Advance settings for 123 ignition

[Mudder]

Dear USA7s members,

 

I recently installed a 123 Ignition on my Kent Xflow.

The installation was very straight forward.

My engine is a stock 1700 Super Sprint. Pete Christensen (Total Performance Engines) flowed the head but other than that the engine is as it got delivered in 1999 (6500 miles).

Compressions are strong and it's running smoothly. Kent 234 cam.

My DCOE 40s are brand new and set up properly.

 

My starting point was the Caterham data for the engine, which calls for 10* BTDC advance below 1000RPM.

I degreed the crank and am sure about TDC, which is about 2 degrees off from the case mark.

I am NOT using Vacuum.

 

I programmed my ignition for a linear advance curve which rises from 10* BTDC to 37* BTDC at 3000RPM until it reaches the REV limiter at 6000RPM.

What threw me off a little is, that there is note 2 in Tony Weale's book about Caterham electronic ignition timing at 14 BTDC.

 

I am interested in any kind of ignition data you guys might have in your archives for the 1700 Super Sprint.

Also, what are other 123 Ignition users programing into their units and what is their reasoning behind it.

 

Cheers

 

 

 

[jbcollier]

Ok, I’m travelling and do not have access to my books so I can’t suggest any curves for you.  That said, your current curve is not good.  You have 37 degrees of “mechanical” advance.  That’s a LOT.  That is added to your initial advance setting so you could easily be rocking 40+ degrees of total advance!  Those kind of numbers are reserved for engines with poor, slow-burning combustion chambers from the 50s and early 60s.

 

I’ll post a better curve when I get home mid-week — if someone else doesn’t come forward with one before then.

[Mudder]

jbcollier,

 

Thanks for chiming in.

I used a timing light to verify my initial settings and it was spot on.

 

I completely understand your reasoning, but that would mean that the 123 app adds my 37* on top of the static timing of 10*.

The switch "include static advance" in the app settings was somewhat unclear to me. Why would I want to leave that out??

What am I missing here?

 

The app documentation of 123 is somewhat confusing to me.

I went mainly by 123ignitionUSA instructions.

I had  No.1 on TDC measured with a dial indicator while the head was off.

Installed the distributor and got the "green light". 

When I loaded the above mentioned curve I had 10* BTDC at around 950RPM.

 

I am looking forward to your ignition setup.

[MV8]

I don't have one of these but read the documentation to see.

The green led is for static timing to TDC, with no static advance.

The "centrifugal" curve in the program duplicates an actual fly weight distributor curve. If your rotor can turn 25 or so degrees without the crank rotating, you have a real flyweight distributor and the program curve should not add any advance beyond the initial 10 deg btdc that is needed because you lined up the green led and locked it down.

The "vacuum advance" curve duplicates an actual vacuum advance using a MAP sensor. Technically, all modern cars have a (more reliable) form of vacuum advance.

Lots of options. Cool product.

[JohnCh]

I think you can use the advance setting on the 123 if the distributor body is positioned for advance >0 deg; however, as MV8 notes, the norm is to affix the distributor at 0 deg, then input the actual timing curve into the software. As an example, below is the curve for my twincam.   Note: advance = 0 deg, and the table starts at 13 deg at 500 rpm.  BTW this was done on the dyno to optimize the curve for my specific engine and local fuel.  Well worth the money as torque notably increased everywhere.

[jbcollier]

I don’t like setting the static point to TDC and then doing everything electronically.  I prefer to static time using the actual desired static timing point.  This gives consistent timing during slow cranking speeds.

 

So, if you use a static timing of 10 degree BTDC, you would subtract that from the timing points kindly shared by JohnCh.

 

500 - 0

1000 - 4

1500 - 8

2000 - 13

2500 - 22

3000 - 23

 

This would be good curve for a crossflow!

Edited April 15 by jbcollier
Brain fart

[jbcollier]

JohnCh:

 

Your curve is fine for a street driven TC that does not see much sustained WOT.  If you do steep, long, mountain passes or track days, I would knock it back a bit to a maximum of 26 to 28 degrees total to reduce WOT heat load on the pistons.

[Mudder]

MV8 >>> spot on!

JohnCH >>> Thanks for sharing your data!! I will try to find a dyno rather sooner than later.

jbcollier >>> Agreed! Another benefit to your method would be more room for adjustment. If you put the dizzy to TDC (as the instructions recommend) you loose 8-10 deg. up front.

 

I would like to understand the "advance science" a little better.

Here are some more thoughts (please correct me if I am wrong or give more data)

 

1. peak pressure pulse is optimum at around 12 to 15 degrees ATDC. That's fixed.

2. what's the elapsed time for initial spark to peak combustion pressure? This most probably changes with compression ratio and octane rating. However, whatever time that is (I guess thousands of a second) it will provide significantly different degrees at different RPMs (linear change)

3. why do most curves stop at 3000 RPM? Could that be related to the availability of weights and springs in the pre-electronic ignition era.

4. does electronic ignition with the proper coil require  even more advance (Caterham electronic ignition/Aldon 14*)

 

Cheers

 

Edited April 15 by Mudder

[jbcollier]

You’re correct that it is the time to peak combustion pressure we can’t change easily.  We move the ignition point earlier to keep it happening at the same time.  However, other things are going on as well.  That is the amount of heat the piston is exposed to expressed in degrees of rotation.  As we add more degrees to keep the ignition happy, more degrees of rotation are having the piston exposed to heat and less without heat.  This means our piston temperatures go up.  We have to balance “ideal” ignition timing with piston heat load.  This is where timing by feel can catch people out.  Yup, maybe you can make more power with your timing further advanced but you might hole a piston as well.

 

Engineers and tuners can change combustion chamber design to increase turbulence and reduce area, this can decrease combustion time, increase efficiency and require significantly less ignition advance.  My Ducati 250 has a classic hemispherical combustion chamber.  With higher compression rations, the combustion chamber gets very long and thin.  Total Ignition advance has to be in the range of 38 to 40 degrees — pistons lead a hard life.  However, add a second spark plug into the chamber and the same engine will happily run 32 degrees and not have any piston issues.

[MV8]

9 hours ago, Mudder said:

I would like to understand the "advance science" a little better.

Here are some more thoughts (please correct me if I am wrong or give more data)

 

1. peak pressure pulse is optimum at around 12 to 15 degrees ATDC. That's fixed.

2. what's the elapsed time for initial spark to peak combustion pressure? This most probably changes with compression ratio and octane rating. However, whatever time that is (I guess thousands of a second) it will provide significantly different degrees at different RPMs (linear change)

3. why do most curves stop at 3000 RPM? Could that be related to the availability of weights and springs in the pre-electronic ignition era.

4. does electronic ignition with the proper coil require  even more advance (Caterham electronic ignition/Aldon 14*)

 

Cheers

 

Electronic/breakerless trigger ignition does not require a timing change, but breakerless isolates the ignition coil circuit (coil primary amps don't run through the points) so the coil can be much higher output for a wider plug gap, with little effect on the ideal advance rate but the total advance needed may be less. Most engine improvements reduce the total   

I think you are referring to Tony Weale's book reference, which is for engines with a specific "UL" specification (UL=UnLeaded?). 95 octane is shown as 95 in the UK (RON measurement), 92 here (AKI measurement or RON + MON/2) for the same octane fuel. Ethanol also has the effect of increasing octane and is factored in at the pump (though the percentage varies with the season despite the pump label due to ), but it can fall out of suspension (leaving low octane fuel), attack all rubber in the system, and absorb water to corrode everything internally (ethanol is hydroscopic like brake fluid, but not as corrosive to older fuel systems as alcohol or methanol). An engine (EFI or carbs) designed to run on gasoline will run leaner on common 10% ethanol fuel with reduced range due to the lower btu content and greater burn rate if the mixture is adjusted.

Ideal advance is not directly proportional to rpm. Mechanical and traditional vac advance are very limited and mechanical all in by 3k is a good compromise. With modern tools, timing can advance to peak around 3k then slowly retard due to the improved burn rate from the turbulence at higher flow rates (like aero drag on a car moving faster). Most efficiency improvement result in less total timing. Cam overlap is similar to egr mixture dilution and requires a higher advance rate and total since it is not an efficiency improvement. How deep do you want to go?  

[Mudder]

jbcollier

 

I see similarities between the combustion chamber of a Ducati and a Twinc.

I wonder how the combustion chamber of a Kent cross-flow (heron type) affects CHTs.

 

MV8

 

Thanks for the enlightenment (I love it)!!

I am not sure how much deeper we should go on this topic. I want to keep it beneficial and entertaining for the other posters, too.

I have a tendency to geek out on topics like that and this might not be other folks' taste.

 

Yes I was referring to the Tony Weale book and the "UL" designation makes perfect sense now.

I try to stay away from E-free gas and can second the reduced range comment.

 

Also, Thanks for shining the light on the 3k compromise.

If I understand it correctly, by stopping the advance at 3000RPM you are effectively retarding the ignition at higher RPMs.

 

I guess I need to find a good dyno outfit in the Colorado Springs/Denver area.

 

Cheers

 

 

[jbcollier]

There actually isn't much similarity at all, thank goodness.  The Ducati has its valves set at an 80° angle IIRC (ie: not good!).  The exhaust port is ok but the intake port is awful with the incoming charge flowing across the valve head.  It takes a lot of work to make the intake port simply bad rather than unbelievably horrible.

 

In contrast, the twink valve angle is much smaller (mid-30s comes to mind but I can't remember for sure) and the ports are beautifully laid out.  Things have moved on, for sure, but the twink head was state of the art at the time.