[TR] TR4a ignition advance

[Darrell Walker]

I should add another point.  I also think the RPM is in dist RPM, as  
most things I've read claim that the mechanical advance should be  
"all in" between 3000 and 3600 RPM (engine).  Also, you probably  
won't see max vacuum advance at the same time as the max mechanical  
advance (vacuum advance goes away at WOT).

-Darrell

On Sep 21, 2007, at 9:38 AM, Darrell Walker wrote:

> This table has been floated around the list before:
>
> Vacuum Advance dist. 40795
>
> Inches Hg           Degree Crank advance
> 2.0                     0
> 3.0                     1
> 4.0                     1.75
> 5.0                     2.5
> 6.0                     2.75
>
> Centrifugal Advance
>
> RPM                    Degrees Crankshaft advance
> 500                     0
> 700                     0-2
> 1200                   5-7
> 1600                   9-11
>
> So if you believe this is indeed crank degrees, you get a total max
> advance of:
>
> 4 + 2.75 + 11 = 17.75 degrees
>
> But I don't believe the above figures are in crank degrees, but
> rather distributor degrees (half of crank).  But the initial advance
> maybe crank.  So that gives you:
>
> 4 + 5.5 + 22 = 31.5 degrees
>
> Which seems like a reasonable number.  I recently read a book on
> powertuning ignition systems, and it claims the combustion chamber
> shape is the biggest factor in how much advance the engine can
> tolerate.  The one that most closely matches the TR head was called a
> "bathtub" chamber, and they said 33-34 degrees.  So that would be in
> line with second calculation.
>
> -Darrell
>
>
> On Sep 21, 2007, at 8:36 AM, spamiam at comcast.net wrote:
>
>> Does anybody know the ignition advance information for the TR4A?
>>
>> I know that stock static advance is 4 degrees BTDC, but what is the
>> full vacuum advance?  What is the full mechanical advance?
>>
>> Someone said to me that these engines can not tolerate all that
>> much total advance (I.E. less than 30 degrees).  I would have
>> expected that a total advance in the mid-30's would have been about
>> right!
>>
>> -Tony
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