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My TR3a has 87mm pistons a Phoenix extractor manifold and HS6 carbs ona TR4a manifold.  The combustion chambers iin the head have been modified to align with the shape of TR4a combustion chambers.

I have been looking at the timing curves in the workshop manual for the TR3 and Tr4a and they are markedly different. They both start with 4 deg static advance but the TR4a curve peaks at 22 deg of centrifugal advance - i.e. 26 deg when you add in the 4 deg of static at 1600 rpm, whereas the Tr3 curve peaks at 28 deg - i.e. 32 deg when you add in the static timing at 5400 rpm.

All of the above figures are based upon crankshaft degrees not camshaft / distributor degrees.

Can anyone explain why there is this significant difference.

Rgds Ian

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Ian,

No, can't explain it, but an old post here that I read last week can show the difference.

A nice curve graph is in that link.

I find timing confusing for my TR3 with Petronic ignition.

I can't set the 4 degrees static, obviously. And my vacuum works great, so do I add the static, the vacuum and centrifugal all together to set the advance?

After much playing with it all, I used the Moss Motors method of "move the distributor to the right, move it to the left, then pick the exact middle."

I seems easy and effective.

Cheers,

Opie

 

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Following on from the above, my car has a 123 ignition distributor.

I plotted a number of the 123 curves along with the TR3 and TR4 ones and came to the conclusion that the 123 curve that I had been using (No. 7) was probably on the best and that curve B would be nearer to the TR3 original.

It's a 10 minute job to change the setting on the 123 dizzy so having changed it I took the car for a 20 mile run to see if it made any difference, and yes it did.  The engine appeared to run more smoothly and the pick up was markedly better.  Also try as I might, I couldn't make the engine pink so all round an improvement but....

I did notice that the engine appeared to run hotter.  Not by much - the width of the needle in the gauge and I appreciate that it is a very warm day so that may have something to do with it but should I expect that a slightly more aggressive advance curve would increase the engine running temperature?

Rgds Ian

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The consensus is that retarded ignition is a cause of an engine running hotter.

From the Rootes forum :- http://www.rootesparts.com/id201.htm

There is a lot of misinformation about ignition timing and cooling. Retarded timing contributes to overheating. Advanced timing helps cooling. Bump up your initial timing a few degrees and see if it helps the car run cooler. It's an easy and practical fix. Of course, if you advance enough to enter pre-ignition or detonation you will start to overheat. Detonation contributes to overheating. If you start to detonate back off the timing. Overheating cars should always run vacuum advance. Vacuum advance helps cooling.

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Ian,

I am curious. My understanding of vacuum advance is that the SU intake port is under the butterfly throttle plate and therefore zero value of vacuum at idle. At midrange, there is vacuum advance added.  At WOT, the vacuum at the port is gone.  If this is all true, then the complete actual advance curve should show vacuum advance as additive only in midrange. The curve's vacuum contribution would  look  like a puppy under a carpet.

True?

Edited by Opie
typo
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Posted (edited)

Hi Opie,

As far as I understand these things, your comments about vacuum advance are correct.  At idle the vacuum port is the wrong side of the butterfly and under acceleration the vacuum in the manifold is reduced; e.g. the old vacuum operated windscreen wipers on Fords sold in UK in the fifties/sixties.

The data that I used for the TR3 curves was taken from the TR3 WSM which showed the vacuum as being a staight addition to the centrifugal but in reality it wouldn't be like that.  Which is why when I was comparing curves on the 123 Unit, I went for the one which was nearest to the TR3 centrifugal curve with the 4 degrees of static timing added.  I probably should have cleaned the graph up and removed the unnecessary curves before I posted it.

Rgds Ian

Screenshot 2020-06-01 at 12.19.39.png

Edited by Ian Vincent
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  • 4 months later...

I have a TR3 with an older 123 Ignition implemented. My friend does not want to change it, I just have to make the best out of it.

Got the engine running again...next step adjusting timing and setting carbs.

I set 6° static. (since none of the curves really fit). Using strob light I got 21° @ 1.700 and 26° @ 2.100. Still need to do rest. What is maximum advance one should aim for? 

It is an original engine, nothing fancy.

Jochem

Edited by JochemsTR
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feel free to elaborate on this text in the TR2-TR3 WSM.

run distributor at 2.700 - 13-15° ??

below is mentioned 2,000 @ 12.5 - 14.5 advance...

 

Advance Curve.JPG

Edited by JochemsTR
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Remember crank speed (and degrees) are twice the distributor figures so running the dizzy in a test rig at 2700 is equivalent to 5400 rpm. Ditto, 15 degrees advance becomes 30 degrees. Add on the 4 degrees static and you have a maximum advance of 34 degrees. Since one can probably assume that if you are pulling 5400 rpm you have your foot flat on the floor, there won’t be much vacuum advance happening. 

Rgds Ian

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Ian, this I understand....I am just curious what max advance I can use....I am hearing max 26...max 28....and now max 30....

ofcourse I will play until the engine starts pinging...just curious what the general max advance is with some of the other 123 users here driving a TR3.

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I am an advocate of using Martin at Distributor Doctors knowledge to set the advance curve, best suited to your engine build. He will do this for any engine if provided with the specification.

Then I use a rolling road to  tune and ensure that the mixture, through the rev range, under load is correct. 

Iain

 

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I would agree with you if one were asking Martin to repair and set up your distributor to match your engine; he would be getting some work out of it.  But I suspect he would not want to become the 'go to' person providing timing curves to all and sundry if there isn't anything in it for him.  Jochems is looking for help in setting up an electronic distributor plus he has already said it is "an original engine nothing fancy", so the original factory settings should be somewhere near correct - always recognising that modern pump fuels are not the same as those available in the 1950s and 60s.

Rgds Ian

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If curve B does the trick:

1000 - 10°

2000 - 23°

3000 - 27°

4500 - 33°

my first data points 1700 - 21° and 2100 - 26° do not seem off much....I will check at 1000 and 3000.....currently Curve F is implemented by PO, maybe I can leave it.

Jochem

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Jochem,

Curve F is very similar to curve B up to about 2000 rpm but above that figure it does allow more advance.  I would just check that you don't get any pinking at higher revs (high speed pre-ignition) because from my limited understanding of these things, that is where you can terminally damage the engine.

Rgds Ian

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For what it’s worth when Geoffrey was tuned recently at Revingtons on the rolling road we had TRouble getting it tuned until we disconnected the vacuum advance tube from the 123 distributor (which I had reinstalled when I first acquired the car). I’ve no idea what the final timing setting was as they’re bespoke to the modified engine but the 123 distributor is set to “B”.

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