #10
Uh, ok. Way over my head, but if I were a little smarter, that would probably be very helpful information. I guess my next question is, can I tune my distrib. to give me a little more performance?
 

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This post will add nothing of value to the conversation, except to bump it up to the top again, but thanks Gary! (IVY66GT)

I really enjoy learning and reading your detail. Like I have posted here and elsewhere, I know enough engine wise to keep it moving and out of the mechanics shop for most things, but have zero abilty to comprehend how to curve a distributor.

But, this level of detail you provide here, when I may learn someday to do this type of work, is going to come in handy, and I will remember your very detailed post.

Your a total treasure trove of info for this hobby, keep it coming!
 

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Impressive breakdown and explanation. It sounds like you are just the man to answer my question. I have a 66 six cyl Mustang. I wish to change out the L.O.M. dist. and replace it with a 1968 Thermactor Equipt. distributor. I was told this will give me better performance that the set up currently there which is SCV carb. mated with L.O.M. I do not wish to go modern. However, how would I tell if a six cyl. 1968 dist. it the right one? I.E. what numbers or identification marks/features would be a clue. Thanks for the education
 
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