pre-programmed curves on 123 ignition - help please?

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max-it-out
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#41 Re: pre-programmed curves on 123 ignition - help please?

Post by max-it-out » Tue Jul 07, 2020 8:52 am

Disappointing that none of the curves match - it makes you wonder if it`s really worth it ( c. £ 400 when you add in the cost of new plugs and leads ).
On the other hand , if the car runs well then maybe it`s ok. Just wonder about that max. advance figure - how high can you go before you risk damage ?
Mark

1968 series 1.5 roadster

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malcolm
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#42 Re: pre-programmed curves on 123 ignition - help please?

Post by malcolm » Tue Jul 07, 2020 9:02 am

max-it-out wrote:
Tue Jul 07, 2020 8:52 am
Just wonder about that max. advance figure - how high can you go before you risk damage ?
I was wondering the same! I'm assuming that if there is no pre-detonation, all is well. Maybe I'm wrong?
Malcolm
I only fit in a 2+2, so got one!
1969 Series 2 2+2
2009 Jaguar XF-S

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#43 Re: pre-programmed curves on 123 ignition - help please?

Post by mgcjag » Tue Jul 07, 2020 9:17 am

Hi Mark.....if your thinking of a 123 then the "Tune" version is obviously the best....you can program in any curve you want......by going with the standard type you are taking pot luck.......Steve
Steve
1969 S2 2+2 & Building a C type replica

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#44 Re: pre-programmed curves on 123 ignition - help please?

Post by Tom W » Tue Jul 07, 2020 9:57 am

One of 2 things will happen if you have too much advance.

Either the engine will pink, and you’ll start doing damage to the internals.

Or, you’ll stop gaining power with further ignition advance, but no pinking. In this case the flame front is still propagating cleanly, but peak cylinder pressure is reached before the crank has reached the optimum position to allow the maximum work to be extracted from the charge. This puts an undue strain on bottom end of the engine.

With ignition advance, as little as is enough is right, rather than more is better. Keep adding it until either the engine pinks, or power stops climbing, then come back a bit for safety.
Tom
1970 S2 FHC

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#45 Re: pre-programmed curves on 123 ignition - help please?

Post by malcolm » Tue Jul 07, 2020 11:16 am

Trouble is, the only way to "come back a little" is either to go to curve 0 which doesn't have enough initial advance, or reduce the static timing. Would it be better to reduce the max. advance from 34 to 32 and have a static advance of 8? Trouble is, that would also reduce the early advance figures by 2 and they are already behind the game on curve number 2 even.
Malcolm
I only fit in a 2+2, so got one!
1969 Series 2 2+2
2009 Jaguar XF-S

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#46 Re: pre-programmed curves on 123 ignition - help please?

Post by mgcjag » Tue Jul 07, 2020 11:36 am

The problam with comparing the 123 curves with the "correct" curve in the service manual is that the correct "curve" is from a distributor test bed 50 odd years ago.......a slightly worn engine and different fuels available today will probably requirer a different curve than the "correct" one..........you are very limited though with the standard 123....this isnt something new..its been known for years that there isnt a suitable curve...thats why quite a few ditched the 123 and went back to their standard dizzy......the tune version though is the one to use...Steve
Steve
1969 S2 2+2 & Building a C type replica

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#47 Re: pre-programmed curves on 123 ignition - help please?

Post by Tom W » Tue Jul 07, 2020 11:53 am

The only way you’ll know for sure is to have the car on a rolling road. That way you can hear more easily when the engine is starting to pink, and measure accurately when the power stops increasing at any given rpm point when the engine is loaded up.

I imagine there’s some leeway built into Jaguar’s curve. If you plot the upper end of the factory curve you get more advance anyway, and that would have been within tolerance. They had to specify something with enough leeway that the cars would still run ok without pinking when they were a bit coked up. Having said that, 60s petrol was a higher octane, so less susceptible to pinking, and any wear in the mechanism would cause the timing to retard from ideal. If your engine has done a few miles, and the compression perhaps isn’t as good as when it were new, it may tolerate a little more advance than the book suggests.

As the curves in the 123 are a preset shape, if there isn’t one that’s right, it’s always going to be a compromise of either too much or too little somewhere in the curve. Too much anywhere isn’t good for the longevity of your engine, so the compromise will have to be too little somewhere else. The best option would be to swap for a programmable 123, or fully mappable ignition system.
Tom
1970 S2 FHC

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#48 Re: pre-programmed curves on 123 ignition - help please?

Post by MarekH » Tue Jul 07, 2020 12:14 pm

A map or curve taken from an archive will be different from that you get from that determined on a rolling road.

Aside from the changes in the salient factors pointed out by Steve, the rolling road operator will instantly see whether the car produces more or less torque as he advances or retards the ignition. This way, he tailors the advance map to your engine and dials out things like resonances in the air coming into the engine and the exhaust gases exiting the exhaust, so the little dips in performance here and there are reduced.

Before mapped ignition was available, the default ignition map simply consisted of static advance, plus vacuum advance plus centrifugal advance and there was no way to fine tune these factors despite the fact they weren't the optimal settings as applied to all parts of the map, or at all of the other running conditions, like air temperature or altitude, etc, etc.

The rolling road session should always be the way to go.

kind regards
Marek

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#49 Re: pre-programmed curves on 123 ignition - help please?

Post by malcolm » Tue Jul 07, 2020 12:46 pm

Maybe rolling road is the way for me then. Do we know good/reliable ones in the Hampshire area?
Malcolm
I only fit in a 2+2, so got one!
1969 Series 2 2+2
2009 Jaguar XF-S

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#50 Re: pre-programmed curves on 123 ignition - help please?

Post by Tom W » Tue Jul 07, 2020 1:01 pm

I can’t make any specific recommendations on who to use, but as a general rule, make sure who you go to wants to do the work. You’re on a hiding to nowhere if you’re trying to work with someone who dislikes the 123, or refuses to understand how it works.
Tom
1970 S2 FHC

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#51 Re: pre-programmed curves on 123 ignition - help please?

Post by christopher storey » Tue Jul 07, 2020 2:31 pm

Malcolm : As you know I have no confidence in the 123 at all, and thus it could be said I am biased , but if you still have your old correct spec distributor, I should send it off to the Distributor Doctor for an overhaul, including the vac capsule, and then when you get it back substitute it for the 123 . It will almost certainly cost no more than a rolling road session, and at least the original cannot blow up on you !

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#52 Re: pre-programmed curves on 123 ignition - help please?

Post by max-it-out » Tue Jul 07, 2020 6:21 pm

123 do another unit ( 123/Jag6 - for long stroke jaguars ) which gives a choice of max advance from 24 - 32 degrees . One that might be ok is a max of 30 degrees @ 3000 , 3300 or 3600 rpm.Can`t tell what the rest of the curve looks like though , because they don`t provide any data .
Mark

1968 series 1.5 roadster

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#53 Re: pre-programmed curves on 123 ignition - help please?

Post by Tom W » Tue Jul 07, 2020 6:53 pm

I think that’s the same one Malcolm and I both have. It’s 24 (or more) additional crankshaft degrees beyond the idle timing, if I understand the documentation correctly. So if it were set at 10 degrees at idle, you’d have 34 degrees at the top end.

The 123 GB universal distributor might be more appropriate with an additional crank shaft degrees between 17 and 26 degrees. I haven’t checked whether the intermediate advance matches the factory curve though.
Tom
1970 S2 FHC

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#54 Re: pre-programmed curves on 123 ignition - help please?

Post by malcolm » Wed Jul 08, 2020 8:28 am

That's correct, it's the Jag 6 for long stroke engines that we (or at least I) have
Malcolm
I only fit in a 2+2, so got one!
1969 Series 2 2+2
2009 Jaguar XF-S

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#55 Re: pre-programmed curves on 123 ignition - help please?

Post by Gfhug » Thu Aug 27, 2020 8:08 pm

Hi Malcolm, did you get any further with your set up and did you recover the fuel consumption you’d lost?

Cheers

Geoff
S2 FHC Light Blue
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#56 Re: pre-programmed curves on 123 ignition - help please?

Post by malcolm » Fri Aug 28, 2020 8:11 am

Hi Geoff! Current situation is that I set it on curve 2, and did a lot more fiddling with the carbs. I'm still unhappy that the 123 doesn't have a really appropriate curve, but the E is now running better than it ever has I think. Plugs a nice colour, great tickover, and performing well. Last fuel consumption test showed 20mpg, but that was over two runs of 20 miles each, starting from cold each time, so the first few miles of each run would have been with some choke on. I reckon a normal longer run will see me back at the 22/23 mpg I used to get.
Malcolm
I only fit in a 2+2, so got one!
1969 Series 2 2+2
2009 Jaguar XF-S

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#57 Re: pre-programmed curves on 123 ignition - help please?

Post by Gfhug » Fri Aug 28, 2020 9:32 am

Thanks Malcolm, I have similar thoughts to you regarding the curves not reflecting what Jaguar had their dizzies set to. And not as happy with the mpg, will try curve 2.

Geoff
S2 FHC Light Blue
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#58 Re: pre-programmed curves on 123 ignition - help please?

Post by mgcjag » Fri Aug 28, 2020 9:41 am

Hi Geoff...what mpg are you not happy with.....it really is not worth chaseing more mpg...unless you have a real problem......if you intend to drive your car hard i dont really think you will find a curve thats suitable....iv messed about on a few Es and couldnt get a 123 setting that works well......They are ok if you just want to drive "moderatly"..... But for any kind of spirited driving you need a standard dizzy (well serviced) or a programable 123.....Steve
Steve
1969 S2 2+2 & Building a C type replica

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#59 Re: pre-programmed curves on 123 ignition - help please?

Post by malcolm » Fri Aug 28, 2020 9:49 am

Not sure the curve has a great impact on mpg, more effect on driveability I think. Feels better on 2. What curve are you currently on Geoff?
I think my tinkering with the carbs had more impact on my mpg. Also, I was testing over a series of 20 mile runs, each one starting from cold. I did some maths on the probable impact on mpg of starting on choke, then running a few miles on reducing choke until fully warmed up. Big impact. Probably need to do at least a 50 mile run before the figure resembles your true long-run mpg.
Not sure if I explained my thoughts very well there! But what sort of journeys are you doing to measure mpg?

Apologies if this appears twice - tried to post a similar one just now and it disappeared!
Malcolm
I only fit in a 2+2, so got one!
1969 Series 2 2+2
2009 Jaguar XF-S

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#60 Re: pre-programmed curves on 123 ignition - help please?

Post by Tom W » Fri Aug 28, 2020 10:04 am

Ignition advance will affect MPG. We’re talking insufficient advance here. Since the spark fires too late, peak cylinder pressure occurs too late in the power stroke. Some of the useful energy that could be extracted from the charge is now wasted as heat down the exhaust. To propel the car at the same speed, a wider throttle opening is required, and so more fuel is used.
Tom
1970 S2 FHC

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