[TR] TR4A - Tuning Update 2

Randall TR3driver at ca.rr.com
Mon Dec 16 10:58:12 MST 2013

> Where did this chart come from? Do you know what weights and 
> springs were
> used on each model? Something doesn't seem correct here.

Sorry, I wasn't paying attention to this thread.  I created that chart originally, using the numbers from Marcel Chichak's database
But I confirmed as much as I could from other sources, including the factory manuals.  

Still, I don't guarantee that any of it is strictly correct, especially the application information.  I was mostly interested in how
the advance curve had changed over the years, and found that the plots were easier to compare than the charts in the books.  So the
application information in the chart is only a rough guideline, and originally intended for my use only.  Then I posted the chart to
illustrate a point I was trying to make, and it went viral :)

For example, I believe most TR4 actually came with the 40795 distributor, and hence the curve I showed for TR4A.

I've got the information on the springs somewhere, but can't lay my hands on it at the moment.  AFAIK the weights were the same for
all 25D4 distributors.

Someday, maybe, I'll get around to checking out what works best on my own engine.  I've known for some time that "all it will take"
is not necessarily the right answer to ignition timing across the range.  The real goal is to line up maximum cylinder pressure with
where it will do the most good, which may or may not be limited by preignition.


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