123 ignition gains?

[Gordon Hunter]

Hi Adam,

I have found a good strong box and will let you know when the courier is booked. Hoping for a little more time to get organised over the weekend.

Gordon

[Volvo Canadian]

Hi - I've often wondered why it is that the advance curves are generally flat for higher rpm. Can anyone explain? I mean really explain. This is something I would definitely like to verify on a rolling-road, as I have not heard any convincing arguments (although there does seem to be a general consensus).

For anyone who doesn't know already, the 123 distributors come as pre-programmed units (with selectable curves), or the 123Tune is user-programmable.

This may incur some 'discussion', but I would also like to know whether it would be good to disable the vacuum advance curve on my 123Tune - I know it is a bear to understand, but I think I have it right. Thanks.

[swedishandgerman]

Hi - I've often wondered why it is that the advance curves are generally flat for higher rpm. Can anyone explain? I mean really explain. This is something I would definitely like to verify on a rolling-road, as I have not heard any convincing arguments (although there does seem to be a general consensus).

Basically, timing gets altered to make sure that the spark happens just at the right time in relation to where the piston is positioned in the chamber to result in the biggest amount of energy

At slow engine speeds, the spark has to happen as the piston is nearly at the top. When it's going fast, the spark needs to happen when the piston is further away from top dead centre. If it happens too far away, it doesn't do anything, if you see what I mean. In other words, there's a point at which making the spark happen earlier has no positive effect.

If you tried this on a dyno, you would find that above a certain engine speed, turning the distributor to give more advance would have no increase in power output

[jimbo1593]

Simple:

known good dizzy - petronix or other quality in-cap solution
unknown dizzy or knackered dizzy - 123

[Volvo Canadian]

Hi - I guess the original question has been answered, so I'll continue with my question, purely because I like to understand things.

"....above a certain engine speed, turning the distributor to give more advance would have no increase in power output."

Why is this the case? Some new factor must come into play, or one could continually increase the advance as rpm increase.

[swedishandgerman]

If the spark timing is too advanced, the spark happens too prematurely. In other words, the piston is too far away from top dead centre for the explosion to have a good result

[Hat]

And the original question was to see before and after on a dyno graph, that would still be interesting, as the torque low down is supposed to be better, also to see how much straighter the lines are....

[swedishandgerman]

If the spark timing is too advanced, the spark happens too prematurely. In other words, the piston is too far away from top dead centre for the explosion to have a good result

I look at it this way: the purpose of the advance mechanism is not to improve what happening at high rpm rather than to improve slow running and idle

Max advance is limited by the distributor because as I explained earlier in this thread, above a certain point, there are no gains by making the spark happen when the piston is too far from TDC. On the contrary, if the spark happens too early at low engine speeds, then - this is difficult to explain - it kind of makes the engine want to run too fast and you can't control if smoothly with throttle. The spark needs to happen nearer TDC at slow engine speeds otherwise the resulting 'bang' is weak.

@ Hat - sorry, I don't know where you can get such a comparison from. I doubt the makers of 123 have a graph specific to a B18, but they might have a comparison for another car perhaps.

[Hat]

I imagine Amazon cars must have done a before and after dyno of it, but found the differences were too small to help sell the product.
These 'dyno days' seem to be quite popular, so I guess one may pop up at some point or other.

[Derek UK]

I don't know if it's possible to create an ignition curve with the 123 Tune version that actually reduces the amount of advance you get over about 3500rpm but both Phil Singher and Steve Berry have found that a small amount of hp can be found by doing so. Probably means the engine will be smoother at higher revs too. Of course mixture has to be optimum at these revs too.
Not too difficult with top end megasquirt but Phil did his with carbs.
Scroll to the end of this article. http://www.1800philes.com/splitting_hairs.html
Comments from owners of 123 Tune welcome.
If you want to experimentally feel the effects of too much advance try the following. (Try at your own risk!) Get the engine up to normal running temps. Mark the position of your distributor so you can return it back to that setting. Loosen the clamp a little, engine running, and rotate clock wise a little. Revs will increase. Rotate a bit more and retighten the clamp at the point that gives the highest revs. It might have gone from 800 to 1500rpm say. Switch off engine and give it a breather for a couple minutes. Try and restart the car. I say try as you should find that the starter really struggles to turn the engine over and the engine may be reluctant to start. Don't keep trying, loosen the clamp and rotate the distributor back to the marks you made. Tighten clamp and the engine should then start normally. This test shows what happens when the spark happens too soon. Piston is still on it's way up when combustion takes place and tries to force the piston back down against the action of the starter.
The improved hp at higher revs if retarding the ignition a bit is probably down to the gas flow which will vary a lot due to the interaction of cam lift, CR, pulse patterns in the inlet and exhaust ports, exhaust manifold flow tuning etc. Valve springs also need to be good. After 100k miles they can be very tired and give very poor valve control leading to poor compression at higher revs, but that's another story.

[swedishandgerman]

Perfect! That's most useful information.

That indicates that 11 degs to 13 degs at idle through to about 32 degs somewhere between 2,500 to 2,800 rpm is good. Of course, this varies from engine type to engine type (cam, carb/carbs etc)

For the sake of over complicating things at this stage, I hadn't brought into discussion the thing about dropping advance back a little at high rpm which is, indeed, to do with the speed of airflow through the chamber at very high rpm. It is something that you can accomplish with a fully tunable ignition. All said, I query how frequently anyone runs their lovely old Volvo's engine at 5,700 rpm?!!

[Groundes-Peace]

After having my B20 engine rebuilt for my 1800S, but using my standard twin SU carbs with the 123Tune set as supplied my car had the following results on a dyno.
Max corrected engine power 110bhp at 5580rpm, with max torque of 152Nm at 4835 rpm. The ignition had a limiter preset to restrict max revs to 5785rpm.

By rejet the carbs, tuning, and altering the ignition curve the figures rose as follows.
Max corrected power 126bhp at 5985rpm, with max torque of 170Nm at 4735rpm.
BY removing the limiter, then engine can rev to 6985rpm, way beyond what I would want to run it to!

[Burdekin]

I don't know if it's possible to create an ignition curve with the 123 Tune version that actually reduces the amount of advance you get over about 3500rpm but both Phil Singher and Steve Berry have found that a small amount of hp can be found by doing so. Probably means the engine will be smoother at higher revs too. Of course mixture has to be optimum at these revs too.
Not too difficult with top end megasquirt but Phil did his with carbs.
Scroll to the end of this article. http://www.1800philes.com/splitting_hairs.html
Comments from owners of 123 Tune welcome.
If you want to experimentally feel the effects of too much advance try the following. (Try at your own risk!) Get the engine up to normal running temps. Mark the position of your distributor so you can return it back to that setting. Loosen the clamp a little, engine running, and rotate clock wise a little. Revs will increase. Rotate a bit more and retighten the clamp at the point that gives the highest revs. It might have gone from 800 to 1500rpm say. Switch off engine and give it a breather for a couple minutes. Try and restart the car. I say try as you should find that the starter really struggles to turn the engine over and the engine may be reluctant to start. Don't keep trying, loosen the clamp and rotate the distributor back to the marks you made. Tighten clamp and the engine should then start normally. This test shows what happens when the spark happens too soon. Piston is still on it's way up when combustion takes place and tries to force the piston back down against the action of the starter.
The improved hp at higher revs if retarding the ignition a bit is probably down to the gas flow which will vary a lot due to the interaction of cam lift, CR, pulse patterns in the inlet and exhaust ports, exhaust manifold flow tuning etc. Valve springs also need to be good. After 100k miles they can be very tired and give very poor valve control leading to poor compression at higher revs, but that's another story.

I based my ignition map on Steve Berry's map when I built my megajolt ignition system, not had it on a dyno though. There was a pic in my thread http://www.volvoforums.org.uk/showthread.php?t=130344 but it's gone now so probably no help.

[Steve121]

I've a 123 from Amazon Cars on my B18, although haven't been able to try it out properly due to the car being as rusty as hell and failed the mot 4 years ago.
However.. I've also an old Lotus Europa (Renault engine) with 123 Tune internals put into the original Dizzy.. very nicely done indeed!
The current advance curve I've programmed it with is based on the cam (290 degree) and combustion chamber type (wedge), so static is 14 degrees, then at 1200rpm a straight line to 36 degrees @ 3200rpm, where the advance stays up to the redline. Runs great, but intend to get it fine tuned on the rolling road. In theory you could have a curve going up and down all over the place (limited only by the number of points to make the curve.. 10 or so, can't remember)

When / if I ever get time to restore the Ammo, I'll do the same for that.

[Burdekin]

I've a 123 from Amazon Cars on my B18, although haven't been able to try it out properly due to the car being as rusty as hell and failed the mot 4 years ago.
However.. I've also an old Lotus Europa (Renault engine) with 123 Tune internals put into the original Dizzy.. very nicely done indeed!
The current advance curve I've programmed it with is based on the cam (290 degree) and combustion chamber type (wedge), so static is 14 degrees, then at 1200rpm a straight line to 36 degrees @ 3200rpm, where the advance stays up to the redline. Runs great, but intend to get it fine tuned on the rolling road. In theory you could have a curve going up and down all over the place (limited only by the number of points to make the curve.. 10 or so, can't remember)

When / if I ever get time to restore the Ammo, I'll do the same for that.

Do they also take into account engine load? I thought the programmable ones did.