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M
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Can someone tell me what, in theory or in general, is the total advance requirement needed for optimum performance of a TR3?
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OP
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Stock.
OP
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Don,
The only reference to advance in any of the books/manuals I have is to intial timing 4 degrees BTDC at idle w/o vacuum. I don't find anything on optimum Total Advance (mechanical + vacuum advance).
I realize that the actual timing and advance will be different for every car.... but there may be an "ideal" point or range for Total Advance. Then, again, I also know that it changes with RPM.
NOTE: According to Jeff Schlemmer, the proper initial timing is now about 14 degrees BTDC at idle w/o vacuum (the exact figure depends on many factors unique to the car in question). He points out that 4 degrees with today's fuels is no longer valid. I assume that the slection of springs in the distributor will determine the advance curve and give Total Advance.
I'm asking just out of curiosity.
The only reference to advance in any of the books/manuals I have is to intial timing 4 degrees BTDC at idle w/o vacuum. I don't find anything on optimum Total Advance (mechanical + vacuum advance).
I realize that the actual timing and advance will be different for every car.... but there may be an "ideal" point or range for Total Advance. Then, again, I also know that it changes with RPM.
NOTE: According to Jeff Schlemmer, the proper initial timing is now about 14 degrees BTDC at idle w/o vacuum (the exact figure depends on many factors unique to the car in question). He points out that 4 degrees with today's fuels is no longer valid. I assume that the slection of springs in the distributor will determine the advance curve and give Total Advance.
I'm asking just out of curiosity.
Geo Hahn
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I do wonder/worry about total advance because it would be so hard to detect pinging (pinking, knocking) if it was occuring at higher RPMs.
For that reason I check advance at high RPM to be sure it isn't some crazy number -- but do not recall what I got or what it should be.
The 4° you mention is, of course, a static advance -- no idea off hand what advance that setting produces at idle (and to complicate that idles speeds vary) but as I recall the centrifugal advance comes on pretty quickly. IOW, I don't understand the remark "4 degrees with today's fuels is no longer valid".
For that reason I check advance at high RPM to be sure it isn't some crazy number -- but do not recall what I got or what it should be.
The 4° you mention is, of course, a static advance -- no idea off hand what advance that setting produces at idle (and to complicate that idles speeds vary) but as I recall the centrifugal advance comes on pretty quickly. IOW, I don't understand the remark "4 degrees with today's fuels is no longer valid".
TR3driver
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Ed, I've posted the link to the factory workshop manual before. Why don't you have a copy? It contains complete information on (TR2) timing.LexTR3 said:
<div class="ubbcode-block"><div class="ubbcode-header">Quote:] I don't find anything on optimum Total Advance (mechanical + vacuum advance).
[/QUOTE]
Just so you (and others) will know, the phrase "total advance" normally means initial timing advance, plus centrifugal (mechanical) advance. Generally, the effects of vacuum advance are ignored, since the vacuum advance is not active at full throttle (where ignition timing is most important).
<div class="ubbcode-block"><div class="ubbcode-header">Quote:] but there may be an "ideal" point or range for Total Advance.
[/QUOTE]
"Ideal" varies with a lot of factors, including camshaft design, combustion chamber design, exhaust system, fuel composition and so on.
<div class="ubbcode-block"><div class="ubbcode-header">Quote:]
NOTE: According to Jeff Schlemmer, the proper initial timing is now about 14 degrees BTDC at idle w/o vacuum [/QUOTE]
Which of course is largely because Jeff has changed the curve in Ed's distributor. He is NOT suggesting that those of us running stock advance curves should set our initial timing to 14 BTDC !
OP
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Randall,
You are right, and I don't want to give the wrong impression. Jeff was talking about my case. But he did point out to me that specifications for cars, set 50 years ago, have changed with the reformulated unleaded gasoline of today if you are after optimum performance. The settings for each car will be different.
I do have the factory workshop manual, downloaded from the Internet, but forgot to look there. Thanks for the reminder. Perhaps I'll find my answer there.
You are right, and I don't want to give the wrong impression. Jeff was talking about my case. But he did point out to me that specifications for cars, set 50 years ago, have changed with the reformulated unleaded gasoline of today if you are after optimum performance. The settings for each car will be different.
I do have the factory workshop manual, downloaded from the Internet, but forgot to look there. Thanks for the reminder. Perhaps I'll find my answer there.
TR3driver
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Chart in TR2/3 Bentley gives max centrifugal advance as 14 degrees (+/- 1 degree). But that is in distributor/camshaft degrees; while the initial timing (and the way most people look at timing) is in crankshaft degrees. So, factory total advance was 4 + (14 * 2) = 32 crank degrees.
There were several minor variations, until distributor 40795 was introduced around 1963. It had a 10 degree stop, so total advance was only 24 crank degrees. Other distributors for "low compression" or "83 mm" engines had other stops as well. The (partial) data I've got handy shows the lowest was the 83mm TR4 (a special order option) with distributor 40850 and a 6 degree stop.
https://i258.photobucket.com/albums/hh260/TR3driver/Etc/image001.jpg
There were several minor variations, until distributor 40795 was introduced around 1963. It had a 10 degree stop, so total advance was only 24 crank degrees. Other distributors for "low compression" or "83 mm" engines had other stops as well. The (partial) data I've got handy shows the lowest was the 83mm TR4 (a special order option) with distributor 40850 and a 6 degree stop.
https://i258.photobucket.com/albums/hh260/TR3driver/Etc/image001.jpg
OP
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Randall,
Great! Thanks very much for the Bentley chart.
BTW: My distributor is set to 14 degrees static and 35 degrees total advance. As you know, I had Advanced Distributors rebuild my distributor and they changed the advance curve. My shop guys did the rest.
All I can say is that the car, as long as I have owned it, has NEVER performed better.
All cars are different... indeed...
Over and out...
Great! Thanks very much for the Bentley chart.
BTW: My distributor is set to 14 degrees static and 35 degrees total advance. As you know, I had Advanced Distributors rebuild my distributor and they changed the advance curve. My shop guys did the rest.
All I can say is that the car, as long as I have owned it, has NEVER performed better.
All cars are different... indeed...
Over and out...
Bremer
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Just for reference:
Kastner writes that his TR4 race engines were at their best with only 28 degrees advance total. Of course, those were highly modified, high compression engines.
Interesting: When testing engines on the dyno they could go through a complete cycle without detonation if they did not linger at any point more than a few seconds. If they held engine speed at at a high level, torque was constant for about 15 seconds, then started to drop and they lost as much as 10 hp. The heat saturation at high loads promotes detonation, which results in less power and possibly engine damage. This may not be relevant for a street engine, though.
Kastner writes that his TR4 race engines were at their best with only 28 degrees advance total. Of course, those were highly modified, high compression engines.
Interesting: When testing engines on the dyno they could go through a complete cycle without detonation if they did not linger at any point more than a few seconds. If they held engine speed at at a high level, torque was constant for about 15 seconds, then started to drop and they lost as much as 10 hp. The heat saturation at high loads promotes detonation, which results in less power and possibly engine damage. This may not be relevant for a street engine, though.