123 tune advance curves

[gungehead]

Hi,
I hope someone can help.
I have a 123 tune on my 1962, 3.8 mk2. It is standard apart from a classic fabs exhaust manifold and large bore system and, of course, the 123 tune. It is 8:1 compression, compression values of between 150 and 160 PSI.
I am trying to set up the advance curves and I am getting confused. The manual shows this -

I have the 40640 dizzy and the test data in the workshop manual suggests the timing should be all in at 3400 revs and there should be around 19 degrees of advance (columns 8 and 9). The manual also says that static timing should be set to 7 degrees btdc, giving total advance of 26 degrees at 3400rpm.
Am I reading this correctly? Some other applications of the 3.8, 8:1 engine have timing of up to 38 degrees all in. This is a big difference.

So, I have set the centrifugal advance to this

but I have currently got the initial static timing set to 10 rather than 7, this can be accommodated (to a degree) in the 123 settings.

The original vacuum values are 8 - 18 - 7 according to the vacuum advance unit number (column 3), and in the dizzy data in the manual, the test data is in dizzy degrees not crank degrees (columns 4 and 5).

The original vacuum values are 8 - 18 - 7 according to the vacuum advance unit number (column 3), and in the dizzy data in the manual, the test data is in dizzy degrees not crank degrees (columns 4 and 5).

So I have set the vacuum advance to this

If you convert the dizzy data for the centrifugal advance to crank degrees, you get all in at 3400 rpm of 2 x 19 + 7 = 45 degrees, far too much. Or is it? Add on 14 degrees vacuum and it is firing closer to bottom dead centre than top.

Do these settings look reasonable?

Thanks for your help.

Dave

[piman]

Hello Dave,

how does the car drive, and does it pink with 10 degrees static setting?

The distributor setting of 19degrees maximum is at a distributor speed of 3,400 rpm. (I have an old book on Lucas ignition) This is equivelant to an engine speed of 6,800 rpm, not one that applies, what the actual mechanical advance at say an engine speed of 4 to 5000 rpm will be I don't know?. If you have an adjustable strobe light you could physically measure it (Disconnect the vacuum advance)
I don't know, what the vacuum advance will be practically, as the maximum would be on the overun so no real engine load. possibly and extra 2 to 4 degees at cruise?

Personally I prefer to have an original distributor rebuilt and calibrated to the Jaguar specification, but I know many like the 123 system.

Alec

[peterheywood52573]

Thats a coincidence. I'm fitting a 123-basic at the moment. I had come to the conclusion that the 19deg at 3400 was crankshaft rpm. I will read this post with interest.

My show-stopper is I have lost the screw, that holds the clamp-plate down. I guess it is 1/4 UNF. I found it worryingly difficult to push the distributor into the block, so I decided to fit the clamp-plate to the distributor first and then deal with fitting the screw with its 2 washers after that. This has not worked out.posting.php?mode=reply&f=112&t=16107# I dropped these 3 items several times and feared I would run out of luck. At least I was right about that.
Peter

[peterheywood52573]

It looks to me that the curve number is different for different models, especially with specials for particular cars. But 123 at least seem to use crankshaft degrees.

[gungehead]

I have been p[laying with the advance curve. The one in the first post left the engine sluggish. So I increased the total advance and it was much more urgent and revved much better. So I then increased the steepness of the mid range curve (1500 - 2500) and it was better. So this is what I have ended up with -

It is much better now, revving to 5000 and pulling all the way. No hint of pinking that I can hear. And no urgency to put it in overdrive.

If the figures in the manual are crank degrees, they are a long way out. If they are dizzy figures, I have a long way to go.

Just a reminder, it has 10 degrees static timing on top of those figures.

I think any improvements due to minor changes now will be difficult to prove and will be subjective.

Any comments on the figures or comparisons with your figures will be very welcome.

[Tom1]

Hi, in response to 123 curves the first set up was mapped in on a rolling road with a static setting of 10 degrees and gave the peak engine performance at 5000 rpm of 201 bhp.
However I find that the car is far more responsive and a much better drive using the second map. Again 10 degrees static set up and all in by 3500rpm.
My car is a 1965 3.8 Manual with 3.54 Powerloc diff, 9.5:1 compression, fast road cams, 2 x HD8s,
Straight port large valve head and Classic fabs exhaust.
On overrun for a split second advance momentarily peaks at just over 40 degrees which is a little close to the recommended max advance for a XK engine but I have not noticed any detrimental effects.

[gungehead]

Hi Tom,
Can you confirm that you have 10 degrees static set on the dizzy, so your 123 figures are all plus 10.
Giving all in figures of 42 degrees from the rolling Road session and 36 degrees as your best road performance figures.

Thanks

Dave

[Tom1]

Hi Dave
I can confirm that I have 10 degrees of static on the distributor giving all in figures of 32 degrees with the vacuum disconnected. With the vacuum connected on overrun it can briefly touch just over 40 degrees.
This rolling road set up suites my modified engine but probably wrong for a standard engine.